package common

import (
	"bytes"
	ed "crypto/ed25519"
	"crypto/sha512"
	"encoding/binary"
	"time"
)

func Float64ToBytes(f float64) []byte {
	buf := make([]byte, 8)
	binary.BigEndian.PutUint64(buf, uint64(f))
	return buf
}

func GetTransactionHash(receiverPubKey []byte, message string, amount float64, createdAt time.Time) []byte {
	amountBytes := Float64ToBytes(amount)
	hash := sha512.New()
	timestamp := createdAt.Unix()
	_ = binary.Write(hash, binary.BigEndian, timestamp)
	hash.Write([]byte(message))
	hash.Write(receiverPubKey)
	hash.Write(amountBytes)
	return hash.Sum(nil)
}

func getSignMsg(txHash []byte, createdAt time.Time) ([]byte, error) {
	buf := bytes.NewBuffer(txHash)
	timestamp := createdAt.Unix()
	if err := binary.Write(buf, binary.BigEndian, timestamp); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}

func SingTransaction(key ed.PrivateKey, txHash []byte, signedAt time.Time) (sig []byte, err error) {
	msg, err := getSignMsg(txHash, signedAt)
	if err != nil {
		return nil, err
	}
	sig = ed.Sign(key, msg)
	return sig, nil
}

func VerifyTransactionSignature(key ed.PublicKey, signature []byte, txHash []byte, signedAt time.Time) (valid bool, err error) {
	msg, err := getSignMsg(txHash, signedAt)
	if err != nil {
		return false, err
	}
	return ed.Verify(key, msg, signature), nil
}