eq2go/internal/packets/builder.go

package packets

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

// PacketBuilder constructs packets from data using parsed packet definitions
type PacketBuilder struct {
	def     *parser.PacketDef
	version uint32
	flags   uint64
	buf     *bytes.Buffer
}

// NewPacketBuilder creates a new packet builder for the given packet definition
func NewPacketBuilder(def *parser.PacketDef, version uint32, flags uint64) *PacketBuilder {
	return &PacketBuilder{
		def:     def,
		version: version,
		flags:   flags,
		buf:     new(bytes.Buffer),
	}
}

// Build constructs a packet from the provided data map
func (b *PacketBuilder) Build(data map[string]any) ([]byte, error) {
	b.buf.Reset()

	err := b.buildStruct(data, b.def)
	if err != nil {
		return nil, err
	}

	return b.buf.Bytes(), nil
}

// buildStruct builds a struct according to the packet definition field order
func (b *PacketBuilder) buildStruct(data map[string]any, def *parser.PacketDef) error {
	order := b.getVersionOrder(def)

	for _, fieldName := range order {
		field, exists := def.Fields[fieldName]
		if !exists {
			continue
		}

		// Skip fields based on conditions
		if !b.checkCondition(field.Condition, data) {
			continue
		}

		fieldType := field.Type
		if field.Type2 != 0 && b.checkCondition(field.Type2Cond, data) {
			fieldType = field.Type2
		}

		value, hasValue := data[fieldName]
		if !hasValue && !field.Optional {
			return fmt.Errorf("required field '%s' not found in data", fieldName)
		}

		if hasValue {
			err := b.buildField(value, field, fieldType, fieldName)
			if err != nil {
				return fmt.Errorf("error building field '%s': %w", fieldName, err)
			}
		} else if field.Optional {
			// Write default value for optional fields
			err := b.writeDefaultValue(field, fieldType)
			if err != nil {
				return fmt.Errorf("error writing default value for field '%s': %w", fieldName, err)
			}
		}
	}

	return nil
}

// buildField writes a single field to the packet buffer
func (b *PacketBuilder) buildField(value any, field parser.FieldDesc, fieldType common.EQ2DataType, fieldName string) error {
	switch fieldType {
	case common.TypeInt8:
		v, ok := value.(uint8)
		if !ok {
			return fmt.Errorf("field '%s' expected uint8, got %T", fieldName, value)
		}
		if field.Oversized > 0 {
			return b.writeOversizedUint8(v, field.Oversized)
		}
		return binary.Write(b.buf, binary.LittleEndian, v)

	case common.TypeInt16:
		v, ok := value.(uint16)
		if !ok {
			return fmt.Errorf("field '%s' expected uint16, got %T", fieldName, value)
		}
		if field.Oversized > 0 {
			return b.writeOversizedUint16(v, field.Oversized)
		}
		return binary.Write(b.buf, binary.LittleEndian, v)

	case common.TypeInt32:
		v, ok := value.(uint32)
		if !ok {
			return fmt.Errorf("field '%s' expected uint32, got %T", fieldName, value)
		}
		if field.Oversized > 0 {
			return b.writeOversizedUint32(v, field.Oversized)
		}
		return binary.Write(b.buf, binary.LittleEndian, v)

	case common.TypeInt64:
		v, ok := value.(uint64)
		if !ok {
			return fmt.Errorf("field '%s' expected uint64, got %T", fieldName, value)
		}
		return binary.Write(b.buf, binary.LittleEndian, v)

	case common.TypeSInt8:
		v, ok := value.(int8)
		if !ok {
			return fmt.Errorf("field '%s' expected int8, got %T", fieldName, value)
		}
		return binary.Write(b.buf, binary.LittleEndian, v)

	case common.TypeSInt16:
		v, ok := value.(int16)
		if !ok {
			return fmt.Errorf("field '%s' expected int16, got %T", fieldName, value)
		}
		if field.Oversized > 0 {
			return b.writeOversizedSint16(v, field.Oversized)
		}
		return binary.Write(b.buf, binary.LittleEndian, v)

	case common.TypeSInt32:
		v, ok := value.(int32)
		if !ok {
			return fmt.Errorf("field '%s' expected int32, got %T", fieldName, value)
		}
		return binary.Write(b.buf, binary.LittleEndian, v)

	case common.TypeSInt64:
		v, ok := value.(int64)
		if !ok {
			return fmt.Errorf("field '%s' expected int64, got %T", fieldName, value)
		}
		return binary.Write(b.buf, binary.LittleEndian, v)

	case common.TypeString8:
		v, ok := value.(string)
		if !ok {
			return fmt.Errorf("field '%s' expected string, got %T", fieldName, value)
		}
		return b.writeEQ2String8(v)

	case common.TypeString16:
		v, ok := value.(string)
		if !ok {
			return fmt.Errorf("field '%s' expected string, got %T", fieldName, value)
		}
		return b.writeEQ2String16(v)

	case common.TypeString32:
		v, ok := value.(string)
		if !ok {
			return fmt.Errorf("field '%s' expected string, got %T", fieldName, value)
		}
		return b.writeEQ2String32(v)

	case common.TypeChar:
		v, ok := value.([]byte)
		if !ok {
			return fmt.Errorf("field '%s' expected []byte, got %T", fieldName, value)
		}
		return b.writeBytes(v, field.Length)

	case common.TypeFloat:
		v, ok := value.(float32)
		if !ok {
			return fmt.Errorf("field '%s' expected float32, got %T", fieldName, value)
		}
		return binary.Write(b.buf, binary.LittleEndian, v)

	case common.TypeDouble:
		v, ok := value.(float64)
		if !ok {
			return fmt.Errorf("field '%s' expected float64, got %T", fieldName, value)
		}
		return binary.Write(b.buf, binary.LittleEndian, v)

	case common.TypeColor:
		v, ok := value.(common.EQ2Color)
		if !ok {
			return fmt.Errorf("field '%s' expected EQ2Color, got %T", fieldName, value)
		}
		return b.writeEQ2Color(v)

	case common.TypeEquipment:
		v, ok := value.(common.EQ2EquipmentItem)
		if !ok {
			return fmt.Errorf("field '%s' expected EQ2EquipmentItem, got %T", fieldName, value)
		}
		return b.writeEQ2Equipment(v)

	case common.TypeArray:
		v, ok := value.([]map[string]any)
		if !ok {
			return fmt.Errorf("field '%s' expected []map[string]any, got %T", fieldName, value)
		}
		return b.buildArray(v, field)

	default:
		return fmt.Errorf("unsupported field type %d for field '%s'", fieldType, fieldName)
	}
}

// buildArray builds an array field
func (b *PacketBuilder) buildArray(items []map[string]any, field parser.FieldDesc) error {
	if field.SubDef == nil {
		return fmt.Errorf("array field missing sub-definition")
	}

	size := len(items)
	if field.MaxArraySize > 0 && size > field.MaxArraySize {
		size = field.MaxArraySize
	}

	for i := 0; i < size; i++ {
		err := b.buildStruct(items[i], field.SubDef)
		if err != nil {
			return fmt.Errorf("error building array item %d: %w", i, err)
		}
	}

	return nil
}

// Helper methods for writing specific data types
func (b *PacketBuilder) writeEQ2String8(s string) error {
	data := []byte(s)
	size := len(data)
	if size > math.MaxUint8 {
		size = math.MaxUint8
	}

	err := binary.Write(b.buf, binary.LittleEndian, uint8(size))
	if err != nil {
		return err
	}

	_, err = b.buf.Write(data[:size])
	return err
}

func (b *PacketBuilder) writeEQ2String16(s string) error {
	data := []byte(s)
	size := len(data)
	if size > math.MaxUint16 {
		size = math.MaxUint16
	}

	err := binary.Write(b.buf, binary.LittleEndian, uint16(size))
	if err != nil {
		return err
	}

	_, err = b.buf.Write(data[:size])
	return err
}

func (b *PacketBuilder) writeEQ2String32(s string) error {
	data := []byte(s)
	size := len(data)
	if size > math.MaxUint32 {
		size = math.MaxUint32
	}

	err := binary.Write(b.buf, binary.LittleEndian, uint32(size))
	if err != nil {
		return err
	}

	_, err = b.buf.Write(data[:size])
	return err
}

func (b *PacketBuilder) writeBytes(data []byte, length int) error {
	if length > 0 && len(data) > length {
		data = data[:length]
	}

	_, err := b.buf.Write(data)
	return err
}

func (b *PacketBuilder) writeEQ2Color(color common.EQ2Color) error {
	err := binary.Write(b.buf, binary.LittleEndian, color.Red)
	if err != nil {
		return err
	}
	err = binary.Write(b.buf, binary.LittleEndian, color.Green)
	if err != nil {
		return err
	}
	return binary.Write(b.buf, binary.LittleEndian, color.Blue)
}

func (b *PacketBuilder) writeEQ2Equipment(item common.EQ2EquipmentItem) error {
	err := binary.Write(b.buf, binary.LittleEndian, item.Type)
	if err != nil {
		return err
	}
	err = b.writeEQ2Color(item.Color)
	if err != nil {
		return err
	}
	return b.writeEQ2Color(item.Highlight)
}

func (b *PacketBuilder) writeOversizedUint8(value uint8, threshold int) error {
	if int(value) >= threshold {
		err := binary.Write(b.buf, binary.LittleEndian, uint8(255))
		if err != nil {
			return err
		}
		return binary.Write(b.buf, binary.LittleEndian, uint16(value))
	}
	return binary.Write(b.buf, binary.LittleEndian, value)
}

func (b *PacketBuilder) writeOversizedUint16(value uint16, threshold int) error {
	if int(value) >= threshold {
		err := binary.Write(b.buf, binary.LittleEndian, uint16(65535))
		if err != nil {
			return err
		}
		return binary.Write(b.buf, binary.LittleEndian, uint32(value))
	}
	return binary.Write(b.buf, binary.LittleEndian, value)
}

func (b *PacketBuilder) writeOversizedUint32(value uint32, threshold int) error {
	if int64(value) >= int64(threshold) {
		err := binary.Write(b.buf, binary.LittleEndian, uint32(4294967295))
		if err != nil {
			return err
		}
		return binary.Write(b.buf, binary.LittleEndian, uint64(value))
	}
	return binary.Write(b.buf, binary.LittleEndian, value)
}

func (b *PacketBuilder) writeOversizedSint16(value int16, threshold int) error {
	if int(value) >= threshold {
		err := binary.Write(b.buf, binary.LittleEndian, int16(-1))
		if err != nil {
			return err
		}
		return binary.Write(b.buf, binary.LittleEndian, int32(value))
	}
	return binary.Write(b.buf, binary.LittleEndian, value)
}

func (b *PacketBuilder) writeDefaultValue(field parser.FieldDesc, fieldType common.EQ2DataType) error {
	switch fieldType {
	case common.TypeInt8:
		return binary.Write(b.buf, binary.LittleEndian, uint8(field.DefaultValue))
	case common.TypeInt16:
		return binary.Write(b.buf, binary.LittleEndian, uint16(field.DefaultValue))
	case common.TypeInt32:
		return binary.Write(b.buf, binary.LittleEndian, uint32(field.DefaultValue))
	case common.TypeInt64:
		return binary.Write(b.buf, binary.LittleEndian, uint64(field.DefaultValue))
	case common.TypeSInt8:
		return binary.Write(b.buf, binary.LittleEndian, field.DefaultValue)
	case common.TypeSInt16:
		return binary.Write(b.buf, binary.LittleEndian, int16(field.DefaultValue))
	case common.TypeSInt32:
		return binary.Write(b.buf, binary.LittleEndian, int32(field.DefaultValue))
	case common.TypeSInt64:
		return binary.Write(b.buf, binary.LittleEndian, int64(field.DefaultValue))
	case common.TypeString8:
		return b.writeEQ2String8("")
	case common.TypeString16:
		return b.writeEQ2String16("")
	case common.TypeString32:
		return b.writeEQ2String32("")
	case common.TypeFloat:
		return binary.Write(b.buf, binary.LittleEndian, float32(field.DefaultValue))
	case common.TypeDouble:
		return binary.Write(b.buf, binary.LittleEndian, float64(field.DefaultValue))
	case common.TypeColor:
		color := common.EQ2Color{Red: field.DefaultValue, Green: field.DefaultValue, Blue: field.DefaultValue}
		return b.writeEQ2Color(color)
	case common.TypeChar:
		if field.Length > 0 {
			defaultBytes := make([]byte, field.Length)
			return b.writeBytes(defaultBytes, field.Length)
		}
	}
	return nil
}

func (b *PacketBuilder) getVersionOrder(def *parser.PacketDef) []string {
	var bestVersion uint32
	for v := range def.Orders {
		if v <= b.version && v > bestVersion {
			bestVersion = v
		}
	}
	return def.Orders[bestVersion]
}

func (b *PacketBuilder) checkCondition(condition string, data map[string]any) bool {
	if condition == "" {
		return true
	}

	// Simple condition evaluation - this would need to be expanded
	// for complex expressions used in the packet definitions
	if value, exists := data[condition]; exists {
		switch v := value.(type) {
		case bool:
			return v
		case int, int8, int16, int32, int64:
			return v != 0
		case uint, uint8, uint16, uint32, uint64:
			return v != 0
		case string:
			return v != ""
		default:
			return true
		}
	}

	return false
}

// BuildPacket is a convenience function that creates a builder and builds a packet in one call
func BuildPacket(packetName string, data map[string]any, version uint32, flags uint64) ([]byte, error) {
	def, exists := GetPacket(packetName)
	if !exists {
		return nil, fmt.Errorf("packet definition '%s' not found", packetName)
	}

	builder := NewPacketBuilder(def, version, flags)
	return builder.Build(data)
}