/*
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 <string.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
}

// 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 rtmpWrite(s.rtmp, data) <= 0 {
		return 0, Err(2)
	}
	return len(data), nil
}

func rtmpWrite(r *C.RTMP, data []byte) int {
	buf := (*C.char)(unsafe.Pointer(&data[0]))
	var pkt *C.RTMPPacket = &r.m_write
	var pend, enc *C.char
	size := len(data)
	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
			}

			buf0 := *(*byte)(unsafe.Pointer(buf))
			buf1 := *(*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(buf)) + uintptr(1)))
			buf2 := *(*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(buf)) + uintptr(2)))
			if buf0 == 'F' && buf1 == 'L' && buf2 == 'V' {
				buf = (*C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(buf)) + uintptr(13)))
				s2 -= 13
			}

			buf = (*C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(buf)) + uintptr(1)))
			pkt.m_packetType = C.uchar(*(*byte)(unsafe.Pointer(buf)))

			pkt.m_nBodySize = C.AMF_DecodeInt24(buf)
			buf = (*C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(buf)) + uintptr(3)))
			pkt.m_nTimeStamp = C.AMF_DecodeInt24(buf)
			buf = (*C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(buf)) + uintptr(4)))
			pkt.m_nTimeStamp |= C.uint(*(*byte)(unsafe.Pointer(buf)) << 24)
			buf = (*C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(buf)) + uintptr(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
			}

			if int(C.RTMPPacket_Alloc(pkt, pkt.m_nBodySize)) == 0 {
				log.Println("Failed to allocate packet")
				return 0
			}

			enc = pkt.m_body
			pend = (*C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(enc)) +
				uintptr(pkt.m_nBodySize)))

			if pkt.m_packetType == C.RTMP_PACKET_TYPE_INFO {
				enc = C.AMF_EncodeString(enc, pend, &av_setDataFrame)
				pkt.m_nBytesRead = (C.uint)(uintptr(unsafe.Pointer(enc)) -
					uintptr(unsafe.Pointer(pkt.m_body)))
			}
		} else {
			enc = (*C.char)(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
		}
		C.memcpy(unsafe.Pointer(enc),unsafe.Pointer(buf),C.ulong(num))
		pkt.m_nBytesRead += C.uint(num)
		s2 -= num
		buf = (*C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(buf)) + uintptr(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 = (*C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(buf)) + uintptr(4)))
			s2 -= 4
			if s2 < 0 {
				break
			}
		}
	}
	return size + s2
}

/*
func sendPacket(r *C.RTMP, pkt *C.RTMPPacket, queue int) int {
	const prevPacket *C.RTMPPacket
	last := 0
	var nSize, hSize, cSize int
	var
}
*/

// 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))
}

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