package main

// TODO learn about chan chan's
// http://marcio.io/2015/07/handling-1-million-requests-per-minute-with-golang/

import (
	"bufio"
	"bytes"
	"crypto/rand"
	"encoding/base64"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"net/http"
	"net/url"
	"os"
	"path"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/emicklei/go-restful"
	"gopkg.in/yaml.v2"
)

// I'm not sure how to pass nested structs, so I de-nested this.
// TODO: Learn if passing nested structs is desirable?
type Conf struct {
	Port     uint `yaml:"port,omitempty"`
	Mailer   ConfMailer
	RootPath string `yaml:"root_path,omitempty"`
}
type ConfMailer struct {
	Url    string `yaml:"url,omitempty"`
	ApiKey string `yaml:"api_key,omitempty"`
	From   string `yaml:"from,omitempty"`
}

type tcpUser struct {
	bufConn   bufferedConn
	userCount chan int
	email     string
}

// So we can peek at net.Conn, which we can't do natively
// https://stackoverflow.com/questions/51472020/how-to-get-the-size-of-available-tcp-data
type bufferedConn struct {
	r    *bufio.Reader
	rout io.Reader
	net.Conn
}

func newBufferedConn(c net.Conn) bufferedConn {
	return bufferedConn{bufio.NewReader(c), nil, c}
}

func (b bufferedConn) Peek(n int) ([]byte, error) {
	return b.r.Peek(n)
}

func (b bufferedConn) Buffered() int {
	return b.r.Buffered()
}

func (b bufferedConn) Read(p []byte) (int, error) {
	if b.rout != nil {
		return b.rout.Read(p)
	}
	return b.r.Read(p)
}

// Just making these all globals right now
// because... I can clean it up later
type myMsg struct {
	sender     net.Conn
	bytes      []byte
	receivedAt time.Time
	channel    string
	email      string
}

var firstMsgs chan myMsg

//var myRooms map[string](chan myMsg)
var myMsgs chan myMsg

//var myUnsortedConns map[net.Conn]bool
var newConns chan net.Conn
var newTcpChat chan bufferedConn
var authTcpChat chan tcpUser
var delTcpChat chan bufferedConn
var newHttpChat chan bufferedConn
var newHttpClient chan bufferedConn
var delHttpChat chan bufferedConn

func usage() {
	fmt.Fprintf(os.Stderr, "\nusage: go run chatserver.go\n")
	flag.PrintDefaults()
	fmt.Println()

	os.Exit(1)
}

// https://blog.questionable.services/article/generating-secure-random-numbers-crypto-rand/
func genAuthCode() (string, error) {
	n := 12
	b := make([]byte, n)
	_, err := rand.Read(b)
	// Note that err == nil only if we read len(b) bytes.
	if err != nil {
		return "", err
	}
	return base64.URLEncoding.EncodeToString(b), nil
}

func handleRaw(bufConn bufferedConn) {
	// TODO
	// What happens if this is being read from range
	// when it's being added here (data race)?
	// Should I use a channel here instead?
	// TODO see https://jameshfisher.com/2017/04/18/golang-tcp-server.html

	var email string
	var code string
	var authn bool

	// Handle all subsequent packets
	buffer := make([]byte, 1024)
	for {
		//fmt.Fprintf(os.Stdout, "[raw] Waiting for message...\n")
		count, err := bufConn.Read(buffer)
		if nil != err {
			if io.EOF != err {
				fmt.Fprintf(os.Stderr, "Non-EOF socket error: %s\n", err)
			}
			fmt.Fprintf(os.Stdout, "Ending socket\n")

			delTcpChat <- bufConn
			break
		}
		buf := buffer[:count]

		// Fun fact: if the buffer's current length (not capacity) is 0
		// then the Read returns 0 without error
		if 0 == count {
			fmt.Fprintf(os.Stdout, "Weird")
			break
		}

		if !authn {
			if "" == email {
				// Indeed telnet sends CRLF as part of the message
				//fmt.Fprintf(os.Stdout, "buf{%s}\n", buf[:count])

				// TODO use safer email testing
				email = strings.TrimSpace(string(buf[:count]))
				emailParts := strings.Split(email, "@")
				if 2 != len(emailParts) {
					fmt.Fprintf(bufConn, "Email: ")
					continue
				}

				// Debugging any weird characters as part of the message (just CRLF)
				//fmt.Fprintf(os.Stdout, "email: '%v'\n", []byte(email))

				// Just for a fun little bit of puzzah
				// Note: Reaction times are about 100ms
				//       Procesing times are about 250ms
				//       Right around 300ms is about when a person literally begins to get bored (begin context switching)
				//       Therefore any interaction should take longer than 100ms (time to register)
				//       and either engage the user or complete before reaching 300ms (not yet bored)
				//       This little ditty is meant to act as a psuedo-progress bar to engage the user
				//       Aside: a keystroke typically takes >=50s to type (probably closer to 200ms between words)
				//       https://stackoverflow.com/questions/22505698/what-is-a-typical-keypress-duration
				var wg sync.WaitGroup
				wg.Add(1)
				go func() {
					time.Sleep(50 * time.Millisecond)
					const msg = "Mailing auth code..."
					for _, r := range msg {
						time.Sleep(20 * time.Millisecond)
						fmt.Fprintf(bufConn, string(r))
					}
					time.Sleep(50 * time.Millisecond)
					wg.Done()
				}()
				if "" != config.Mailer.ApiKey {
					wg.Add(1)
					go func() {
						code, err = sendAuthCode(config.Mailer, strings.TrimSpace(email))
						wg.Done()
					}()
				} else {
					code, err = genAuthCode()
				}
				wg.Wait()
				if nil != err {
					// TODO handle better
					// (not sure why a random number would fail,
					//  but on a machine without internet the calls
					//  to mailgun APIs would fail)
					panic(err)
				}
				// so I don't have to actually go check my email
				fmt.Fprintf(os.Stdout, "\n== AUTHORIZATION ==\n[cheat code for %s]: %s\n", email, code)
				time.Sleep(150 * time.Millisecond)
				fmt.Fprintf(bufConn, " done\n")
				time.Sleep(150 * time.Millisecond)
				fmt.Fprintf(bufConn, "Auth Code: ")
				continue
			}

			if code != strings.TrimSpace(string(buf[:count])) {
				fmt.Fprintf(bufConn, "Incorrect Code\nAuth Code: ")
			} else {
				authn = true
				time.Sleep(150 * time.Millisecond)
				fmt.Fprintf(bufConn, "\n")
				u := tcpUser{
					bufConn:   bufConn,
					email:     email,
					userCount: make(chan int, 1),
				}
				authTcpChat <- u
				// prevent data race on len(myRawConns)
				// XXX (there can't be a race between these two lines, right?)
				count := <-u.userCount
				u.userCount = nil
				time.Sleep(50 * time.Millisecond)
				fmt.Fprintf(bufConn, "\n")
				time.Sleep(50 * time.Millisecond)
				fmt.Fprintf(bufConn, "Welcome to #general (%d users)!", count)
				time.Sleep(50 * time.Millisecond)
				fmt.Fprintf(bufConn, "\n")
				time.Sleep(50 * time.Millisecond)
				// TODO /help /join <room> /users /channels /block <user> /upgrade <http/ws>
				//fmt.Fprintf(bufConn, "(TODO `/help' for list of commands)")
				time.Sleep(100 * time.Millisecond)
				fmt.Fprintf(bufConn, "\n")

				// this would be cool, but won't work since other messages will come
				// in before the person responds
				//fmt.Fprintf(bufConn, "\n%s> ", email)
			}
			continue
		}

		//fmt.Fprintf(os.Stdout, "Queing message...\n")
		//myRooms["general"] <- myMsg{
		myMsgs <- myMsg{
			receivedAt: time.Now(),
			sender:     bufConn,
			bytes:      buf[0:count],
			channel:    "general",
			email:      email,
		}
		//fmt.Fprintf(bufConn, "> ")
	}
}

func handleSorted(conn bufferedConn) {
	// Wish List for protocol detection
	// * PROXY protocol (and loop)
	// * HTTP CONNECT (proxy) (and loop)
	// * tls (and loop) https://github.com/polvi/sni
	// * http/ws
	// * irc
	// * fallback to telnet

	// At this piont we've already at least one byte via Peek()
	// so the first packet is available in the buffer

	// Note: Realistically no tls/http/irc client is going to send so few bytes
	//       (and no router is going to chunk so small)
	//       that it cannot reasonably detect the protocol in the first packet
	//       However, typical MTU is 1,500 and HTTP can have a 2k URL
	//       so expecting to find the "HTTP/1.1" in the Peek is not always reasonable
	n := conn.Buffered()
	firstMsg, err := conn.Peek(n)
	if nil != err {
		conn.Close()
		return
	}
	var protocol string
	// between A and z
	if firstMsg[0] >= 65 && firstMsg[0] <= 122 {
		i := bytes.Index(firstMsg, []byte(" /"))
		if -1 != i {
			protocol = "HTTP"
			// very likely HTTP
			j := bytes.IndexAny(firstMsg, "\r\n")
			if -1 != j {
				k := bytes.Index(bytes.ToLower(firstMsg[:j]), []byte("HTTP/1"))
				if -1 != k {
					// positively HTTP
				}
			}
		}
	} else if 0x16 /*22*/ == firstMsg[0] {
		// Because I don't always remember off the top of my head what the first byte is
		// http://blog.fourthbit.com/2014/12/23/traffic-analysis-of-an-ssl-slash-tls-session
		// https://tlseminar.github.io/first-few-milliseconds/
		// TODO I want to learn about ALPN
		protocol = "TLS"
	}

	if "" == protocol {
		fmt.Fprintf(conn, "\n\nWelcome to Sample Chat! You're not an HTTP client, assuming Telnet.\nYou must authenticate via email to participate\n\nEmail: ")
		newTcpChat <- conn
		return
	} else if "HTTP" != protocol {
		defer conn.Close()
		fmt.Fprintf(conn, "\n\nNot yet supported. Try HTTP or Telnet\n\n")
		return
	}

	newHttpClient <- conn

	/*
	   firstMsgs <- myMsg{
	     receivedAt: time.Now(),
	     sender: conn,
	     bytes: firstMsg,
	     channel: "general",
	   }

	   // TODO
	   // * TCP-CHAT
	   // * HTTP
	   // * TLS

	   // Handle all subsequent packets
	   buf := make([]byte, 1024)
	   for {
	     fmt.Fprintf(os.Stdout, "[sortable] Waiting for message...\n")
	     count, err := conn.Read(buf)
	     if nil != err {
	       if io.EOF != err {
	         fmt.Fprintf(os.Stderr, "Non-EOF socket error: %s\n", err)
	       }
	       fmt.Fprintf(os.Stdout, "Ending socket\n")
	       break
	     }
	     // Fun fact: if the buffer's current length (not capacity) is 0
	     // then the Read returns 0 without error
	     if 0 == count {
	       // fmt.Fprintf(os.Stdout, "Weird")
	       continue
	     }
	     //myRooms["general"] <- myMsg{
	     myMsgs <- myMsg{
	       receivedAt: time.Now(),
	       sender: conn,
	       bytes: buf[0:count],
	       channel: "general",
	     }
	   }
	*/
}

func handleConnection(netConn net.Conn) {
	ts := time.Now()
	fmt.Fprintf(os.Stdout, "[New Connection] (%s) welcome %s\n", ts, netConn.RemoteAddr().String())

	m := sync.Mutex{}
	virgin := true

	// Why don't these work?
	//buf := make([]byte, 0, 1024)
	//buf := []byte{}
	// But this does

	bufConn := newBufferedConn(netConn)
	//myUnsortedConns[bufConn] = true
	go func() {
		// Handle First Packet
		_, err := bufConn.Peek(1)
		//fmsg, err := bufConn.Peek(1)
		if nil != err {
			panic(err)
		}
		//fmt.Fprintf(os.Stdout, "[First Byte] %s\n", fmsg)

		m.Lock()
		if virgin {
			virgin = false
			newHttpChat <- bufConn
		} else {
			newTcpChat <- bufConn
		}
		m.Unlock()
	}()

	time.Sleep(250 * 1000000)
	// If we still haven't received data from the client
	// assume that the client must be expecting a welcome from us
	m.Lock()
	if virgin {
		virgin = false
		// don't block for this
		// let it be handled after the unlock
		defer fmt.Fprintf(netConn, "\n\nWelcome to Sample Chat! You appear to be using Telnet.\nYou must authenticate via email to participate\n\nEmail: ")
	}
	m.Unlock()
}

func sendAuthCode(cnf ConfMailer, to string) (string, error) {
	code, err := genAuthCode()
	if nil != err {
		return "", err
	}

	// TODO use go text templates with HTML escaping
	text := "Your authorization code:\n\n" + code
	html := "Your authorization code:<br><br>" + code

	// https://stackoverflow.com/questions/24493116/how-to-send-a-post-request-in-go
	// https://stackoverflow.com/questions/16673766/basic-http-auth-in-go
	client := http.Client{}

	form := url.Values{}
	form.Add("from", cnf.From)
	form.Add("to", to)
	form.Add("subject", "Sample Chat Auth Code: "+code)
	form.Add("text", text)
	form.Add("html", html)

	req, err := http.NewRequest("POST", cnf.Url, strings.NewReader(form.Encode()))
	if nil != err {
		return "", err
	}
	//req.PostForm = form
	req.Header.Add("User-Agent", "golang http.Client - Sample Chat App Authenticator")
	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
	req.SetBasicAuth("api", cnf.ApiKey)

	resp, err := client.Do(req)
	if nil != err {
		return "", err
	}

	defer resp.Body.Close()
	// Security XXX
	// we trust mailgun implicitly and this is just a demo
	// hence no DoS check on body size for now
	body, err := ioutil.ReadAll(resp.Body)
	if nil != err {
		return "", err
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 || "{" != string(body[0]) {
		fmt.Fprintf(os.Stdout, "[Mailgun] Uh-oh...\n[Maigun] Baby Brent says: %s\n", body)
	} else {
		fmt.Fprintf(os.Stdout, "[Mailgun] Status: %d", resp.StatusCode)
	}

	return code, nil
}

type myServer struct {
	chans chan bufferedConn
	net.Listener
}

func (m *myServer) Accept() (net.Conn, error) {
	bufConn := <-m.chans
	return bufConn, nil
}

func newMyServer(l net.Listener) *myServer {
	return &myServer{make(chan bufferedConn), l}
}

var config Conf

func serveStatic(req *restful.Request, resp *restful.Response) {
	actual := path.Join(config.RootPath, req.PathParameter("subpath"))
	fmt.Printf("serving %s ... (from %s)\n", actual, req.PathParameter("subpath"))
	http.ServeFile(
		resp.ResponseWriter,
		req.Request,
		actual)
}
func serveHello(req *restful.Request, resp *restful.Response) {
	fmt.Fprintf(resp, "{\"msg\":\"hello\"}")
}

func main() {
	flag.Usage = usage
	port := flag.Uint("telnet-port", 0, "tcp telnet chat port")
	confname := flag.String("conf", "./config.yml", "yaml config file")
	flag.Parse()

	confstr, err := ioutil.ReadFile(*confname)
	fmt.Fprintf(os.Stdout, "-conf=%s\n", *confname)
	if nil != err {
		fmt.Fprintf(os.Stderr, "%s\nUsing defaults instead\n", err)
		confstr = []byte("{\"port\":" + strconv.Itoa(int(*port)) + "}")
	}
	err = yaml.Unmarshal(confstr, &config)
	if nil != err {
		config = Conf{}
	}
	if "" == config.RootPath {
		// TODO Embed the public dir at the default
		config.RootPath = "./public"
	}

	myRawConns := make(map[bufferedConn]bool)
	firstMsgs = make(chan myMsg, 128)
	//myRooms = make(map[string](chan myMsg))
	newConns = make(chan net.Conn, 128)
	authTcpChat = make(chan tcpUser, 128)
	newTcpChat = make(chan bufferedConn, 128)
	newHttpChat = make(chan bufferedConn, 128)
	newHttpClient = make(chan bufferedConn, 128)
	//myUnsortedConns = make(map[net.Conn]bool)

	// TODO dynamically select on channels?
	// https://stackoverflow.com/questions/19992334/how-to-listen-to-n-channels-dynamic-select-statement
	//myRooms["general"] = make(chan myMsg, 128)
	myMsgs = make(chan myMsg, 128)

	var addr string
	if 0 != int(*port) {
		addr = ":" + strconv.Itoa(int(*port))
	} else {
		addr = ":" + strconv.Itoa(int(config.Port))
	}

	// https://golang.org/pkg/net/#Conn
	sock, err := net.Listen("tcp", addr)
	if nil != err {
		fmt.Fprintf(os.Stderr, "Couldn't bind to TCP socket %q: %s\n", addr, err)
		os.Exit(2)
	}
	fmt.Println("Listening on", addr)

	go func() {
		for {
			conn, err := sock.Accept()
			if err != nil {
				// Not sure what kind of error this could be or how it could happen.
				// Could a connection abort or end before it's handled?
				fmt.Fprintf(os.Stderr, "Error accepting connection:\n%s\n", err)
			}
			newConns <- conn
		}
	}()

	// Learning by Example
	// https://github.com/emicklei/go-restful/blob/master/examples/restful-multi-containers.go
	// https://github.com/emicklei/go-restful/blob/master/examples/restful-basic-authentication.go
	// https://github.com/emicklei/go-restful/blob/master/examples/restful-serve-static.go
	// https://github.com/emicklei/go-restful/blob/master/examples/restful-pre-post-filters.go
	container := restful.NewContainer()

	wsStatic := new(restful.WebService)
	wsStatic.Path("/")
	wsStatic.Route(wsStatic.GET("/").To(serveStatic))
	wsStatic.Route(wsStatic.GET("/{subpath:*}").To(serveStatic))
	container.Add(wsStatic)

	wsApi := new(restful.WebService)
	wsApi.Path("/api")
	wsApi.Route(wsApi.GET("/api/hello").To(serveHello))
	/*
		ws.Route(ws.POST("/api/authn").To(createAuth))
		ws.Route(ws.POST("/api/authn/{email}").To(createAuth))
		ws.Route(ws.GET("/api").Filter(basicAuthenticate).To(hello2))
	*/
	container.Add(wsApi)

	server := &http.Server{
		Addr:    addr,
		Handler: container,
	}
	myHttpServer := newMyServer(sock)
	go func() {
		server.Serve(myHttpServer)
	}()

	// Main event loop handling most access to shared data
	for {
		select {
		case conn := <-newConns:
			// This is short lived
			go handleConnection(conn)
		case u := <-authTcpChat:
			// allow to receive messages
			// (and be counted among the users)
			myRawConns[u.bufConn] = true
			// is chan chan the right way to handle this?
			u.userCount <- len(myRawConns)
			myMsgs <- myMsg{
				sender: nil,
				// TODO fmt.Fprintf()? template?
				bytes:      []byte("<" + u.email + "> joined #general\n"),
				receivedAt: time.Now(),
				channel:    "general",
				email:      "system",
			}
		case bufConn := <-newTcpChat:
			go handleRaw(bufConn)
		case bufConn := <-delTcpChat:
			// we can safely ignore this error
			bufConn.Close()
			delete(myRawConns, bufConn)
		case bufConn := <-newHttpChat:
			go handleSorted(bufConn)
		//case msg := <- myRooms["general"]:
		//delete(myRooms["general"], bufConn)
		case bufConn := <-newHttpClient:
			// this will be Accept()ed immediately by restful
			myHttpServer.chans <- bufConn
		case msg := <-myMsgs:
			t := msg.receivedAt
			tf := "%d-%02d-%02d %02d:%02d:%02d (%s)"
			var sender string
			if nil != msg.sender {
				sender = msg.sender.RemoteAddr().String()
			} else {
				sender = "system"
			}
			// I wonder if we could use IP detection to get the client's tz
			// ... could probably make time for this in the authentication loop
			zone, _ := msg.receivedAt.Zone()

			//ts, err := msg.receivedAt.MarshalJSON()
			fmt.Fprintf(os.Stdout, tf+" [%s] (%s):\n\t%s",
				t.Year(), t.Month(), t.Day(),
				t.Hour(), t.Minute(), t.Second(), zone,
				sender,
				msg.email, msg.bytes)

			for conn, _ := range myRawConns {
				// Don't echo back to the original client
				if msg.sender == conn {
					continue
				}

				// To ask: Why do I have to pass in conn to prevent a data race? Is it garbage collection?
				// Don't block the rest of the loop
				// TODO maybe use a chan to send to the socket's event loop
				go func(conn bufferedConn) {
					// Protect against malicious clients to prevent DoS
					// https://blog.cloudflare.com/the-complete-guide-to-golang-net-http-timeouts/
					timeoutDuration := 5 * time.Second
					conn.SetWriteDeadline(time.Now().Add(timeoutDuration))
					_, err := fmt.Fprintf(conn, tf+" [%s]: %s",
						t.Year(), t.Month(), t.Day(),
						t.Hour(), t.Minute(), t.Second(), zone,
						msg.email, msg.bytes)
					if nil != err {
						delTcpChat <- conn
					}
				}(conn)
			}
		case msg := <-firstMsgs:
			fmt.Fprintf(os.Stdout, "f [First Message]\n")
			ts, err := msg.receivedAt.MarshalJSON()
			if nil != err {
				fmt.Fprintf(os.Stderr, "f [Error] %s\n", err)
			}
			fmt.Fprintf(os.Stdout, "f [Timestamp] %s\n", ts)
			fmt.Fprintf(os.Stdout, "f [Remote] %s\n", msg.sender.RemoteAddr().String())
			fmt.Fprintf(os.Stdout, "f [Message] %s\n", msg.bytes)
		}
	}
}