// 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; In PostgreSQL the current schema is changed to the one specified here
}

// 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`)

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)

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

	dbType := getDbType(db)
	searchPath := `public`
	if o.TableName == `` {
		o.TableName = DefaultTableName
	}

	if o.Schema != `` {
		err = createSchemaIfNotExists(tx, o.Schema)
		if err != nil {
			return err
		}

		if dbType == `pq` {
			_ = tx.QueryRow(`SHOW search_path`).Scan(&searchPath)

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

	versionTable, err := createTableIfNotExists(tx, o.Schema, o.TableName)
	if err != nil {
		return err
	}

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

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

	for i := v + 1; i <= version; i++ {
		fileName := fmt.Sprintf(fileFormat, i)
		errorf := func(e error) error { return fmt.Errorf(`migration "%s" failed: %w`, fileName, e) }

		script, err := fs.ReadFile(assets, fileName)
		if err != nil {
			return errorf(ErrUpdatesMissing)
		}

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

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

	if dbType == `pq` && 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
}