package store

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

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

// Migrate 应用尚未执行的迁移。T0.1 仅为空执行器加 0001 占位；完整备份与表结构见 T0.3。
func Migrate(db *sql.DB) error {
	if _, err := db.Exec(`
CREATE TABLE IF NOT EXISTS schema_migrations (
  version INTEGER PRIMARY KEY,
  applied_at INTEGER NOT NULL
)`); err != nil {
		return fmt.Errorf("ensure schema_migrations: %w", err)
	}

	entries, err := fs.ReadDir(migrationFS, "migrations")
	if err != nil {
		return fmt.Errorf("read migrations: %w", err)
	}
	var names []string
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".sql") {
			continue
		}
		names = append(names, e.Name())
	}
	sort.Strings(names)

	for _, name := range names {
		version, err := parseMigrationVersion(name)
		if err != nil {
			return err
		}
		var exists int
		err = db.QueryRow(`SELECT 1 FROM schema_migrations WHERE version = ?`, version).Scan(&exists)
		if err == nil {
			continue
		}
		if err != sql.ErrNoRows {
			return fmt.Errorf("check migration %d: %w", version, err)
		}

		body, err := migrationFS.ReadFile("migrations/" + name)
		if err != nil {
			return fmt.Errorf("read migration %s: %w", name, err)
		}
		sqlText := strings.TrimSpace(string(body))
		tx, err := db.Begin()
		if err != nil {
			return fmt.Errorf("begin migration %d: %w", version, err)
		}
		if sqlText != "" {
			if _, err := tx.Exec(sqlText); err != nil {
				_ = tx.Rollback()
				return fmt.Errorf("apply migration %d: %w", version, err)
			}
		}
		if _, err := tx.Exec(
			`INSERT INTO schema_migrations(version, applied_at) VALUES(?, ?)`,
			version,
			time.Now().UnixMilli(),
		); err != nil {
			_ = tx.Rollback()
			return fmt.Errorf("record migration %d: %w", version, err)
		}
		if err := tx.Commit(); err != nil {
			return fmt.Errorf("commit migration %d: %w", version, err)
		}
	}
	return nil
}

func parseMigrationVersion(name string) (int, error) {
	base := strings.TrimSuffix(name, ".sql")
	parts := strings.SplitN(base, "_", 2)
	if len(parts) < 1 {
		return 0, fmt.Errorf("invalid migration name: %s", name)
	}
	v, err := strconv.Atoi(parts[0])
	if err != nil {
		return 0, fmt.Errorf("invalid migration version in %s: %w", name, err)
	}
	return v, nil
}