package main

import (
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"runtime"
)

func main() {
	runTests()
}

func runTests() {
	type testT struct {
		name string
		fs   fs.FS
	}
	tests := []testT{
		{name: "Normal path 1", fs: os.DirFS("C:\\")},
		{name: "UNC Path 1", fs: os.DirFS("\\\\?\\C:\\")},
		{name: "Normal path 2", fs: OSDirFS("C:\\")},
		{name: "UNC Path 2", fs: OSDirFS("\\\\?\\C:\\")},
	}
	for _, t := range tests {
		fmt.Println("Testing:", t.name)
		err := testFS(t.fs)
		if err != nil {
			fmt.Println("Error:", err)
		} else {
			fmt.Println("OK")
		}
	}
}

func testFS(tfs fs.FS) error {
	err := fs.WalkDir(tfs, ".", func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		return fmt.Errorf("dummy")
	})
	if err != nil && err.Error() != "dummy" {
		return err
	}
	return nil
}

type osDirFS string

func OSDirFS(dir string) fs.FS {
	return osDirFS(dir)
}

func containsAny(s, chars string) bool {
	for i := 0; i < len(s); i++ {
		for j := 0; j < len(chars); j++ {
			if s[i] == chars[j] {
				return true
			}
		}
	}
	return false
}

func (dir osDirFS) Open(name string) (fs.File, error) {
	if !fs.ValidPath(name) || runtime.GOOS == "windows" && containsAny(name, `\:`) {
		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrInvalid}
	}

	f, err := os.Open(filepath.Join(string(dir), filepath.FromSlash(name)))
	if err != nil {
		return nil, err // nil fs.File
	}
	return f, nil
}

func (dir osDirFS) Stat(name string) (fs.FileInfo, error) {
	if !fs.ValidPath(name) || runtime.GOOS == "windows" && containsAny(name, `\:`) {
		return nil, &fs.PathError{Op: "stat", Path: name, Err: fs.ErrInvalid}
	}
	f, err := os.Stat(filepath.Join(string(dir), filepath.FromSlash(name)))
	if err != nil {
		return nil, err
	}
	return f, nil
}