package main

import (
	"container/list"
	"flag"
	"fmt"
	"net"
	"net/http"
	"net/http/pprof"
	"net/url"
	"os"
	"os/signal"
	"strings"
	"sync"
	"sync/atomic"
	"syscall"
	"time"
)

type UpstreamConfig map[string]*url.URL

func (config *UpstreamConfig) String() string {
	return fmt.Sprintf("%+v", (*map[string]*url.URL)(config))
}

func (config *UpstreamConfig) Set(value string) error {
	parts := strings.SplitN(value, "=", 2)
	if len(parts) < 2 {
		return fmt.Errorf("format error: not in name=url format: %s", value)
	}
	name := parts[0]
	if _, ok := (*config)[name]; ok {
		return fmt.Errorf("config error: remote %s already specified", name)
	}
	u, err := url.Parse(parts[1])
	if err != nil {
		return fmt.Errorf("format error: unable to parse url %s: %w", parts[1], err)
	}
	(*config)[name] = u
	fmt.Printf("Added remote %s with url %s\n", name, u)
	return nil
}

var listen = flag.String("listen", "unix:/var/run/tsb/tsb.sock", "Listen address of the service")

var upstreams = make(UpstreamConfig)

type UpstreamContext struct {
	viewerCond         *sync.Cond
	viewer             int64
	upstreamChan       chan []byte
	clientsChanList    *list.List
	newClientsChanList *list.List
	newChanLock        *sync.Mutex
}

var upstreamContexts = make(map[string]*UpstreamContext)
var upstreamContextLock = &sync.Mutex{}

func GetUpstreamContext(name string) *UpstreamContext {
	upstreamContextLock.Lock()
	defer upstreamContextLock.Unlock()
	ctx, ok := upstreamContexts[name]
	if !ok {
		ctx = &UpstreamContext{
			viewerCond:         sync.NewCond(&sync.Mutex{}),
			viewer:             0,
			upstreamChan:       make(chan []byte),
			clientsChanList:    list.New(),
			newClientsChanList: list.New(),
			newChanLock:        &sync.Mutex{},
		}
		upstreamContexts[name] = ctx
		go upstreamFiber(name)
		go broadcastFiber(name)
	}
	return ctx
}

type ClientChannel struct {
	Notify chan struct{}
	Data   chan []byte
	ctx    *UpstreamContext
}

func NewClientChannel(name string) *ClientChannel {
	ctx := GetUpstreamContext(name)
	ch := &ClientChannel{
		Notify: make(chan struct{}),
		Data:   make(chan []byte, 1024),
		ctx:    ctx,
	}
	ctx.newChanLock.Lock()
	ctx.newClientsChanList.PushBack(ch)
	ctx.newChanLock.Unlock()
	cntViewer := atomic.AddInt64(&ctx.viewer, 1)
	ctx.viewerCond.Broadcast()
	fmt.Printf("Current viewers for stream %s: %d\n", name, cntViewer)
	return ch
}

// Close the notify channel, to the server will stop sending data and remove this entry.
func (ch *ClientChannel) Close() {
	close(ch.Notify)
	atomic.AddInt64(&ch.ctx.viewer, -1)
}

func init() {
	flag.Var(&upstreams, "upstream", "Upstream in name=URL format, may specify multiple times.")
}

func upstreamFiber(name string) {
	ctx := GetUpstreamContext(name)
	client := &http.Client{}
	req := &http.Request{
		Method: "GET",
		URL:    upstreams[name],
		Close:  true,
	}
	for {
		ctx.viewerCond.L.Lock()
		if ctx.viewer == 0 {
			fmt.Printf("No active viewers for stream %s, idling around :)\n", name)
			ctx.viewerCond.Wait()
		}
		ctx.viewerCond.L.Unlock()
		fmt.Printf("Connecting to upstream for stream %s ...\n", name)
		r := (func() *http.Response {
			for {
				r, err := client.Do(req)
				if err != nil {
					fmt.Fprintf(os.Stderr, "Unable to request %s for stream %s: %v\n", upstreams[name], name, err)
					time.Sleep(5 * time.Second)
					continue
				}
				if r.StatusCode != 200 {
					fmt.Fprintf(os.Stderr, "Request to %s for stream %s failed with status code %d\n", upstreams[name], name, err)
					time.Sleep(5 * time.Second)
					continue
				}
				return r
			}
		})()
		body := r.Body
		for {
			if ctx.viewer == 0 {
				fmt.Printf("No active viewers for %s, stopping reading from upstream.\n", name)
				break
			}
			buff := make([]byte, 65536)
			n, err := body.Read(buff)
			if err != nil {
				fmt.Fprintf(os.Stderr, "Upstream for stream %s request reached EOF\n", name)
				break
			}
			ctx.upstreamChan <- buff[:n]
		}
		body.Close()
	}
}

func broadcastFiber(name string) {
	ctx := GetUpstreamContext(name)
	for {
		chunk := <-ctx.upstreamChan
		// Send to all existing clients
		e := ctx.clientsChanList.Front()
	enumerate_client:
		for e != nil {
			ch := e.Value.(*ClientChannel)
			// Note: select in Golang is not ordered!
			select {
			case <-ch.Notify:
				// Closed client, remove this entry
				close(ch.Data)
				next := e.Next()
				ctx.clientsChanList.Remove(e)
				e = next
				continue enumerate_client
			default:
			}
			select {
			case ch.Data <- chunk:
			default:
			}
			e = e.Next()
		}
		// Try to serve all new clients, but don't get locked up here :)
		if ctx.newClientsChanList.Len() > 0 && ctx.newChanLock.TryLock() {
			ctx.clientsChanList.PushBackList(ctx.newClientsChanList)
			ctx.newClientsChanList.Init()
			ctx.newChanLock.Unlock()
		}
	}
}

func clientHandler(w http.ResponseWriter, r *http.Request) {
	remote := r.RemoteAddr
	if r.Header.Get("X-Remote-Addr") != "" {
		remote = r.Header.Get("X-Remote-Addr")
	}
	fmt.Printf("Client connection from %s accepted.\n", remote)
	name := r.URL.Path
	if _, ok := upstreams[name]; !ok {
		http.NotFound(w, r)
		return
	}
	w.Header().Add("Content-Type", "video/MP2T")
	w.WriteHeader(200)
	if r.Method == http.MethodHead {
		// Fuck you golang, you should never eat write but fail
		return
	}
	if r.Method != http.MethodGet {
		w.WriteHeader(405)
		return
	}
	ch := NewClientChannel(name)
	defer ch.Close()
	for {
		chunk := <-ch.Data
		_, err := w.Write(chunk)
		if err != nil {
			fmt.Printf("Write to remote client %s failed, closing...\n", remote)
			break
		}
	}
}

func viewersHandler(w http.ResponseWriter, r *http.Request) {
	w.Header().Add("Content-Type", "text/plain")
	w.WriteHeader(200)
	name := r.URL.Path
	if name == "" {
		totalViewer := int64(0)
		upstreamContextLock.Lock()
		for name, ctx := range upstreamContexts {
			totalViewer += ctx.viewer
			fmt.Fprintf(w, "%s: %d\n", name, ctx.viewer)
		}
		upstreamContextLock.Unlock()
		fmt.Fprintf(w, "sum: %d\n", totalViewer)
	} else {
		if _, ok := upstreams[name]; !ok {
			http.NotFound(w, r)
			return
		}
		upstreamContextLock.Lock()
		ctx, ok := upstreamContexts[name]
		if !ok {
			fmt.Fprintf(w, "%s: 0\n", name)
		} else {
			fmt.Fprintf(w, "%s: %d\n", name, ctx.viewer)
		}
		upstreamContextLock.Unlock()
	}
}

func main() {
	flag.Parse()
	var listener net.Listener
	var err error
	if strings.HasPrefix(*listen, "unix:") {
		if listener, err = net.Listen("unix", (*listen)[5:]); err != nil {
			panic(err)
		}
	} else {
		if listener, err = net.Listen("tcp", *listen); err != nil {
			panic(err)
		}
	}
	handler := http.NewServeMux()
	handler.Handle("/stream/", http.StripPrefix("/stream/", http.HandlerFunc(clientHandler)))
	handler.Handle("/viewers/", http.StripPrefix("/viewers/", http.HandlerFunc(viewersHandler)))
	handler.HandleFunc("/debug/pprof/", pprof.Index)
	handler.HandleFunc("/debug/pprof/cmdline", pprof.Cmdline)
	handler.HandleFunc("/debug/pprof/profile", pprof.Profile)
	handler.HandleFunc("/debug/pprof/symbol", pprof.Symbol)
	handler.HandleFunc("/debug/pprof/trace", pprof.Trace)
	server := &http.Server{
		Handler: handler,
	}
	go server.Serve(listener)
	ch := make(chan os.Signal)
	signal.Notify(ch, syscall.SIGINT, syscall.SIGTERM)
	select {
	case sig := <-ch:
		fmt.Fprintf(os.Stderr, "Caught signal %v, exiting...\n", sig)
		os.Exit(0)
	}
}