package database

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"net/netip"
	"sync"
	"testing"
	"time"

	"git.eeqj.de/sneak/routewatch/internal/config"
	"git.eeqj.de/sneak/routewatch/internal/logger"
	"github.com/google/uuid"
)

// tempStoreMemory is the PRAGMA temp_store value meaning "hold temp B-trees in
// memory"; the DSN change must leave temp_store below this so they spill to disk.
const tempStoreMemory = 2

// autoVacuumIncremental is the PRAGMA auto_vacuum value meaning "incremental".
const autoVacuumIncremental = 2

// vacuumTestRoutes is how many routes the vacuum test writes and then deletes,
// enough to leave many free pages in the file.
const vacuumTestRoutes = 2000

// heldConnections is how many pooled connections the pragma test holds open at
// once so each is a distinct SQLite connection that parsed the DSN.
const heldConnections = 5

// testPeerIP is the peer every route in the IP lookup test is learned from.
const testPeerIP = "192.0.2.254"

// Parameters for the checkpoint-contention regression test.
const (
	// contentionIterations is how many batch writes race the checkpoint loop.
	contentionIterations = 400
	// contendedASNCount is the small set of ASNs the batches reuse, so most
	// batches update existing rows and exercise the read-before-write path.
	contendedASNCount = 16
	// asnSecondBand offsets a second ASN per batch so each batch writes more
	// than one row.
	asnSecondBand = 100
)

// TestGetIPInfoFindsMostSpecificLiveRoute stores nested live prefixes for both
// families and checks that a lookup returns the most specific one covering the
// address, ErrNoRoute when none covers it, and the next less specific prefix
// once the only route of the most specific one is withdrawn.
func TestGetIPInfoFindsMostSpecificLiveRoute(t *testing.T) {
	t.Parallel()

	cfg := &config.Config{StateDir: t.TempDir()}

	db, err := New(cfg, logger.New())
	if err != nil {
		t.Fatalf("failed to create database: %v", err)
	}
	defer func() { _ = db.Close() }()

	// Nested live prefixes, each originated by its own AS.
	origins := map[string]int{
		"10.0.0.0/8":        64500,
		"10.1.0.0/16":       64501,
		"10.1.2.0/24":       64502,
		"2001:db8::/32":     64500,
		"2001:db8:1::/48":   64501,
		"2001:db8:1:2::/64": 64502,
	}
	writeOriginRoutes(t, db, origins)

	// lookup checks that ip resolves to the live prefix want, or to ErrNoRoute
	// when want is empty.
	lookup := func(ip, want string) {
		t.Helper()

		info, err := db.GetIPInfo(ip)
		if want == "" {
			if !errors.Is(err, ErrNoRoute) {
				t.Errorf("GetIPInfo(%s) = %+v, %v; want ErrNoRoute", ip, info, err)
			}

			return
		}

		if err != nil {
			t.Errorf("GetIPInfo(%s): %v", ip, err)

			return
		}

		if info.Netblock != want || info.MaskLength != netip.MustParsePrefix(want).Bits() ||
			info.ASN != origins[want] {
			t.Errorf("GetIPInfo(%s) = %s (mask %d) AS%d, want %s AS%d",
				ip, info.Netblock, info.MaskLength, info.ASN, want, origins[want])
		}
	}

	lookup("10.1.2.3", "10.1.2.0/24")
	lookup("::ffff:10.1.2.3", "10.1.2.0/24")
	lookup("10.1.3.4", "10.1.0.0/16")
	lookup("10.2.0.1", "10.0.0.0/8")
	lookup("192.0.2.1", "")
	lookup("2001:db8:1:2::3", "2001:db8:1:2::/64")
	lookup("2001:db8:1:3::4", "2001:db8:1::/48")
	lookup("2001:db8:2::1", "2001:db8::/32")
	lookup("2001:db9::1", "")

	err = db.DeleteLiveRouteBatch([]LiveRouteDeletion{
		{
			Prefix: "10.1.2.0/24", OriginASN: 64502,
			PeerIP: testPeerIP, IPVersion: ipVersionV4,
		},
		{
			Prefix: "2001:db8:1:2::/64", OriginASN: 64502,
			PeerIP: testPeerIP, IPVersion: ipVersionV6,
		},
	})
	if err != nil {
		t.Fatalf("DeleteLiveRouteBatch: %v", err)
	}

	lookup("10.1.2.3", "10.1.0.0/16")
	lookup("2001:db8:1:2::3", "2001:db8:1::/48")
}

// TestGetIPInfoIgnoresShortRoutes checks that the IP lookup does not report a
// default route, or a route shorter than /8 for IPv4 or /16 for IPv6, as the
// route for an address, and that a route of exactly /8 or /16, or longer, still
// is. The prefixes are written out so that a wrong limit fails the test.
func TestGetIPInfoIgnoresShortRoutes(t *testing.T) {
	t.Parallel()

	cfg := &config.Config{StateDir: t.TempDir()}

	db, err := New(cfg, logger.New())
	if err != nil {
		t.Fatalf("failed to create database: %v", err)
	}
	defer func() { _ = db.Close() }()

	// announce writes one live route for prefix, originated by asn.
	announce := func(prefix string, asn int) {
		t.Helper()

		writeOriginRoutes(t, db, map[string]int{prefix: asn})
	}

	// lookup checks that ip resolves to the live prefix netblock from asn.
	lookup := func(ip, netblock string, asn int) {
		t.Helper()

		info, err := db.GetIPInfo(ip)
		if err != nil {
			t.Errorf("GetIPInfo(%s): %v", ip, err)

			return
		}

		if info.Netblock != netblock || info.ASN != asn {
			t.Errorf("GetIPInfo(%s) = %s AS%d, want %s AS%d",
				ip, info.Netblock, info.ASN, netblock, asn)
		}
	}

	// Default and very short routes, and routes one bit shorter than each limit.
	announce("2000::/3", 64500)
	announce("0.0.0.0/0", 64500)
	announce("2000::/15", 64500)
	announce("192.0.0.0/7", 64500)

	for _, ip := range []string{"2001:db8::1", "192.0.2.1"} {
		info, err := db.GetIPInfo(ip)
		if !errors.Is(err, ErrNoRoute) {
			t.Errorf("GetIPInfo(%s) with only short routes = %+v, %v; "+
				"want ErrNoRoute", ip, info, err)
		}
	}

	// Routes of exactly the minimum length are used.
	announce("2001::/16", 64501)
	announce("192.0.0.0/8", 64501)

	lookup("2001:db8::1", "2001::/16", 64501)
	lookup("192.0.2.1", "192.0.0.0/8", 64501)

	announce("2001:db8::/32", 64502)

	lookup("2001:db8::1", "2001:db8::/32", 64502)
}

// writeOriginRoutes writes one live route from testPeerIP for each prefix in
// origins, originated by the AS it maps to.
func writeOriginRoutes(t *testing.T, db *Database, origins map[string]int) {
	t.Helper()

	ts := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
	routes := make([]*LiveRoute, 0, len(origins))

	for prefix, asn := range origins {
		routes = append(routes, &LiveRoute{
			ID:          uuid.New(),
			Prefix:      prefix,
			MaskLength:  netip.MustParsePrefix(prefix).Bits(),
			IPVersion:   detectIPVersion(prefix),
			OriginASN:   asn,
			PeerIP:      testPeerIP,
			ASPath:      []int{asn},
			NextHop:     testPeerIP,
			LastUpdated: ts,
		})
	}

	err := db.UpsertLiveRouteBatch(routes)
	if err != nil {
		t.Fatalf("UpsertLiveRouteBatch: %v", err)
	}
}

// TestConnectionPoolPragmas holds several pooled connections open at once and
// checks each one carries the per-connection settings from the DSN, plus the
// process-wide hard heap limit, and sees the new file with auto_vacuum
// incremental.
func TestConnectionPoolPragmas(t *testing.T) {
	t.Parallel()

	cfg := &config.Config{StateDir: t.TempDir()}

	db, err := New(cfg, logger.New())
	if err != nil {
		t.Fatalf("failed to create database: %v", err)
	}
	defer func() { _ = db.Close() }()

	ctx := context.Background()

	// Hold distinct connections open simultaneously so the pool must open a new
	// one (each parsing the DSN) rather than hand back the same connection.
	conns := make([]*sql.Conn, 0, heldConnections)
	defer func() {
		for _, c := range conns {
			_ = c.Close()
		}
	}()

	for i := range heldConnections {
		c, err := db.db.Conn(ctx)
		if err != nil {
			t.Fatalf("failed to open connection %d: %v", i, err)
		}

		conns = append(conns, c)
	}

	for i, c := range conns {
		cacheSize := readPragma(ctx, t, c, i, "cache_size")
		if cacheSize != sqliteCacheSizeKiB {
			t.Errorf("conn %d: cache_size = %d, want %d",
				i, cacheSize, sqliteCacheSizeKiB)
		}

		busyTimeout := readPragma(ctx, t, c, i, "busy_timeout")
		if busyTimeout != sqliteBusyTimeoutMs {
			t.Errorf("conn %d: busy_timeout = %d, want %d",
				i, busyTimeout, sqliteBusyTimeoutMs)
		}

		tempStore := readPragma(ctx, t, c, i, "temp_store")
		if tempStore == tempStoreMemory {
			t.Errorf("conn %d: temp_store = %d, want anything but %d (MEMORY)",
				i, tempStore, tempStoreMemory)
		}

		hardHeapLimit := readPragma(ctx, t, c, i, "hard_heap_limit")
		if hardHeapLimit != sqliteHardHeapLimitBytes {
			t.Errorf("conn %d: hard_heap_limit = %d, want %d",
				i, hardHeapLimit, sqliteHardHeapLimitBytes)
		}

		autoVacuum := readPragma(ctx, t, c, i, "auto_vacuum")
		if autoVacuum != autoVacuumIncremental {
			t.Errorf("conn %d: auto_vacuum = %d, want %d (incremental)",
				i, autoVacuum, autoVacuumIncremental)
		}
	}
}

// readPragma reads the integer value of PRAGMA name on connection i, c.
func readPragma(
	ctx context.Context, t *testing.T, c *sql.Conn, i int, name string,
) int64 {
	t.Helper()

	var value int64

	err := c.QueryRowContext(ctx, "PRAGMA "+name).Scan(&value)
	if err != nil {
		t.Fatalf("conn %d: failed to read %s: %v", i, name, err)
	}

	return value
}

// TestVacuumReturnsFreePages checks that after routes are deleted from a new
// database, one Vacuum call returns every page they used. The deletes leave
// fewer free pages than the 1000 Vacuum frees per call, so none may remain.
// With auto_vacuum off (issue https://git.eeqj.de/sneak/routewatch/issues/43)
// the free pages stayed in the file, and with the PRAGMA run by ExecContext
// Vacuum freed only one page per call.
func TestVacuumReturnsFreePages(t *testing.T) {
	t.Parallel()

	cfg := &config.Config{StateDir: t.TempDir()}

	db, err := New(cfg, logger.New())
	if err != nil {
		t.Fatalf("failed to create database: %v", err)
	}
	defer func() { _ = db.Close() }()

	ctx := context.Background()
	ts := time.Now().UTC()

	const asn = 64500

	routes := make([]*LiveRoute, 0, vacuumTestRoutes)
	deletions := make([]LiveRouteDeletion, 0, vacuumTestRoutes)

	for i := range vacuumTestRoutes {
		route := mkV4Route(t, fmt.Sprintf("10.%d.%d.0/24", i/256, i%256), asn, ts)
		routes = append(routes, route)
		deletions = append(deletions, LiveRouteDeletion{
			Prefix:    route.Prefix,
			OriginASN: asn,
			PeerIP:    route.PeerIP,
			IPVersion: ipVersionV4,
		})
	}

	err = db.UpsertLiveRouteBatch(routes)
	if err != nil {
		t.Fatalf("failed to write routes: %v", err)
	}

	err = db.DeleteLiveRouteBatch(deletions)
	if err != nil {
		t.Fatalf("failed to delete routes: %v", err)
	}

	var before int

	err = db.db.QueryRowContext(ctx, "PRAGMA freelist_count").Scan(&before)
	if err != nil {
		t.Fatalf("failed to read freelist_count: %v", err)
	}

	if before == 0 {
		t.Fatalf("no free pages after deleting %d routes", vacuumTestRoutes)
	}

	err = db.Vacuum(ctx)
	if err != nil {
		t.Fatalf("Vacuum failed: %v", err)
	}

	var after int

	err = db.db.QueryRowContext(ctx, "PRAGMA freelist_count").Scan(&after)
	if err != nil {
		t.Fatalf("failed to read freelist_count: %v", err)
	}

	if after != 0 {
		t.Errorf("free pages after Vacuum = %d of %d, want 0", after, before)
	}
}

// TestBatchWriteDuringCheckpoint reproduces issue #25. A batch write reads
// (SELECT) before it writes (INSERT/UPDATE). Under the default deferred locking
// the transaction begins as a reader and, when the maintainer's WAL checkpoint
// holds the write lock, its upgrade to writer fails immediately with "database
// is locked" without honouring busy_timeout, dropping the batch. With
// _txlock=immediate the transaction takes the write lock at BEGIN and waits, so
// no batch is dropped. The checkpoint runs without the Database mutex, exactly
// as the background maintainer does in production.
func TestBatchWriteDuringCheckpoint(t *testing.T) {
	t.Parallel()

	cfg := &config.Config{StateDir: t.TempDir()}

	db, err := New(cfg, logger.New())
	if err != nil {
		t.Fatalf("failed to create database: %v", err)
	}
	defer func() { _ = db.Close() }()

	ctx, cancel := context.WithCancel(context.Background())

	var wg sync.WaitGroup
	wg.Add(1)

	go func() {
		defer wg.Done()

		for {
			select {
			case <-ctx.Done():
				return
			default:
				_ = db.Checkpoint(ctx) // errors are the checkpoint's own to absorb
			}
		}
	}()

	ts := time.Now().UTC()
	for i := range contentionIterations {
		asns := map[int]time.Time{
			i % contendedASNCount:                   ts,
			(i % contendedASNCount) + asnSecondBand: ts,
		}

		err := db.GetOrCreateASNBatch(asns)
		if err != nil {
			cancel()
			wg.Wait()
			t.Fatalf("batch write failed under checkpoint contention: %v", err)
		}
	}

	cancel()
	wg.Wait()
}