// Package database provides SQLite database access.
package database

import (
	"context"
	"database/sql"
	"embed"
	"fmt"
	"log/slog"
	"path/filepath"
	"sort"
	"strings"

	"go.uber.org/fx"
	"sneak.berlin/go/pixa/internal/config"
	"sneak.berlin/go/pixa/internal/logger"

	_ "modernc.org/sqlite" // SQLite driver registration
)

//go:embed schema/*.sql
var schemaFS embed.FS

// Params defines dependencies for Database.
type Params struct {
	fx.In
	Logger *logger.Logger
	Config *config.Config
}

// Database wraps the SQL database connection.
type Database struct {
	db     *sql.DB
	log    *slog.Logger
	config *config.Config
}

// ParseMigrationVersion extracts the numeric version prefix from a migration
// filename. Filenames must follow the pattern "<version>.sql" or
// "<version>_<description>.sql", where version is a zero-padded numeric
// string (e.g. "001", "002"). Returns the version string and an error if
// the filename does not match the expected pattern.
func ParseMigrationVersion(filename string) (string, error) {
	name := strings.TrimSuffix(filename, filepath.Ext(filename))
	if name == "" {
		return "", fmt.Errorf("invalid migration filename %q: empty name", filename)
	}

	// Split on underscore to separate version from description.
	// If there's no underscore, the entire stem is the version.
	version := name
	if idx := strings.IndexByte(name, '_'); idx >= 0 {
		version = name[:idx]
	}

	if version == "" {
		return "", fmt.Errorf("invalid migration filename %q: empty version prefix", filename)
	}

	// Validate the version is purely numeric.
	for _, ch := range version {
		if ch < '0' || ch > '9' {
			return "", fmt.Errorf(
				"invalid migration filename %q: version %q contains non-numeric character %q",
				filename, version, string(ch),
			)
		}
	}

	return version, nil
}

// New creates a new Database instance.
func New(lc fx.Lifecycle, params Params) (*Database, error) {
	s := &Database{
		log:    params.Logger.Get(),
		config: params.Config,
	}

	s.log.Info("Database instantiated")

	lc.Append(fx.Hook{
		OnStart: func(ctx context.Context) error {
			s.log.Info("Database OnStart Hook")

			return s.connect(ctx)
		},
		OnStop: func(_ context.Context) error {
			s.log.Info("Database OnStop Hook")
			if s.db != nil {
				return s.db.Close()
			}

			return nil
		},
	})

	return s, nil
}

func (s *Database) connect(ctx context.Context) error {
	dbURL := s.config.DBURL

	s.log.Info("connecting to database", "url", dbURL)

	db, err := sql.Open("sqlite", dbURL)
	if err != nil {
		s.log.Error("failed to open database", "error", err)

		return err
	}

	if err := db.PingContext(ctx); err != nil {
		s.log.Error("failed to ping database", "error", err)

		return err
	}

	s.db = db
	s.log.Info("database connected")

	return s.runMigrations(ctx)
}

// collectMigrations reads the embedded schema directory and returns
// migration filenames sorted lexicographically.
func collectMigrations() ([]string, error) {
	entries, err := schemaFS.ReadDir("schema")
	if err != nil {
		return nil, fmt.Errorf("failed to read schema directory: %w", err)
	}

	var migrations []string

	for _, entry := range entries {
		if !entry.IsDir() && strings.HasSuffix(entry.Name(), ".sql") {
			migrations = append(migrations, entry.Name())
		}
	}

	sort.Strings(migrations)

	return migrations, nil
}

// ensureMigrationsTable creates the schema_migrations tracking table if
// it does not already exist.
func ensureMigrationsTable(ctx context.Context, db *sql.DB) error {
	_, err := db.ExecContext(ctx, `
		CREATE TABLE IF NOT EXISTS schema_migrations (
			version TEXT PRIMARY KEY,
			applied_at DATETIME DEFAULT CURRENT_TIMESTAMP
		)
	`)
	if err != nil {
		return fmt.Errorf("failed to create migrations table: %w", err)
	}

	return nil
}

// applyMigrations applies all pending migrations to db, using log for
// informational output (may be nil for silent operation).
func applyMigrations(ctx context.Context, db *sql.DB, log *slog.Logger) error {
	if err := ensureMigrationsTable(ctx, db); err != nil {
		return err
	}

	migrations, err := collectMigrations()
	if err != nil {
		return err
	}

	for _, migration := range migrations {
		version, parseErr := ParseMigrationVersion(migration)
		if parseErr != nil {
			return parseErr
		}

		// Check if already applied.
		var count int

		err := db.QueryRowContext(ctx,
			"SELECT COUNT(*) FROM schema_migrations WHERE version = ?",
			version,
		).Scan(&count)
		if err != nil {
			return fmt.Errorf("failed to check migration status: %w", err)
		}

		if count > 0 {
			if log != nil {
				log.Debug("migration already applied", "version", version)
			}

			continue
		}

		// Read and apply migration.
		content, readErr := schemaFS.ReadFile(filepath.Join("schema", migration))
		if readErr != nil {
			return fmt.Errorf("failed to read migration %s: %w", migration, readErr)
		}

		if log != nil {
			log.Info("applying migration", "version", version)
		}

		_, execErr := db.ExecContext(ctx, string(content))
		if execErr != nil {
			return fmt.Errorf("failed to apply migration %s: %w", migration, execErr)
		}

		// Record migration as applied.
		_, recErr := db.ExecContext(ctx,
			"INSERT INTO schema_migrations (version) VALUES (?)",
			version,
		)
		if recErr != nil {
			return fmt.Errorf("failed to record migration %s: %w", migration, recErr)
		}

		if log != nil {
			log.Info("migration applied successfully", "version", version)
		}
	}

	return nil
}

func (s *Database) runMigrations(ctx context.Context) error {
	return applyMigrations(ctx, s.db, s.log)
}

// DB returns the underlying sql.DB.
func (s *Database) DB() *sql.DB {
	return s.db
}

// ApplyMigrations applies all migrations to the given database.
// This is useful for testing where you want to use the real schema
// without the full fx lifecycle.
func ApplyMigrations(db *sql.DB) error {
	return applyMigrations(context.Background(), db, nil)
}