/*
Copyright (c) 2015, T. Jameson Little <t.jameson.little@gmail.com>
All rights reserved.

Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this
list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation and/or
other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its contributors
may be used to endorse or promote products derived from this software without
specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF

LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
OF THE POSSIBILITY OF SUCH DAMAGE.
*/

package rtp

import (
	"net"
	"fmt"
)

const (
	RTP_VERSION = 2
)

const (
	hasRtpPadding = 1 << 5
	hasRtpExt     = 1 << 4
)

type RtpPacket struct {
	Version        byte
	Padding        bool
	Ext            bool
	Marker         bool
	PayloadType    byte
	SequenceNumber uint
	Timestamp      uint
	SyncSource     uint
	CSRC []uint
	ExtHeader uint
	ExtData   []byte
	Payload []byte
}

type Session struct {
	Rtp  net.PacketConn
	Rtcp net.PacketConn
	RtpChan  <-chan RtpPacket
	RtcpChan <-chan []byte
	rtpChan  chan<- RtpPacket
	rtcpChan chan<- []byte
}

func New(rtp, rtcp net.PacketConn) *Session {
	rtpChan := make(chan RtpPacket, 10)
	rtcpChan := make(chan []byte, 10)
	s := &Session{
		Rtp:      rtp,
		Rtcp:     rtcp,
		RtpChan:  rtpChan,
		RtcpChan: rtcpChan,
		rtpChan:  rtpChan,
		rtcpChan: rtcpChan,
	}
	go s.HandleRtpConn(rtp)
	go s.HandleRtcpConn(rtcp)
	return s
}

func toUint(arr []byte) (ret uint) {
	for i, b := range arr {
		ret |= uint(b) << (8 * uint(len(arr)-i-1))
	}
	return ret
}

func (s *Session) HandleRtpConn(conn net.PacketConn) {
	buf := make([]byte, 4096)
	for {
		n, _, err := conn.ReadFrom(buf)
		if err != nil {
			panic(err)
		}

		cpy := make([]byte, n)
		copy(cpy, buf)
		go s.handleRtp(cpy)
	}
}

func (s *Session) HandleRtcpConn(conn net.PacketConn) {
	buf := make([]byte, 4096)
	for {
		n, _, err := conn.ReadFrom(buf)
		if err != nil {
			panic(err)
		}
		cpy := make([]byte, n)
		copy(cpy, buf)
		go s.handleRtcp(cpy)
	}
}

func (s *Session) handleRtp(buf []byte) {
	fmt.Println(buf)
	packet := RtpPacket{
		Version:        (buf[0] & 0xC0)>>6,
		Padding:        buf[0]&hasRtpPadding != 0,
		Ext:            buf[0]&hasRtpExt != 0,
		Marker:         buf[1]&1 != 0,
		PayloadType:    buf[1] >> 1,
		SequenceNumber: toUint(buf[2:4]),
		Timestamp:      toUint(buf[4:8]),
		SyncSource:     toUint(buf[8:12]),
    CSRC:           make([]uint, buf[0]>>4),
	}

	if packet.Version != RTP_VERSION {
		fmt.Printf("Packet version: %v", packet.Version)
		panic("Unsupported version")
	}


	i := 12

	for j := range packet.CSRC {
		packet.CSRC[j] = toUint(buf[i : i+4])
		i += 4
	}

	if packet.Ext {
		packet.ExtHeader = toUint(buf[i : i+2])
		length := toUint(buf[i+2 : i+4])
		i += 4
		if length > 0 {
			packet.ExtData = buf[i : i+int(length)*4]
			i += int(length) * 4
		}
	}

	packet.Payload = buf[i:]

	s.rtpChan <- packet
}

func (s *Session) handleRtcp(buf []byte) {
	// TODO: implement rtcp
}