package database

import (
	"fmt"
	"io/fs"
	"slices"
	"sort"
	"strconv"
	"strings"

	"gorm.io/gorm"
)

// Atomically run migrations found from the given filesystem (with the format `<SERIAL_NUM>*.up.sql`).
// Skips already applied migrations, but fails on malformed or iisconfigured entries. Notably atomic
// execution must be utilized to automatically roll back any partially applied migrations.
func RunMigrations(db *gorm.DB, migrationsFS fs.FS) error {
	return db.Transaction(func(tx *gorm.DB) error {
		if err := tx.Exec(`
			CREATE TABLE IF NOT EXISTS schema_migrations (
				version INTEGER PRIMARY KEY
			)
		`).Error; err != nil {
			return err
		}

		// Query already applied migrations to prevent duplicate execution
		var applied []int
		if err := tx.Table("schema_migrations").Pluck("version", &applied).Error; err != nil {
			return err
		}

		migrationFiles, err := fs.Glob(migrationsFS, "*.up.sql")
		if err != nil {
			return err
		}

		for _, f := range sortMigrations(migrationFiles) {
			version, err := strconv.Atoi(strings.Split(f, "_")[0])
			if err != nil {
				return fmt.Errorf("invalid migration filename: %s", f)
			}

			if slices.Contains(applied, version) {
				continue
			}

			sql, err := fs.ReadFile(migrationsFS, f)
			if err != nil {
				return err
			}

			if err := tx.Exec(string(sql)).Error; err != nil {
				return err
			}

			if err := tx.Exec(`
				INSERT INTO schema_migrations (version) VALUES (?)
			`, version).Error; err != nil {
				return err
			}
		}

		return nil
	})
}

// Sort the given migration files to ascending order based on the filename integer prefix to then
// be executed sequentially.
func sortMigrations(files []string) []string {
	sort.Slice(files, func(i, j int) bool {
		v1, _ := strconv.Atoi(strings.Split(files[i], "_")[0])
		v2, _ := strconv.Atoi(strings.Split(files[j], "_")[0])
		return v1 < v2
	})
	return files
}