package handshake

import (
	"errors"
	"fmt"

	"github.com/lucas-clemente/quic-go/qerr"

	"github.com/bifurcation/mint"
	"github.com/lucas-clemente/quic-go/internal/protocol"
	"github.com/lucas-clemente/quic-go/internal/utils"
)

type extensionHandlerClient struct {
	ourParams  *TransportParameters
	paramsChan chan TransportParameters

	initialVersion    protocol.VersionNumber
	supportedVersions []protocol.VersionNumber
	version           protocol.VersionNumber

	logger utils.Logger
}

var _ mint.AppExtensionHandler = &extensionHandlerClient{}
var _ TLSExtensionHandler = &extensionHandlerClient{}

// NewExtensionHandlerClient creates a new extension handler for the client.
func NewExtensionHandlerClient(
	params *TransportParameters,
	initialVersion protocol.VersionNumber,
	supportedVersions []protocol.VersionNumber,
	version protocol.VersionNumber,
	logger utils.Logger,
) TLSExtensionHandler {
	// The client reads the transport parameters from the Encrypted Extensions message.
	// The paramsChan is used in the session's run loop's select statement.
	// We have to use an unbuffered channel here to make sure that the session actually processes the transport parameters immediately.
	paramsChan := make(chan TransportParameters)
	return &extensionHandlerClient{
		ourParams:         params,
		paramsChan:        paramsChan,
		initialVersion:    initialVersion,
		supportedVersions: supportedVersions,
		version:           version,
		logger:            logger,
	}
}

func (h *extensionHandlerClient) Send(hType mint.HandshakeType, el *mint.ExtensionList) error {
	if hType != mint.HandshakeTypeClientHello {
		return nil
	}
	h.logger.Debugf("Sending Transport Parameters: %s", h.ourParams)
	chtp := &clientHelloTransportParameters{
		InitialVersion: h.initialVersion,
		Parameters:     *h.ourParams,
	}
	return el.Add(&tlsExtensionBody{data: chtp.Marshal()})
}

func (h *extensionHandlerClient) Receive(hType mint.HandshakeType, el *mint.ExtensionList) error {
	ext := &tlsExtensionBody{}
	found, err := el.Find(ext)
	if err != nil {
		return err
	}

	if hType != mint.HandshakeTypeEncryptedExtensions {
		if found {
			return fmt.Errorf("Unexpected QUIC extension in handshake message %d", hType)
		}
		return nil
	}

	// hType == mint.HandshakeTypeEncryptedExtensions
	if !found {
		return errors.New("EncryptedExtensions message didn't contain a QUIC extension")
	}

	eetp := &encryptedExtensionsTransportParameters{}
	if err := eetp.Unmarshal(ext.data); err != nil {
		return err
	}
	// check that the negotiated_version is the current version
	if eetp.NegotiatedVersion != h.version {
		return qerr.Error(qerr.VersionNegotiationMismatch, "current version doesn't match negotiated_version")
	}
	// check that the current version is included in the supported versions
	if !protocol.IsSupportedVersion(eetp.SupportedVersions, h.version) {
		return qerr.Error(qerr.VersionNegotiationMismatch, "current version not included in the supported versions")
	}
	// if version negotiation was performed, check that we would have selected the current version based on the supported versions sent by the server
	if h.version != h.initialVersion {
		negotiatedVersion, ok := protocol.ChooseSupportedVersion(h.supportedVersions, eetp.SupportedVersions)
		if !ok || h.version != negotiatedVersion {
			return qerr.Error(qerr.VersionNegotiationMismatch, "would have picked a different version")
		}
	}

	// check that the server sent a stateless reset token
	if len(eetp.Parameters.StatelessResetToken) == 0 {
		return errors.New("server didn't sent stateless_reset_token")
	}
	h.logger.Debugf("Received Transport Parameters: %s", &eetp.Parameters)
	h.paramsChan <- eetp.Parameters
	return nil
}

func (h *extensionHandlerClient) GetPeerParams() <-chan TransportParameters {
	return h.paramsChan
}