/*
   Copyright 2024 Josh Deprez

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package rtmp

import (
	"bytes"
	"encoding/binary"
	"fmt"

	"github.com/sfiera/multitalk/pkg/ddp"
)

// DataPacket represents an RTMP Data packet.
type DataPacket struct {
	RouterAddr    ddp.Addr
	Extended      bool
	NetworkTuples []NetworkTuple
}

// NetworkTuple represents routing information.
type NetworkTuple struct {
	Extended   bool
	RangeStart ddp.Network
	RangeEnd   ddp.Network
	Distance   uint8
}

func (nt *NetworkTuple) Size() int {
	if nt.Extended {
		return 6
	} else {
		return 3
	}
}

// Marshal marshals an RTMP Data packet.
func (dp *DataPacket) Marshal() ([]byte, error) {
	b := bytes.NewBuffer(nil)
	write16(b, dp.RouterAddr.Network)
	b.WriteByte(8)
	b.WriteByte(byte(dp.RouterAddr.Node))
	if !dp.Extended {
		write16(b, uint16(0))
		b.WriteByte(0x82)
	}
	for _, nt := range dp.NetworkTuples {
		write16(b, nt.RangeStart)
		if !nt.Extended {
			b.WriteByte(nt.Distance)
			continue
		}
		b.WriteByte(nt.Distance | 0x80)
		write16(b, nt.RangeEnd)
		b.WriteByte(0x82)
	}
	return b.Bytes(), nil
}

// UnmarshalDataPacket unmarshals a DataPacket.
func UnmarshalDataPacket(data []byte) (*DataPacket, error) {
	if len(data) < 7 || (len(data)-4)%3 != 0 {
		return nil, fmt.Errorf("invalid input length %d for RTMP Data packet", len(data))
	}
	if data[2] != 8 {
		return nil, fmt.Errorf("unsupported node ID length %d for RTMP Data packet", data[2])
	}
	dp := &DataPacket{
		RouterAddr: ddp.Addr{
			Network: ddp.Network(binary.BigEndian.Uint16(data[:2])),
			Node:    ddp.Node(data[3]),
		},
		Extended: true,
	}
	data = data[4:]

	first := true
	for len(data) > 0 {
		if len(data) < 3 {
			return nil, fmt.Errorf("insufficient remaining input length %d for RTMP Data network tuple", len(data))
		}
		nt := NetworkTuple{
			RangeStart: ddp.Network(binary.BigEndian.Uint16(data[:2])),
			Distance:   data[2],
		}
		data = data[3:]
		if nt.RangeStart == 0 {
			// if non-extended, first tuple should contain version
			if !first {
				return nil, fmt.Errorf("invalid RTMP network tuple range start 0")
			}
			// initial non-extended tuple with Distance field containing version
			if nt.Distance != 0x82 {
				return nil, fmt.Errorf("unsupported RTMP version %x", nt.Distance)
			}
			dp.Extended = false
			first = false
			continue
		}
		nt.Extended = nt.Distance&0x80 != 0
		if !nt.Extended {
			// ordinary non-extended tuple
			nt.RangeEnd = nt.RangeStart
			if first && nt.RangeStart != 0 {
				return nil, fmt.Errorf("first RTMP network tuple is not version tuple")
			}
			dp.NetworkTuples = append(dp.NetworkTuples, nt)
			continue
		}

		// extended tuple
		if len(data) < 3 {
			return nil, fmt.Errorf("insufficient remaining input length %d for RTMP Data extended network tuple", len(data))
		}
		nt.Distance &^= 0x80
		nt.RangeEnd = ddp.Network(binary.BigEndian.Uint16(data[:2]))
		if first {
			if data[2] != 0x82 {
				return nil, fmt.Errorf("unsupported RTMP version %x", data[2])
			}
		}
		first = false
		dp.NetworkTuples = append(dp.NetworkTuples, nt)
		data = data[3:]
	}

	return dp, nil
}