/*
The MIT License (MIT)

Copyright (c) 2014 Mitchell Hashimoto

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

package proc

import (
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
)

// UnixProcess is an implementation of Process that contains Unix-specific
// fields and information.
type UnixProcess struct {
	pid   int
	ppid  int
	state rune
	pgrp  int
	sid   int

	binary  string
	cmdline string
}

func (p *UnixProcess) Pid() int {
	return p.pid
}

func (p *UnixProcess) PPid() int {
	return p.ppid
}

func (p *UnixProcess) Executable() string {
	return p.binary
}

// Refresh reloads all the data associated with this process.
func (p *UnixProcess) Refresh() error {
	statPath := fmt.Sprintf("/proc/%d/stat", p.pid)
	dataBytes, err := ioutil.ReadFile(statPath)
	if err != nil {
		return err
	}

	// First, parse out the image name
	data := string(dataBytes)
	binStart := strings.IndexRune(data, '(') + 1
	binEnd := strings.IndexRune(data[binStart:], ')')
	p.binary = data[binStart : binStart+binEnd]

	// Move past the image name and start parsing the rest
	data = data[binStart+binEnd+2:]
	_, err = fmt.Sscanf(data,
		"%c %d %d %d",
		&p.state,
		&p.ppid,
		&p.pgrp,
		&p.sid)

	// retrieve the cmdline for the process as well
	cmdlineFilePath := fmt.Sprintf("/proc/%d/cmdline", p.pid)
	dataBytes, err = ioutil.ReadFile(cmdlineFilePath)
	if err != nil {
		return err
	}

	p.cmdline = strings.TrimSpace(string(dataBytes))

	return err
}

func findProcess(pid int) (*UnixProcess, error) {
	dir := fmt.Sprintf("/proc/%d", pid)
	_, err := os.Stat(dir)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}

		return nil, err
	}

	return newUnixProcess(pid)
}

func findProcessSearch(binary, cmdlinePattern string) (*UnixProcess, error) {
	if cmdlinePattern == "" {
		return nil, fmt.Errorf("no cmdline search pattern provided")
	}

	procs, err := processes()
	if err != nil {
		return nil, err
	}

	b := filepath.Base(binary)

	for i := range procs {
		if procs[i].binary == b {
			if matched, _ := regexp.MatchString(cmdlinePattern, procs[i].cmdline); matched {
				return procs[i], nil
			}
		}
	}

	return nil, nil
}

func processes() ([]*UnixProcess, error) {
	d, err := os.Open("/proc")
	if err != nil {
		return nil, err
	}
	defer d.Close()

	results := make([]*UnixProcess, 0, 50)
	for {
		fis, err := d.Readdir(10)
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, err
		}

		for _, fi := range fis {
			// We only care about directories, since all pids are dirs
			if !fi.IsDir() {
				continue
			}

			// We only care if the name starts with a numeric
			name := fi.Name()
			if name[0] < '0' || name[0] > '9' {
				continue
			}

			// From this point forward, any errors we just ignore, because
			// it might simply be that the process doesn't exist anymore.
			pid, err := strconv.ParseInt(name, 10, 0)
			if err != nil {
				continue
			}

			p, err := newUnixProcess(int(pid))
			if err != nil {
				continue
			}

			results = append(results, p)
		}
	}

	return results, nil
}

func newUnixProcess(pid int) (*UnixProcess, error) {
	p := &UnixProcess{pid: pid}
	return p, p.Refresh()
}