package mps

import (
	"encoding/binary"
	"io"
)

const (
	DEBIT = byte(iota)
	CREDIT
	STARTAUTOPAY
	ENDAUTOPAY
)

// | 4 byte magic string "MPS7" | 1 byte version | 4 byte (uint32) # of records |

// | 1 byte record type enum | 4 byte (uint32) Unix timestamp | 8 byte (uint64) user ID |
type Record struct {
	Type   byte
	Time   uint32
	UserId uint64
	Amount float64
}

type TransactionLog struct {
	Header  Header
	Records []Record
}

// | 4 byte magic string "MPS7" | 1 byte version | 4 byte (uint32) # of records |
type Header struct {
	Magic       [4]byte
	Version     int8
	RecordCount uint32
}

func parseHeader(r io.Reader, h *Header) error {
	err := binary.Read(r, binary.BigEndian, h)
	return err
}

func parseRecord(r io.Reader, record *Record) error {
	err := binary.Read(r, binary.BigEndian, &record.Type)
	if err != nil {
		return err
	}

	err = binary.Read(r, binary.BigEndian, &record.Time)
	if err != nil {
		return err
	}
	err = binary.Read(r, binary.BigEndian, &record.UserId)

	if err != nil {
		return err
	}

	if record.Type == CREDIT || record.Type == DEBIT {
		err = binary.Read(r, binary.BigEndian, &record.Amount)
		if err != nil {
			return err
		}
	}

	return nil
}

func Parse(r io.Reader) (*TransactionLog, error) {
	var tx TransactionLog
	err := parseHeader(r, &tx.Header)
	if err != nil {
		return nil, err
	}

	for i := 0; i < int(tx.Header.RecordCount); i++ {
		var record Record
		err := parseRecord(r, &record)
		if err != nil {
			return nil, err
		}
		tx.Records = append(tx.Records, record)
	}

	return &tx, nil
}