package main

import (
	"crypto/rand"
	"encoding/binary"
	"errors"
	"fmt"
)

const HeaderSize int = 32 + 1 + 4 + 4

type SessionID [32]byte

type Packet struct {
	// headerLength uint32
	sid        SessionID
	flag       HeaderFlag
	sync       uint32
	dataLength uint32
	data       []byte
}

func PacketFromBytes(bytes []byte) Packet {
	sid := SessionID(bytes[0:32])
	flag := HeaderFlag(bytes[32])
	sync := binary.LittleEndian.Uint32(bytes[33:37])
	dataLength := binary.LittleEndian.Uint32(bytes[37:41])
	pck := Packet{
		sid:        sid,
		flag:       flag,
		sync:       sync,
		dataLength: dataLength,
		data:       bytes[41 : 41+dataLength],
	}
	return pck
}

func NewAck(pckToAck *Packet) *Packet {
	data := make([]byte, 4)
	binary.LittleEndian.PutUint32(data, pckToAck.sync)
	return &Packet{
		sid:        pckToAck.sid,
		flag:       Ack,
		sync:       pckToAck.sync + 1,
		dataLength: uint32(4),
		data:       data,
	}
}

func NewRequest(path string) *Packet {
	data := []byte(path)
	buf := make([]byte, 32)
	_, err := rand.Read(buf)
	if err != nil {
		panic(err)
	}

	return &Packet{
		sid:        SessionID(buf),
		flag:       Request,
		sync:       0,
		dataLength: uint32(len(data)),
		data:       data,
	}
}

func NewFile(lastPck *Packet, data []byte) *Packet {
	return &Packet{
		sid:        lastPck.sid,
		flag:       File,
		sync:       lastPck.sync + 1,
		dataLength: uint32(len(data)),
		data:       data,
	}
}

func NewEnd(lastFilePck *Packet) *Packet {
	data := make([]byte, 4)
	binary.LittleEndian.PutUint32(data, lastFilePck.sync)
	return &Packet{
		sid:        lastFilePck.sid,
		flag:       End,
		sync:       lastFilePck.sync + 1,
		dataLength: uint32(4),
		data:       data,
	}
}

func NewResend(sync uint32, lastPck *Packet) *Packet {
	data := make([]byte, 4)
	binary.LittleEndian.PutUint32(data, sync)
	return &Packet{
		sid:        lastPck.sid,
		flag:       Resend,
		sync:       lastPck.sync + 1,
		dataLength: uint32(4),
		data:       data,
	}
}

func NewPte(fileSize uint32, lastPck *Packet) *Packet {
	data := make([]byte, 4)
	binary.LittleEndian.PutUint32(data, fileSize)
	return &Packet{
		sid:        lastPck.sid,
		flag:       PTE,
		sync:       lastPck.sync + 1,
		dataLength: uint32(4),
		data:       data,
	}
}

func (pck *Packet) GetUint32Payload() (uint32, error) {
	flag := pck.flag
	if flag != PTE && flag != Ack && flag != End && flag != Resend {
		return 0, errors.New(fmt.Sprintf("Can not get Sync from Packet Type with flag: %v", flag))
	}
	return binary.LittleEndian.Uint32(pck.data), nil
}

func (pck *Packet) GetFilePath() (string, error) {
	if pck.flag != Request {
		return "", errors.New("Can not get FilePath from Packet that is not Request")
	}
	return string(pck.data), nil
}

func (pck *Packet) ToBytes() []byte {
	arr := make([]byte, HeaderSize+int(pck.dataLength))
	copy(arr[0:32], pck.sid[:])
	arr[32] = byte(pck.flag)
	binary.LittleEndian.PutUint32(arr[33:37], pck.sync)
	binary.LittleEndian.PutUint32(arr[37:41], pck.dataLength)
	copy(arr[41:], pck.data)

	return arr
}

type HeaderFlag uint8

const (
	Request HeaderFlag = iota
	PTE     HeaderFlag = iota
	Ack     HeaderFlag = iota
	File    HeaderFlag = iota
	End     HeaderFlag = iota
	Resend  HeaderFlag = iota
)