// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This part copied directly from golang.org/src/path/filepath/path.go (Go
// 1.6) and lightly modified to be methods on BasicFilesystem.

// In our Walk() all paths given to a WalkFunc() are relative to the
// filesystem root.

package fs

import (
	"errors"
	"path/filepath"
)

var ErrInfiniteRecursion = errors.New("infinite filesystem recursion detected")

type ancestorDirList struct {
	list []FileInfo
	fs   Filesystem
}

func (ancestors *ancestorDirList) Push(info FileInfo) {
	l.Debugf("ancestorDirList: Push '%s'", info.Name())
	ancestors.list = append(ancestors.list, info)
}

func (ancestors *ancestorDirList) Pop() FileInfo {
	aLen := len(ancestors.list)
	info := ancestors.list[aLen-1]
	l.Debugf("ancestorDirList: Pop '%s'", info.Name())
	ancestors.list = ancestors.list[:aLen-1]
	return info
}

func (ancestors *ancestorDirList) Contains(info FileInfo) bool {
	l.Debugf("ancestorDirList: Contains '%s'", info.Name())
	for _, ancestor := range ancestors.list {
		if ancestors.fs.SameFile(info, ancestor) {
			return true
		}
	}
	return false
}

// WalkFunc is the type of the function called for each file or directory
// visited by Walk. The path argument contains the argument to Walk as a
// prefix; that is, if Walk is called with "dir", which is a directory
// containing the file "a", the walk function will be called with argument
// "dir/a". The info argument is the FileInfo for the named path.
//
// If there was a problem walking to the file or directory named by path, the
// incoming error will describe the problem and the function can decide how
// to handle that error (and Walk will not descend into that directory). If
// an error is returned, processing stops. The sole exception is when the function
// returns the special value SkipDir. If the function returns SkipDir when invoked
// on a directory, Walk skips the directory's contents entirely.
// If the function returns SkipDir when invoked on a non-directory file,
// Walk skips the remaining files in the containing directory.
type WalkFunc func(path string, info FileInfo, err error) error

type walkFilesystem struct {
	Filesystem
	checkInfiniteRecursion bool
}

func NewWalkFilesystem(next Filesystem) Filesystem {
	fs := &walkFilesystem{
		Filesystem: next,
	}
	for _, opt := range next.Options() {
		if _, ok := opt.(*OptionJunctionsAsDirs); ok {
			fs.checkInfiniteRecursion = true
			break
		}
	}
	return fs
}

// walk recursively descends path, calling walkFn.
func (f *walkFilesystem) walk(path string, info FileInfo, walkFn WalkFunc, ancestors *ancestorDirList) error {
	l.Debugf("walk: path=%s", path)
	path, err := Canonicalize(path)
	if err != nil {
		return err
	}

	err = walkFn(path, info, nil)
	if err != nil {
		if info.IsDir() && err == SkipDir {
			return nil
		}
		return err
	}

	if !info.IsDir() && path != "." {
		return nil
	}

	if f.checkInfiniteRecursion {
		if !ancestors.Contains(info) {
			ancestors.Push(info)
			defer ancestors.Pop()
		} else {
			return walkFn(path, info, ErrInfiniteRecursion)
		}
	}

	names, err := f.DirNames(path)
	if err != nil {
		return walkFn(path, info, err)
	}

	for _, name := range names {
		filename := filepath.Join(path, name)
		fileInfo, err := f.Lstat(filename)
		if err != nil {
			if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir {
				return err
			}
		} else {
			err = f.walk(filename, fileInfo, walkFn, ancestors)
			if err != nil {
				if !fileInfo.IsDir() || err != SkipDir {
					return err
				}
			}
		}
	}
	return nil
}

// Walk walks the file tree rooted at root, calling walkFn for each file or
// directory in the tree, including root. All errors that arise visiting files
// and directories are filtered by walkFn. The files are walked in lexical
// order, which makes the output deterministic but means that for very
// large directories Walk can be inefficient.
// Walk does not follow symbolic links.
func (f *walkFilesystem) Walk(root string, walkFn WalkFunc) error {
	info, err := f.Lstat(root)
	if err != nil {
		return walkFn(root, nil, err)
	}
	var ancestors *ancestorDirList
	if f.checkInfiniteRecursion {
		ancestors = &ancestorDirList{fs: f.Filesystem}
	}
	return f.walk(root, info, walkFn, ancestors)
}

func (f *walkFilesystem) underlying() (Filesystem, bool) {
	return f.Filesystem, true
}

func (*walkFilesystem) wrapperType() filesystemWrapperType {
	return filesystemWrapperTypeWalk
}
