package main

import (
	"database/sql"
	"embed"
	"fmt"
	"io/fs"
	"log"
	"path/filepath"
)

const (
	migrationDir         = `sql/migrations`
	migrationFilePattern = `%04d.sqlite3`
)

var migrations []string

//go:embed sql/migrations/*.sqlite3
var migrationsFS embed.FS

func init() {
	readMigrations()
}

func readMigrations() {
	i := 1

	_ = fs.WalkDir(migrationsFS, migrationDir, func(path string, d fs.DirEntry, err error) error {
		if !d.IsDir() {
			expected := fmt.Sprintf(migrationFilePattern, i)
			if filepath.Base(path) == expected {
				data, err := fs.ReadFile(migrationsFS, path)
				if err != nil {
					log.Fatalf("Could not read migration: %v", err)
				}

				migrations = append(migrations, string(data))

				i += 1
			}
		}

		return nil
	})
}

func Transaction(db *sql.DB, f func(*sql.Tx) error) error {
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	err = f(tx)
	if err != nil {
		return err
	}

	return tx.Commit()
}

func Migrate(db *sql.DB, index int) error {
	return Transaction(db, func(tx *sql.Tx) error {
		_, err := tx.Exec(migrations[index])
		return err
	})
}

func UserVersion(db *sql.DB) (int, error) {
	var version int

	err := Transaction(db, func(tx *sql.Tx) error {
		return tx.QueryRow(`PRAGMA user_version`).Scan(&version)
	})
	if err != nil {
		return 0, err
	}

	return version, nil
}

func MigrateToLatest(db *sql.DB) error {
	for i := range migrations {
		v, err := UserVersion(db)
		if err != nil {
			return fmt.Errorf("Failed UserVersion() inside MigrateToLatest(): %w", err)
		}

		if i == v {
			err = Migrate(db, i)
			if err != nil {
				return fmt.Errorf("Failed Migrate() inside MigrateToLatest(): %w", err)
			}
		}
	}

	return nil
}