package main

import (
	"bufio"
	"io"
	"log"
	"net"
	"time"
)

// read all messages from client.
func read(rc io.ReadCloser, id int, msg chan<- string, done chan<- int) {
	defer rc.Close()

	scanner := bufio.NewScanner(rc)
	for scanner.Scan() {
		msg <- scanner.Text()
	}

	done <- id
}

// write 'tick' message to all clients.
func write(conns []net.Conn) {
	for _, c := range conns {
		if c != nil {
			io.WriteString(c, "tick\n")
		}
	}
}

// add a client and read messages if there is room.
func addClient(conns []net.Conn, conn net.Conn, msg chan<- string, done chan<- int) []net.Conn {
	for i, c := range conns {
		if c == nil {
			go read(conn, i, msg, done)
			conns[i] = conn
			return conns
		}
	}

	// reject the client if we are full
	conn.Close()
	return conns
}

func main() {
	conns := make([]net.Conn, 15)

	connC := make(chan net.Conn, 0)
	msgC := make(chan string, 0)
	doneC := make(chan int, 0)

	listener, err := net.Listen("tcp", ":8080")
	if err != nil {
		log.Fatalf("listening on :8080: %s", err.Error())
	}

	go func() {
		for {
			c, err := listener.Accept()
			if err == nil {
				connC <- c
			}
		}
	}()

	ticker := time.NewTicker(time.Second)

	for {
		select {

		case conn := <-connC:
			conns = addClient(conns, conn, msgC, doneC)

		case id := <-doneC:
			conns[id] = nil

		case msg := <-msgC:
			log.Printf("client said: %s", msg)

		case <-ticker.C:
			write(conns)
		}
	}
}