package main

import (
	"bytes"
	"flag"
	"fmt"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"
)

const (
	workbench = `build`
)

var (
	key    = ""
	repo   = ""
	commit = ""
	task   = ""
	image  = ""
	port   = ""
)

func init() {
	flag.StringVar(&key, "key", "", "Path to SSH private key")
	flag.StringVar(&repo, "repo", "", "Source code as valid Git URL")
	flag.StringVar(&commit, "commit", "", "Commit or commit-ish reference for checkout")
	flag.StringVar(&task, "task", "", "Shell code to execute for the build")
	flag.StringVar(&image, "image", "", "QEMU qcow2 image which contains the VM")
	flag.StringVar(&port, "port", "", "localhost port which is connected to VM SSH server")
}

func main() {
	flag.Parse()

	log.SetFlags(0)

	log.Println("Starting craft")
	defer log.Println("Exiting craft")

	vm := qemu()
	err := vm.Start()
	if err != nil {
		log.Fatal(err)
	}
	defer func() {
		err := vm.Process.Kill()
		if err != nil {
			log.Fatal(err)
		}
	}()

	waitBoot()

	checkoutSources(repo, commit)
	craft()
}

func runCommand(name string, args ...string) {
	log.Printf("Remote execution: %s %s\n", name, strings.Join(args, " "))
	command := sshCommand(name, args...)
	command.Stderr = os.Stderr
	command.Stdout = os.Stdout
	err := command.Run()
	if err != nil {
		log.Fatal(err)
	}
}

func qemu() *exec.Cmd {
	return exec.Command(
		"qemu-system-x86_64",
		"-enable-kvm",
		"-m",
		"4G",
		"-net",
		"nic,model=virtio",
		"-net",
		fmt.Sprintf(
			"user,hostfwd=tcp:127.0.0.1:%s-:22",
			port,
		),
		"-drive",
		fmt.Sprintf(
			"file=%s,media=disk,snapshot=on,if=virtio",
			image,
		),
		"-smp",
		"cpus=4",
		"-nographic",
	)
}

func sshCommand(name string, arg ...string) *exec.Cmd {
	return exec.Command(
		"ssh",
		append([]string{
			"-p",
			port,
			"-o",
			"UserKnownHostsFile=/dev/null",
			"-o",
			"StrictHostKeyChecking=no",
			"-i",
			key,
			"root@localhost",
			name,
		}, arg...)...,
	)
}

func waitBoot() {
	retries := 5
	initialDelay := 1 * time.Second

	log.Println("Waiting for VM to boot")
	time.Sleep(initialDelay) // without that `ssh` returns too quickly
	for range retries {
		cmd := sshCommand("true")
		err := cmd.Run()
		if err == nil {
			log.Println("VM booted")
			return
		}
	}
	log.Fatalf("Could not reach VM %d times - giving up", retries)
}

func craft() {
	script := fmt.Sprintf(`#!/bin/sh

cd %s
%s
`, workbench, task)

	cmd := sshCommand("sh")
	cmd.Stdin = bytes.NewBufferString(script)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	err := cmd.Run()
	if err != nil {
		log.Fatal(err)
	}
}

func checkoutSources(repo string, commit string) string {
	runCommand(
		"git",
		"clone",
		repo,
		workbench,
	)

	runCommand(
		"git",
		"--git-dir",
		filepath.Join(workbench, ".git"),
		"--work-tree",
		workbench,
		"checkout",
		commit,
	)

	runCommand(
		"git",
		"-C",
		workbench,
		"submodule",
		"update",
		"--depth=1",
		"--init",
		"--recursive",
	)

	return workbench
}