// Package db opens the SQLite database and applies embedded SQL
// migrations in filename order at startup. Uses modernc.org/sqlite
// (pure Go, no cgo).
package db

import (
	"database/sql"
	"embed"
	"fmt"
	"io/fs"
	"path/filepath"
	"sort"
	"strings"

	_ "modernc.org/sqlite"
)

//go:embed migrations/*.sql
var migrationsFS embed.FS

// Open opens the SQLite DB at path, enabling foreign keys and WAL,
// and applies every embedded migration in filename order.
func Open(path string) (*sql.DB, error) {
	dsn := fmt.Sprintf("file:%s?_pragma=foreign_keys(1)&_pragma=journal_mode(WAL)&_pragma=busy_timeout(5000)", filepath.ToSlash(path))
	db, err := sql.Open("sqlite", dsn)
	if err != nil {
		return nil, fmt.Errorf("open sqlite: %w", err)
	}
	if err := db.Ping(); err != nil {
		_ = db.Close()
		return nil, fmt.Errorf("ping sqlite: %w", err)
	}
	if err := migrate(db); err != nil {
		_ = db.Close()
		return nil, err
	}
	return db, nil
}

func migrate(db *sql.DB) error {
	entries, err := fs.ReadDir(migrationsFS, "migrations")
	if err != nil {
		return fmt.Errorf("read migrations: %w", err)
	}
	names := make([]string, 0, len(entries))
	for _, e := range entries {
		if !e.IsDir() && strings.HasSuffix(e.Name(), ".sql") {
			names = append(names, e.Name())
		}
	}
	sort.Strings(names)

	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS schema_migrations (name TEXT PRIMARY KEY, applied_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP)`); err != nil {
		return fmt.Errorf("ensure schema_migrations: %w", err)
	}

	for _, name := range names {
		var applied int
		if err := db.QueryRow(`SELECT COUNT(1) FROM schema_migrations WHERE name = ?`, name).Scan(&applied); err != nil {
			return fmt.Errorf("check migration %s: %w", name, err)
		}
		if applied > 0 {
			continue
		}
		content, err := migrationsFS.ReadFile("migrations/" + name)
		if err != nil {
			return fmt.Errorf("read migration %s: %w", name, err)
		}
		tx, err := db.Begin()
		if err != nil {
			return fmt.Errorf("begin migration %s: %w", name, err)
		}
		if _, err := tx.Exec(string(content)); err != nil {
			_ = tx.Rollback()
			return fmt.Errorf("apply migration %s: %w", name, err)
		}
		if _, err := tx.Exec(`INSERT INTO schema_migrations(name) VALUES(?)`, name); err != nil {
			_ = tx.Rollback()
			return fmt.Errorf("record migration %s: %w", name, err)
		}
		if err := tx.Commit(); err != nil {
			return fmt.Errorf("commit migration %s: %w", name, err)
		}
	}
	return nil
}