/*
   SysUtils - a library to assist with various system-related functions
   Copyright (C) 2020  Brent Saner

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

package paths

import (
	"errors"
	`fmt`
	"os"
	"os/user"
	"path/filepath"
	`runtime`
	// "strconv"
	"strings"

	// "syscall"
)

/*
	ExpandHome will take a tilde(~)-prefixed path and resolve it to the actual path in-place.
	Note that it only works for current user; the syntax ~someotheruser/foo/bar is currently unsupported.
*/
func ExpandHome(path *string) (err error) {

	var usr *user.User

	// Props to this guy.
	// https://stackoverflow.com/a/43578461/733214
	if len(*path) == 0 {
		err = errors.New("empty path")
		return
	} else if (*path)[0] != '~' {
		return
	}

	// E(ffective)UID (e.g. chown'd user for SUID)
	/*
		uid := strconv.Itoa(syscall.Geteuid())
		usr, err := user.LookupId(euid)
	*/
	// (Real)UID (invoking user)
	if usr, err = user.Current(); err != nil {
		return err
	}
	*path = filepath.Join(usr.HomeDir, (*path)[1:])

	return
}

// GetPathEnv returns a slice of the PATH variable's items.
func GetPathEnv() (paths []string, err error) {

	var pathVar string = "PATH"
	var sep string = ":"

	paths = make([]string, 0)

	if runtime.GOOS == "windows" {
		pathVar = "Path"
		sep = ";"
	}

	for _, p := range strings.Split(os.Getenv(pathVar), sep) {
		if err = RealPath(&p); err != nil {
			return
		}
		paths = append(paths, p)
	}
	return
}

// MakeDirIfNotExist will create a directory at a given path if it doesn't exist.
func MakeDirIfNotExist(path string) (err error) {

	var stat os.FileInfo
	var exists bool
	var locPath string = path

	if exists, stat, err = RealPathExistsStat(&locPath); err != nil {
		if !exists {
			// This, at least as of golang 1.15, uses the user's umask.
			// It does not actually create a dir with 0777.
			// It's up to the caller to do an os.Chmod() on the path after, if desired.
			if err = os.MkdirAll(locPath, 0777); err != nil {
				return
			}
			err = nil
			return
		} else {
			return
		}
	}

	// So it exists, but it probably isn't a dir.
	if !stat.Mode().IsDir() {
		err = errors.New(fmt.Sprintf("path %v exists but is not a directory", locPath))
		return
	}

	// This should probably never happen. Probably.
	err = errors.New("undefined")
	return
}

// RealPath will transform a given path into the very best guess for an absolute path in-place.
func RealPath(path *string) (err error) {

	if err = ExpandHome(path); err != nil {
		return
	}

	if *path, err = filepath.Abs(*path); err != nil {
		return
	}

	return
}

/*
	RealPathExists is like RealPath, but will also return a boolean as to whether the path
	actually exists or not.

	It's hacky, but the "exists" bool along with err is a sort of proto-state-machine.
	If err != nil and bool is true, the error occurred during path absolution.
	If err != nil and bool is false, the path does not exist.
*/
func RealPathExists(path *string) (exists bool, err error) {

	if err = RealPath(path); err != nil {
		exists = true
		return
	}

	if _, err = os.Stat(*path); err != nil {
		return
	}

	exists = true

	return
}

// RealPathExistsStat is like RealPathExists except it will also return the os.FileInfo for the path (assuming it exists).
func RealPathExistsStat(path *string) (exists bool, stat os.FileInfo, err error) {

	// See the comments for RealPathExists for details on this.
	if err = RealPath(path); err != nil {
		exists = true
		return
	}

	if stat, err = os.Stat(*path); err != nil {
		return
	}

	exists = true

	return
}