package rtcp

import (
	"encoding/binary"
)

// RTCP packet types.
const (
	typeSenderReport      = 200
	typeReceiverReport    = 201
	typeSourceDescription = 202
)

// SDES Item types.
const (
	typeCName = 1
)

const (
	reportBlockSize = 6
)

type ReceiverReport struct {
	Header

	SenderSSRC uint32
	Blocks     []ReportBlock
	Extensions [][4]byte
}

func (r *ReceiverReport) Bytes() []byte {
	l := 8 + 4*reportBlockSize*len(r.Blocks) + 4*len(r.Extensions)
	buf := make([]byte, l)

	l = 1 + reportBlockSize*len(r.Blocks) + len(r.Extensions)
	r.writeHeader(buf, l)
	binary.BigEndian.PutUint32(buf[4:], r.SenderSSRC)

	idx := 8
	for _, b := range r.Blocks {
		binary.BigEndian.PutUint32(buf[idx:], b.SSRC)
		idx += 4
		binary.BigEndian.PutUint32(buf[idx:], b.PacketsLost)
		buf[idx] = b.FractionLost
		idx += 4
		binary.BigEndian.PutUint32(buf[idx:], b.HighestSequence)
		idx += 4
		binary.BigEndian.PutUint32(buf[idx:], b.Jitter)
		idx += 4
		binary.BigEndian.PutUint32(buf[idx:], b.LSR)
		idx += 4
		binary.BigEndian.PutUint32(buf[idx:], b.DLSR)
		idx += 4
	}

	for _, e := range r.Extensions {
		copy(buf[idx:], e[:])
		idx += 4
	}

	return buf
}

type ReportBlock struct {
	SSRC            uint32 // Source identifier.
	FractionLost    uint8  // Fraction of packets lost.
	PacketsLost     uint32 // Cumulative number of packets lost.
	HighestSequence uint32 // Extended highest sequence number received.
	Jitter          uint32 // Interarrival jitter.
	LSR             uint32 // Last sender report timestamp.
	DLSR            uint32 // Delay since last sender report.
}

type SourceDescription struct {
	Header

	Chunks []Chunk
}

func (d *SourceDescription) Bytes() []byte {
	bodyLen := d.bodyLen()
	rem := bodyLen % 4
	if rem != 0 {
		bodyLen += 4 - rem
	}
	l := 4 + bodyLen
	buf := make([]byte, l)
	d.writeHeader(buf, bodyLen/4)
	idx := 4
	for _, c := range d.Chunks {
		binary.BigEndian.PutUint32(buf[idx:], c.SSRC)
		idx += 4
		for _, i := range c.Items {
			buf[idx] = i.Type
			idx++
			buf[idx] = byte(len(i.Text))
			idx++
			copy(buf[idx:], i.Text)
			idx += len(i.Text)
		}
	}
	return buf
}

func (d *SourceDescription) bodyLen() int {
	l := 0
	for _, c := range d.Chunks {
		l += c.len()
	}
	return l
}

type Header struct {
	Version     uint8 // RTCP version.
	Padding     bool  // Padding indicator.
	ReportCount uint8 // Number of reports contained.
	Type        uint8 // Type of RTCP packet.
}

type SDESItem struct {
	Type uint8
	Text []byte
}

type Chunk struct {
	SSRC  uint32
	Items []SDESItem
}

func (c *Chunk) len() int {
	tot := 4
	for _, i := range c.Items {
		tot += 2 + len(i.Text)
	}
	return tot
}

func (h Header) writeHeader(buf []byte, l int) {
	buf[0] = h.Version<<6 | asByte(h.Padding)<<5 | 0x1f&h.ReportCount
	buf[1] = h.Type
	binary.BigEndian.PutUint16(buf[2:], uint16(l))
}

func asByte(b bool) byte {
	if b {
		return 0x01
	}
	return 0x00
}