eq2go/internal/packets/reader.go

package packets

import (
	"encoding/binary"
	"eq2emu/internal/common"
	"eq2emu/internal/packets/parser"
	"fmt"
	"io"
	"math"
)

// PacketReader reads packet data based on packet definitions
type PacketReader struct {
	data []byte
	pos  int
}

// NewPacketReader creates a new packet reader
func NewPacketReader(data []byte) *PacketReader {
	return &PacketReader{
		data: data,
		pos:  0,
	}
}

// ParsePacketFields parses packet data using a packet definition
func ParsePacketFields(data []byte, packetName string, version uint32) (map[string]any, error) {
	def, exists := GetPacket(packetName)
	if !exists {
		return nil, fmt.Errorf("packet definition '%s' not found", packetName)
	}

	reader := NewPacketReader(data)
	return reader.parseStruct(def, version)
}

// parseStruct parses a struct according to packet definition
func (r *PacketReader) parseStruct(def *parser.PacketDef, version uint32) (map[string]any, error) {
	result := make(map[string]any)
	
	// Get field order for this version
	order := r.getVersionOrder(def, version)
	
	for _, fieldName := range order {
		field, exists := def.Fields[fieldName]
		if !exists {
			continue
		}
		
		// For simplicity, skip conditional fields for now
		if field.Condition != "" {
			continue
		}
		
		fieldType := field.Type
		if field.Type2 != 0 {
			fieldType = field.Type2
		}
		
		value, err := r.readField(field, fieldType, fieldName, result)
		if err != nil {
			return nil, fmt.Errorf("error reading field '%s': %w", fieldName, err)
		}
		
		if value != nil {
			result[fieldName] = value
		}
	}
	
	return result, nil
}

// readField reads a single field from the packet data
func (r *PacketReader) readField(field parser.FieldDesc, fieldType common.EQ2DataType, fieldName string, context map[string]any) (any, error) {
	switch fieldType {
	case common.TypeInt8:
		return r.readUint8()
	case common.TypeInt16:
		return r.readUint16()
	case common.TypeInt32:
		return r.readUint32()
	case common.TypeInt64:
		return r.readUint64()
	case common.TypeSInt8:
		return r.readInt8()
	case common.TypeSInt16:
		return r.readInt16()
	case common.TypeSInt32:
		return r.readInt32()
	case common.TypeSInt64:
		return r.readInt64()
	case common.TypeString8:
		return r.readEQ2String8()
	case common.TypeString16:
		return r.readEQ2String16()
	case common.TypeString32:
		return r.readEQ2String32()
	case common.TypeFloat:
		return r.readFloat32()
	case common.TypeDouble:
		return r.readFloat64()
	case common.TypeChar:
		if field.Length > 0 {
			return r.readBytes(field.Length)
		}
		return nil, fmt.Errorf("char field '%s' has no length specified", fieldName)
	default:
		// For unsupported types, skip the field
		return nil, nil
	}
}

// Low-level read functions
func (r *PacketReader) readUint8() (uint8, error) {
	if r.pos+1 > len(r.data) {
		return 0, io.EOF
	}
	value := r.data[r.pos]
	r.pos++
	return value, nil
}

func (r *PacketReader) readInt8() (int8, error) {
	value, err := r.readUint8()
	return int8(value), err
}

func (r *PacketReader) readUint16() (uint16, error) {
	if r.pos+2 > len(r.data) {
		return 0, io.EOF
	}
	value := binary.LittleEndian.Uint16(r.data[r.pos:])
	r.pos += 2
	return value, nil
}

func (r *PacketReader) readInt16() (int16, error) {
	value, err := r.readUint16()
	return int16(value), err
}

func (r *PacketReader) readUint32() (uint32, error) {
	if r.pos+4 > len(r.data) {
		return 0, io.EOF
	}
	value := binary.LittleEndian.Uint32(r.data[r.pos:])
	r.pos += 4
	return value, nil
}

func (r *PacketReader) readInt32() (int32, error) {
	value, err := r.readUint32()
	return int32(value), err
}

func (r *PacketReader) readUint64() (uint64, error) {
	if r.pos+8 > len(r.data) {
		return 0, io.EOF
	}
	value := binary.LittleEndian.Uint64(r.data[r.pos:])
	r.pos += 8
	return value, nil
}

func (r *PacketReader) readInt64() (int64, error) {
	value, err := r.readUint64()
	return int64(value), err
}

func (r *PacketReader) readFloat32() (float32, error) {
	if r.pos+4 > len(r.data) {
		return 0, io.EOF
	}
	bits := binary.LittleEndian.Uint32(r.data[r.pos:])
	r.pos += 4
	return math.Float32frombits(bits), nil
}

func (r *PacketReader) readFloat64() (float64, error) {
	if r.pos+8 > len(r.data) {
		return 0, io.EOF
	}
	bits := binary.LittleEndian.Uint64(r.data[r.pos:])
	r.pos += 8
	return math.Float64frombits(bits), nil
}

func (r *PacketReader) readBytes(n int) ([]byte, error) {
	if r.pos+n > len(r.data) {
		return nil, io.EOF
	}
	data := make([]byte, n)
	copy(data, r.data[r.pos:r.pos+n])
	r.pos += n
	return data, nil
}

func (r *PacketReader) readEQ2String8() (string, error) {
	length, err := r.readUint8()
	if err != nil {
		return "", err
	}
	if length == 0 {
		return "", nil
	}
	data, err := r.readBytes(int(length))
	if err != nil {
		return "", err
	}
	return string(data), nil
}

func (r *PacketReader) readEQ2String16() (string, error) {
	length, err := r.readUint16()
	if err != nil {
		return "", err
	}
	if length == 0 {
		return "", nil
	}
	data, err := r.readBytes(int(length))
	if err != nil {
		return "", err
	}
	return string(data), nil
}

func (r *PacketReader) readEQ2String32() (string, error) {
	length, err := r.readUint32()
	if err != nil {
		return "", err
	}
	if length == 0 {
		return "", nil
	}
	data, err := r.readBytes(int(length))
	if err != nil {
		return "", err
	}
	return string(data), nil
}

// getVersionOrder returns the field order for the specified version
func (r *PacketReader) getVersionOrder(def *parser.PacketDef, version uint32) []string {
	var bestVersion uint32
	for v := range def.Orders {
		if v <= version && v > bestVersion {
			bestVersion = v
		}
	}
	if order, exists := def.Orders[bestVersion]; exists {
		return order
	}
	return []string{}
}