/*
NAME
  rtmp.go

DESCRIPTION
  See Readme.md

AUTHOR
  Saxon Nelson-Milton <saxon@ausocean.org>
  Dan Kortschak <dan@ausocean.org>

LICENSE
  rtmp.go is Copyright (C) 2017 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
  along with revid in gpl.txt.  If not, see http://www.gnu.org/licenses.
*/

package rtmp

/*
#cgo CFLAGS: -I/usr/local/include/librtmp
#cgo LDFLAGS: -lrtmp -Wl,-rpath=/usr/local/lib

#include <stdlib.h>
#include <rtmp.h>

RTMP* start_session(RTMP* rtmp, char* url, uint connect_timeout);
int write_frame(RTMP* rtmp, char* data, uint data_length);
int end_session(RTMP* rtmp);
*/
import "C"

import (
	"errors"
	"log"
	"strconv"
	"unsafe"
)

const (
	minDataSize = 11
)

// Session provides an interface for sending flv tags over rtmp.
type Session interface {
	Open() error
	Write([]byte) (int, error)
	Close() error
}

// session provides parameters required for an rtmp communication session.
type session struct {
	rtmp    *C.RTMP
	url     string
	timeout uint
}

var _ Session = (*session)(nil)

// NewSession returns a new session.
func NewSession(url string, connectTimeout uint) Session {
	return &session{
		url:     url,
		timeout: connectTimeout,
	}
}

// C.AVal is in amf.h
// See #define AVC(str) {str, sizeof(str)-1} in amf.h
func AVC(str string) C.AVal {
	var aval C.AVal
	aval.av_val = C.CString(str)
	aval.av_len = C.int(len(str))
	return aval
}

// av_setDataFrame is a static const global in rtmp.c
var av_setDataFrame = AVC("@setDataFrame")

// Open establishes an rtmp connection with the url passed into the
// constructor
func (s *session) Open() error {
	if s.rtmp != nil {
		return errors.New("rtmp: attempt to start already running session")
	}
	var err error
	s.rtmp, err = C.start_session(s.rtmp, C.CString(s.url), C.uint(s.timeout))
	if s.rtmp == nil {
		return err
	}
	return nil
}

func byteSliceToCArr(buf []byte) *C.char {
	return (*C.char)(unsafe.Pointer(&buf[0]))
}

func (s *session) rtmpWrite(r *C.RTMP, buf []byte) int {
	var pkt *C.RTMPPacket = &r.m_write
	var enc unsafe.Pointer
	size := len(buf)
	s2 := size
	var ret, num int

	pkt.m_nChannel = 0x04
	pkt.m_nInfoField2 = r.m_stream_id

	for s2 > 0 {
		if pkt.m_nBytesRead == 0 {
			if size < minDataSize {
				log.Printf("size: %d\n", size)
				log.Printf("too small \n")
				return 0
			}

			if buf[0] == 'F' && buf[1] == 'L' && buf[2] == 'V' {
				buf = buf[13:]
				s2 -= 13
			}

			buf = buf[1:]
			pkt.m_packetType = C.uchar(buf[0])
			pkt.m_nBodySize = C.AMF_DecodeInt24(byteSliceToCArr(buf))
			buf = buf[3:]
			pkt.m_nTimeStamp = C.AMF_DecodeInt24(byteSliceToCArr(buf))
			buf = buf[3:]
			buf = buf[1:]
			pkt.m_nTimeStamp |= C.uint(buf[0] << 24)
			buf = buf[3:]
			s2 -= 11

			if ((pkt.m_packetType == C.RTMP_PACKET_TYPE_AUDIO ||
				pkt.m_packetType == C.RTMP_PACKET_TYPE_VIDEO) &&
				pkt.m_nTimeStamp == 0) || pkt.m_packetType == C.RTMP_PACKET_TYPE_INFO {

				pkt.m_headerType = C.RTMP_PACKET_SIZE_LARGE
				if pkt.m_packetType == C.RTMP_PACKET_TYPE_INFO {
					pkt.m_nBodySize += 16
				}
			} else {
				pkt.m_headerType = C.RTMP_PACKET_SIZE_MEDIUM
			}

			// C: if (!RTMPPacket_Alloc(pkt, pkt->m_nBodySize))
			if int(C.RTMPPacket_Alloc(pkt, pkt.m_nBodySize)) == 0 {
				log.Println("Failed to allocated packet")
				return 0
			}

			enc = unsafe.Pointer(pkt.m_body)
			pend := unsafe.Pointer(uintptr(enc) + uintptr(pkt.m_nBodySize))

			if pkt.m_packetType == C.RTMP_PACKET_TYPE_INFO {
				enc = unsafe.Pointer(C.AMF_EncodeString((*C.char)(enc), (*C.char)(pend),
					&av_setDataFrame))

				// C-code: pkt.m_nBytesRead enc - pkt.m_body
				pkt.m_nBytesRead = (C.uint)(uintptr(enc) -
					uintptr(unsafe.Pointer(pkt.m_body)))
			}
		} else {
			//C-code: enc = pkt.m_body + pkt.m_nBytesRead
			enc = unsafe.Pointer(uintptr(unsafe.Pointer(pkt.m_body)) +
				uintptr(pkt.m_nBytesRead))
		}

		num = int(pkt.m_nBodySize - pkt.m_nBytesRead)

		if num > s2 {
			num = s2
		}

		encSlice := C.GoBytes(enc, C.int(num))
		copy(encSlice, buf)

		pkt.m_nBytesRead += C.uint(num)
		s2 -= num
		buf = buf[num:]

		if pkt.m_nBytesRead == pkt.m_nBodySize {
			ret = int(C.RTMP_SendPacket(r, pkt, 0))
			C.RTMPPacket_Free(pkt)
			pkt.m_nBytesRead = 0
			if ret == 0 {
				return -1
			}
			buf = buf[4:]
			s2 -= 4
			if s2 < 0 {
				break
			}
		}
	}
	return size + s2
}

// Write writes a frame (flv tag) to the rtmp connection
func (s *session) Write(data []byte) (int, error) {
	if s.rtmp == nil {
		return 0, Err(3)
	}
	if C.RTMP_IsConnected(s.rtmp) <= 0 {
		return 0, Err(1)
	}
	if s.rtmpWrite(s.rtmp, data) <= 0 {
		return 0, Err(2)
	}
	return len(data), nil
}

// Close terminates the rtmp connection
func (s *session) Close() error {
	if s.rtmp == nil {
		return Err(3)
	}
	ret := C.end_session(s.rtmp)
	s.rtmp = nil
	if ret != 0 {
		return Err(ret)
	}
	return nil
}

var rtmpErrs = [...]string{
	1: "rtmp: not connected",
	2: "rtmp: write error",
	3: "rtmp: not started",
}

type Err uint

func (e Err) Error() string {
	if 0 <= int(e) && int(e) < len(rtmpErrs) {
		s := rtmpErrs[e]
		if s != "" {
			return s
		}
	}
	return "rtmp: " + strconv.Itoa(int(e))
}