/*
NAME
  client.go

DESCRIPTION
  client.go provides an implemntation of a basic RTCP client that will send
	receiver reports, and receive sender reports to parse relevant statistics.

AUTHORS
  Saxon A. Nelson-Milton <saxon@ausocean.org>

LICENSE
  This is Copyright (C) 2019 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 	for more details.

  You should have received a copy of the GNU General Public License
  in gpl.txt.  If not, see http://www.gnu.org/licenses.
*/

package rtcp

import (
	"encoding/binary"
	"errors"
	"fmt"
	"math"
	"net"
	"sync"
	"time"

	"bitbucket.org/ausocean/utils/logger"
)

const (
	senderSSRC        = 3605043418
	defaultClientName = "client"
	delayUnit         = 1.0 / 65536.0
	pkg               = "rtcp: "
	rtcpVer           = 2
)

type log func(lvl int8, msg string, args ...interface{})

// client is an RTCP client that will hadle receiving SenderReports from a server
// and sending out ReceiverReports.
type client struct {
	ErrChan chan error

	cAddr       *net.UDPAddr
	sAddr       *net.UDPAddr
	name        string
	sourceSSRC  uint32
	mu          sync.Mutex
	sequence    uint32
	senderTs    [64]byte
	interval    time.Duration
	receiveTime time.Time
	buf         [200]byte
	conn        *net.UDPConn
	wg          sync.WaitGroup
	quitSend    chan struct{}
	quitRecv    chan struct{}
	log
}

// NewClient returns a pointer to a new client.
func NewClient(clientAddress, serverAddress, name string, sendInterval time.Duration, rtpSSRC uint32, l log) (*client, error) {
	if name == "" {
		name = defaultClientName
	}

	c := &client{
		name:       name,
		ErrChan:    make(chan error, 2),
		quitSend:   make(chan struct{}),
		quitRecv:   make(chan struct{}),
		interval:   sendInterval,
		sourceSSRC: rtpSSRC,
		log:        l,
	}

	var err error
	c.cAddr, err = net.ResolveUDPAddr("udp", clientAddress)
	if err != nil {
		return nil, errors.New(fmt.Sprintf("can't resolve client address, failed with error: %v\n", err))
	}

	c.sAddr, err = net.ResolveUDPAddr("udp", serverAddress)
	if err != nil {
		return nil, errors.New(fmt.Sprintf("can't resolve server address, failed with error: %v\n", err))
	}

	c.conn, err = net.DialUDP("udp", c.cAddr, c.sAddr)
	if err != nil {
		return nil, errors.New(fmt.Sprintf("can't dial, failed with error: %v\n", err))
	}
	return c, nil
}

// Start starts the listen and send routines. This will start the process of
// receiving and parsing sender reports, and the process of sending receiver
// reports to the server.
func (c *client) Start() {
	c.log(logger.Debug, pkg+"client is starting")
	c.wg.Add(1)
	go c.recv()
	c.wg.Add(1)
	go c.send()
}

// Stop sends a quit signal to the send and receive routines and closes the
// UDP connection. It will wait until both routines have returned.
func (c *client) Stop() {
	c.log(logger.Debug, pkg+"client is stopping")
	close(c.quitSend)
	close(c.quitRecv)
	c.conn.Close()
	c.wg.Wait()
}

// recv reads from the UDP connection and parses SenderReports.
func (c *client) recv() {
	defer c.wg.Done()
	c.log(logger.Debug, pkg+"client is receiving")
	buf := make([]byte, 4096)
	for {
		select {
		case <-c.quitRecv:
			return
		default:
			n, _, err := c.conn.ReadFromUDP(buf)
			if err != nil {
				c.ErrChan <- err
				continue
			}
			c.log(logger.Debug, pkg+"sender report received", "report", buf[:n])
			c.parse(buf[:n])
		}
	}
}

// send writes receiver reports to the server.
func (c *client) send() {
	defer c.wg.Done()
	c.log(logger.Debug, pkg+"client is sending")
	for {
		select {
		case <-c.quitSend:
			return
		default:
			time.Sleep(c.interval)

			report := ReceiverReport{
				Header: Header{
					Version:     rtcpVer,
					Padding:     false,
					ReportCount: 1,
					Type:        typeReceiverReport,
				},
				SenderSSRC: senderSSRC,
				Blocks: []ReportBlock{
					ReportBlock{
						SSRC:            c.sourceSSRC,
						FractionLost:    0,
						PacketsLost:     math.MaxUint32,
						HighestSequence: c.highestSequence(),
						Jitter:          c.jitter(),
						LSR:             c.lastSenderTs(),
						DLSR:            c.delay(),
					},
				},
				Extensions: nil,
			}

			description := SourceDescription{
				Header: Header{
					Version:     rtcpVer,
					Padding:     false,
					ReportCount: 1,
					Type:        typeSourceDescription,
				},
				Chunks: []Chunk{
					Chunk{
						SSRC: senderSSRC,
						Items: []SDESItem{
							SDESItem{
								Type: typeCName,
								Text: []byte(c.name),
							},
						},
					},
				},
			}

			c.log(logger.Debug, pkg+"sending receiver report")
			_, err := c.conn.Write(c.formPayload(&report, &description))
			if err != nil {
				c.ErrChan <- err
			}
		}
	}
}

// formPayload takes a pointer to a ReceiverReport and a pointer to a
// Source Description and calls Bytes on both, writing to the underlying client
// buf. A slice to the combined writtem memory is returned.
func (c *client) formPayload(r *ReceiverReport, d *SourceDescription) []byte {
	rl := len(r.Bytes(c.buf[:]))
	dl := len(d.Bytes(c.buf[rl:]))
	t := rl + dl
	if t > cap(c.buf) {
		panic("client buf not big enough")
	}
	return c.buf[:t]
}

// parse will read important statistics from sender reports.
func (c *client) parse(buf []byte) {
	c.received()
	msw, lsw, err := Timestamp(buf)
	if err != nil {
		c.ErrChan <- errors.New(fmt.Sprintf("could not get timestamp from sender report, failed with error: %v", err))
	}
	c.setSenderTs(msw, lsw)
}

// UpdateSequence will allow updating of the highest sequence number received
// through an RTP stream.
func (c *client) UpdateSequence(s uint32) {
	c.mu.Lock()
	c.sequence = s
	c.mu.Unlock()
}

// highestSequence will return the highest sequence number received through RTP.
func (c *client) highestSequence() uint32 {
	var s uint32
	c.mu.Lock()
	s = c.sequence
	c.mu.Unlock()
	return s
}

// jitter returns the interarrival jitter as described by RTCP specifications:
// https://tools.ietf.org/html/rfc3550
func (c *client) jitter() uint32 {
	return 0
}

// setSenderTs allows us to safely set the current sender report timestamp.
func (c *client) setSenderTs(msw, lsw uint32) {
	c.mu.Lock()
	binary.BigEndian.PutUint32(c.senderTs[:], msw)
	binary.BigEndian.PutUint32(c.senderTs[4:], lsw)
	c.mu.Unlock()
}

// lastSenderTs returns the timestamp of the most recent sender report.
func (c *client) lastSenderTs() uint32 {
	var ts uint32
	c.mu.Lock()
	ts = binary.BigEndian.Uint32(c.senderTs[2:])
	c.mu.Unlock()
	return ts
}

// delay returns the duration between the receive time of the last sender report
// and now. This is called when forming a receiver report.
func (c *client) delay() uint32 {
	var receiveTime time.Time
	c.mu.Lock()
	receiveTime = c.receiveTime
	c.mu.Unlock()
	now := time.Now()
	return uint32(now.Sub(receiveTime).Seconds() / delayUnit)
}

// received is called when a sender report is received to mark the receive time.
func (c *client) received() {
	c.mu.Lock()
	c.receiveTime = time.Now()
	c.mu.Unlock()
}