package filterfs

import "io/fs"
import "fmt"

// Filter returns true to include a file name and false to exclude it.
type Filter func(name string) bool

type FS struct {
	underlying fs.FS
	filter     Filter
}

func Apply(sys fs.FS, filter Filter) FS {
	return FS{sys, filter}
}

type File struct {
	underlying fs.ReadDirFile
	filter     Filter
}

func (f File) Stat() (fs.FileInfo, error) {
	return f.underlying.Stat()
}

func (f File) Read(buf []byte) (int, error) {
	return f.underlying.Read(buf)
}

func (f File) Close() error {
	return f.underlying.Close()
}

func filterEntries(filter Filter, entries []fs.DirEntry) []fs.DirEntry {
	result := []fs.DirEntry{}
	for _, entry := range entries {
		if filter(entry.Name()) {
			result = append(result, entry)
		}
	}
	return result
}

func (f File) ReadDir(n int) ([]fs.DirEntry, error) {
	entries, err := f.underlying.ReadDir(n)
	if err != nil {
		return entries, err
	}
	return filterEntries(f.filter, entries), nil
}

func (sys FS) Open(name string) (fs.File, error) {
	file, err := sys.underlying.Open(name)
	if err != nil {
		return nil, err
	}
	if dir, ok := file.(fs.ReadDirFile); ok {
		return File{dir, sys.filter}, nil
	} else {
		return file, nil
	}
}

func (sys FS) Glob(pattern string) ([]string, error) {
	entries, err := fs.Glob(sys.underlying, pattern)
	if err != nil {
		return entries, err
	}
	result := []string{}
	for _, entry := range entries {
		if sys.filter(entry) {
			result = append(result, entry)
		}
	}
	fmt.Printf("%v\n", entries)
	fmt.Printf("%v\n", result)
	return result, nil
}

/*
func (sys FS) ReadDir(fname string) ([]fs.DirEntry, error) {
	entries, err := fs.ReadDir(sys.underlying, fname)
	if err != nil {
		return entries, err
	}
	return filterEntries(sys.filter, entries), nil
}
*/

var _ fs.FS = &FS{}
var _ fs.GlobFS = &FS{}
var _ fs.ReadDirFS = &FS{}