// Package migrate allows you to update your database from your application
package migrate

import (
	"database/sql"
	"errors"
	"fmt"
	"io/fs"
	"strconv"
)

// Options contains all settings
type Options struct {
	TableName string // Name used for version info table; defaults to DefaultTableName if not set
	Schema    string // Schema used for version info table; For PostgreSQL, ignored if not set
}

// DefaultTableName is the name used when no TableName is specified in Options
const DefaultTableName = `version`

// ErrUpdatesMissing indicates an update is missing, making it impossible to execute the migration
var ErrUpdatesMissing = errors.New(`Missing migration files`)

// ErrDatabaseNewer indicates that the database version is newer than the requested version. We throw an error because downgrades might cause dataloss
var ErrDatabaseNewer = errors.New(`Current version is newer than the requested version`)

const fileFormat = `%04d.sql`

// AssetFunc is a function that returns the data for the given name
type AssetFunc func(string) ([]byte, error)

// Migrate executes all migrations
// Filenames need to have incrementing numbers
// Downgrading is not supported as it could result in data loss
func Migrate(db *sql.DB, o Options, assets fs.FS) error {
	entries, err := fs.ReadDir(assets, `.`)
	if err != nil {
		panic(`failed to read list of files`)
	}
	version := len(entries)

	if o.TableName == `` {
		o.TableName = DefaultTableName
	}

	searchPath := `public`
	_ = db.QueryRow(`SHOW search_path`).Scan(&searchPath)

	if o.Schema != `` {
		_, _ = db.Exec(`CREATE SCHEMA IF NOT EXISTS ` + o.Schema)

		_, err = db.Exec(`SET search_path TO ` + o.Schema)
		if err != nil {
			return err
		}
	}

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

	_, err = tx.Exec(`CREATE TABLE IF NOT EXISTS ` + o.TableName + ` (Version integer NOT NULL PRIMARY KEY)`)
	if err != nil {
		return err
	}

	row := tx.QueryRow(`SELECT Version FROM ` + o.TableName + ` ORDER BY Version DESC`)

	var v int
	err = row.Scan(&v)
	if err != sql.ErrNoRows && err != nil {
		return err
	}

	if v > version {
		return ErrDatabaseNewer
	}

	for i := v + 1; i <= version; i++ {
		script, err := fs.ReadFile(assets, fmt.Sprintf(fileFormat, i))
		if err != nil {
			return ErrUpdatesMissing
		}

		_, err = tx.Exec(string(script))
		if err != nil {
			return err
		}

		_, err = tx.Exec(`INSERT INTO ` + o.TableName + ` VALUES (` + strconv.Itoa(i) + `)`)
		if err != nil {
			return err
		}
	}

	if o.Schema != `` {
		_, err = tx.Exec(`SET search_path TO ` + searchPath)
		if err != nil {
			return err
		}
	}

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

	return nil
}