package vfscopy

import (
	"os"
	"io"
	"path/filepath"
	"path"
	"strings"
	"errors"
)

// FileSystem is copied from http.FileSystem
type FileSystem interface {
    Open(name string) (File, error)
}

// File is copied from http.File
type File interface {
    io.Closer
    io.Reader
    io.Seeker
    Readdir(count int) ([]os.FileInfo, error)
    Stat() (os.FileInfo, error)
}

// Dir is an implementation of a Virtual FileSystem
type Dir string

// mapDirOpenError maps the provided non-nil error from opening name
// to a possibly better non-nil error. In particular, it turns OS-specific errors
// about opening files in non-directories into os.ErrNotExist. See Issue 18984.
func mapDirOpenError(originalErr error, name string) error {
	if os.IsNotExist(originalErr) || os.IsPermission(originalErr) {
		return originalErr
	}

	parts := strings.Split(name, string(filepath.Separator))
	for i := range parts {
		if parts[i] == "" {
			continue
		}
		fi, err := os.Stat(strings.Join(parts[:i+1], string(filepath.Separator)))
		if err != nil {
			return originalErr
		}
		if !fi.IsDir() {
			return os.ErrNotExist
		}
	}
	return originalErr
}

// Open opens a file relative to a virtual filesystem
func (d Dir) Open(name string) (File, error) {
	if filepath.Separator != '/' && strings.ContainsRune(name, filepath.Separator) {
		return nil, errors.New("http: invalid character in file path")
	}
	dir := string(d)
	if dir == "" {
		dir = "."
	}
	fullName := filepath.Join(dir, filepath.FromSlash(path.Clean("/"+name)))
	f, err := os.Open(fullName)
	if err != nil {
		return nil, mapDirOpenError(err, fullName)
	}
	return f, nil
}