/*
   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 (
	"bytes"
	"errors"
	"fmt"
	"io/ioutil"
	"os"
	"os/user"
	"path/filepath"
	// "strconv"
	"strings"
	// "syscall"
)

var err error

func ExpandHome(path *string) (err error) {
	// Props to this guy.
	// https://stackoverflow.com/a/43578461/733214
	if len(*path) == 0 {
		return errors.New("empty path")
	} 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)
	*/
	// R(real)UID (invoking user)
	usr, err := user.Current()
	if err != nil {
		return
	}
	*path = filepath.Join(usr.HomeDir, (*path)[1:])
	return
}

func GetPathEnv() (s []string, err error) {
	s = make([]string, 0)
	for _, p := range strings.Split(os.Getenv("PATH"), ":") {
		if err = RealPath(&p); err != nil {
			return
		}
		s = append(s, p)
	}

	return
}

func GetEnvPid(pid uint32) (env map[string]string, err error) {

	var envBytes []byte
	var envArr [][]byte
	var procPath string
	var exists bool

	env = make(map[string]string)

	procPath = fmt.Sprintf("/proc/%v/environ", pid)

	if exists, err = RealPathExists(&procPath); err != nil {
		return
	}
	if !exists {
		err = errors.New(fmt.Sprintf("information for pid %v does not exist", pid))
	}
	if envBytes, err = ioutil.ReadFile(procPath); err != nil {
		return
	}

	envArr = bytes.Split(envBytes, []byte{0x0})
	for _, b := range envArr {
		// s := strings.TrimSpace(string(b))
		s := string(b)
		e := strings.SplitN(s, "=", 2)
		for _, i := range e {
			if len(i) != 2 {
				continue
			}
			env[string(i[0])] = string(i[1])
		}
	}

	return
}

func MakeDirIfNotExist(path *string) error {
	exists, stat, err := RealPathExistsStat(path)
	if 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.
			os.MkdirAll(*path, 0777)
			return nil
		} else {
			return err
		}
	}
	// So it exists, but it probably isn't a dir.
	if !stat.Mode().IsDir() {
		return errors.New(fmt.Sprintf("path %v exists but is not a directory", *path))
	}
	// This should probably never happen. Probably.
	return errors.New("undefined behaviour")
}

func RealPath(path *string) error {
	err := ExpandHome(path)
	if err != nil {
		return err
	}
	*path, err = filepath.Abs(*path)
	if err != nil {
		return err
	}
	return nil
}

func RealPathExists(path *string) (exists bool, err error) {
	if err = RealPath(path); err != nil {
		return
	}
	if _, err := os.Stat(*path); err != nil {
		if os.IsNotExist(err) {
			exists = false
			err = nil
		} else {
			return
		}
	} else {
		exists = true
	}

	return
}

func RealPathExistsStat(path *string) (exists bool, stat os.FileInfo, err error) {
	if err = RealPath(path); err != nil {
		return
	}
	if stat, err = os.Stat(*path); err != nil {
		if os.IsNotExist(err) {
			exists = false
			err = nil
		} else {
			return
		}
	} else {
		exists = true
	}

	return
}