// Modified from github.com/facebookgo/symwalk

// BSD License

// For symwalk software

// Copyright (c) 2015, Facebook, Inc. All rights reserved.

// Redistribution and use in source and binary forms, with or without modification,
// are permitted provided that the following conditions are met:

//  * Redistributions of source code must retain the above copyright notice, this
//    list of conditions and the following disclaimer.

//  * Redistributions in binary form must reproduce the above copyright notice,
//    this list of conditions and the following disclaimer in the documentation
//    and/or other materials provided with the distribution.

//  * Neither the name Facebook nor the names of its contributors may be used to
//    endorse or promote products derived from this software without specific
//    prior written permission.

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
// ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
// ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package fsutil

import (
	"os"
	"path/filepath"
)

// symwalkFunc calls the provided WalkFn for regular files.
// However, when it encounters a symbolic link, it resolves the link fully using the
// filepath.EvalSymlinks function and recursively calls symwalk.Walk on the resolved path.
// This ensures that unlink filepath.Walk, traversal does not stop at symbolic links.
//
// Note that symwalk.Walk does not terminate if there are any non-terminating loops in
// the file structure.
func walk(filename string, linkDirname string, walkFn filepath.WalkFunc) error {
	symWalkFunc := func(path string, info os.FileInfo, err error) error {

		if fname, err := filepath.Rel(filename, path); err == nil {
			path = filepath.Join(linkDirname, fname)
		} else {
			return err
		}

		if err == nil && info.Mode()&os.ModeSymlink == os.ModeSymlink {
			finalPath, err := filepath.EvalSymlinks(path)
			if err != nil {
				// don't bail out if symlink is invalid
				return walkFn(path, info, err)
			}
			info, err := os.Lstat(finalPath)
			if err != nil {
				return walkFn(path, info, err)
			}
			if info.IsDir() {
				return walk(finalPath, path, walkFn)
			}
		}

		return walkFn(path, info, err)
	}
	return filepath.Walk(filename, symWalkFunc)
}

// SymWalk extends filepath.Walk to also follow symlinks
func SymWalk(path string, walkFn filepath.WalkFunc) error {
	return walk(path, path, walkFn)
}