package x

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

func fileExists(fileSystem fs.FS, fileName string) (bool, error) {
	_, err := fs.Stat(fileSystem, fileName)
	if err == nil {
		return true, nil
	}
	if os.IsNotExist(err) {
		return false, fmt.Errorf("File %q does not exist.", fileName)
	}
	return false, err // test case should return here
}

func FileValid(fileSystem fs.FS, fileName string) (string, error) {
	fileExists, err := fileExists(fileSystem, fileName)
	if !fileExists || err != nil {
		return "", err
	}

	return "success", nil
}

package x

import (
	"io/fs"
	"testing"
	"testing/fstest"
)

var (
	fakeFS = fstest.MapFS{
		"secret-folder":          {Mode: 0000},
		"secret-folder/readme.md": {},
	}
)

func TestFileValidPermissionDenied(t *testing.T) {
	fileName := "readme.md"
	fsys, _ := fs.Sub(fakeFS, "secret-folder")
	wantOut := ""

	out, err := FileValid(fsys, fileName)
	if out != wantOut || err == nil {
		t.Errorf("want %q, nil got %q, %v", wantOut, out, err)
	}
}