package db

import (
	"database/sql"
	"fmt"
	"io/fs"
	"sort"
	"strings"
)

func Migrate(database *sql.DB, migrationFS fs.FS) error {
	if _, err := database.Exec(`CREATE TABLE IF NOT EXISTS schema_version (version INTEGER PRIMARY KEY)`); err != nil {
		return fmt.Errorf("create schema_version: %w", err)
	}

	subFS, err := fs.Sub(migrationFS, "migrations")
	if err != nil {
		return fmt.Errorf("sub migrations: %w", err)
	}

	files, err := fs.ReadDir(subFS, ".")
	if err != nil {
		return fmt.Errorf("read migrations: %w", err)
	}

	var currentVersion int
	if err := database.QueryRow("SELECT COALESCE(MAX(version), 0) FROM schema_version").Scan(&currentVersion); err != nil {
		return fmt.Errorf("get current version: %w", err)
	}

	type migration struct {
		version int
		sql     string
	}
	var migrations []migration
	for _, f := range files {
		if f.IsDir() || !strings.HasSuffix(f.Name(), ".sql") {
			continue
		}
		var ver int
		if _, err := fmt.Sscanf(f.Name(), "%d_", &ver); err != nil {
			continue
		}
		content, err := fs.ReadFile(subFS, f.Name())
		if err != nil {
			return fmt.Errorf("read migration %s: %w", f.Name(), err)
		}
		migrations = append(migrations, migration{version: ver, sql: string(content)})
	}

	sort.Slice(migrations, func(i, j int) bool { return migrations[i].version < migrations[j].version })

	for _, m := range migrations {
		if m.version <= currentVersion {
			continue
		}
		tx, err := database.Begin()
		if err != nil {
			return fmt.Errorf("begin tx for migration %d: %w", m.version, err)
		}
		if _, err := tx.Exec(m.sql); err != nil {
			tx.Rollback()
			return fmt.Errorf("run migration %d: %w", m.version, err)
		}
		if _, err := tx.Exec("INSERT INTO schema_version (version) VALUES (?)", m.version); err != nil {
			tx.Rollback()
			return fmt.Errorf("record migration %d: %w", m.version, err)
		}
		if err := tx.Commit(); err != nil {
			return fmt.Errorf("commit migration %d: %w", m.version, err)
		}
	}

	return nil
}