package database

import (
	"cmp"
	"context"
	"database/sql"
	_ "embed"
	"encoding/json"
	"errors"
	"fmt"
	"maps"
	"math/rand/v2"
	"net"
	"net/netip"
	"os"
	"path/filepath"
	"runtime"
	"slices"
	"sync"
	"time"

	"git.eeqj.de/sneak/routewatch/internal/config"
	"git.eeqj.de/sneak/routewatch/internal/logger"
	"git.eeqj.de/sneak/routewatch/pkg/asinfo"
	_ "github.com/mattn/go-sqlite3" // CGO SQLite driver
)

// IMPORTANT: NO schema changes are to be made outside of schema.sql
// We do NOT support migrations. All schema changes MUST be made in schema.sql only.
//
//go:embed schema.sql
var dbSchema string

const (
	dirPermissions = 0750 // rwxr-x---
	ipVersionV4    = 4
	ipVersionV6    = 6
	ipv4Bits       = 32
	ipv6Bits       = 128

	tableLiveRoutesV4 = "live_routes_v4"
	tableLiveRoutesV6 = "live_routes_v6"

	// Names of the IP versions in error and log messages.
	ipv4Family = "IPv4"
	ipv6Family = "IPv6"
)

// The IP lookup does not use routes shorter than these mask lengths. A default
// route or a route this short only says where a peer sends traffic it has no
// better route for; it does not say who holds the address.
const (
	minLookupMaskLengthV4 = 8
	minLookupMaskLengthV6 = 16
)

// SQLite memory tuning (README "Memory"). cache_size and busy_timeout go in the
// DSN so every pooled connection gets them; the connection kept for writing
// then sets its own cache size. The heap limits are process-wide and set once.
const (
	// maxConns is the size of the connection pool: the connection kept for
	// writing and 9 reading connections.
	maxConns = 10
	// sqliteReadCacheSizeKiB is the page cache of each reading connection;
	// negative means KiB. -16384 = 16 MiB, at most 144 MiB for the 9. A reading
	// connection's cache is emptied whenever another connection has written
	// since its last read, many times a minute, so a large one is wasted.
	sqliteReadCacheSizeKiB = -16384
	// sqliteWriteCacheSizeKiB is the page cache of the connection kept for
	// writing, -1048576 = 1 GiB. It keeps its pages from one write to the next,
	// so the index pages the route writes touch stay in memory.
	sqliteWriteCacheSizeKiB = -1048576
	// sqliteBusyTimeoutMs is how long a connection waits on a locked database.
	sqliteBusyTimeoutMs = 5000
	// sqliteSoftHeapLimitBytes (1.5 GiB) makes SQLite recycle its cache rather
	// than allocate once its C heap passes this size. It is above the caches
	// together, so it does not shrink them.
	sqliteSoftHeapLimitBytes = 1610612736
	// sqliteHardHeapLimitBytes (2 GiB) fails a statement with SQLITE_NOMEM
	// instead of growing the C heap without bound.
	sqliteHardHeapLimitBytes = 2147483648
)

// Settings of the ANALYZE that Analyze runs.
const (
	// analysisLimit is about how many rows of each index ANALYZE reads
	// (PRAGMA analysis_limit); SQLite estimates the rest.
	analysisLimit = 1000
	// optimizeAllTables is the PRAGMA optimize mask that runs ANALYZE (0x2)
	// on every table that has an index without statistics or whose size has
	// changed tenfold since it was last analyzed, not only on the tables this
	// connection has queried (0x10000).
	optimizeAllTables = 0x10002
)

// Bounds on the work GetRandomPrefixesByLength does to pick its sample.
const (
	// maxPrefixesToShuffle is the most prefixes of one mask length that are
	// read in full and shuffled to pick the sample. A mask length with more is
	// sampled with random lookups.
	maxPrefixesToShuffle = 5000
	// sampleLookupsPerPrefix is the most random lookups made for each prefix
	// asked for.
	sampleLookupsPerPrefix = 4
)

// Common errors
var (
	// ErrInvalidIP is returned when an IP address is malformed
	ErrInvalidIP = errors.New("invalid IP address")
	// ErrNoRoute is returned when no route is found for an IP
	ErrNoRoute = errors.New("no route found")
	// ErrNoStaleASN is returned when no ASN needs WHOIS refresh
	ErrNoStaleASN = errors.New("no stale ASN found")

	errInvalidASN       = errors.New("invalid ASN")
	errSameASNInPeering = errors.New("cannot create peering with same ASN")
)

// Database manages the SQLite database connection and operations.
type Database struct {
	db *sql.DB
	// writer is the connection kept for writing, taken from db when the
	// database opens. Every write uses it while holding mu.
	writer   *sql.Conn
	logger   *logger.Logger
	path     string
	mu       sync.Mutex
	lockedAt time.Time
	lockedBy string
	counts   *liveCounts
}

// New creates a new database connection and initializes the schema.
func New(cfg *config.Config, logger *logger.Logger) (*Database, error) {
	dbPath := filepath.Join(cfg.GetStateDir(), "db.sqlite")

	// Log database path
	logger.Info("Opening database", "path", dbPath)

	// Ensure directory exists
	dir := filepath.Dir(dbPath)

	err := os.MkdirAll(dir, dirPermissions)
	if err != nil {
		return nil, fmt.Errorf("failed to create database directory: %w", err)
	}

	// Per-connection SQLite settings go in the DSN so every pooled connection
	// gets them, not just the one that runs the Initialize pragmas. _txlock=
	// immediate makes every transaction take the write lock at BEGIN. Without it
	// a transaction that reads before writing starts as a reader and, when it
	// then writes while another connection holds the write lock, fails at once
	// with "database is locked" without waiting for _busy_timeout.
	// _auto_vacuum=incremental lets Vacuum return free pages to the filesystem.
	// SQLite only accepts it before the database file is first written, and the
	// switch to WAL writes it, so it must be here: the driver applies it on open,
	// before _journal_mode. On an existing file it changes nothing.
	dsn := fmt.Sprintf(
		"file:%s?_cache_size=%d&_synchronous=OFF&_busy_timeout=%d"+
			"&_auto_vacuum=incremental&_journal_mode=WAL&_txlock=immediate",
		dbPath,
		sqliteReadCacheSizeKiB,
		sqliteBusyTimeoutMs,
	)

	db, err := sql.Open("sqlite3", dsn)
	if err != nil {
		return nil, fmt.Errorf("failed to open database: %w", err)
	}

	ctx := context.Background()

	err = db.PingContext(ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to ping database: %w", err)
	}

	// Set connection pool parameters
	// Multiple connections allow concurrent reads while writes are serialized
	db.SetMaxOpenConns(maxConns)
	db.SetMaxIdleConns(maxConns)
	db.SetConnMaxLifetime(0)

	writer, err := db.Conn(ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to open the writing connection: %w", err)
	}

	_, err = writer.ExecContext(ctx,
		fmt.Sprintf("PRAGMA cache_size=%d", sqliteWriteCacheSizeKiB))
	if err != nil {
		return nil, fmt.Errorf("failed to set the writing connection's cache: %w",
			err)
	}

	database := &Database{
		db: db, writer: writer, logger: logger, path: dbPath,
		counts: &liveCounts{},
	}

	err = database.Initialize()
	if err != nil {
		return nil, fmt.Errorf("failed to initialize database: %w", err)
	}

	// Seed the in-memory statistics counters from the tables once, before the
	// streamer starts writing. From here on every write keeps them current, so
	// the stats endpoints never scan the tables to report counts.
	err = database.seedCounts(context.Background())
	if err != nil {
		return nil, fmt.Errorf("failed to seed statistics counters: %w", err)
	}

	return database, nil
}

// Initialize creates the database schema if it doesn't exist.
func (d *Database) Initialize() error {
	// Set SQLite pragmas for performance. Per-connection settings (cache_size,
	// synchronous, busy_timeout, journal_mode) live in the DSN, and New sets the
	// writing connection's cache_size; temp_store is left at its default so
	// DISTINCT temp B-trees spill to disk instead of C heap. The heap limits
	// below are process-wide, so setting them once here is enough for the whole
	// pool.
	pragmas := []string{
		"PRAGMA journal_mode=WAL", // Write-Ahead Logging
		fmt.Sprintf("PRAGMA soft_heap_limit=%d", sqliteSoftHeapLimitBytes),
		fmt.Sprintf("PRAGMA hard_heap_limit=%d", sqliteHardHeapLimitBytes),
	}

	for _, pragma := range pragmas {
		err := d.exec(pragma)
		if err != nil {
			d.logger.Warn("Failed to set pragma", "pragma", pragma, "error", err)
		}
	}

	// Run WAL checkpoint on startup to consolidate any existing WAL
	var walPages, checkpointedPages, movedPages int

	err := d.writer.QueryRowContext(context.Background(),
		"PRAGMA wal_checkpoint(TRUNCATE)",
	).Scan(&walPages, &checkpointedPages, &movedPages)
	if err != nil {
		d.logger.Warn("Failed to checkpoint WAL on startup", "error", err)
	} else {
		d.logger.Info("WAL checkpoint on startup",
			"wal_pages", walPages,
			"checkpointed", checkpointedPages,
			"moved", movedPages,
		)
	}

	err = d.exec(dbSchema)
	if err != nil {
		return err
	}

	return nil
}

// Close closes the writing connection and then the connection pool.
func (d *Database) Close() error {
	return errors.Join(d.writer.Close(), d.db.Close())
}

// A live-route upsert sets the origin AS of the peer's route for the prefix
// when the announcement changes it, then updates the rest of the route, and
// inserts the route only when that update matched no row. A live route is keyed
// by prefix and peer, so an announcement replaces the peer's route for the
// prefix whatever its origin AS. The update's rows-affected count (1 for an
// existing key, 0 for a new one) is what lets the in-memory route counters stay
// exact without a COUNT(*). Callers hold the database write lock, so no other
// writer can insert the same key between the statements.
//
// SQLite rewrites a row's entry in every index on a column an UPDATE sets, even
// when the value stays the same, so the update sets only the columns that
// change: mask_length follows from the prefix, and origin_asn has a statement
// of its own that changes nothing when the origin AS stays the same, as it
// mostly does.
const (
	updateLiveRouteOriginV4SQL = `UPDATE live_routes_v4 SET origin_asn = ?
		WHERE prefix = ? AND peer_ip = ? AND origin_asn != ?`

	updateLiveRouteV4SQL = `UPDATE live_routes_v4
		SET as_path = ?, next_hop = ?, last_updated = ?
		WHERE prefix = ? AND peer_ip = ?`

	insertLiveRouteV4SQL = `INSERT INTO live_routes_v4
		(prefix, mask_length, origin_asn, peer_ip, as_path, next_hop,
		last_updated) VALUES (?, ?, ?, ?, ?, ?, ?)`

	updateLiveRouteOriginV6SQL = `UPDATE live_routes_v6 SET origin_asn = ?
		WHERE prefix = ? AND peer_ip = ? AND origin_asn != ?`

	updateLiveRouteV6SQL = `UPDATE live_routes_v6
		SET as_path = ?, next_hop = ?, last_updated = ?
		WHERE prefix = ? AND peer_ip = ?`

	insertLiveRouteV6SQL = `INSERT INTO live_routes_v6
		(prefix, mask_length, origin_asn, peer_ip, as_path, next_hop,
		last_updated) VALUES (?, ?, ?, ?, ?, ?, ?)`
)

// Before a new route is inserted and after a route is deleted, the write looks
// up whether any live route has that prefix, to keep the in-memory prefix
// distribution exact. The lookup reads one entry of the prefix index.
const (
	prefixHasLiveRouteV4SQL = `SELECT EXISTS
		(SELECT 1 FROM live_routes_v4 WHERE prefix = ?)`
	prefixHasLiveRouteV6SQL = `SELECT EXISTS
		(SELECT 1 FROM live_routes_v6 WHERE prefix = ?)`
)

// A deletion removes the live route the peer has for the prefix, if any.
const (
	deleteLiveRouteV4SQL = `DELETE FROM live_routes_v4
		WHERE prefix = ? AND peer_ip = ?`
	deleteLiveRouteV6SQL = `DELETE FROM live_routes_v6
		WHERE prefix = ? AND peer_ip = ?`
)

// upsertRouteRow updates a live route with the origin and update statements of
// its IP version's table, inserting it when no row matched. It reports whether
// a new row was inserted and whether that row is the first live route for its
// prefix.
func upsertRouteRow(
	ctx context.Context, setOrigin, upd, ins, has *sql.Stmt, route *LiveRoute,
	pathJSON string,
) (bool, bool, error) {
	_, err := setOrigin.ExecContext(ctx, route.OriginASN, route.Prefix,
		route.PeerIP, route.OriginASN)
	if err != nil {
		return false, false, err
	}

	res, err := upd.ExecContext(ctx, pathJSON, route.NextHop, route.LastUpdated,
		route.Prefix, route.PeerIP)
	if err != nil {
		return false, false, err
	}

	affected, err := res.RowsAffected()
	if err != nil {
		return false, false, err
	}

	if affected > 0 {
		return false, false, nil
	}

	var prefixHadRoute bool

	err = has.QueryRowContext(ctx, route.Prefix).Scan(&prefixHadRoute)
	if err != nil {
		return false, false, err
	}

	_, err = ins.ExecContext(ctx, route.Prefix, route.MaskLength,
		route.OriginASN, route.PeerIP, pathJSON, route.NextHop,
		route.LastUpdated)
	if err != nil {
		return false, false, err
	}

	return true, !prefixHadRoute, nil
}

// upsertRoutesInTable upserts routes, all of one IP version, in the live route
// table of that version. It returns how many new rows it inserted and the mask
// lengths of the prefixes that got their first live route.
func upsertRoutesInTable(
	ctx context.Context, tx *loggingTx, routes []*LiveRoute, ipVersion int,
) (int, []int, error) {
	if len(routes) == 0 {
		return 0, nil, nil
	}

	family, originSQL, updateSQL := ipv4Family, updateLiveRouteOriginV4SQL,
		updateLiveRouteV4SQL
	insertSQL, lookupSQL := insertLiveRouteV4SQL, prefixHasLiveRouteV4SQL

	if ipVersion == ipVersionV6 {
		family, originSQL, updateSQL = ipv6Family, updateLiveRouteOriginV6SQL,
			updateLiveRouteV6SQL
		insertSQL, lookupSQL = insertLiveRouteV6SQL, prefixHasLiveRouteV6SQL
	}

	setOrigin, err := tx.PrepareContext(ctx, originSQL)
	if err != nil {
		return 0, nil, fmt.Errorf("failed to prepare %s origin statement: %w",
			family, err)
	}
	defer func() { _ = setOrigin.Close() }()

	upd, err := tx.PrepareContext(ctx, updateSQL)
	if err != nil {
		return 0, nil, fmt.Errorf("failed to prepare %s update statement: %w",
			family, err)
	}
	defer func() { _ = upd.Close() }()

	ins, err := tx.PrepareContext(ctx, insertSQL)
	if err != nil {
		return 0, nil, fmt.Errorf("failed to prepare %s insert statement: %w",
			family, err)
	}
	defer func() { _ = ins.Close() }()

	has, err := tx.PrepareContext(ctx, lookupSQL)
	if err != nil {
		return 0, nil, fmt.Errorf(
			"failed to prepare %s prefix lookup statement: %w", family, err)
	}
	defer func() { _ = has.Close() }()

	var newRows int
	// Mask lengths of the prefixes that get their first live route.
	var newPrefixMaskLengths []int

	for _, route := range routes {
		pathJSON, err := json.Marshal(route.ASPath)
		if err != nil {
			return 0, nil, fmt.Errorf("failed to encode AS path: %w", err)
		}

		inserted, newPrefix, err := upsertRouteRow(ctx, setOrigin, upd, ins, has,
			route, string(pathJSON))
		if err != nil {
			return 0, nil, fmt.Errorf("failed to upsert route %s: %w",
				route.Prefix, err)
		}

		if inserted {
			newRows++
		}

		if newPrefix {
			newPrefixMaskLengths = append(newPrefixMaskLengths, route.MaskLength)
		}
	}

	return newRows, newPrefixMaskLengths, nil
}

// UpsertLiveRouteBatch inserts or updates multiple live routes in a single
// transaction, the IPv4 routes first and then the IPv6 routes.
func (d *Database) UpsertLiveRouteBatch(routes []*LiveRoute) error {
	if len(routes) == 0 {
		return nil
	}

	d.lock("UpsertLiveRouteBatch")
	defer d.unlock()

	tx, err := d.beginTx()
	if err != nil {
		return fmt.Errorf("failed to begin transaction: %w", err)
	}
	defer d.rollback(tx)

	// The rows are written in key order, peer then prefix, so consecutive writes
	// land on the same index pages. The sort is stable, so of two updates of
	// one route the later one is still written last.
	sorted := slices.SortedStableFunc(slices.Values(routes),
		func(a, b *LiveRoute) int {
			return cmp.Or(cmp.Compare(a.PeerIP, b.PeerIP),
				cmp.Compare(a.Prefix, b.Prefix))
		})

	var routesV4, routesV6 []*LiveRoute

	for _, route := range sorted {
		if route.IPVersion == ipVersionV4 {
			routesV4 = append(routesV4, route)
		} else {
			routesV6 = append(routesV6, route)
		}
	}

	ctx := context.Background()

	newV4, newPrefixMaskLengthsV4, err := upsertRoutesInTable(ctx, tx,
		routesV4, ipVersionV4)
	if err != nil {
		return err
	}

	newV6, newPrefixMaskLengthsV6, err := upsertRoutesInTable(ctx, tx,
		routesV6, ipVersionV6)
	if err != nil {
		return err
	}

	err = tx.Commit()
	if err != nil {
		return fmt.Errorf("failed to commit transaction: %w", err)
	}

	d.counts.addRoutes(newV4, newV6)
	d.counts.addToDistribution(newPrefixMaskLengthsV4, newPrefixMaskLengthsV6, 1)

	return nil
}

// deleteRouteRow runs one deletion with the delete statement of its IP
// version's table. It returns how many rows it removed and whether that left
// the prefix with no live route.
func deleteRouteRow(
	ctx context.Context, deleteStmt, has *sql.Stmt, del LiveRouteDeletion,
) (int64, bool, error) {
	res, err := deleteStmt.ExecContext(ctx, del.Prefix, del.PeerIP)
	if err != nil {
		return 0, false, fmt.Errorf("failed to delete route %s: %w",
			del.Prefix, err)
	}

	// The feed often withdraws a route that is not live, which deletes
	// nothing, so the in-memory route counters use the rows-affected count.
	affected, err := res.RowsAffected()
	if err != nil {
		return 0, false, fmt.Errorf("failed to count deleted route %s: %w",
			del.Prefix, err)
	}

	if affected == 0 {
		return 0, false, nil
	}

	// The prefix leaves the distribution when no live route has it any more.
	var prefixHasRoute bool

	err = has.QueryRowContext(ctx, del.Prefix).Scan(&prefixHasRoute)
	if err != nil {
		return 0, false, fmt.Errorf("failed to look up prefix %s: %w",
			del.Prefix, err)
	}

	return affected, !prefixHasRoute, nil
}

// deleteRoutesInTable runs deletions, all of one IP version, on the live route
// table of that version. It returns how many rows it removed and the mask
// lengths of the prefixes it left with no live route.
func deleteRoutesInTable(
	ctx context.Context, tx *loggingTx, deletions []LiveRouteDeletion,
	ipVersion int,
) (int64, []int, error) {
	if len(deletions) == 0 {
		return 0, nil, nil
	}

	family, deleteSQL, lookupSQL := ipv4Family, deleteLiveRouteV4SQL,
		prefixHasLiveRouteV4SQL
	if ipVersion == ipVersionV6 {
		family, deleteSQL, lookupSQL = ipv6Family, deleteLiveRouteV6SQL,
			prefixHasLiveRouteV6SQL
	}

	deleteStmt, err := tx.PrepareContext(ctx, deleteSQL)
	if err != nil {
		return 0, nil, fmt.Errorf("failed to prepare %s delete statement: %w",
			family, err)
	}
	defer func() { _ = deleteStmt.Close() }()

	has, err := tx.PrepareContext(ctx, lookupSQL)
	if err != nil {
		return 0, nil, fmt.Errorf(
			"failed to prepare %s prefix lookup statement: %w", family, err)
	}
	defer func() { _ = has.Close() }()

	var deleted int64
	// Mask lengths of the prefixes left with no live route.
	var gonePrefixMaskLengths []int

	for _, del := range deletions {
		affected, prefixGone, err := deleteRouteRow(ctx, deleteStmt, has, del)
		if err != nil {
			return 0, nil, err
		}

		deleted += affected

		if !prefixGone {
			continue
		}

		maskLength, err := prefixMaskLength(del.Prefix)
		if err != nil {
			return 0, nil, err
		}

		gonePrefixMaskLengths = append(gonePrefixMaskLengths, maskLength)
	}

	return deleted, gonePrefixMaskLengths, nil
}

// DeleteLiveRouteBatch deletes multiple live routes in a single transaction,
// the IPv4 routes first and then the IPv6 routes.
func (d *Database) DeleteLiveRouteBatch(deletions []LiveRouteDeletion) error {
	if len(deletions) == 0 {
		return nil
	}

	d.lock("DeleteLiveRouteBatch")
	defer d.unlock()

	tx, err := d.beginTx()
	if err != nil {
		return fmt.Errorf("failed to begin transaction: %w", err)
	}
	defer d.rollback(tx)

	// The rows are deleted in key order, peer then prefix, as
	// UpsertLiveRouteBatch writes them.
	sorted := slices.SortedFunc(slices.Values(deletions),
		func(a, b LiveRouteDeletion) int {
			return cmp.Or(cmp.Compare(a.PeerIP, b.PeerIP),
				cmp.Compare(a.Prefix, b.Prefix))
		})

	var deletionsV4, deletionsV6 []LiveRouteDeletion

	for _, del := range sorted {
		if del.IPVersion == ipVersionV4 {
			deletionsV4 = append(deletionsV4, del)
		} else {
			deletionsV6 = append(deletionsV6, del)
		}
	}

	ctx := context.Background()

	deletedV4, gonePrefixMaskLengthsV4, err := deleteRoutesInTable(ctx, tx,
		deletionsV4, ipVersionV4)
	if err != nil {
		return err
	}

	deletedV6, gonePrefixMaskLengthsV6, err := deleteRoutesInTable(ctx, tx,
		deletionsV6, ipVersionV6)
	if err != nil {
		return err
	}

	err = tx.Commit()
	if err != nil {
		return fmt.Errorf("failed to commit transaction: %w", err)
	}

	d.counts.addRoutes(-int(deletedV4), -int(deletedV6))
	d.counts.addToDistribution(gonePrefixMaskLengthsV4, gonePrefixMaskLengthsV6, -1)

	return nil
}

// Deleting all live routes of a peer. The first query of each table selects the
// mask length of each of the peer's routes whose prefix no other peer has a
// live route for: the delete takes those prefixes out of the prefix
// distribution.
const (
	peerOnlyRouteMaskLengthsV4SQL = `SELECT r.mask_length
		FROM live_routes_v4 AS r WHERE r.peer_ip = ?
		AND NOT EXISTS (SELECT 1 FROM live_routes_v4 AS o
		WHERE o.prefix = r.prefix AND o.peer_ip != r.peer_ip)`
	deletePeerLiveRoutesV4SQL = `DELETE FROM live_routes_v4 WHERE peer_ip = ?`

	peerOnlyRouteMaskLengthsV6SQL = `SELECT r.mask_length
		FROM live_routes_v6 AS r WHERE r.peer_ip = ?
		AND NOT EXISTS (SELECT 1 FROM live_routes_v6 AS o
		WHERE o.prefix = r.prefix AND o.peer_ip != r.peer_ip)`
	deletePeerLiveRoutesV6SQL = `DELETE FROM live_routes_v6 WHERE peer_ip = ?`
)

// deletePeerRoutes deletes all live routes of peerIP from one table, given that
// table's two statements above. It returns how many routes it deleted and the
// mask length of each prefix it left with no live route.
func deletePeerRoutes(
	ctx context.Context, tx *loggingTx,
	onlyRouteMaskLengthsSQL, deleteSQL, peerIP string,
) (int64, []int, error) {
	rows, err := tx.QueryContext(ctx, onlyRouteMaskLengthsSQL, peerIP)
	if err != nil {
		return 0, nil, err
	}
	defer func() { _ = rows.Close() }()

	var goneMaskLengths []int

	for rows.Next() {
		var maskLength int

		err := rows.Scan(&maskLength)
		if err != nil {
			return 0, nil, err
		}

		goneMaskLengths = append(goneMaskLengths, maskLength)
	}

	err = rows.Err()
	if err != nil {
		return 0, nil, err
	}

	res, err := tx.ExecContext(ctx, deleteSQL, peerIP)
	if err != nil {
		return 0, nil, err
	}

	deleted, err := res.RowsAffected()
	if err != nil {
		return 0, nil, err
	}

	return deleted, goneMaskLengths, nil
}

// DeleteLiveRoutesOfPeer deletes every live route of the peer, IPv4 and IPv6,
// in one transaction, as when the peer's BGP session goes down. It returns how
// many routes it deleted.
func (d *Database) DeleteLiveRoutesOfPeer(peerIP string) (int, error) {
	d.lock("DeleteLiveRoutesOfPeer")
	defer d.unlock()

	tx, err := d.beginTx()
	if err != nil {
		return 0, fmt.Errorf("failed to begin transaction: %w", err)
	}
	defer d.rollback(tx)

	ctx := context.Background()

	deletedV4, goneMaskLengthsV4, err := deletePeerRoutes(ctx, tx,
		peerOnlyRouteMaskLengthsV4SQL, deletePeerLiveRoutesV4SQL, peerIP)
	if err != nil {
		return 0, fmt.Errorf("failed to delete the IPv4 routes of peer %s: %w",
			peerIP, err)
	}

	deletedV6, goneMaskLengthsV6, err := deletePeerRoutes(ctx, tx,
		peerOnlyRouteMaskLengthsV6SQL, deletePeerLiveRoutesV6SQL, peerIP)
	if err != nil {
		return 0, fmt.Errorf("failed to delete the IPv6 routes of peer %s: %w",
			peerIP, err)
	}

	err = tx.Commit()
	if err != nil {
		return 0, fmt.Errorf("failed to commit transaction: %w", err)
	}

	d.counts.addRoutes(-int(deletedV4), -int(deletedV6))
	d.counts.addToDistribution(goneMaskLengthsV4, goneMaskLengthsV6, -1)

	return int(deletedV4 + deletedV6), nil
}

// insertPrefixesInTable inserts the prefixes, all of one IP version, that the
// prefix table of that version does not hold yet, each first seen at its time
// in prefixes. A prefix already stored is left as it is. It returns how many it
// inserted.
func insertPrefixesInTable(
	ctx context.Context, tx *loggingTx, prefixes map[string]time.Time,
	ipVersion int,
) (int, error) {
	if len(prefixes) == 0 {
		return 0, nil
	}

	family := ipv4Family
	insertSQL := "INSERT INTO prefixes_v4 (prefix, first_seen) VALUES (?, ?) " +
		"ON CONFLICT (prefix) DO NOTHING"

	if ipVersion == ipVersionV6 {
		family = ipv6Family
		insertSQL = "INSERT INTO prefixes_v6 (prefix, first_seen) VALUES (?, ?) " +
			"ON CONFLICT (prefix) DO NOTHING"
	}

	insertStmt, err := tx.PrepareContext(ctx, insertSQL)
	if err != nil {
		return 0, fmt.Errorf("failed to prepare %s insert statement: %w",
			family, err)
	}
	defer func() { _ = insertStmt.Close() }()

	var newPrefixes int

	// The rows are written in key order, as UpsertLiveRouteBatch writes routes.
	for _, prefix := range slices.Sorted(maps.Keys(prefixes)) {
		res, err := insertStmt.ExecContext(ctx, prefix, prefixes[prefix])
		if err != nil {
			return 0, fmt.Errorf("failed to insert prefix %s: %w", prefix, err)
		}

		// One row for a new prefix, none for one already stored.
		inserted, err := res.RowsAffected()
		if err != nil {
			return 0, fmt.Errorf("failed to count inserted prefix %s: %w",
				prefix, err)
		}

		if inserted > 0 {
			newPrefixes++
		}
	}

	return newPrefixes, nil
}

// UpdatePrefixesBatch stores, in a single transaction, the prefixes that are
// not stored yet, each first seen at its time in prefixes: the IPv4 prefixes
// first and then the IPv6 prefixes.
func (d *Database) UpdatePrefixesBatch(prefixes map[string]time.Time) error {
	if len(prefixes) == 0 {
		return nil
	}

	d.lock("UpdatePrefixesBatch")
	defer d.unlock()

	tx, err := d.beginTx()
	if err != nil {
		return fmt.Errorf("failed to begin transaction: %w", err)
	}
	defer d.rollback(tx)

	prefixesV4 := make(map[string]time.Time)
	prefixesV6 := make(map[string]time.Time)

	for prefix, timestamp := range prefixes {
		if detectIPVersion(prefix) == ipVersionV4 {
			prefixesV4[prefix] = timestamp
		} else {
			prefixesV6[prefix] = timestamp
		}
	}

	ctx := context.Background()

	newV4, err := insertPrefixesInTable(ctx, tx, prefixesV4, ipVersionV4)
	if err != nil {
		return err
	}

	newV6, err := insertPrefixesInTable(ctx, tx, prefixesV6, ipVersionV6)
	if err != nil {
		return err
	}

	err = tx.Commit()
	if err != nil {
		return fmt.Errorf("failed to commit transaction: %w", err)
	}

	d.counts.addPrefixes(newV4, newV6)

	return nil
}

// newASN returns a new ASN record first and last seen at timestamp, with the
// handle and description from the AS info lookup when it knows the number.
func newASN(number int, timestamp time.Time) ASN {
	asn := ASN{
		ASN:       number,
		FirstSeen: timestamp,
		LastSeen:  timestamp,
	}

	// Look up ASN info
	if info, ok := asinfo.Get(number); ok {
		asn.Handle = info.Handle
		asn.Description = info.Description
	}

	return asn
}

// upsertASN updates the last_seen time of ASN number with the given
// statements, inserting the ASN when it is new. It reports whether it inserted
// it.
func upsertASN(
	ctx context.Context, selectStmt, updateStmt, insertStmt *sql.Stmt,
	number int, timestamp time.Time,
) (bool, error) {
	var (
		asn                 ASN
		handle, description sql.NullString
	)

	err := selectStmt.QueryRowContext(ctx, number).Scan(&asn.ASN, &handle,
		&description, &asn.FirstSeen, &asn.LastSeen)
	if err == nil {
		// ASN exists, update last_seen
		_, err = updateStmt.ExecContext(ctx, timestamp, number)
		if err != nil {
			return false, fmt.Errorf("failed to update ASN %d: %w", number, err)
		}

		return false, nil
	}

	if !errors.Is(err, sql.ErrNoRows) {
		return false, fmt.Errorf("failed to query ASN %d: %w", number, err)
	}

	// ASN doesn't exist, create it
	asn = newASN(number, timestamp)

	_, err = insertStmt.ExecContext(ctx, asn.ASN, asn.Handle,
		asn.Description, asn.FirstSeen, asn.LastSeen)
	if err != nil {
		return false, fmt.Errorf("failed to insert ASN %d: %w", number, err)
	}

	return true, nil
}

// GetOrCreateASNBatch creates or updates multiple ASNs in a single transaction
func (d *Database) GetOrCreateASNBatch(asns map[int]time.Time) error {
	if len(asns) == 0 {
		return nil
	}

	d.lock("GetOrCreateASNBatch")
	defer d.unlock()

	ctx := context.Background()

	tx, err := d.beginTx()
	if err != nil {
		return fmt.Errorf("failed to begin transaction: %w", err)
	}
	defer d.rollback(tx)

	// Prepare statements
	selectStmt, err := tx.PrepareContext(ctx,
		"SELECT asn, handle, description, first_seen, last_seen "+
			"FROM asns WHERE asn = ?")
	if err != nil {
		return fmt.Errorf("failed to prepare select statement: %w", err)
	}
	defer func() { _ = selectStmt.Close() }()

	updateStmt, err := tx.PrepareContext(ctx,
		"UPDATE asns SET last_seen = ? WHERE asn = ?")
	if err != nil {
		return fmt.Errorf("failed to prepare update statement: %w", err)
	}
	defer func() { _ = updateStmt.Close() }()

	insertStmt, err := tx.PrepareContext(ctx,
		"INSERT INTO asns (asn, handle, description, first_seen, last_seen) "+
			"VALUES (?, ?, ?, ?, ?)")
	if err != nil {
		return fmt.Errorf("failed to prepare insert statement: %w", err)
	}
	defer func() { _ = insertStmt.Close() }()

	var newASNs int

	for number, timestamp := range asns {
		inserted, err := upsertASN(ctx, selectStmt, updateStmt, insertStmt,
			number, timestamp)
		if err != nil {
			return err
		}

		if inserted {
			newASNs++
		}
	}

	err = tx.Commit()
	if err != nil {
		return fmt.Errorf("failed to commit transaction: %w", err)
	}

	d.counts.addASNs(newASNs)

	return nil
}

// GetOrCreateASN retrieves an existing ASN or creates a new one if it doesn't
// exist.
func (d *Database) GetOrCreateASN(number int, timestamp time.Time) (*ASN, error) {
	d.lock("GetOrCreateASN")
	defer d.unlock()

	tx, err := d.beginTx()
	if err != nil {
		return nil, err
	}
	defer d.rollback(tx)

	var (
		asn                 ASN
		handle, description sql.NullString
	)

	err = tx.QueryRow("SELECT asn, handle, description, first_seen, last_seen "+
		"FROM asns WHERE asn = ?", number).
		Scan(&asn.ASN, &handle, &description, &asn.FirstSeen, &asn.LastSeen)
	if err == nil {
		// ASN exists, update last_seen
		asn.Handle = handle.String
		asn.Description = description.String

		_, err = tx.Exec("UPDATE asns SET last_seen = ? WHERE asn = ?",
			timestamp, number)
		if err != nil {
			return nil, err
		}

		asn.LastSeen = timestamp

		err = tx.Commit()
		if err != nil {
			d.logger.Error("Failed to commit transaction for ASN update",
				"asn", number, "error", err)

			return nil, err
		}

		return &asn, nil
	}

	if !errors.Is(err, sql.ErrNoRows) {
		return nil, err
	}

	// ASN doesn't exist, create it with ASN info lookup
	asn = newASN(number, timestamp)

	_, err = tx.Exec("INSERT INTO asns "+
		"(asn, handle, description, first_seen, last_seen) "+
		"VALUES (?, ?, ?, ?, ?)",
		asn.ASN, asn.Handle, asn.Description, asn.FirstSeen, asn.LastSeen)
	if err != nil {
		return nil, err
	}

	err = tx.Commit()
	if err != nil {
		d.logger.Error("Failed to commit transaction for ASN creation",
			"asn", number, "error", err)

		return nil, err
	}

	d.counts.addASNs(1)

	return &asn, nil
}

// GetOrCreatePrefix retrieves an existing prefix or creates a new one if it
// doesn't exist.
func (d *Database) GetOrCreatePrefix(
	prefix string, timestamp time.Time) (*Prefix, error) {
	d.lock("GetOrCreatePrefix")
	defer d.unlock()

	tx, err := d.beginTx()
	if err != nil {
		return nil, err
	}
	defer d.rollback(tx)

	// Determine table based on IP version
	ipVersion := detectIPVersion(prefix)

	tableName := "prefixes_v4"
	if ipVersion == ipVersionV6 {
		tableName = "prefixes_v6"
	}

	var p Prefix

	query := fmt.Sprintf("SELECT prefix, first_seen FROM %s WHERE prefix = ?",
		tableName)

	err = tx.QueryRow(query, prefix).Scan(&p.Prefix, &p.FirstSeen)
	if err == nil {
		// Prefix exists; the deferred rollback ends the read.
		p.IPVersion = ipVersion

		return &p, nil
	}

	if !errors.Is(err, sql.ErrNoRows) {
		return nil, err
	}

	// Prefix doesn't exist, create it
	p = Prefix{Prefix: prefix, IPVersion: ipVersion, FirstSeen: timestamp}
	insertQuery := fmt.Sprintf("INSERT INTO %s "+
		"(prefix, first_seen) VALUES (?, ?)", tableName)

	_, err = tx.Exec(insertQuery, p.Prefix, p.FirstSeen)
	if err != nil {
		return nil, err
	}

	err = tx.Commit()
	if err != nil {
		d.logger.Error("Failed to commit transaction for prefix creation",
			"prefix", prefix, "error", err)

		return nil, err
	}

	if ipVersion == ipVersionV4 {
		d.counts.addPrefixes(1, 0)
	} else {
		d.counts.addPrefixes(0, 1)
	}

	return &p, nil
}

// RecordAnnouncement inserts a new BGP announcement or withdrawal into the
// database.
func (d *Database) RecordAnnouncement(announcement *Announcement) error {
	d.lock("RecordAnnouncement")
	defer d.unlock()

	err := d.exec(`
		INSERT INTO announcements (id, prefix_id, peer_asn, origin_asn, path,
			next_hop, timestamp, is_withdrawal)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?)`,
		announcement.ID.String(), announcement.PrefixID.String(),
		announcement.PeerASN, announcement.OriginASN,
		announcement.Path, announcement.NextHop, announcement.Timestamp,
		announcement.IsWithdrawal)

	return err
}

// RecordPeering records a peering relationship between two ASNs.
func (d *Database) RecordPeering(asA, asB int, timestamp time.Time) error {
	// Validate ASNs
	if asA <= 0 || asB <= 0 {
		return fmt.Errorf("%w: asA=%d, asB=%d", errInvalidASN, asA, asB)
	}

	if asA == asB {
		return fmt.Errorf("%w: %d", errSameASNInPeering, asA)
	}

	// Normalize: ensure asA < asB
	if asA > asB {
		asA, asB = asB, asA
	}

	d.lock("RecordPeering")
	defer d.unlock()

	tx, err := d.beginTx()
	if err != nil {
		return err
	}
	defer d.rollback(tx)

	var exists bool

	err = tx.QueryRow(
		"SELECT EXISTS(SELECT 1 FROM peerings WHERE as_a = ? AND as_b = ?)",
		asA, asB).Scan(&exists)
	if err != nil {
		return err
	}

	if exists {
		_, err = tx.Exec(
			"UPDATE peerings SET last_seen = ? WHERE as_a = ? AND as_b = ?",
			timestamp, asA, asB)
	} else {
		_, err = tx.Exec(`
			INSERT INTO peerings (id, as_a, as_b, first_seen, last_seen)
			VALUES (?, ?, ?, ?, ?)`,
			generateUUID().String(), asA, asB, timestamp, timestamp)
	}

	if err != nil {
		return err
	}

	err = tx.Commit()
	if err != nil {
		d.logger.Error("Failed to commit transaction for peering",
			"as_a", asA,
			"as_b", asB,
			"error", err,
		)

		return err
	}

	if !exists {
		d.counts.addPeerings(1)
	}

	return nil
}

// UpdatePeerBatch updates or creates multiple BGP peer records in a single transaction
func (d *Database) UpdatePeerBatch(peers map[string]PeerUpdate) error {
	if len(peers) == 0 {
		return nil
	}

	d.lock("UpdatePeerBatch")
	defer d.unlock()

	ctx := context.Background()

	tx, err := d.beginTx()
	if err != nil {
		return fmt.Errorf("failed to begin transaction: %w", err)
	}
	defer d.rollback(tx)

	// Prepare statements
	checkStmt, err := tx.PrepareContext(ctx,
		"SELECT EXISTS(SELECT 1 FROM bgp_peers WHERE peer_ip = ?)")
	if err != nil {
		return fmt.Errorf("failed to prepare check statement: %w", err)
	}
	defer func() { _ = checkStmt.Close() }()

	updateStmt, err := tx.PrepareContext(ctx,
		"UPDATE bgp_peers SET peer_asn = ?, last_seen = ?, "+
			"last_message_type = ? WHERE peer_ip = ?")
	if err != nil {
		return fmt.Errorf("failed to prepare update statement: %w", err)
	}
	defer func() { _ = updateStmt.Close() }()

	insertStmt, err := tx.PrepareContext(ctx,
		"INSERT INTO bgp_peers (id, peer_ip, peer_asn, first_seen, "+
			"last_seen, last_message_type) VALUES (?, ?, ?, ?, ?, ?)")
	if err != nil {
		return fmt.Errorf("failed to prepare insert statement: %w", err)
	}
	defer func() { _ = insertStmt.Close() }()

	var newPeers int

	for _, update := range peers {
		var exists bool

		err = checkStmt.QueryRowContext(ctx, update.PeerIP).Scan(&exists)
		if err != nil {
			return fmt.Errorf("failed to check peer %s: %w", update.PeerIP, err)
		}

		if exists {
			_, err = updateStmt.ExecContext(ctx, update.PeerASN,
				update.Timestamp, update.MessageType, update.PeerIP)
		} else {
			_, err = insertStmt.ExecContext(ctx,
				generateUUID().String(), update.PeerIP, update.PeerASN,
				update.Timestamp, update.Timestamp, update.MessageType)
		}

		if err != nil {
			return fmt.Errorf("failed to update peer %s: %w", update.PeerIP, err)
		}

		if !exists {
			newPeers++
		}
	}

	err = tx.Commit()
	if err != nil {
		return fmt.Errorf("failed to commit transaction: %w", err)
	}

	d.counts.addPeers(newPeers)

	return nil
}

// UpdatePeer updates or creates a BGP peer record
func (d *Database) UpdatePeer(
	peerIP string, peerASN int, messageType string, timestamp time.Time,
) error {
	d.lock("UpdatePeer")
	defer d.unlock()

	tx, err := d.beginTx()
	if err != nil {
		return err
	}
	defer d.rollback(tx)

	var exists bool

	err = tx.QueryRow(
		"SELECT EXISTS(SELECT 1 FROM bgp_peers WHERE peer_ip = ?)", peerIP,
	).Scan(&exists)
	if err != nil {
		return err
	}

	if exists {
		_, err = tx.Exec(
			"UPDATE bgp_peers SET peer_asn = ?, last_seen = ?, "+
				"last_message_type = ? WHERE peer_ip = ?",
			peerASN, timestamp, messageType, peerIP,
		)
	} else {
		_, err = tx.Exec(
			"INSERT INTO bgp_peers (id, peer_ip, peer_asn, first_seen, "+
				"last_seen, last_message_type) VALUES (?, ?, ?, ?, ?, ?)",
			generateUUID().String(), peerIP, peerASN, timestamp, timestamp,
			messageType,
		)
	}

	if err != nil {
		return err
	}

	err = tx.Commit()
	if err != nil {
		d.logger.Error("Failed to commit transaction for peer update",
			"peer_ip", peerIP,
			"peer_asn", peerASN,
			"error", err,
		)

		return err
	}

	if !exists {
		d.counts.addPeers(1)
	}

	return nil
}

// GetStats returns database statistics
func (d *Database) GetStats() (Stats, error) {
	return d.GetStatsContext(context.Background())
}

// GetStatsContext returns database statistics with context support.
//
// The row counts (ASNs, prefixes, peerings, peers, live routes) and the prefix
// distribution come from the in-memory counters, seeded at startup and kept
// current on every write. The oldest/newest route timestamps are read from the
// ends of the last_updated index, and the file size from a stat(). No part of
// the read scans a table or a whole index.
func (d *Database) GetStatsContext(ctx context.Context) (Stats, error) {
	var stats Stats

	// Row counts and prefix distribution from memory, as a single consistent
	// snapshot.
	d.counts.fill(&stats)

	// Database file size is a cheap stat() on the file.
	fileInfo, err := os.Stat(d.path)
	if err != nil {
		d.logger.Warn("Failed to get database file size", "error", err)
	} else {
		stats.FileSizeBytes = fileInfo.Size()
	}

	// Oldest and newest route timestamps read one row from each end of the
	// last_updated index (a log-time lookup, not a scan). Selecting the column
	// directly lets the driver parse the DATETIME into time.Time; the old
	// MIN/MAX union scan returned an untyped string that failed to scan and
	// logged a warning on every call.
	oldest, newest, err := d.routeTimestampRange(ctx)
	if err != nil {
		// Display-only fields; log but keep the rest of the stats.
		d.logger.Warn("Failed to get route timestamps", "error", err)
	} else {
		stats.OldestRoute = oldest
		stats.NewestRoute = newest
	}

	return stats, nil
}

// UpsertLiveRoute inserts or updates a live route
func (d *Database) UpsertLiveRoute(route *LiveRoute) error {
	d.lock("UpsertLiveRoute")
	defer d.unlock()

	pathJSON, err := json.Marshal(route.ASPath)
	if err != nil {
		return fmt.Errorf("failed to encode AS path: %w", err)
	}

	originSQL, updateSQL := updateLiveRouteOriginV4SQL, updateLiveRouteV4SQL
	insertSQL, lookupSQL := insertLiveRouteV4SQL, prefixHasLiveRouteV4SQL

	if route.IPVersion == ipVersionV6 {
		originSQL, updateSQL = updateLiveRouteOriginV6SQL, updateLiveRouteV6SQL
		insertSQL, lookupSQL = insertLiveRouteV6SQL, prefixHasLiveRouteV6SQL
	}

	ctx := context.Background()

	// The write lock is held, so no other writer can insert this key between the
	// update and the insert even though they are separate autocommit statements.
	setOrigin, err := d.writer.PrepareContext(ctx, originSQL)
	if err != nil {
		return fmt.Errorf("failed to prepare origin statement: %w", err)
	}
	defer func() { _ = setOrigin.Close() }()

	upd, err := d.writer.PrepareContext(ctx, updateSQL)
	if err != nil {
		return fmt.Errorf("failed to prepare update statement: %w", err)
	}
	defer func() { _ = upd.Close() }()

	ins, err := d.writer.PrepareContext(ctx, insertSQL)
	if err != nil {
		return fmt.Errorf("failed to prepare insert statement: %w", err)
	}
	defer func() { _ = ins.Close() }()

	has, err := d.writer.PrepareContext(ctx, lookupSQL)
	if err != nil {
		return fmt.Errorf("failed to prepare prefix lookup statement: %w", err)
	}
	defer func() { _ = has.Close() }()

	inserted, newPrefix, err := upsertRouteRow(ctx, setOrigin, upd, ins, has,
		route, string(pathJSON))
	if err != nil {
		return fmt.Errorf("failed to upsert route %s: %w", route.Prefix, err)
	}

	if inserted {
		if route.IPVersion == ipVersionV4 {
			d.counts.addRoutes(1, 0)
		} else {
			d.counts.addRoutes(0, 1)
		}
	}

	if newPrefix {
		if route.IPVersion == ipVersionV4 {
			d.counts.addToDistribution([]int{route.MaskLength}, nil, 1)
		} else {
			d.counts.addToDistribution(nil, []int{route.MaskLength}, 1)
		}
	}

	return nil
}

// DeleteLiveRoute deletes the live route the peer has for the prefix
func (d *Database) DeleteLiveRoute(prefix, peerIP string) error {
	d.lock("DeleteLiveRoute")
	defer d.unlock()

	// Determine table based on prefix IP version
	_, ipnet, err := net.ParseCIDR(prefix)
	if err != nil {
		return fmt.Errorf("invalid prefix format: %w", err)
	}

	isV4 := ipnet.IP.To4() != nil

	// The delete and the prefix lookup after it share one transaction, so the
	// in-memory counts change only once both have succeeded.
	tx, err := d.beginTx()
	if err != nil {
		return fmt.Errorf("failed to begin transaction: %w", err)
	}
	defer d.rollback(tx)

	// Literal per-table queries (rather than one formatted with the table name)
	// so the delete carries no dynamically built SQL.
	deleteSQL := deleteLiveRouteV6SQL
	if isV4 {
		deleteSQL = deleteLiveRouteV4SQL
	}

	res, err := tx.Exec(deleteSQL, prefix, peerIP)
	if err != nil {
		return err
	}

	affected, err := res.RowsAffected()
	if err != nil {
		return err
	}

	if affected == 0 {
		return nil
	}

	// The prefix leaves the distribution when no live route has it any more.
	lookupSQL := prefixHasLiveRouteV6SQL
	if isV4 {
		lookupSQL = prefixHasLiveRouteV4SQL
	}

	var prefixHasRoute bool

	err = tx.QueryRow(lookupSQL, prefix).Scan(&prefixHasRoute)
	if err != nil {
		return err
	}

	err = tx.Commit()
	if err != nil {
		return fmt.Errorf("failed to commit transaction: %w", err)
	}

	if isV4 {
		d.counts.addRoutes(-int(affected), 0)
	} else {
		d.counts.addRoutes(0, -int(affected))
	}

	if !prefixHasRoute {
		maskLength, _ := ipnet.Mask.Size()
		if isV4 {
			d.counts.addToDistribution([]int{maskLength}, nil, -1)
		} else {
			d.counts.addToDistribution(nil, []int{maskLength}, -1)
		}
	}

	return nil
}

// GetPrefixDistribution returns the distribution of unique prefixes by mask
// length
func (d *Database) GetPrefixDistribution() (
	[]PrefixDistribution, []PrefixDistribution, error,
) {
	return d.GetPrefixDistributionContext(context.Background())
}

// GetPrefixDistributionContext returns the distribution of unique prefixes by
// mask length with context support. It reads every live route, so the stats
// read does not call it; it seeds the in-memory distribution once at startup.
func (d *Database) GetPrefixDistributionContext(ctx context.Context) (
	[]PrefixDistribution, []PrefixDistribution, error,
) {
	var ipv4, ipv6 []PrefixDistribution

	// IPv4 distribution - count unique prefixes from v4 table
	query := `
		SELECT mask_length, COUNT(DISTINCT prefix) as count
		FROM live_routes_v4
		GROUP BY mask_length
		ORDER BY mask_length
	`

	rows4, err := d.db.QueryContext(ctx, query)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to query IPv4 distribution: %w", err)
	}
	defer func() {
		if rows4 != nil {
			_ = rows4.Close()
		}
	}()

	for rows4.Next() {
		var dist PrefixDistribution

		err := rows4.Scan(&dist.MaskLength, &dist.Count)
		if err != nil {
			return nil, nil, fmt.Errorf("failed to scan IPv4 distribution: %w",
				err)
		}

		ipv4 = append(ipv4, dist)
	}

	// A read that stops partway ends the loop without an error of its own.
	err = rows4.Err()
	if err != nil {
		return nil, nil, fmt.Errorf("failed to read IPv4 distribution: %w", err)
	}

	// IPv6 distribution - count unique prefixes from v6 table
	query = `
		SELECT mask_length, COUNT(DISTINCT prefix) as count
		FROM live_routes_v6
		GROUP BY mask_length
		ORDER BY mask_length
	`

	rows6, err := d.db.QueryContext(ctx, query)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to query IPv6 distribution: %w", err)
	}
	defer func() {
		if rows6 != nil {
			_ = rows6.Close()
		}
	}()

	for rows6.Next() {
		var dist PrefixDistribution

		err := rows6.Scan(&dist.MaskLength, &dist.Count)
		if err != nil {
			return nil, nil, fmt.Errorf("failed to scan IPv6 distribution: %w",
				err)
		}

		ipv6 = append(ipv6, dist)
	}

	err = rows6.Err()
	if err != nil {
		return nil, nil, fmt.Errorf("failed to read IPv6 distribution: %w", err)
	}

	return ipv4, ipv6, nil
}

// GetLiveRouteCounts returns the count of IPv4 and IPv6 routes
func (d *Database) GetLiveRouteCounts() (int, int, error) {
	return d.GetLiveRouteCountsContext(context.Background())
}

// GetLiveRouteCountsContext returns the count of IPv4 and IPv6 routes with
// context support
func (d *Database) GetLiveRouteCountsContext(
	ctx context.Context,
) (int, int, error) {
	var ipv4Count, ipv6Count int

	// Get IPv4 count from dedicated table
	err := d.db.QueryRowContext(ctx, "SELECT COUNT(*) FROM live_routes_v4").
		Scan(&ipv4Count)
	if err != nil {
		return 0, 0, fmt.Errorf("failed to count IPv4 routes: %w", err)
	}

	// Get IPv6 count from dedicated table
	err = d.db.QueryRowContext(ctx, "SELECT COUNT(*) FROM live_routes_v6").
		Scan(&ipv6Count)
	if err != nil {
		return 0, 0, fmt.Errorf("failed to count IPv6 routes: %w", err)
	}

	return ipv4Count, ipv6Count, nil
}

// GetASDetails returns detailed information about an AS including prefixes
func (d *Database) GetASDetails(asn int) (*ASN, []LiveRoute, error) {
	return d.GetASDetailsContext(context.Background(), asn)
}

// GetASDetailsContext returns detailed information about an AS including
// prefixes with context support
func (d *Database) GetASDetailsContext(
	ctx context.Context, asn int,
) (*ASN, []LiveRoute, error) {
	// Get AS information
	var (
		asnInfo             ASN
		handle, description sql.NullString
	)

	err := d.db.QueryRowContext(ctx,
		"SELECT asn, handle, description, first_seen, last_seen "+
			"FROM asns WHERE asn = ?",
		asn,
	).Scan(&asnInfo.ASN, &handle, &description, &asnInfo.FirstSeen,
		&asnInfo.LastSeen)
	if err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return nil, nil, fmt.Errorf("%w: AS%d", ErrNoRoute, asn)
		}

		return nil, nil, fmt.Errorf("failed to query AS: %w", err)
	}

	asnInfo.Handle = handle.String
	asnInfo.Description = description.String

	// Get prefixes announced by this AS from both tables
	queryV4 := `
		SELECT prefix, mask_length, MAX(last_updated) as last_updated
		FROM live_routes_v4
		WHERE origin_asn = ?
		GROUP BY prefix, mask_length
	`

	allPrefixes, err := d.originPrefixes(ctx, queryV4, asn, ipVersionV4)
	if err != nil {
		return &asnInfo, nil, err
	}

	queryV6 := `
		SELECT prefix, mask_length, MAX(last_updated) as last_updated
		FROM live_routes_v6
		WHERE origin_asn = ?
		GROUP BY prefix, mask_length
	`

	prefixesV6, err := d.originPrefixes(ctx, queryV6, asn, ipVersionV6)
	if err != nil {
		return &asnInfo, allPrefixes, err
	}

	return &asnInfo, append(allPrefixes, prefixesV6...), nil
}

// ASPeer represents a peering relationship with another AS including handle,
// description, and timestamps.
//
//nolint:tagliatelle // field names are the existing JSON API
type ASPeer struct {
	ASN         int       `json:"asn"`
	Handle      string    `json:"handle"`
	Description string    `json:"description"`
	FirstSeen   time.Time `json:"first_seen"`
	LastSeen    time.Time `json:"last_seen"`
}

// GetASPeers returns all ASes that peer with the given AS
func (d *Database) GetASPeers(asn int) ([]ASPeer, error) {
	return d.GetASPeersContext(context.Background(), asn)
}

// GetASPeersContext returns all ASes that peer with the given AS with context
// support
func (d *Database) GetASPeersContext(
	ctx context.Context, asn int,
) ([]ASPeer, error) {
	query := `
		SELECT 
			CASE 
				WHEN p.as_a = ? THEN p.as_b 
				ELSE p.as_a 
			END as peer_asn,
			COALESCE(a.handle, '') as handle,
			COALESCE(a.description, '') as description,
			p.first_seen,
			p.last_seen
		FROM peerings p
		LEFT JOIN asns a ON a.asn = CASE 
			WHEN p.as_a = ? THEN p.as_b 
			ELSE p.as_a 
		END
		WHERE p.as_a = ? OR p.as_b = ?
		ORDER BY peer_asn
	`

	rows, err := d.db.QueryContext(ctx, query, asn, asn, asn, asn)
	if err != nil {
		return nil, fmt.Errorf("failed to query AS peers: %w", err)
	}
	defer func() { _ = rows.Close() }()

	var peers []ASPeer

	for rows.Next() {
		var peer ASPeer

		err := rows.Scan(&peer.ASN, &peer.Handle, &peer.Description,
			&peer.FirstSeen, &peer.LastSeen)
		if err != nil {
			d.logger.Error("Failed to scan peer row", "error", err, "asn", asn)

			continue
		}

		peers = append(peers, peer)
	}

	err = rows.Err()
	if err != nil {
		return nil, fmt.Errorf("error iterating AS peers: %w", err)
	}

	return peers, nil
}

// GetPrefixDetails returns detailed information about a prefix
func (d *Database) GetPrefixDetails(
	prefix string,
) ([]LiveRoute, map[int]ASN, error) {
	return d.GetPrefixDetailsContext(context.Background(), prefix)
}

// GetPrefixDetailsContext returns the live routes for a prefix and, keyed by
// AS number, the handle and description of each AS that originates it.
func (d *Database) GetPrefixDetailsContext(
	ctx context.Context, prefix string,
) ([]LiveRoute, map[int]ASN, error) {
	// Determine if it's IPv4 or IPv6 by parsing the prefix
	_, ipnet, err := net.ParseCIDR(prefix)
	if err != nil {
		return nil, nil, fmt.Errorf("invalid prefix format: %w", err)
	}

	tableName := tableLiveRoutesV4
	ipVersion := ipVersionV4

	if ipnet.IP.To4() == nil {
		tableName = tableLiveRoutesV6
		ipVersion = ipVersionV6
	}

	query := fmt.Sprintf(`
		SELECT lr.origin_asn, lr.peer_ip, lr.as_path, lr.next_hop,
			   lr.last_updated, a.handle, a.description
		FROM %s lr
		LEFT JOIN asns a ON a.asn = lr.origin_asn
		WHERE lr.prefix = ?
		ORDER BY lr.origin_asn, lr.peer_ip
	`, tableName)

	rows, err := d.db.QueryContext(ctx, query, prefix)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to query prefix details: %w", err)
	}
	defer func() { _ = rows.Close() }()

	var routes []LiveRoute

	origins := make(map[int]ASN)

	for rows.Next() {
		var (
			route               LiveRoute
			pathJSON            string
			handle, description sql.NullString
		)

		err := rows.Scan(
			&route.OriginASN, &route.PeerIP, &pathJSON, &route.NextHop,
			&route.LastUpdated, &handle, &description,
		)
		if err != nil {
			continue
		}

		// Decode AS path
		err = json.Unmarshal([]byte(pathJSON), &route.ASPath)
		if err != nil {
			route.ASPath = []int{}
		}

		route.Prefix = prefix
		route.IPVersion = ipVersion
		route.MaskLength, _ = ipnet.Mask.Size()
		routes = append(routes, route)
		origins[route.OriginASN] = ASN{
			ASN:         route.OriginASN,
			Handle:      handle.String,
			Description: description.String,
		}
	}

	err = rows.Err()
	if err != nil {
		return nil, nil, fmt.Errorf("failed to read prefix details: %w", err)
	}

	if len(routes) == 0 {
		return nil, nil, fmt.Errorf("%w: %s", ErrNoRoute, prefix)
	}

	return routes, origins, nil
}

// GetRandomPrefixesByLength returns a random sample of prefixes with the
// specified mask length
func (d *Database) GetRandomPrefixesByLength(
	maskLength, ipVersion, limit int,
) ([]LiveRoute, error) {
	return d.GetRandomPrefixesByLengthContext(context.Background(),
		maskLength, ipVersion, limit)
}

// GetRandomPrefixesByLengthContext returns limit prefixes with the given mask
// length picked at random, or all of them when there are fewer, each once with
// its most recently updated live route, for a limit up to
// maxPrefixesToShuffle. However many routes there are, it makes at most
// maxPrefixesToShuffle+1 index searches to list prefixes, at most
// sampleLookupsPerPrefix random lookups for each prefix asked for, and one
// index search for each listed prefix's newest route.
func (d *Database) GetRandomPrefixesByLengthContext(
	ctx context.Context, maskLength, ipVersion, limit int) ([]LiveRoute, error) {
	tableName := tableLiveRoutesV4
	if ipVersion == ipVersionV6 {
		tableName = tableLiveRoutesV6
	}

	// Reading one prefix more than maxPrefixesToShuffle tells whether these
	// are all the prefixes with this mask length.
	prefixes, err := d.firstPrefixesByLength(ctx, tableName, maskLength,
		maxPrefixesToShuffle+1)
	if err != nil {
		return nil, err
	}

	//nolint:gosec // The sample needs variety, not unpredictability.
	rand.Shuffle(len(prefixes), func(i, j int) {
		prefixes[i], prefixes[j] = prefixes[j], prefixes[i]
	})

	if len(prefixes) > maxPrefixesToShuffle {
		prefixes, err = d.samplePrefixesByLength(ctx, tableName, maskLength,
			limit, prefixes)
		if err != nil {
			return nil, err
		}
	}

	prefixes = prefixes[:min(limit, len(prefixes))]

	return d.newestRouteOfEachPrefix(ctx, tableName, ipVersion, prefixes)
}

// GetNextStaleASN returns a random ASN that needs WHOIS data refresh.
func (d *Database) GetNextStaleASN(
	ctx context.Context, staleThreshold time.Duration,
) (int, error) {
	cutoff := time.Now().Add(-staleThreshold)

	// Select a random stale ASN using ORDER BY RANDOM()
	query := `
		SELECT asn FROM asns
		WHERE whois_updated_at IS NULL
		   OR whois_updated_at < ?
		ORDER BY RANDOM()
		LIMIT 1
	`

	var asn int

	err := d.db.QueryRowContext(ctx, query, cutoff).Scan(&asn)
	if err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return 0, ErrNoStaleASN
		}

		return 0, fmt.Errorf("failed to get stale ASN: %w", err)
	}

	return asn, nil
}

// WHOISStats contains statistics about WHOIS data freshness.
//
//nolint:tagliatelle // field names are the existing JSON API
type WHOISStats struct {
	TotalASNs    int `json:"total_asns"`
	StaleASNs    int `json:"stale_asns"`
	FreshASNs    int `json:"fresh_asns"`
	NeverFetched int `json:"never_fetched"`
}

// GetWHOISStats returns statistics about WHOIS data freshness.
func (d *Database) GetWHOISStats(
	ctx context.Context, staleThreshold time.Duration,
) (*WHOISStats, error) {
	cutoff := time.Now().Add(-staleThreshold)

	query := `
		SELECT
			COUNT(*) as total,
			COALESCE(SUM(CASE WHEN whois_updated_at IS NULL
				THEN 1 ELSE 0 END), 0) as never_fetched,
			COALESCE(SUM(CASE WHEN whois_updated_at IS NOT NULL
				AND whois_updated_at < ? THEN 1 ELSE 0 END), 0) as stale,
			COALESCE(SUM(CASE WHEN whois_updated_at IS NOT NULL
				AND whois_updated_at >= ? THEN 1 ELSE 0 END), 0) as fresh
		FROM asns
	`

	var stats WHOISStats

	err := d.db.QueryRowContext(ctx, query, cutoff, cutoff).Scan(
		&stats.TotalASNs,
		&stats.NeverFetched,
		&stats.StaleASNs,
		&stats.FreshASNs,
	)
	if err != nil {
		return nil, fmt.Errorf("failed to get WHOIS stats: %w", err)
	}

	return &stats, nil
}

// UpdateASNWHOIS updates an ASN record with WHOIS data.
func (d *Database) UpdateASNWHOIS(
	ctx context.Context, update *ASNWHOISUpdate,
) error {
	d.lock("UpdateASNWHOIS")
	defer d.unlock()

	query := `
		UPDATE asns SET
			as_name = ?,
			org_name = ?,
			org_id = ?,
			address = ?,
			country_code = ?,
			abuse_email = ?,
			abuse_phone = ?,
			tech_email = ?,
			tech_phone = ?,
			rir = ?,
			rir_registration_date = ?,
			rir_last_modified = ?,
			whois_raw = ?,
			whois_updated_at = ?
		WHERE asn = ?
	`

	_, err := d.writer.ExecContext(ctx, query,
		update.ASName,
		update.OrgName,
		update.OrgID,
		update.Address,
		update.CountryCode,
		update.AbuseEmail,
		update.AbusePhone,
		update.TechEmail,
		update.TechPhone,
		update.RIR,
		update.RIRRegDate,
		update.RIRLastMod,
		update.WHOISRaw,
		time.Now(),
		update.ASN,
	)
	if err != nil {
		return fmt.Errorf("failed to update ASN WHOIS: %w", err)
	}

	return nil
}

// GetIPInfo returns comprehensive IP information for the /ip endpoint.
func (d *Database) GetIPInfo(ip string) (*IPInfo, error) {
	return d.GetIPInfoContext(context.Background(), ip)
}

// ipInfoQuery reads the live route for one prefix with its peer count, the
// prefix's first_seen and the origin AS's details. %[1]s is the live route
// table and %[2]s the prefix table of the address's IP version.
const ipInfoQuery = `
		SELECT
			lr.prefix,
			lr.mask_length,
			lr.origin_asn,
			lr.last_updated,
			(SELECT COUNT(DISTINCT peer_ip) FROM %[1]s
				WHERE prefix = lr.prefix) as num_peers,
			p.first_seen,
			a.handle,
			a.description,
			a.as_name,
			a.org_name,
			a.org_id,
			a.address,
			a.country_code,
			a.abuse_email,
			a.rir,
			a.whois_updated_at
		FROM %[1]s lr
		LEFT JOIN %[2]s p ON p.prefix = lr.prefix
		LEFT JOIN asns a ON a.asn = lr.origin_asn
		WHERE lr.prefix = ?
		LIMIT 1
	`

// GetIPInfoContext returns comprehensive IP information with context support.
//
// It finds the most specific live route for the address with point lookups on
// the prefix index: for each mask length from the longest (32 or 128) down to
// minLookupMaskLengthV4 or minLookupMaskLengthV6 it looks up the address's
// network prefix at that length, and the first length with a live route wins.
// That is at most 25 or 113 indexed lookups, however many routes are live. The
// prefix is looked up in the text form net/netip prints, which is the form the
// prefix handler stores.
func (d *Database) GetIPInfoContext(
	ctx context.Context, ip string,
) (*IPInfo, error) {
	addr, err := netip.ParseAddr(ip)
	if err != nil {
		return nil, fmt.Errorf("%w: %s", ErrInvalidIP, ip)
	}
	// An IPv4 address written in IPv6 form (::ffff:192.0.2.1) is an IPv4 lookup.
	addr = addr.Unmap()

	info := &IPInfo{IP: ip, IPVersion: ipVersionV6}
	minMaskLength := minLookupMaskLengthV6

	routesTable, prefixesTable := tableLiveRoutesV6, "prefixes_v6"
	if addr.Is4() {
		routesTable, prefixesTable = tableLiveRoutesV4, "prefixes_v4"
		minMaskLength = minLookupMaskLengthV4
		info.IPVersion = ipVersionV4
	}

	// Route info with peer count and prefix first_seen
	query := fmt.Sprintf(ipInfoQuery, routesTable, prefixesTable)

	stmt, err := d.db.PrepareContext(ctx, query)
	if err != nil {
		return nil, fmt.Errorf("failed to prepare route query: %w", err)
	}
	defer func() { _ = stmt.Close() }()

	var (
		handle, description, asName, orgName, orgID sql.NullString
		address, countryCode, abuseEmail, rir       sql.NullString
		prefixFirstSeen, whoisUpdatedAt             sql.NullTime
	)

	found := false

	for bits := addr.BitLen(); bits >= minMaskLength; bits-- {
		prefix := netip.PrefixFrom(addr, bits).Masked().String()

		err := stmt.QueryRowContext(ctx, prefix).Scan(
			&info.Netblock, &info.MaskLength, &info.ASN, &info.LastSeen,
			&info.NumPeers, &prefixFirstSeen, &handle, &description,
			&asName, &orgName, &orgID, &address, &countryCode, &abuseEmail,
			&rir, &whoisUpdatedAt,
		)
		if errors.Is(err, sql.ErrNoRows) {
			continue
		}

		if err != nil {
			return nil, fmt.Errorf("failed to query routes: %w", err)
		}

		found = true

		break
	}

	if !found {
		return nil, fmt.Errorf("%w for IP %s", ErrNoRoute, ip)
	}

	info.Handle = handle.String
	info.Description = description.String
	info.ASName = asName.String
	info.OrgName = orgName.String
	info.OrgID = orgID.String
	info.Address = address.String
	info.CountryCode = countryCode.String
	info.AbuseEmail = abuseEmail.String
	info.RIR = rir.String

	if prefixFirstSeen.Valid {
		info.FirstSeen = prefixFirstSeen.Time
	}

	// Check if WHOIS data needs refresh (never fetched or older than 30 days).
	// A route with origin 0 has no known origin, so no AS to look up.
	const staleThreshold = 30 * 24 * time.Hour

	info.NeedsWHOISRefresh = info.ASN != 0 && (!whoisUpdatedAt.Valid ||
		time.Since(whoisUpdatedAt.Time) > staleThreshold)

	return info, nil
}

// Vacuum runs incremental vacuum to return up to 1000 unused pages to the
// filesystem. Like Analyze and Checkpoint, it holds the database lock, so it
// and the batch writes wait for each other instead of failing on SQLite's
// write lock, and returns ctx's error without running if ctx ended while it
// waited: the writing connection it uses does not check ctx itself.
func (d *Database) Vacuum(ctx context.Context) error {
	// Free up to 1000 pages per call (~4MB with default 4KB page size)
	// This keeps each vacuum operation quick
	const pagesToFree = 1000

	d.lock("Vacuum")
	defer d.unlock()

	err := ctx.Err()
	if err != nil {
		return fmt.Errorf("failed to run incremental vacuum: %w", err)
	}

	rows, err := d.writer.QueryContext(ctx,
		fmt.Sprintf("PRAGMA incremental_vacuum(%d)", pagesToFree))
	if err != nil {
		return fmt.Errorf("failed to run incremental vacuum: %w", err)
	}
	defer func() { _ = rows.Close() }()

	// SQLite frees one page each time the statement steps, and each step
	// returns a row, so every row must be read for the pragma to free more
	// than one page.
	for rows.Next() {
	}

	err = rows.Err()
	if err != nil {
		return fmt.Errorf("failed to run incremental vacuum: %w", err)
	}

	return nil
}

// Analyze updates the query planner statistics. It runs ANALYZE, through
// PRAGMA optimize, only on the tables that have an index without statistics or
// whose size has changed tenfold since they were last analyzed: even with
// analysisLimit, ANALYZE counts every entry of each index, so it takes longer
// as the tables grow. It holds the database lock.
func (d *Database) Analyze(ctx context.Context) error {
	d.lock("Analyze")
	defer d.unlock()

	err := ctx.Err()
	if err != nil {
		return fmt.Errorf("failed to analyze database: %w", err)
	}

	// analysis_limit is a setting of the connection, so it is set in the same
	// call as PRAGMA optimize, which runs both statements on one connection.
	_, err = d.writer.ExecContext(ctx, fmt.Sprintf(
		"PRAGMA analysis_limit=%d; PRAGMA optimize=%#x",
		analysisLimit, optimizeAllTables))
	if err != nil {
		return fmt.Errorf("failed to analyze database: %w", err)
	}

	return nil
}

// Checkpoint runs a WAL checkpoint to transfer data from the WAL to the main database.
// Uses TRUNCATE mode which blocks writers briefly but ensures complete checkpoint,
// keeping the WAL small for fast read performance. It holds the database lock.
func (d *Database) Checkpoint(ctx context.Context) error {
	d.lock("Checkpoint")
	defer d.unlock()

	err := ctx.Err()
	if err != nil {
		return fmt.Errorf("failed to checkpoint WAL: %w", err)
	}

	_, err = d.writer.ExecContext(ctx, "PRAGMA wal_checkpoint(TRUNCATE)")
	if err != nil {
		return fmt.Errorf("failed to checkpoint WAL: %w", err)
	}

	return nil
}

// Ping checks if the database connection is alive with a lightweight query.
func (d *Database) Ping(ctx context.Context) error {
	var result int

	err := d.db.QueryRowContext(ctx, "SELECT 1").Scan(&result)
	if err != nil {
		return fmt.Errorf("database ping failed: %w", err)
	}

	return nil
}

// The debug messages lock logs, with the operation's name, when it starts to
// wait for the database mutex and when it holds it.
const (
	lockWaitMessage = "Acquiring database lock"
	lockHeldMessage = "Database lock acquired"
)

// lock acquires the database mutex and logs debug information
func (d *Database) lock(operation string) {
	// Get caller information
	_, file, line, _ := runtime.Caller(1)
	caller := fmt.Sprintf("%s:%d", filepath.Base(file), line)

	d.logger.Debug(lockWaitMessage, "operation", operation, "caller", caller)

	d.mu.Lock()
	d.lockedAt = time.Now()
	d.lockedBy = fmt.Sprintf("%s (%s)", operation, caller)

	d.logger.Debug(lockHeldMessage, "operation", operation, "caller", caller)
}

// unlock releases the database mutex and logs debug information including
// hold duration
func (d *Database) unlock() {
	holdDuration := time.Since(d.lockedAt)
	lockedBy := d.lockedBy

	d.lockedAt = time.Time{}
	d.lockedBy = ""
	d.mu.Unlock()

	d.logger.Debug("Database lock released",
		"held_by", lockedBy, "duration_ms", holdDuration.Milliseconds())
}

// beginTx starts a new transaction on the writing connection, with logging
func (d *Database) beginTx() (*loggingTx, error) {
	tx, err := d.writer.BeginTx(context.Background(), nil)
	if err != nil {
		return nil, err
	}

	return &loggingTx{Tx: tx, logger: d.logger}, nil
}

// rollback rolls back tx unless it has already been committed, and logs a
// failure. Every write defers it right after beginning its transaction.
func (d *Database) rollback(tx *loggingTx) {
	err := tx.Rollback()
	if err != nil && !errors.Is(err, sql.ErrTxDone) {
		d.logger.Error("Failed to rollback transaction", "error", err)
	}
}

// routeTimestampRange returns the earliest and latest last_updated across both
// live route tables, or nil values when both tables are empty. Each query reads
// one row from an end of the last_updated index rather than scanning the tables.
func (d *Database) routeTimestampRange(
	ctx context.Context,
) (*time.Time, *time.Time, error) {
	var oldest, newest *time.Time

	oldestV4, ok, err := d.scanRouteTimestamp(ctx, "SELECT last_updated "+
		"FROM live_routes_v4 ORDER BY last_updated ASC LIMIT 1")
	if err != nil {
		return nil, nil, err
	}

	if ok {
		oldest = &oldestV4
	}

	oldestV6, ok, err := d.scanRouteTimestamp(ctx, "SELECT last_updated "+
		"FROM live_routes_v6 ORDER BY last_updated ASC LIMIT 1")
	if err != nil {
		return nil, nil, err
	}

	if ok && (oldest == nil || oldestV6.Before(*oldest)) {
		oldest = &oldestV6
	}

	newestV4, ok, err := d.scanRouteTimestamp(ctx, "SELECT last_updated "+
		"FROM live_routes_v4 ORDER BY last_updated DESC LIMIT 1")
	if err != nil {
		return nil, nil, err
	}

	if ok {
		newest = &newestV4
	}

	newestV6, ok, err := d.scanRouteTimestamp(ctx, "SELECT last_updated "+
		"FROM live_routes_v6 ORDER BY last_updated DESC LIMIT 1")
	if err != nil {
		return nil, nil, err
	}

	if ok && (newest == nil || newestV6.After(*newest)) {
		newest = &newestV6
	}

	return oldest, newest, nil
}

// scanRouteTimestamp runs a single-row timestamp query. The bool is false when
// the table is empty. The query selects the last_updated column directly so the
// driver parses the DATETIME value into a time.Time.
func (d *Database) scanRouteTimestamp(
	ctx context.Context, query string,
) (time.Time, bool, error) {
	var ts time.Time

	err := d.db.QueryRowContext(ctx, query).Scan(&ts)
	switch {
	case errors.Is(err, sql.ErrNoRows):
		return time.Time{}, false, nil
	case err != nil:
		return time.Time{}, false, err
	default:
		return ts, true, nil
	}
}

// originPrefixes runs query, which selects the prefix, mask length and latest
// last_updated of every prefix asn originates in the live route table of
// ipVersion. Rows that fail to scan or whose timestamp does not parse are
// logged and skipped.
func (d *Database) originPrefixes(
	ctx context.Context, query string, asn, ipVersion int,
) ([]LiveRoute, error) {
	family := ipv4Family
	if ipVersion == ipVersionV6 {
		family = ipv6Family
	}

	rows, err := d.db.QueryContext(ctx, query, asn)
	if err != nil {
		return nil, fmt.Errorf("failed to query %s prefixes: %w", family, err)
	}
	defer func() { _ = rows.Close() }()

	var routes []LiveRoute

	for rows.Next() {
		var (
			route          LiveRoute
			lastUpdatedStr string
		)

		err := rows.Scan(&route.Prefix, &route.MaskLength, &lastUpdatedStr)
		if err != nil {
			d.logger.Error("Failed to scan "+family+" prefix row",
				"error", err, "asn", asn)

			continue
		}

		// Parse the timestamp string
		route.LastUpdated, err = time.Parse("2006-01-02 15:04:05-07:00",
			lastUpdatedStr)
		if err != nil {
			// Try without timezone
			route.LastUpdated, err = time.Parse("2006-01-02 15:04:05",
				lastUpdatedStr)
			if err != nil {
				d.logger.Error("Failed to parse timestamp",
					"error", err, "timestamp", lastUpdatedStr)

				continue
			}
		}

		route.OriginASN = asn
		route.IPVersion = ipVersion
		routes = append(routes, route)
	}

	err = rows.Err()
	if err != nil {
		return nil, fmt.Errorf("failed to read %s prefixes: %w", family, err)
	}

	return routes, nil
}

// firstPrefixesByLength returns the first n prefixes, in text order, with the
// given mask length. Each prefix is one search of the mask length and prefix
// index for the prefix after the previous one, so the read does not grow with
// the number of peers that carry a prefix, as a SELECT DISTINCT would.
func (d *Database) firstPrefixesByLength(
	ctx context.Context, tableName string, maskLength, n int) ([]string, error) {
	//nolint:gosec // Table name is hardcoded based on IP version
	query := fmt.Sprintf(`
		SELECT prefix FROM %s
		WHERE mask_length = ? AND prefix > ?
		ORDER BY prefix
		LIMIT 1
	`, tableName)

	stmt, err := d.db.PrepareContext(ctx, query)
	if err != nil {
		return nil, fmt.Errorf("failed to prepare prefix query: %w", err)
	}
	defer func() { _ = stmt.Close() }()

	var prefixes []string

	previous := "" // every prefix sorts after the empty string

	for len(prefixes) < n {
		var prefix string

		err := stmt.QueryRowContext(ctx, maskLength, previous).Scan(&prefix)
		if errors.Is(err, sql.ErrNoRows) {
			break
		}

		if err != nil {
			return nil, fmt.Errorf("failed to list prefixes: %w", err)
		}

		prefixes = append(prefixes, prefix)
		previous = prefix
	}

	return prefixes, nil
}

// samplePrefixesByLength picks limit distinct prefixes with the given mask
// length at random, in at most sampleLookupsPerPrefix lookups for each prefix
// asked for. ORDER BY RANDOM() would read every route with that mask length.
// Instead each lookup draws a row id between those of the first and last route
// with that mask length and takes the prefix of the first such route at or
// after it. SQLite keeps the row id at the end of every index entry, so the
// mask length index is ordered by mask length, then row id, and the lookup is
// one search of it.
//
// The sample is uneven, as the page needs a varied sample, not an even one: a
// route is picked in proportion to the row ids between it and the previous
// route with that mask length, including the row ids of routes with other mask
// lengths and of withdrawn routes. A route that follows a long run of
// withdrawn routes is picked far more often than one that directly follows
// another route with that mask length.
//
// Should the lookups keep landing on prefixes already picked, the rest are
// taken from shuffled, prefixes of that length in random order.
func (d *Database) samplePrefixesByLength(
	ctx context.Context, tableName string, maskLength, limit int,
	shuffled []string,
) ([]string, error) {
	//nolint:gosec // Table name is hardcoded based on IP version
	rangeQuery := fmt.Sprintf(`
		SELECT
			(SELECT MIN(rowid) FROM %[1]s WHERE mask_length = ?),
			(SELECT MAX(rowid) FROM %[1]s WHERE mask_length = ?)
	`, tableName)

	var first, last sql.NullInt64

	err := d.db.QueryRowContext(ctx, rangeQuery, maskLength, maskLength).
		Scan(&first, &last)
	if err != nil {
		return nil, fmt.Errorf("failed to read row id range: %w", err)
	}

	if !first.Valid {
		// Every route with this mask length was withdrawn since they were listed.
		return nil, nil
	}

	//nolint:gosec // Table name is hardcoded based on IP version
	lookupQuery := fmt.Sprintf(`
		SELECT prefix FROM %s
		WHERE mask_length = ? AND rowid >= ?
		ORDER BY rowid
		LIMIT 1
	`, tableName)

	stmt, err := d.db.PrepareContext(ctx, lookupQuery)
	if err != nil {
		return nil, fmt.Errorf("failed to prepare prefix lookup: %w", err)
	}
	defer func() { _ = stmt.Close() }()

	picked := make(map[string]bool, limit)
	prefixes := make([]string, 0, limit)
	pick := func(prefix string) {
		if !picked[prefix] {
			picked[prefix] = true
			prefixes = append(prefixes, prefix)
		}
	}

	maxLookups := limit * sampleLookupsPerPrefix
	for lookups := 0; lookups < maxLookups && len(prefixes) < limit; lookups++ {
		//nolint:gosec // The sample needs variety, not unpredictability.
		rowID := first.Int64 + rand.Int64N(last.Int64-first.Int64+1)

		var prefix string

		err := stmt.QueryRowContext(ctx, maskLength, rowID).Scan(&prefix)
		if errors.Is(err, sql.ErrNoRows) {
			// The routes from rowID on were withdrawn since the range was read.
			continue
		}

		if err != nil {
			return nil, fmt.Errorf("failed to look up prefix: %w", err)
		}

		pick(prefix)
	}

	for _, prefix := range shuffled {
		if len(prefixes) == limit {
			break
		}

		pick(prefix)
	}

	return prefixes, nil
}

// newestRouteOfEachPrefix returns the most recently updated live route of each
// prefix, one search of the prefix and last_updated index per prefix however
// many peers carry it. A prefix whose routes were all withdrawn since it was
// picked is left out.
func (d *Database) newestRouteOfEachPrefix(
	ctx context.Context, tableName string, ipVersion int, prefixes []string,
) ([]LiveRoute, error) {
	//nolint:gosec // Table name is hardcoded based on IP version
	query := fmt.Sprintf(`
		SELECT prefix, mask_length, origin_asn, as_path, peer_ip, last_updated
		FROM %s
		WHERE prefix = ?
		ORDER BY last_updated DESC
		LIMIT 1
	`, tableName)

	stmt, err := d.db.PrepareContext(ctx, query)
	if err != nil {
		return nil, fmt.Errorf("failed to prepare route query: %w", err)
	}
	defer func() { _ = stmt.Close() }()

	routes := make([]LiveRoute, 0, len(prefixes))

	for _, prefix := range prefixes {
		route := LiveRoute{IPVersion: ipVersion}

		var pathJSON string

		err := stmt.QueryRowContext(ctx, prefix).Scan(
			&route.Prefix,
			&route.MaskLength,
			&route.OriginASN,
			&pathJSON,
			&route.PeerIP,
			&route.LastUpdated,
		)
		if errors.Is(err, sql.ErrNoRows) {
			continue
		}

		if err != nil {
			return nil, fmt.Errorf("failed to query route of %s: %w", prefix, err)
		}

		err = json.Unmarshal([]byte(pathJSON), &route.ASPath)
		if err != nil {
			route.ASPath = []int{}
		}

		routes = append(routes, route)
	}

	return routes, nil
}