/*
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"
	_ "fmt"
	"log"
	"math"
	"reflect"
	"strconv"
	"unsafe"
)

const (
	minDataSize = 11
)

const (
	RTMP_PACKET_SIZE_LARGE  = 0
	RTMP_PACKET_SIZE_MEDIUM = 1
	RTMP_PACKET_SIZE_SMALL  = 2
	RTMP_PACKET_TYPE_INFO   = 0x12
	RTMP_PACKET_TYPE_AUDIO  = 0x08
	RTMP_PACKET_TYPE_VIDEO  = 0x09
)

// 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 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 C.RTMP_Write(s.rtmp,(*C.char)(unsafe.Pointer(&data[0])),C.int(len(data))) == 0 {
	if rtmpWrite(s.rtmp, data) == 0 {
		return 0, Err(2)
	}
	return len(data), nil
}

// memmove copies n bytes from "from" to "to".
//go:linkname memmove runtime.memmove
func memmove(to, from unsafe.Pointer, n uintptr)

// rtmpWrite writes data to the current rtmp connection encapsulated by r
func rtmpWrite(r *C.RTMP, data []byte) int {
	buf := sliceToPtr(data)
	// TODO: port RTMPPacket
	var pkt = &r.m_write
	var pend, enc unsafe.Pointer
	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
			}

			if indxPtr(buf,0) == 'F' && indxPtr(buf,1) == 'L' && indxPtr(buf,2) == 'V' {
				buf = unsafe.Pointer(uintptr(buf) + uintptr(13))
				s2 -= 13
			}

			pkt.m_packetType = C.uchar(indxPtr(buf,0))
			buf = incPtr(buf, 1)
			// TODO: port this
			pkt.m_nBodySize = C.AMF_DecodeInt24((*C.char)(buf))
			buf = incPtr(buf, 3)
			// TODO: replace with ported version
			pkt.m_nTimeStamp = C.AMF_DecodeInt24((*C.char)(buf))
			buf = incPtr(buf, 3)
			pkt.m_nTimeStamp |= C.uint(indxPtr(buf,0)) << 24
			buf = incPtr(buf, 4)
			s2 -= 11

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

				pkt.m_headerType = RTMP_PACKET_SIZE_LARGE

				if pkt.m_packetType == RTMP_PACKET_TYPE_INFO {
					pkt.m_nBodySize += 16
				}
			} else {
				pkt.m_headerType = RTMP_PACKET_SIZE_MEDIUM
			}
			// TODO: Port this
			if int(C.RTMPPacket_Alloc(pkt, pkt.m_nBodySize)) == 0 {
				log.Println("Failed to allocate packet")
				return 0
			}

			enc = unsafe.Pointer(pkt.m_body)
			pend = incPtr(enc, int(pkt.m_nBodySize))

			if pkt.m_packetType == RTMP_PACKET_TYPE_INFO {
				// TODO: Port this
				enc = unsafe.Pointer(C.AMF_EncodeString((*C.char)(enc), (*C.char)(pend), &setDataFrame))
				pkt.m_nBytesRead = C.uint(math.Abs(float64(uintptr(enc) -
					uintptr(unsafe.Pointer(pkt.m_body)))))
			}

		} else {
			enc = incPtr(unsafe.Pointer(pkt.m_body), int(pkt.m_nBytesRead))
		}
		num = int(pkt.m_nBodySize - pkt.m_nBytesRead)
		if num > s2 {
			num = s2
		}

		memmove(enc,buf,uintptr(num))
		//copy(ptrToSlice(enc, num), ptrToSlice(buf, num))
		pkt.m_nBytesRead += C.uint(num)
		s2 -= num
		buf = incPtr(buf, num)
		if pkt.m_nBytesRead == pkt.m_nBodySize {
			// TODO: Port this
			ret = int(C.RTMP_SendPacket(r, pkt, 0))
			// TODO: Port this
			C.RTMPPacket_Free(pkt)
			pkt.m_nBytesRead = 0
			if ret == 0 {
				return -1
			}
			buf = incPtr(buf, 4)
			s2 -= 4
			if s2 < 0 {
				break
			}
		}
	}
	return size + s2
}

// indxPtr replicates C array indexing using an unsafe pointer
func indxPtr(ptr unsafe.Pointer, inc int) byte {
	return *(*byte)(incPtr(ptr,inc))
}

// sliceToPtr get's the address of the first data element and returns as unsafe
// pointer
func sliceToPtr(data []byte) unsafe.Pointer {
	return unsafe.Pointer(&data[0])
}

// ptrToSlice returns a slice given unsafe pointer and size - no allocation and
// copying is required - same data is used.
func ptrToSlice(data unsafe.Pointer, size int) []byte {
	var ret []byte
	shDest := (*reflect.SliceHeader)(unsafe.Pointer(&ret))
	shDest.Data = uintptr(data)
	shDest.Len = size
	shDest.Cap = size
	return ret
}

// incPtr attempts to replicate C like pointer arithmatic functionality
func incPtr(ptr unsafe.Pointer, inc int) unsafe.Pointer {
	return unsafe.Pointer(uintptr(ptr) + uintptr(inc))
}
/*
func sendPacket(r *C.RTMP, pkt *C.RTMPPacket, queue int) int {
	const prevPacket *C.RTMPPacket
	last := 0
	var nSize, hSize, cSize, nChunkSize, tlen int
	var header, hptr, hend, buffer *C.char
	var goHbuf [RTMP_MAX_HEADER_SIZE]byte
	var hbuf = (*C.char)(unsafe.Pointer(&goHbuf[0]))
	var c C.char
	var t int32
	var tbuf *C.char = nil
	var toff *C.char = nil

	if packet.m_nChannel >= r.m_channelsAllocatedOut {
		n := int(packet.m_nChannel+10)
		packets := C.realloc(r.m_vecChannelsOut, unsafe.Sizeof(*C.RTMPPacket) * n)

		if packets == 0 {
			C.free(r.m_vecChannelsOut)
			r.m_vecChannelsOut = nil
			r.m_channelsAllocatedOut = 0
			return 0
		}
		r.m_vecChannelsOut = packets
		C.memset(r.m_vecChannelsOut + r.m_channelsAllocatedOut, 0,
			unsafe.Sizeof(*RTMPPacket) * (n-r.m_channelsAllocatedOut))
		r.m_channelsAllocatedOut = n
	}

	prevPackt = (*RTMPPacket)(unsafe.Pointer() )
}
*/

// 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))
}