// Copyright (c) 2009 The Go Authors. 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 of Google Inc. 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
// OWNER 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 safeexec provides alternatives for exec package functions to avoid
// accidentally executing binaries found in the current working directory on
// Windows.
package safeexec

import (
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

func chkStat(file string) error {
	d, err := os.Stat(file)
	if err != nil {
		return err
	}
	if d.IsDir() {
		return os.ErrPermission
	}
	return nil
}

func hasExt(file string) bool {
	i := strings.LastIndex(file, ".")
	if i < 0 {
		return false
	}
	return strings.LastIndexAny(file, `:\/`) < i
}

func findExecutable(file string, exts []string) (string, error) {
	if len(exts) == 0 {
		return file, chkStat(file)
	}
	if hasExt(file) {
		if chkStat(file) == nil {
			return file, nil
		}
	}
	for _, e := range exts {
		if f := file + e; chkStat(f) == nil {
			return f, nil
		}
	}
	return "", os.ErrNotExist
}

// LookPath searches for an executable named file in the
// directories named by the PATH environment variable.
// If file contains a slash, it is tried directly and the PATH is not consulted.
// LookPath also uses PATHEXT environment variable to match
// a suitable candidate.
// The result may be an absolute path or a path relative to the current directory.
func LookPath(file string) (string, error) {
	var exts []string
	x := os.Getenv(`PATHEXT`)
	if x != "" {
		for _, e := range strings.Split(strings.ToLower(x), `;`) {
			if e == "" {
				continue
			}
			if e[0] != '.' {
				e = "." + e
			}
			exts = append(exts, e)
		}
	} else {
		exts = []string{".com", ".exe", ".bat", ".cmd"}
	}

	if strings.ContainsAny(file, `:\/`) {
		if f, err := findExecutable(file, exts); err == nil {
			return f, nil
		} else {
			return "", &exec.Error{file, err}
		}
	}

	// https://github.com/golang/go/issues/38736
	// if f, err := findExecutable(filepath.Join(".", file), exts); err == nil {
	// 	return f, nil
	// }

	path := os.Getenv("path")
	for _, dir := range filepath.SplitList(path) {
		if f, err := findExecutable(filepath.Join(dir, file), exts); err == nil {
			return f, nil
		}
	}
	return "", &exec.Error{file, exec.ErrNotFound}
}