package rpc

import (
	"bytes"
	"encoding/base64"
	"github.com/daglabs/btcd/btcec"
	"github.com/daglabs/btcd/btcjson"
	"github.com/daglabs/btcd/util"
	"github.com/daglabs/btcd/util/daghash"
	"github.com/daglabs/btcd/wire"
)

// handleVerifyMessage implements the verifyMessage command.
func handleVerifyMessage(s *Server, cmd interface{}, closeChan <-chan struct{}) (interface{}, error) {
	c := cmd.(*btcjson.VerifyMessageCmd)

	// Decode the provided address.
	params := s.cfg.DAGParams
	addr, err := util.DecodeAddress(c.Address, params.Prefix)
	if err != nil {
		return nil, &btcjson.RPCError{
			Code:    btcjson.ErrRPCInvalidAddressOrKey,
			Message: "Invalid address or key: " + err.Error(),
		}
	}

	// Only P2PKH addresses are valid for signing.
	if _, ok := addr.(*util.AddressPubKeyHash); !ok {
		return nil, &btcjson.RPCError{
			Code:    btcjson.ErrRPCType,
			Message: "Address is not a pay-to-pubkey-hash address",
		}
	}

	// Decode base64 signature.
	sig, err := base64.StdEncoding.DecodeString(c.Signature)
	if err != nil {
		return nil, &btcjson.RPCError{
			Code:    btcjson.ErrRPCParse.Code,
			Message: "Malformed base64 encoding: " + err.Error(),
		}
	}

	// Validate the signature - this just shows that it was valid at all.
	// we will compare it with the key next.
	var buf bytes.Buffer
	wire.WriteVarString(&buf, "Bitcoin Signed Message:\n")
	wire.WriteVarString(&buf, c.Message)
	expectedMessageHash := daghash.DoubleHashB(buf.Bytes())
	pk, wasCompressed, err := btcec.RecoverCompact(btcec.S256(), sig,
		expectedMessageHash)
	if err != nil {
		// Mirror Bitcoin Core behavior, which treats error in
		// RecoverCompact as invalid signature.
		return false, nil
	}

	// Reconstruct the pubkey hash.
	var serializedPK []byte
	if wasCompressed {
		serializedPK = pk.SerializeCompressed()
	} else {
		serializedPK = pk.SerializeUncompressed()
	}
	address, err := util.NewAddressPubKeyHashFromPublicKey(serializedPK, params.Prefix)
	if err != nil {
		// Again mirror Bitcoin Core behavior, which treats error in public key
		// reconstruction as invalid signature.
		return false, nil
	}

	// Return boolean if addresses match.
	return address.EncodeAddress() == c.Address, nil
}