package ifs

import (
	"errors"
	"io"
	"io/fs"
	"path"
)

var SkipDir = fs.SkipDir

func WalkDir(fsys FS, root string, fn fs.WalkDirFunc) error {
	info, err := fs.Stat(fsys, root)
	if err != nil {
		err = fn(root, nil, err)
	} else {
		err = walkDir(fsys, root, &statDirEntry{info}, fn)
	}
	if err == SkipDir {
		return nil
	}
	return err
}

type ReadDirFn func(fs.DirEntry) error

func ReadDir(fsys fs.FS, name string, fn ReadDirFn) error {
	file, err := fsys.Open(name)
	if err != nil {
		return err
	}
	defer file.Close()
	dir, ok := file.(fs.ReadDirFile)
	if !ok {
		return &fs.PathError{Op: "readdir", Path: name, Err: errors.New("not implemented")}
	}

	for {
		list, err := dir.ReadDir(100)
		if err != nil && err != io.EOF {
			return err
		}
		for _, dirent := range list {
			if err := fn(dirent); err != nil {
				return err
			}
		}
		if err == io.EOF {
			break
		}
	}

	return nil
}

func walkDir(fsys fs.FS, name string, d fs.DirEntry, walkDirFn fs.WalkDirFunc) error {
	if err := walkDirFn(name, d, nil); err != nil || !d.IsDir() {
		if err == SkipDir && d.IsDir() {
			// Successfully skipped directory.
			err = nil
		}
		return err
	}

	if err := ReadDir(fsys, name, func(d1 fs.DirEntry) error {
		name1 := path.Join(name, d1.Name())
		if err := walkDir(fsys, name1, d1, walkDirFn); err != nil {
			if err == SkipDir {
				return nil
			}
			return err
		}
		return nil
	}); err != nil {
		// Second call, to report ReadDir error.
		err = walkDirFn(name, d, err)
		if err != nil {
			if err == SkipDir && d.IsDir() {
				err = nil
			}
			return err
		}
	}

	return nil
}

type statDirEntry struct {
	info fs.FileInfo
}

func (d *statDirEntry) Name() string               { return d.info.Name() }
func (d *statDirEntry) IsDir() bool                { return d.info.IsDir() }
func (d *statDirEntry) Type() fs.FileMode          { return d.info.Mode().Type() }
func (d *statDirEntry) Info() (fs.FileInfo, error) { return d.info, nil }