package tor

import (
	"errors"
	"fmt"
	"github.com/yawning/bulb"
	"log"
	"net"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"path"
	"strings"
	"time"
)

// Manager checks connectivity of the Tor process used to support Cwtch
type Manager struct {
	socksPort   int
	controlPort int
	process     *exec.Cmd
}

// NewTorManager Instantiates a new connection manager, returns non-nil error if it fails to connect to a tor daemon on the given ports.
func NewTorManager(socksPort int, controlPort int, torPath string, torrc string) (*Manager, error) {
	torManager := new(Manager)
	torManager.socksPort = socksPort
	torManager.controlPort = controlPort

	err := torManager.TestConnection()

	if err == nil {
		log.Printf("using existing tor proxy")
		return torManager, nil
	}

	// try to start tor

	cmd := exec.Command(torPath, "-f", torrc)

	// on Android, home can be set to '/' which is not writeable
	if os.Getenv("HOME") == "" {
		cmd.Env = append(os.Environ(), fmt.Sprintf("HOME=%s", path.Dir(torrc)))
	}

	log.Printf("starting local tor proxy")
	err = cmd.Start()
	if err != nil {
		log.Printf("starting tor failed %v", err)
		return nil, err
	}
	torManager.process = cmd

	// for 30 seconds check every 5 if tor is up and working
	for i := 0; i < 6; i++ {
		time.Sleep(time.Second * 5)
		err = torManager.TestConnection()
		if err == nil {
			break
		}
	}
	return torManager, err
}

type proxyStatus int

const (
	proxyStatusOK proxyStatus = iota
	proxyStatusWrongType
	proxyStatusCannotConnect
	proxyStatusTimeout
)

// Shutdown kills the managed Tor Process
func (tm *Manager) Shutdown() {
	if tm.process != nil {
		if err := tm.process.Process.Kill(); err != nil {
			log.Fatal("failed to kill process: ", err)
		}
	}
}

// Detect whether a proxy is connectable and is a Tor proxy
func checkTorProxy(proxyAddress string) proxyStatus {
	// A trick to do this without making an outward connection is,
	// paradoxically, to try to open it as http.
	// This is documented in section 4 here: https://github.com/torproject/torspec/blob/master/socks-extensions.txt
	client := &http.Client{Timeout: 2 * time.Second}
	response, err := client.Get("http://" + proxyAddress + "/")
	if err != nil {
		switch t := err.(type) {
		case *url.Error:
			switch t.Err.(type) {
			case *net.OpError: // Network-level error. Will in turn contain a os.SyscallError
				return proxyStatusCannotConnect
			default:
				// http.error unfortunately not exported, need to match on string
				// net/http: request canceled
				if strings.Index(t.Err.Error(), "request canceled") != -1 {
					return proxyStatusTimeout
				}
			}
		}
		// Protocol-level errors mean that http failed, so it's not Tor
		return proxyStatusWrongType
	}
	defer response.Body.Close()
	if response.Status != "501 Tor is not an HTTP Proxy" {
		return proxyStatusWrongType
	}
	return proxyStatusOK
}

func proxyStatusMessage(status proxyStatus) string {
	switch status {
	case proxyStatusWrongType:
		return "Proxy specified is not a Tor proxy"
	case proxyStatusCannotConnect:
		return "Cannot connect to Tor proxy"
	case proxyStatusTimeout:
		return "Proxy timeout"
	default:
		return "Unknown proxy error"
	}
}

// TestConnection returns nil if both the socks and control ports of the Tor connection are active, otherwise it returns an error.
func (tm *Manager) TestConnection() error {
	proxyStatus := checkTorProxy(fmt.Sprintf("127.0.0.1:%d", tm.socksPort))
	controlAddress := fmt.Sprintf("127.0.0.1:%d", tm.controlPort)
	if proxyStatus == proxyStatusOK {
		c, err := bulb.Dial("tcp4", controlAddress)
		if c != nil {
			c.Close()
		}
		if err == nil {
			return nil
		}
		return fmt.Errorf("could not connect to Tor Control Port %v %v", tm.controlPort, err)
	}
	return errors.New(proxyStatusMessage(proxyStatus))
}