/*
NAME
  client.go

DESCRIPTION
  client.go provides an RTP client, Client, that will receive RTP on a UDP
  connection, perform an operation on the packets and then store in a ringBuffer
  that can be read from Read, an implemntation of io.Reader.

AUTHOR
  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 rtp

import (
	"io"
	"net"
	"sync"
	"time"

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

// Misc consts.
const (
	chanSize = 10
	pkg      = "rtp: "
)

// RingBuffer consts.
const (
	ringBufferSize        = 100
	ringBufferElementSize = 4096
)

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

// Client describes an RTP client that can receive an RTP stream and implements
// io.Reader.
type Client struct {
	conn *net.UDPConn   // The UDP connection RTP packets will be read from.
	wg   sync.WaitGroup // Used to wait for recv routine to finish.
	done chan struct{}  // Used to terminate the recv routine.
	ring *ring.Buffer   // Processed data from RTP packets will be stored here.
	err  chan error     // Errors encountered during recv will be sent to this chan.
	rt   time.Duration  // Read timeout used when reading from the ringbuffer.
	log
}

// NewClient returns a pointer to a new Client.
//
// addr is the address of form <ip>:<port> that we expect to receive
// RTP at. op is a function, if non nil, that will be used to perform an
// operation on each received RTP packet. For example, the op func may parse
// out the RTP payload. The result of the operation is then what is stored
// in the ringBuffer for reading. l is a logging function defined by the
// signuture of the log type defined above. rt is the read timeout used when
// reading from the client ringbuffer.
func NewClient(addr string, l log, rt time.Duration) (*Client, error) {
	c := &Client{
		done: make(chan struct{}, chanSize),
		ring: ring.NewBuffer(ringBufferSize, ringBufferElementSize, 0),
		log:  l,
		err:  make(chan error),
		rt:   rt,
	}

	a, err := net.ResolveUDPAddr("udp", addr)
	if err != nil {
		return nil, err
	}

	c.conn, err = net.ListenUDP("udp", a)
	if err != nil {
		return nil, err
	}

	return c, nil
}

// Start will start the recv routine.
func (c *Client) Start() {
	c.log(logger.Info, pkg+"starting client")
	c.wg.Add(1)
	go c.recv()
}

// Stop will send a done signal to the receive routine, and also close the
// connection.
func (c *Client) Stop() {
	c.log(logger.Info, pkg+"stopping client")
	c.conn.Close()
	close(c.done)
	c.wg.Wait()
}

// Err returns the client err channel as receive only.
func (c *Client) Err() <-chan error {
	return c.err
}

// recv will read RTP packets from the UDP connection, perform the operation
// on them given at creation of the Client and then store the result in the
// ringBuffer for Reading.
func (c *Client) recv() {
	defer c.wg.Done()
	buf := make([]byte, ringBufferElementSize)
	for {
		select {
		case <-c.done:
			c.log(logger.Debug, pkg+"done signal received")
			return
		default:
			c.log(logger.Debug, pkg+"waiting for packet")
			n, _, err := c.conn.ReadFromUDP(buf)
			if err != nil {
				c.err <- err
				continue
			}
			c.log(logger.Debug, pkg+"packet received", "packet", buf[:n])

			_, err = c.ring.Write(buf[:n])
			c.ring.Flush()
			if err != nil {
				c.err <- err
				continue
			}
		}
	}
}

// Read implements io.Reader.
//
// Read will get the next chunk from the ringBuffer and copy the bytes to p.
func (c *Client) Read(p []byte) (int, error) {
	c.log(logger.Debug, pkg+"user reading data")
	chunk, err := c.ring.Next(c.rt)
	if err != nil {
		return 0, io.EOF
	}
	n := copy(p, chunk.Bytes())
	chunk.Close()
	chunk = nil
	return n, nil
}