package migrate

import (
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

type Direction string

const (
	Up   Direction = "up"
	Down Direction = "down"
)

type Migration struct {
	Name string
	Path string
	SQL  string
}

type Runner struct {
	Dir string
}

func (r Runner) Load(direction Direction) ([]Migration, error) {
	var files []string

	err := filepath.WalkDir(r.Dir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}

		base := filepath.Base(path)
		extMatch := strings.HasSuffix(base, fmt.Sprintf(".%s.sql", direction))
		flatMatch := base == fmt.Sprintf("%s.sql", direction)
		if extMatch || flatMatch {
			files = append(files, path)
		}
		return nil
	})
	if err != nil {
		return nil, err
	}

	sort.Strings(files)
	if direction == Down {
		reverse(files)
	}

	migrations := make([]Migration, 0, len(files))
	for _, path := range files {
		raw, err := os.ReadFile(path)
		if err != nil {
			return nil, err
		}
		migrations = append(migrations, Migration{
			Name: strings.TrimPrefix(path, r.Dir+string(filepath.Separator)),
			Path: path,
			SQL:  string(raw),
		})
	}

	return migrations, nil
}

func reverse[T any](values []T) {
	for i, j := 0, len(values)-1; i < j; i, j = i+1, j-1 {
		values[i], values[j] = values[j], values[i]
	}
}