// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Program gops is a tool to list currently running Go processes.
package main

import (
	"flag"
	"fmt"
	"log"
	"os"

	"github.com/google/gops/internal/objfile"

	ps "github.com/keybase/go-ps"
)

const helpText = `Usage: gops is a tool to list and diagnose Go processes.

    gops                  Lists all Go processes currently running.
    gops [cmd] -p=<pid>   See the section below.

Commands: 
    stack     Prints the stack trace.
    gc        Runs the garbage collector and blocks until successful.
    memstats  Prints the garbage collection stats.
    version   Prints the Go version used to build the program.

All commands require the agent running on the Go process.
`

// TODO(jbd): add link that explains the use of agent.

func main() {
	if len(os.Args) < 2 {
		processes()
		return
	}

	cmd := os.Args[1]
	if cmd == "help" {
		usage("")
	}
	fn, ok := cmds[cmd]
	if !ok {
		usage("unknown subcommand")
	}

	var pid int
	flag.IntVar(&pid, "p", -1, "")
	flag.CommandLine.Parse(os.Args[2:])
	if pid == -1 {
		usage("missing -p=<pid> flag")
	}

	if err := fn(pid); err != nil {
		fmt.Fprintf(os.Stderr, "%v\n", err)
		os.Exit(1)
	}
}

func processes() {
	pss, err := ps.Processes()
	if err != nil {
		log.Fatal(err)
	}
	var undetermined int
	for _, pr := range pss {
		if pr.Pid() == 0 {
			// ignore system process
			continue
		}
		name, err := pr.Path()
		if err != nil {
			undetermined++
			continue
		}
		ok, err := isGo(name)
		if err != nil {
			// TODO(jbd): worth to report the number?
			continue
		}
		if ok {
			// TODO(jbd): List if the program is running the agent.
			fmt.Printf("%d\t%v\t(%v)\n", pr.Pid(), pr.Executable(), name)
		}
	}
	if undetermined > 0 {
		fmt.Printf("\n%d processes left undetermined\n", undetermined)
	}
}

func isGo(executable string) (ok bool, err error) {
	obj, err := objfile.Open(executable)
	if err != nil {
		return false, err
	}
	defer obj.Close()

	symbols, err := obj.Symbols()
	if err != nil {
		return false, err
	}

	// TODO(jbd): find a faster way to determine Go programs.
	for _, s := range symbols {
		if s.Name == "runtime.buildVersion" {
			return true, nil
		}
	}
	return false, nil
}

func usage(msg string) {
	if msg != "" {
		fmt.Printf("gops: %v\n", msg)
	}
	fmt.Fprintf(os.Stderr, "%v\n", helpText)
	os.Exit(1)
}