package main

import (
	"bufio"
	"flag"
	"fmt"
	"os"
	"os/exec"

	"runtime"
	"strings"
	"syscall"

	"github.com/derekparker/delve/command"
	"github.com/derekparker/delve/goreadline"
	"github.com/derekparker/delve/proctl"
)

type term struct {
	stdin *bufio.Reader
}

const historyFile string = ".dbg_history"

func main() {
	// We must ensure here that we are running on the same thread during
	// the execution of dbg. This is due to the fact that ptrace(2) expects
	// all commands after PTRACE_ATTACH to come from the same thread.
	runtime.LockOSThread()

	var (
		pid     int
		proc    string
		run     bool
		err     error
		dbgproc *proctl.DebuggedProcess
		t       = newTerm()
		cmds    = command.DebugCommands()
	)

	flag.IntVar(&pid, "pid", 0, "Pid of running process to attach to.")
	flag.StringVar(&proc, "proc", "", "Path to process to run and debug.")
	flag.BoolVar(&run, "run", false, "Compile program and begin debug session.")
	flag.Parse()

	if flag.NFlag() == 0 {
		flag.Usage()
		os.Exit(0)
	}

	start := func(name string) *proctl.DebuggedProcess {
		proc := exec.Command(name)
		proc.Stdout = os.Stdout

		err = proc.Start()
		if err != nil {
			die(1, "Could not start process:", err)
		}

		dbgproc, err = proctl.NewDebugProcess(proc.Process.Pid)
		if err != nil {
			die(1, "Could not start debugging process:", err)
		}

		return dbgproc
	}

	switch {
	case run:
		const debugname = "debug"
		cmd := exec.Command("go", "build", "-o", debugname, "-gcflags", "-N -l")
		err := cmd.Run()
		if err != nil {
			die(1, "Could not compile program:", err)
		}
		defer os.Remove(debugname)

		dbgproc = start("./" + debugname)
	case pid != 0:
		dbgproc, err = proctl.NewDebugProcess(pid)
		if err != nil {
			die(1, "Could not start debugging process:", err)
		}
	case proc != "":
		dbgproc = start(proc)
	}

	goreadline.LoadHistoryFromFile(historyFile)

	for {
		cmdstr, err := t.promptForInput()
		if err != nil {
			die(1, "Prompt for input failed.\n")
		}

		cmdstr, args := parseCommand(cmdstr)

		if cmdstr == "exit" {
			err := goreadline.WriteHistoryToFile(historyFile)
			fmt.Println(err)
			handleExit(t, dbgproc, 0)
		}

		cmd := cmds.Find(cmdstr)
		err = cmd(dbgproc, args...)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Command failed: %s\n", err)
		}
	}
}

func handleExit(t *term, dbp *proctl.DebuggedProcess, status int) {
	fmt.Println("Would you like to kill the process? [y/n]")
	answer, err := t.stdin.ReadString('\n')
	if err != nil {
		die(2, err.Error())
	}

	fmt.Println("Detaching from process...")
	err = syscall.PtraceDetach(dbp.Process.Pid)
	if err != nil {
		die(2, "Could not detach", err)
	}

	if answer == "y\n" {
		fmt.Println("Killing process", dbp.Process.Pid)

		err := dbp.Process.Kill()
		if err != nil {
			fmt.Println("Could not kill process", err)
		}
	}

	die(status, "Hope I was of service hunting your bug!")
}

func die(status int, args ...interface{}) {
	fmt.Fprint(os.Stderr, args)
	fmt.Fprint(os.Stderr, "\n")
	os.Exit(status)
}

func newTerm() *term {
	return &term{
		stdin: bufio.NewReader(os.Stdin),
	}
}

func parseCommand(cmdstr string) (string, []string) {
	vals := strings.Split(cmdstr, " ")
	return vals[0], vals[1:]
}

func (t *term) promptForInput() (string, error) {
	prompt := "dlv> "
	line := *goreadline.ReadLine(&prompt)
	line = strings.TrimSuffix(line, "\n")
	if line != "" {
		goreadline.AddHistory(line)
	}

	return line, nil
}