package crypto

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/ecdsa"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"

	"github.com/ethereum/go-ethereum/crypto"
)

const (
	aesNonceLength = 12
)

// Sign signs the hash of an arbitrary string
func Sign(content string, identity *ecdsa.PrivateKey) (string, error) {
	signature, err := crypto.Sign(crypto.Keccak256([]byte(content)), identity)
	if err != nil {
		return "", err
	}

	return hex.EncodeToString(signature), nil
}

// VerifySignatures verifys tuples of signatures content/hash/public key
func VerifySignatures(signaturePairs [][3]string) error {
	for _, signaturePair := range signaturePairs {
		content := crypto.Keccak256([]byte(signaturePair[0]))

		signature, err := hex.DecodeString(signaturePair[1])
		if err != nil {
			return err
		}

		publicKeyBytes, err := hex.DecodeString(signaturePair[2])
		if err != nil {
			return err
		}

		publicKey, err := crypto.UnmarshalPubkey(publicKeyBytes)
		if err != nil {
			return err
		}

		recoveredKey, err := crypto.SigToPub(
			content,
			signature,
		)
		if err != nil {
			return err
		}

		if crypto.PubkeyToAddress(*recoveredKey) != crypto.PubkeyToAddress(*publicKey) {
			return errors.New("identity key and signature mismatch")
		}
	}

	return nil
}

// ExtractSignatures extract from tuples of signatures content a public key
func ExtractSignatures(signaturePairs [][2]string) ([]string, error) {
	response := make([]string, len(signaturePairs))
	for i, signaturePair := range signaturePairs {
		content := crypto.Keccak256([]byte(signaturePair[0]))

		signature, err := hex.DecodeString(signaturePair[1])
		if err != nil {
			return nil, err
		}

		recoveredKey, err := crypto.SigToPub(
			content,
			signature,
		)
		if err != nil {
			return nil, err
		}

		response[i] = fmt.Sprintf("%x", crypto.FromECDSAPub(recoveredKey))
	}

	return response, nil
}

func EncryptSymmetric(key, plaintext []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

	// Never use more than 2^32 random nonces with a given key because of the risk of a repeat.
	salt, err := generateSecureRandomData(aesNonceLength)
	if err != nil {
		return nil, err
	}

	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}

	encrypted := aesgcm.Seal(nil, salt, plaintext, nil)
	return append(encrypted, salt...), nil
}

func DecryptSymmetric(key []byte, cyphertext []byte) ([]byte, error) {
	// symmetric messages are expected to contain the 12-byte nonce at the end of the payload
	if len(cyphertext) < aesNonceLength {
		return nil, errors.New("missing salt or invalid payload in symmetric message")
	}
	salt := cyphertext[len(cyphertext)-aesNonceLength:]

	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}
	decrypted, err := aesgcm.Open(nil, salt, cyphertext[:len(cyphertext)-aesNonceLength], nil)
	if err != nil {
		return nil, err
	}

	return decrypted, nil
}

func containsOnlyZeros(data []byte) bool {
	for _, b := range data {
		if b != 0 {
			return false
		}
	}
	return true
}

func validateDataIntegrity(k []byte, expectedSize int) bool {
	if len(k) != expectedSize {
		return false
	}
	if containsOnlyZeros(k) {
		return false
	}
	return true
}

func generateSecureRandomData(length int) ([]byte, error) {
	res := make([]byte, length)

	_, err := rand.Read(res)
	if err != nil {
		return nil, err
	}

	if !validateDataIntegrity(res, length) {
		return nil, errors.New("crypto/rand failed to generate secure random data")
	}

	return res, nil
}