package store

import (
	"context"
	"embed"
	"sort"
	"strconv"
	"strings"
)

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

// Migrate applies any pending SQL migrations in order within a single transaction.
func (s *Store) Migrate(ctx context.Context) error {
	conn, err := s.pool.Acquire(ctx)
	if err != nil {
		return err
	}
	defer conn.Release()

	tx, err := conn.Begin(ctx)
	if err != nil {
		return err
	}
	defer func() {
		if tx != nil {
			tx.Rollback(ctx)
		}
	}()

	_, err = tx.Exec(ctx, `CREATE TABLE IF NOT EXISTS schema_migrations (
       version INT PRIMARY KEY
   )`)
	if err != nil {
		return err
	}

	entries, err := migrationFiles.ReadDir("migrations")
	if err != nil {
		return err
	}

	type mig struct {
		ver  int
		name string
	}
	var migs []mig
	for _, e := range entries {
		name := e.Name()
		if !strings.HasSuffix(name, ".sql") {
			continue
		}
		parts := strings.SplitN(name, "_", 2)
		v, err := strconv.Atoi(parts[0])
		if err != nil {
			continue
		}
		migs = append(migs, mig{ver: v, name: name})
	}
	sort.Slice(migs, func(i, j int) bool { return migs[i].ver < migs[j].ver })

	for _, m := range migs {
		var exists bool
		err = tx.QueryRow(ctx, "SELECT EXISTS(SELECT 1 FROM schema_migrations WHERE version=$1)", m.ver).Scan(&exists)
		if err != nil {
			return err
		}
		if exists {
			continue
		}
		data, err := migrationFiles.ReadFile("migrations/" + m.name)
		if err != nil {
			return err
		}
		if _, err = tx.Exec(ctx, string(data)); err != nil {
			return err
		}
		if _, err = tx.Exec(ctx, "INSERT INTO schema_migrations(version) VALUES($1)", m.ver); err != nil {
			return err
		}
	}

	if err = tx.Commit(ctx); err != nil {
		return err
	}
	tx = nil
	return nil
}