Protocol/packets/apppacket.go

package packets

import (
	"encoding/binary"
)

// DefaultOpcodeSize is the default opcode size for application packets
var DefaultOpcodeSize uint8 = 2

// EmuOpcode represents an emulator opcode
type EmuOpcode uint16

// Common emulator opcodes
const (
	OpUnknown EmuOpcode = 0
	// Add other opcodes as needed from op_codes.h
)

// AppPacket handles high-level game opcodes and application data
// This is the main packet type used by game logic
type AppPacket struct {
	*Packet

	emuOpcode  EmuOpcode // Cached emulator opcode
	opcodeSize uint8     // Size of opcode in bytes (1 or 2)
}

// NewAppPacket creates a new application packet
func NewAppPacket() *AppPacket {
	return &AppPacket{
		Packet:     NewPacket(0, nil),
		emuOpcode:  OpUnknown,
		opcodeSize: DefaultOpcodeSize,
	}
}

// NewAppPacketWithOp creates a new application packet with opcode
func NewAppPacketWithOp(op EmuOpcode) *AppPacket {
	app := &AppPacket{
		Packet:     NewPacket(0, nil),
		opcodeSize: DefaultOpcodeSize,
	}
	app.SetOpcode(op)
	return app
}

// NewAppPacketWithSize creates a new application packet with opcode and size
func NewAppPacketWithSize(op EmuOpcode, size uint32) *AppPacket {
	app := &AppPacket{
		Packet:     NewPacket(0, make([]byte, size)),
		opcodeSize: DefaultOpcodeSize,
	}
	app.SetOpcode(op)
	return app
}

// NewAppPacketWithData creates a new application packet with opcode and data
func NewAppPacketWithData(op EmuOpcode, data []byte) *AppPacket {
	app := &AppPacket{
		Packet:     NewPacket(0, data),
		opcodeSize: DefaultOpcodeSize,
	}
	app.SetOpcode(op)
	return app
}

// NewAppPacketFromRaw creates app packet from raw buffer (used by ProtoPacket)
// Assumes first bytes are opcode based on opcodeSize
func NewAppPacketFromRaw(buf []byte, opcodeSize uint8) *AppPacket {
	if opcodeSize == 0 {
		opcodeSize = DefaultOpcodeSize
	}

	app := &AppPacket{
		Packet:     NewPacket(0, nil),
		opcodeSize: opcodeSize,
	}

	if opcodeSize == 1 && len(buf) >= 1 {
		app.Opcode = uint16(buf[0])
		if len(buf) > 1 {
			app.Buffer = make([]byte, len(buf)-1)
			copy(app.Buffer, buf[1:])
		}
	} else if len(buf) >= 2 {
		app.Opcode = binary.BigEndian.Uint16(buf[:2])
		if len(buf) > 2 {
			app.Buffer = make([]byte, len(buf)-2)
			copy(app.Buffer, buf[2:])
		}
	}

	return app
}

// Size returns total packet size including opcode
func (a *AppPacket) Size() uint32 {
	return uint32(len(a.Buffer)) + uint32(a.opcodeSize)
}

// SetOpcodeSize sets the opcode size
func (a *AppPacket) SetOpcodeSize(size uint8) {
	a.opcodeSize = size
}

// SetOpcode sets the emulator opcode
func (a *AppPacket) SetOpcode(op EmuOpcode) {
	a.emuOpcode = op
	// In full implementation, this would convert to protocol opcode
	// using opcode manager. For now, direct assignment
	a.Opcode = uint16(op)
}

// GetOpcode returns the emulator opcode (with caching)
func (a *AppPacket) GetOpcode() EmuOpcode {
	if a.emuOpcode == OpUnknown {
		// In full implementation, convert from protocol opcode
		a.emuOpcode = EmuOpcode(a.Opcode)
	}
	return a.emuOpcode
}

// Copy creates a deep copy of this application packet
func (a *AppPacket) Copy() *AppPacket {
	newApp := &AppPacket{
		Packet:     NewPacket(a.Opcode, a.Buffer),
		emuOpcode:  a.emuOpcode,
		opcodeSize: a.opcodeSize,
	}
	newApp.Packet.CopyInfo(a.Packet)
	return newApp
}

// Serialize writes the application packet to a destination buffer
// Handles special opcode encoding rules for application-level packets
func (a *AppPacket) Serialize(dest []byte) uint32 {
	opcodeBytes := a.opcodeSize
	pos := 0

	if a.opcodeSize == 1 {
		// Single-byte opcode
		dest[pos] = byte(a.Opcode)
		pos++
	} else {
		// Two-byte opcode with special encoding rules
		// Application opcodes with low byte = 0x00 need extra 0x00 prefix
		if (a.Opcode & 0x00ff) == 0 {
			dest[pos] = 0
			pos++
			binary.BigEndian.PutUint16(dest[pos:], a.Opcode)
			pos += 2
			opcodeBytes++
		} else {
			binary.BigEndian.PutUint16(dest[pos:], a.Opcode)
			pos += 2
		}
	}

	// Copy packet data after opcode
	copy(dest[pos:], a.Buffer)

	return uint32(len(a.Buffer)) + uint32(opcodeBytes)
}

// Combine combines this packet with another application packet
func (a *AppPacket) Combine(rhs *AppPacket) bool {
	const opAppCombined = 0x19 // OP_AppCombined

	// Check if we can combine these packets
	totalSize := a.Size() + rhs.Size()
	if totalSize > 512 { // Reasonable max combined packet size
		return false
	}

	// If this isn't already a combined packet, convert it
	if a.Opcode != opAppCombined {
		// Create combined packet structure
		oldSize := a.Size()
		newSize := oldSize + rhs.Size() + 2 // +2 for size headers

		newBuffer := make([]byte, newSize)
		pos := 0

		// Write first packet size and data
		newBuffer[pos] = byte(oldSize)
		pos++

		// Serialize first packet
		tmpBuf := make([]byte, oldSize)
		a.Serialize(tmpBuf)
		copy(newBuffer[pos:], tmpBuf)
		pos += int(oldSize)

		// Write second packet size and data
		rhsSize := rhs.Size()
		newBuffer[pos] = byte(rhsSize)
		pos++

		// Serialize second packet
		tmpBuf = make([]byte, rhsSize)
		rhs.Serialize(tmpBuf)
		copy(newBuffer[pos:], tmpBuf)

		// Update this packet to be a combined packet
		a.Opcode = opAppCombined
		a.Buffer = newBuffer
		return true
	}

	// This is already a combined packet, add to it
	rhsSize := rhs.Size()
	if rhsSize >= 255 {
		// Oversized packet handling
		newBuffer := make([]byte, len(a.Buffer)+int(rhsSize)+3)
		copy(newBuffer, a.Buffer)
		pos := len(a.Buffer)

		newBuffer[pos] = 255 // Oversized marker
		pos++
		binary.BigEndian.PutUint16(newBuffer[pos:], uint16(rhsSize))
		pos += 2

		tmpBuf := make([]byte, rhsSize)
		rhs.Serialize(tmpBuf)
		copy(newBuffer[pos:], tmpBuf)

		a.Buffer = newBuffer
	} else {
		// Normal sized addition
		newBuffer := make([]byte, len(a.Buffer)+int(rhsSize)+1)
		copy(newBuffer, a.Buffer)
		pos := len(a.Buffer)

		newBuffer[pos] = byte(rhsSize)
		pos++

		tmpBuf := make([]byte, rhsSize)
		rhs.Serialize(tmpBuf)
		copy(newBuffer[pos:], tmpBuf)

		a.Buffer = newBuffer
	}

	return true
}