package protocol

import (
	"encoding/binary"
	"fmt"
	"io"
	"reflect"
	"strconv"
	"unicode/utf16"
)

/*
	this file handles serializing (and deserializing) structs to alignment-strict c structures generated via `tools/genstructs.py`.
	see script for details on usage!
*/

type Packet struct {
	readWriter io.ReadWriter
}

func NewPacket(readWriter io.ReadWriter) Packet {
	return Packet{
		readWriter: readWriter,
	}
}

func (pkt Packet) encodeStructField(field reflect.StructField, value reflect.Value) error {
	// log.Printf("Encoding '%s'", field.Name)

	switch field.Type.Kind() {
	case reflect.String: // all strings in fusionfall packets are encoded as utf16, we'll need to encode it
		sz, err := strconv.Atoi(field.Tag.Get("size"))
		if err != nil {
			return fmt.Errorf("failed to grab string 'size' tag")
		}

		buf16 := utf16.Encode([]rune(value.String()))

		// len(buf16) needs to be the same size as sz
		if len(buf16) > sz {
			// truncate
			buf16 = buf16[:sz]
		} else {
			// grow
			// TODO: probably a better way to do this?
			for len(buf16) < sz {
				buf16 = append(buf16, 0)
			}
		}

		// write
		if err := binary.Write(pkt.readWriter, binary.LittleEndian, buf16); err != nil {
			return err
		}
	default:
		if err := pkt.Encode(value.Interface()); err != nil {
			return err
		}
	}

	// write padding bytes
	pad, err := strconv.Atoi(field.Tag.Get("pad"))
	if err == nil {
		dummy := make([]byte, pad)
		if _, err := pkt.readWriter.Write(dummy); err != nil {
			return err
		}
	}

	return nil
}

func (pkt Packet) Encode(data interface{}) error {
	rv := reflect.Indirect(reflect.ValueOf(data))

	switch rv.Kind() {
	case reflect.Struct:
		// walk through each struct fields
		sz := rv.NumField()
		for i := 0; i < sz; i++ {
			if err := pkt.encodeStructField(rv.Type().Field(i), rv.Field(i)); err != nil {
				return err
			}
		}
	default:
		// we pass everything else to go's binary package
		if err := binary.Write(pkt.readWriter, binary.LittleEndian, data); err != nil {
			return err
		}
	}

	return nil
}

func (pkt Packet) decodeStructField(field reflect.StructField, value reflect.Value) error {
	// log.Printf("Decoding '%s'", field.Name)

	switch field.Type.Kind() {
	case reflect.String: // all strings in fusionfall packets are encoded as utf16, we'll need to decode it
		sz, err := strconv.Atoi(field.Tag.Get("size"))
		if err != nil {
			return fmt.Errorf("failed to grab string 'size' tag")
		}

		buf16 := make([]uint16, sz)
		if err := binary.Read(pkt.readWriter, binary.LittleEndian, buf16); err != nil {
			return err
		}

		// find null terminator
		var realSize int
		for ; realSize < len(buf16); realSize++ {
			if buf16[realSize] == 0 {
				break
			}
		}

		value.SetString(string(utf16.Decode(buf16[:realSize])))
	default:
		if err := pkt.Decode(value.Addr().Interface()); err != nil {
			return err
		}
	}

	// consume padding bytes
	pad, err := strconv.Atoi(field.Tag.Get("pad"))
	if err == nil {
		dummy := make([]byte, pad)
		if _, err := pkt.readWriter.Read(dummy); err != nil {
			return err
		}
	}

	return nil
}

func (pkt Packet) Decode(data interface{}) error {
	rv := reflect.Indirect(reflect.ValueOf(data))

	switch rv.Kind() {
	case reflect.Struct:
		// walk through each struct fields
		sz := rv.NumField()
		for i := 0; i < sz; i++ {
			if err := pkt.decodeStructField(rv.Type().Field(i), rv.Field(i)); err != nil {
				return err
			}
		}
	default:
		if err := binary.Read(pkt.readWriter, binary.LittleEndian, data); err != nil {
			return err
		}
	}

	return nil
}