// Package database provides SQLite storage for BGP routing data including ASNs, prefixes, announcements and peerings.
package database

import (
	"database/sql"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"runtime"
	"time"

	"github.com/google/uuid"
	_ "modernc.org/sqlite" // Pure Go SQLite driver
)

const (
	dirPermissions = 0750 // rwxr-x---
	dbSchema       = `
CREATE TABLE IF NOT EXISTS asns (
	id TEXT PRIMARY KEY,
	number INTEGER UNIQUE NOT NULL,
	first_seen DATETIME NOT NULL,
	last_seen DATETIME NOT NULL
);

CREATE TABLE IF NOT EXISTS prefixes (
	id TEXT PRIMARY KEY,
	prefix TEXT UNIQUE NOT NULL,
	ip_version INTEGER NOT NULL, -- 4 for IPv4, 6 for IPv6
	first_seen DATETIME NOT NULL,
	last_seen DATETIME NOT NULL
);

CREATE TABLE IF NOT EXISTS announcements (
	id TEXT PRIMARY KEY,
	prefix_id TEXT NOT NULL,
	asn_id TEXT NOT NULL,
	origin_asn_id TEXT NOT NULL,
	path TEXT NOT NULL,
	next_hop TEXT,
	timestamp DATETIME NOT NULL,
	is_withdrawal BOOLEAN NOT NULL DEFAULT 0,
	FOREIGN KEY (prefix_id) REFERENCES prefixes(id),
	FOREIGN KEY (asn_id) REFERENCES asns(id),
	FOREIGN KEY (origin_asn_id) REFERENCES asns(id)
);

CREATE TABLE IF NOT EXISTS asn_peerings (
	id TEXT PRIMARY KEY,
	from_asn_id TEXT NOT NULL,
	to_asn_id TEXT NOT NULL,
	first_seen DATETIME NOT NULL,
	last_seen DATETIME NOT NULL,
	FOREIGN KEY (from_asn_id) REFERENCES asns(id),
	FOREIGN KEY (to_asn_id) REFERENCES asns(id),
	UNIQUE(from_asn_id, to_asn_id)
);

-- BGP peers that send us messages
CREATE TABLE IF NOT EXISTS bgp_peers (
	id TEXT PRIMARY KEY,
	peer_ip TEXT UNIQUE NOT NULL,
	peer_asn INTEGER NOT NULL,
	first_seen DATETIME NOT NULL,
	last_seen DATETIME NOT NULL,
	last_message_type TEXT
);

-- Live routing table: current state of announced routes
CREATE TABLE IF NOT EXISTS live_routes (
	id TEXT PRIMARY KEY,
	prefix_id TEXT NOT NULL,
	origin_asn_id TEXT NOT NULL,
	peer_asn INTEGER NOT NULL,
	next_hop TEXT,
	announced_at DATETIME NOT NULL,
	withdrawn_at DATETIME,
	FOREIGN KEY (prefix_id) REFERENCES prefixes(id),
	FOREIGN KEY (origin_asn_id) REFERENCES asns(id),
	UNIQUE(prefix_id, origin_asn_id, peer_asn)
);

CREATE INDEX IF NOT EXISTS idx_prefixes_ip_version ON prefixes(ip_version);
CREATE INDEX IF NOT EXISTS idx_prefixes_version_prefix ON prefixes(ip_version, prefix);
CREATE INDEX IF NOT EXISTS idx_announcements_timestamp ON announcements(timestamp);
CREATE INDEX IF NOT EXISTS idx_announcements_prefix_id ON announcements(prefix_id);
CREATE INDEX IF NOT EXISTS idx_announcements_asn_id ON announcements(asn_id);
CREATE INDEX IF NOT EXISTS idx_asn_peerings_from_asn ON asn_peerings(from_asn_id);
CREATE INDEX IF NOT EXISTS idx_asn_peerings_to_asn ON asn_peerings(to_asn_id);

-- Indexes for live routes table
CREATE INDEX IF NOT EXISTS idx_live_routes_active 
	ON live_routes(prefix_id, origin_asn_id) 
	WHERE withdrawn_at IS NULL;

CREATE INDEX IF NOT EXISTS idx_live_routes_origin 
	ON live_routes(origin_asn_id) 
	WHERE withdrawn_at IS NULL;

CREATE INDEX IF NOT EXISTS idx_live_routes_prefix 
	ON live_routes(prefix_id) 
	WHERE withdrawn_at IS NULL;

-- Indexes for bgp_peers table
CREATE INDEX IF NOT EXISTS idx_bgp_peers_asn ON bgp_peers(peer_asn);
CREATE INDEX IF NOT EXISTS idx_bgp_peers_last_seen ON bgp_peers(last_seen);
`
)

// Database manages the SQLite database connection and operations.
type Database struct {
	db     *sql.DB
	logger *slog.Logger
}

// Config holds database configuration
type Config struct {
	Path string
}

// getDefaultDatabasePath returns the appropriate database path for the OS
func getDefaultDatabasePath() string {
	const dbFilename = "db.sqlite"

	switch runtime.GOOS {
	case "darwin":
		// macOS: ~/Library/Application Support/berlin.sneak.app.routewatch/db.sqlite
		home, err := os.UserHomeDir()
		if err != nil {
			return dbFilename
		}
		appSupport := filepath.Join(home, "Library", "Application Support", "berlin.sneak.app.routewatch")
		if err := os.MkdirAll(appSupport, dirPermissions); err != nil {
			return dbFilename
		}

		return filepath.Join(appSupport, dbFilename)
	default:
		// Linux and others: /var/lib/routewatch/db.sqlite
		dbDir := "/var/lib/routewatch"
		if err := os.MkdirAll(dbDir, dirPermissions); err != nil {
			// Fall back to user's home directory if can't create system directory
			home, err := os.UserHomeDir()
			if err != nil {
				return dbFilename
			}
			userDir := filepath.Join(home, ".local", "share", "routewatch")
			if err := os.MkdirAll(userDir, dirPermissions); err != nil {
				return dbFilename
			}

			return filepath.Join(userDir, dbFilename)
		}

		return filepath.Join(dbDir, dbFilename)
	}
}

// NewConfig provides default database configuration
func NewConfig() Config {
	return Config{
		Path: getDefaultDatabasePath(),
	}
}

// New creates a new database connection and initializes the schema.
func New(logger *slog.Logger) (*Database, error) {
	config := NewConfig()

	return NewWithConfig(config, logger)
}

// NewWithConfig creates a new database connection with custom configuration
func NewWithConfig(config Config, logger *slog.Logger) (*Database, error) {
	// Log database path
	logger.Info("Opening database", "path", config.Path)

	// Ensure directory exists
	dir := filepath.Dir(config.Path)
	if err := os.MkdirAll(dir, dirPermissions); err != nil {
		return nil, fmt.Errorf("failed to create database directory: %w", err)
	}

	// Add connection parameters for modernc.org/sqlite
	dsn := fmt.Sprintf("file:%s?_busy_timeout=5000&_journal_mode=WAL", config.Path)
	db, err := sql.Open("sqlite", dsn)
	if err != nil {
		return nil, fmt.Errorf("failed to open database: %w", err)
	}

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

	// Set connection pool parameters
	db.SetMaxOpenConns(1) // Force serialization since SQLite doesn't handle true concurrency well
	db.SetMaxIdleConns(1)
	db.SetConnMaxLifetime(0)

	database := &Database{db: db, logger: logger}

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

	return database, nil
}

// Initialize creates the database schema if it doesn't exist.
func (d *Database) Initialize() error {
	_, err := d.db.Exec(dbSchema)

	return err
}

// Close closes the database connection.
func (d *Database) Close() error {
	return d.db.Close()
}

// 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) {
	tx, err := d.db.Begin()
	if err != nil {
		return nil, err
	}
	defer func() {
		if err := tx.Rollback(); err != nil && err != sql.ErrTxDone {
			d.logger.Error("Failed to rollback transaction", "error", err)
		}
	}()

	var asn ASN
	var idStr string
	err = tx.QueryRow("SELECT id, number, first_seen, last_seen FROM asns WHERE number = ?", number).
		Scan(&idStr, &asn.Number, &asn.FirstSeen, &asn.LastSeen)

	if err == nil {
		// ASN exists, update last_seen
		asn.ID, _ = uuid.Parse(idStr)
		_, err = tx.Exec("UPDATE asns SET last_seen = ? WHERE id = ?", timestamp, asn.ID.String())
		if err != nil {
			return nil, err
		}
		asn.LastSeen = timestamp

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

			return nil, err
		}

		return &asn, nil
	}

	if err != sql.ErrNoRows {
		return nil, err
	}

	// ASN doesn't exist, create it
	asn = ASN{
		ID:        generateUUID(),
		Number:    number,
		FirstSeen: timestamp,
		LastSeen:  timestamp,
	}
	_, err = tx.Exec("INSERT INTO asns (id, number, first_seen, last_seen) VALUES (?, ?, ?, ?)",
		asn.ID.String(), asn.Number, asn.FirstSeen, asn.LastSeen)
	if err != nil {
		return nil, err
	}

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

		return nil, err
	}

	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) {
	tx, err := d.db.Begin()
	if err != nil {
		return nil, err
	}
	defer func() {
		if err := tx.Rollback(); err != nil && err != sql.ErrTxDone {
			d.logger.Error("Failed to rollback transaction", "error", err)
		}
	}()

	var p Prefix
	var idStr string
	err = tx.QueryRow("SELECT id, prefix, ip_version, first_seen, last_seen FROM prefixes WHERE prefix = ?", prefix).
		Scan(&idStr, &p.Prefix, &p.IPVersion, &p.FirstSeen, &p.LastSeen)

	if err == nil {
		// Prefix exists, update last_seen
		p.ID, _ = uuid.Parse(idStr)
		_, err = tx.Exec("UPDATE prefixes SET last_seen = ? WHERE id = ?", timestamp, p.ID.String())
		if err != nil {
			return nil, err
		}
		p.LastSeen = timestamp

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

			return nil, err
		}

		return &p, nil
	}

	if err != sql.ErrNoRows {
		return nil, err
	}

	// Prefix doesn't exist, create it
	p = Prefix{
		ID:        generateUUID(),
		Prefix:    prefix,
		IPVersion: detectIPVersion(prefix),
		FirstSeen: timestamp,
		LastSeen:  timestamp,
	}
	_, err = tx.Exec("INSERT INTO prefixes (id, prefix, ip_version, first_seen, last_seen) VALUES (?, ?, ?, ?, ?)",
		p.ID.String(), p.Prefix, p.IPVersion, p.FirstSeen, p.LastSeen)
	if err != nil {
		return nil, err
	}

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

		return nil, err
	}

	return &p, nil
}

// RecordAnnouncement inserts a new BGP announcement or withdrawal into the database.
func (d *Database) RecordAnnouncement(announcement *Announcement) error {
	_, err := d.db.Exec(`
		INSERT INTO announcements (id, prefix_id, asn_id, origin_asn_id, path, next_hop, timestamp, is_withdrawal)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?)`,
		announcement.ID.String(), announcement.PrefixID.String(),
		announcement.ASNID.String(), announcement.OriginASNID.String(),
		announcement.Path, announcement.NextHop, announcement.Timestamp, announcement.IsWithdrawal)

	return err
}

// RecordPeering records a peering relationship between two ASNs.
func (d *Database) RecordPeering(fromASNID, toASNID string, timestamp time.Time) error {
	tx, err := d.db.Begin()
	if err != nil {
		return err
	}
	defer func() {
		if err := tx.Rollback(); err != nil && err != sql.ErrTxDone {
			d.logger.Error("Failed to rollback transaction", "error", err)
		}
	}()

	var exists bool
	err = tx.QueryRow("SELECT EXISTS(SELECT 1 FROM asn_peerings WHERE from_asn_id = ? AND to_asn_id = ?)",
		fromASNID, toASNID).Scan(&exists)
	if err != nil {
		return err
	}

	if exists {
		_, err = tx.Exec("UPDATE asn_peerings SET last_seen = ? WHERE from_asn_id = ? AND to_asn_id = ?",
			timestamp, fromASNID, toASNID)
	} else {
		_, err = tx.Exec(`
			INSERT INTO asn_peerings (id, from_asn_id, to_asn_id, first_seen, last_seen)
			VALUES (?, ?, ?, ?, ?)`,
			generateUUID().String(), fromASNID, toASNID, timestamp, timestamp)
	}
	if err != nil {
		return err
	}

	if err = tx.Commit(); err != nil {
		d.logger.Error("Failed to commit transaction for peering",
			"from_asn_id", fromASNID,
			"to_asn_id", toASNID,
			"error", err,
		)

		return err
	}

	return nil
}

// UpdateLiveRoute updates the live routing table for an announcement
func (d *Database) UpdateLiveRoute(
	prefixID, originASNID uuid.UUID,
	peerASN int,
	nextHop string,
	timestamp time.Time,
) error {
	// Check if route already exists
	var routeID sql.NullString
	err := d.db.QueryRow(`
		SELECT id FROM live_routes 
		WHERE prefix_id = ? AND origin_asn_id = ? AND peer_asn = ? AND withdrawn_at IS NULL`,
		prefixID.String(), originASNID.String(), peerASN).Scan(&routeID)

	if err != nil && err != sql.ErrNoRows {
		return err
	}

	if routeID.Valid {
		// Route exists and is active, update it
		_, err = d.db.Exec(`
			UPDATE live_routes 
			SET next_hop = ?, announced_at = ?
			WHERE id = ?`,
			nextHop, timestamp, routeID.String)
	} else {
		// Either new route or re-announcement of withdrawn route
		_, err = d.db.Exec(`
			INSERT OR REPLACE INTO live_routes 
			(id, prefix_id, origin_asn_id, peer_asn, next_hop, announced_at, withdrawn_at)
			VALUES (?, ?, ?, ?, ?, ?, NULL)`,
			generateUUID().String(), prefixID.String(), originASNID.String(),
			peerASN, nextHop, timestamp)
	}

	return err
}

// WithdrawLiveRoute marks a route as withdrawn in the live routing table
func (d *Database) WithdrawLiveRoute(prefixID uuid.UUID, peerASN int, timestamp time.Time) error {
	_, err := d.db.Exec(`
		UPDATE live_routes 
		SET withdrawn_at = ?
		WHERE prefix_id = ? AND peer_asn = ? AND withdrawn_at IS NULL`,
		timestamp, prefixID.String(), peerASN)

	return err
}

// GetActiveLiveRoutes returns all currently active routes (not withdrawn)
func (d *Database) GetActiveLiveRoutes() ([]LiveRoute, error) {
	rows, err := d.db.Query(`
		SELECT id, prefix_id, origin_asn_id, peer_asn, next_hop, announced_at
		FROM live_routes 
		WHERE withdrawn_at IS NULL
		ORDER BY announced_at DESC`)
	if err != nil {
		return nil, err
	}
	defer func() {
		_ = rows.Close()
	}()

	var routes []LiveRoute
	for rows.Next() {
		var route LiveRoute
		var idStr, prefixIDStr, originASNIDStr string
		err := rows.Scan(&idStr, &prefixIDStr, &originASNIDStr,
			&route.PeerASN, &route.NextHop, &route.AnnouncedAt)
		if err != nil {
			return nil, err
		}

		route.ID, _ = uuid.Parse(idStr)
		route.PrefixID, _ = uuid.Parse(prefixIDStr)
		route.OriginASNID, _ = uuid.Parse(originASNIDStr)

		routes = append(routes, route)
	}

	return routes, rows.Err()
}

// UpdatePeer updates or creates a BGP peer record
func (d *Database) UpdatePeer(peerIP string, peerASN int, messageType string, timestamp time.Time) error {
	tx, err := d.db.Begin()
	if err != nil {
		return err
	}
	defer func() {
		if err := tx.Rollback(); err != nil && err != sql.ErrTxDone {
			d.logger.Error("Failed to rollback transaction", "error", err)
		}
	}()

	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
	}

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

		return err
	}

	return nil
}

// GetStats returns database statistics
func (d *Database) GetStats() (Stats, error) {
	var stats Stats

	// Count ASNs
	err := d.db.QueryRow("SELECT COUNT(*) FROM asns").Scan(&stats.ASNs)
	if err != nil {
		return stats, err
	}

	// Count prefixes
	err = d.db.QueryRow("SELECT COUNT(*) FROM prefixes").Scan(&stats.Prefixes)
	if err != nil {
		return stats, err
	}

	// Count IPv4 and IPv6 prefixes
	const ipVersionV4 = 4
	err = d.db.QueryRow("SELECT COUNT(*) FROM prefixes WHERE ip_version = ?", ipVersionV4).Scan(&stats.IPv4Prefixes)
	if err != nil {
		return stats, err
	}

	const ipVersionV6 = 6
	err = d.db.QueryRow("SELECT COUNT(*) FROM prefixes WHERE ip_version = ?", ipVersionV6).Scan(&stats.IPv6Prefixes)
	if err != nil {
		return stats, err
	}

	// Count peerings
	err = d.db.QueryRow("SELECT COUNT(*) FROM asn_peerings").Scan(&stats.Peerings)
	if err != nil {
		return stats, err
	}

	// Count live routes
	err = d.db.QueryRow("SELECT COUNT(*) FROM live_routes WHERE withdrawn_at IS NULL").Scan(&stats.LiveRoutes)
	if err != nil {
		return stats, err
	}

	return stats, nil
}