package apimiddleware

import (
	"bytes"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"regexp"
	"strconv"
	"strings"

	"github.com/prysmaticlabs/prysm/v3/api/gateway/apimiddleware"
	"github.com/prysmaticlabs/prysm/v3/api/grpc"
	"github.com/prysmaticlabs/prysm/v3/beacon-chain/rpc/eth/events"
	"github.com/r3labs/sse"
)

const (
	versionHeader        = "Eth-Consensus-Version"
	grpcVersionHeader    = "Grpc-metadata-Eth-Consensus-Version"
	jsonMediaType        = "application/json"
	octetStreamMediaType = "application/octet-stream"
)

// match a number with optional decimals
var priorityRegex = regexp.MustCompile(`q=(\d+(?:\.\d+)?)`)

type sszConfig struct {
	fileName     string
	responseJson SszResponse
}

func handleGetBeaconStateSSZ(m *apimiddleware.ApiProxyMiddleware, endpoint apimiddleware.Endpoint, w http.ResponseWriter, req *http.Request) (handled bool) {
	config := sszConfig{
		fileName:     "beacon_state.ssz",
		responseJson: &SszResponseJson{},
	}
	return handleGetSSZ(m, endpoint, w, req, config)
}

func handleGetBeaconBlockSSZ(m *apimiddleware.ApiProxyMiddleware, endpoint apimiddleware.Endpoint, w http.ResponseWriter, req *http.Request) (handled bool) {
	config := sszConfig{
		fileName:     "beacon_block.ssz",
		responseJson: &SszResponseJson{},
	}
	return handleGetSSZ(m, endpoint, w, req, config)
}

func handleGetBeaconStateSSZV2(m *apimiddleware.ApiProxyMiddleware, endpoint apimiddleware.Endpoint, w http.ResponseWriter, req *http.Request) (handled bool) {
	config := sszConfig{
		fileName:     "beacon_state.ssz",
		responseJson: &VersionedSSZResponseJson{},
	}
	return handleGetSSZ(m, endpoint, w, req, config)
}

func handleGetBeaconBlockSSZV2(m *apimiddleware.ApiProxyMiddleware, endpoint apimiddleware.Endpoint, w http.ResponseWriter, req *http.Request) (handled bool) {
	config := sszConfig{
		fileName:     "beacon_block.ssz",
		responseJson: &VersionedSSZResponseJson{},
	}
	return handleGetSSZ(m, endpoint, w, req, config)
}

func handleGetBlindedBeaconBlockSSZ(
	m *apimiddleware.ApiProxyMiddleware,
	endpoint apimiddleware.Endpoint,
	w http.ResponseWriter,
	req *http.Request,
) (handled bool) {
	config := sszConfig{
		fileName:     "beacon_block.ssz",
		responseJson: &VersionedSSZResponseJson{},
	}
	return handleGetSSZ(m, endpoint, w, req, config)
}

func handleSubmitBlockSSZ(m *apimiddleware.ApiProxyMiddleware, endpoint apimiddleware.Endpoint, w http.ResponseWriter, req *http.Request) (handled bool) {
	return handlePostSSZ(m, endpoint, w, req)
}

func handleSubmitBlindedBlockSSZ(
	m *apimiddleware.ApiProxyMiddleware,
	endpoint apimiddleware.Endpoint,
	w http.ResponseWriter,
	req *http.Request,
) (handled bool) {
	return handlePostSSZ(m, endpoint, w, req)
}

func handleProduceBlockSSZ(m *apimiddleware.ApiProxyMiddleware, endpoint apimiddleware.Endpoint, w http.ResponseWriter, req *http.Request) (handled bool) {
	config := sszConfig{
		fileName:     "produce_beacon_block.ssz",
		responseJson: &VersionedSSZResponseJson{},
	}
	return handleGetSSZ(m, endpoint, w, req, config)
}

func handleProduceBlindedBlockSSZ(
	m *apimiddleware.ApiProxyMiddleware,
	endpoint apimiddleware.Endpoint,
	w http.ResponseWriter,
	req *http.Request,
) (handled bool) {
	config := sszConfig{
		fileName:     "produce_blinded_beacon_block.ssz",
		responseJson: &VersionedSSZResponseJson{},
	}
	return handleGetSSZ(m, endpoint, w, req, config)
}

func handleGetSSZ(
	m *apimiddleware.ApiProxyMiddleware,
	endpoint apimiddleware.Endpoint,
	w http.ResponseWriter,
	req *http.Request,
	config sszConfig,
) (handled bool) {
	ssz, err := sszRequested(req)
	if err != nil {
		apimiddleware.WriteError(w, apimiddleware.InternalServerError(err), nil)
		return true
	}
	if !ssz {
		return false
	}

	if errJson := prepareSSZRequestForProxying(m, endpoint, req); errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	grpcResponse, errJson := m.ProxyRequest(req)
	if errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	grpcResponseBody, errJson := apimiddleware.ReadGrpcResponseBody(grpcResponse.Body)
	if errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	respHasError, errJson := apimiddleware.HandleGrpcResponseError(endpoint.Err, grpcResponse, grpcResponseBody, w)
	if errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	if respHasError {
		return true
	}
	if errJson := apimiddleware.DeserializeGrpcResponseBodyIntoContainer(grpcResponseBody, config.responseJson); errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	respVersion, responseSsz, errJson := serializeMiddlewareResponseIntoSSZ(config.responseJson)
	if errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	if errJson := writeSSZResponseHeaderAndBody(grpcResponse, w, responseSsz, respVersion, config.fileName); errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	if errJson := apimiddleware.Cleanup(grpcResponse.Body); errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}

	return true
}

func handlePostSSZ(m *apimiddleware.ApiProxyMiddleware, endpoint apimiddleware.Endpoint, w http.ResponseWriter, req *http.Request) (handled bool) {
	if !sszPosted(req) {
		return false
	}

	if errJson := prepareSSZRequestForProxying(m, endpoint, req); errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	prepareCustomHeaders(req)
	if errJson := preparePostedSSZData(req); errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}

	grpcResponse, errJson := m.ProxyRequest(req)
	if errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	grpcResponseBody, errJson := apimiddleware.ReadGrpcResponseBody(grpcResponse.Body)
	if errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	respHasError, errJson := apimiddleware.HandleGrpcResponseError(endpoint.Err, grpcResponse, grpcResponseBody, w)
	if errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}
	if respHasError {
		return true
	}
	if errJson := apimiddleware.Cleanup(grpcResponse.Body); errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
		return true
	}

	return true
}

func sszRequested(req *http.Request) (bool, error) {
	accept := req.Header.Values("Accept")
	if len(accept) == 0 {
		return false, nil
	}
	types := strings.Split(accept[0], ",")
	currentType, currentPriority := "", 0.0
	for _, t := range types {
		values := strings.Split(t, ";")
		name := values[0]
		if name != jsonMediaType && name != octetStreamMediaType {
			continue
		}
		// no params specified
		if len(values) == 1 {
			priority := 1.0
			if priority > currentPriority {
				currentType, currentPriority = name, priority
			}
			continue
		}
		params := values[1]
		match := priorityRegex.FindAllStringSubmatch(params, 1)
		if len(match) != 1 {
			continue
		}
		priority, err := strconv.ParseFloat(match[0][1], 32)
		if err != nil {
			return false, err
		}
		if priority > currentPriority {
			currentType, currentPriority = name, priority
		}
	}

	return currentType == octetStreamMediaType, nil
}

func sszPosted(req *http.Request) bool {
	ct, ok := req.Header["Content-Type"]
	if !ok {
		return false
	}
	if len(ct) != 1 {
		return false
	}
	return ct[0] == octetStreamMediaType
}

func prepareSSZRequestForProxying(m *apimiddleware.ApiProxyMiddleware, endpoint apimiddleware.Endpoint, req *http.Request) apimiddleware.ErrorJson {
	req.URL.Scheme = "http"
	req.URL.Host = m.GatewayAddress
	req.RequestURI = ""
	if errJson := apimiddleware.HandleURLParameters(endpoint.Path, req, endpoint.RequestURLLiterals); errJson != nil {
		return errJson
	}
	if errJson := apimiddleware.HandleQueryParameters(req, endpoint.RequestQueryParams); errJson != nil {
		return errJson
	}
	// We have to add new segments after handling parameters because it changes URL segment indexing.
	req.URL.Path = "/internal" + req.URL.Path + "/ssz"
	return nil
}

func prepareCustomHeaders(req *http.Request) {
	ver := req.Header.Get(versionHeader)
	if ver != "" {
		req.Header.Del(versionHeader)
		req.Header.Add(grpcVersionHeader, ver)
	}
}

func preparePostedSSZData(req *http.Request) apimiddleware.ErrorJson {
	buf, err := io.ReadAll(req.Body)
	if err != nil {
		return apimiddleware.InternalServerErrorWithMessage(err, "could not read body")
	}
	j := SszRequestJson{Data: base64.StdEncoding.EncodeToString(buf)}
	data, err := json.Marshal(j)
	if err != nil {
		return apimiddleware.InternalServerErrorWithMessage(err, "could not prepare POST data")
	}
	req.Body = io.NopCloser(bytes.NewBuffer(data))
	req.ContentLength = int64(len(data))
	req.Header.Set("Content-Type", jsonMediaType)
	return nil
}

func serializeMiddlewareResponseIntoSSZ(respJson SszResponse) (version string, ssz []byte, errJson apimiddleware.ErrorJson) {
	// Serialize the SSZ part of the deserialized value.
	data, err := base64.StdEncoding.DecodeString(respJson.SSZData())
	if err != nil {
		return "", nil, apimiddleware.InternalServerErrorWithMessage(err, "could not decode response body into base64")
	}
	return strings.ToLower(respJson.SSZVersion()), data, nil
}

func writeSSZResponseHeaderAndBody(grpcResp *http.Response, w http.ResponseWriter, respSsz []byte, respVersion, fileName string) apimiddleware.ErrorJson {
	var statusCodeHeader string
	for h, vs := range grpcResp.Header {
		// We don't want to expose any gRPC metadata in the HTTP response, so we skip forwarding metadata headers.
		if strings.HasPrefix(h, "Grpc-Metadata") {
			if h == "Grpc-Metadata-"+grpc.HttpCodeMetadataKey {
				statusCodeHeader = vs[0]
			}
		} else {
			for _, v := range vs {
				w.Header().Set(h, v)
			}
		}
	}
	w.Header().Set("Content-Length", strconv.Itoa(len(respSsz)))
	w.Header().Set("Content-Type", octetStreamMediaType)
	w.Header().Set("Content-Disposition", "attachment; filename="+fileName)
	w.Header().Set(versionHeader, respVersion)
	if statusCodeHeader != "" {
		code, err := strconv.Atoi(statusCodeHeader)
		if err != nil {
			return apimiddleware.InternalServerErrorWithMessage(err, "could not parse status code")
		}
		w.WriteHeader(code)
	} else {
		w.WriteHeader(grpcResp.StatusCode)
	}
	if _, err := io.Copy(w, io.NopCloser(bytes.NewReader(respSsz))); err != nil {
		return apimiddleware.InternalServerErrorWithMessage(err, "could not write response message")
	}
	return nil
}

func handleEvents(m *apimiddleware.ApiProxyMiddleware, _ apimiddleware.Endpoint, w http.ResponseWriter, req *http.Request) (handled bool) {
	sseClient := sse.NewClient("http://" + m.GatewayAddress + "/internal" + req.URL.RequestURI())
	sseClient.Headers["Grpc-Timeout"] = "0S"
	eventChan := make(chan *sse.Event)

	// We use grpc-gateway as the server side of events, not the sse library.
	// Because of this subscribing to streams doesn't work as intended, resulting in each event being handled by all subscriptions.
	// To handle events properly, we subscribe just once using a placeholder value ('events') and handle all topics inside this subscription.
	if err := sseClient.SubscribeChan("events", eventChan); err != nil {
		apimiddleware.WriteError(w, apimiddleware.InternalServerError(err), nil)
		sseClient.Unsubscribe(eventChan)
		return
	}

	errJson := receiveEvents(eventChan, w, req)
	if errJson != nil {
		apimiddleware.WriteError(w, errJson, nil)
	}

	sseClient.Unsubscribe(eventChan)
	return true
}

func receiveEvents(eventChan <-chan *sse.Event, w http.ResponseWriter, req *http.Request) apimiddleware.ErrorJson {
	for {
		select {
		case msg := <-eventChan:
			var data interface{}

			// The message's event comes to us with trailing whitespace. Remove it here for
			// ease of future processing.
			msg.Event = bytes.TrimSpace(msg.Event)

			switch string(msg.Event) {
			case events.HeadTopic:
				data = &EventHeadJson{}
			case events.BlockTopic:
				data = &ReceivedBlockDataJson{}
			case events.AttestationTopic:
				data = &AttestationJson{}

				// Data received in the aggregated att event does not fit the expected event stream output.
				// We extract the underlying attestation from event data
				// and assign the attestation back to event data for further processing.
				aggEventData := &AggregatedAttReceivedDataJson{}
				if err := json.Unmarshal(msg.Data, aggEventData); err != nil {
					return apimiddleware.InternalServerError(err)
				}
				var attData []byte
				var err error
				// If true, then we have an unaggregated attestation
				if aggEventData.Aggregate == nil {
					unaggEventData := &UnaggregatedAttReceivedDataJson{}
					if err := json.Unmarshal(msg.Data, unaggEventData); err != nil {
						return apimiddleware.InternalServerError(err)
					}
					attData, err = json.Marshal(unaggEventData)
					if err != nil {
						return apimiddleware.InternalServerError(err)
					}
				} else {
					attData, err = json.Marshal(aggEventData.Aggregate)
					if err != nil {
						return apimiddleware.InternalServerError(err)
					}
				}
				msg.Data = attData
			case events.VoluntaryExitTopic:
				data = &SignedVoluntaryExitJson{}
			case events.FinalizedCheckpointTopic:
				data = &EventFinalizedCheckpointJson{}
			case events.ChainReorgTopic:
				data = &EventChainReorgJson{}
			case events.SyncCommitteeContributionTopic:
				data = &SignedContributionAndProofJson{}
			case "error":
				data = &EventErrorJson{}
			default:
				return &apimiddleware.DefaultErrorJson{
					Message: fmt.Sprintf("Event type '%s' not supported", string(msg.Event)),
					Code:    http.StatusInternalServerError,
				}
			}

			if errJson := writeEvent(msg, w, data); errJson != nil {
				return errJson
			}
			if errJson := flushEvent(w); errJson != nil {
				return errJson
			}
		case <-req.Context().Done():
			return nil
		}
	}
}

func writeEvent(msg *sse.Event, w http.ResponseWriter, data interface{}) apimiddleware.ErrorJson {
	if err := json.Unmarshal(msg.Data, data); err != nil {
		return apimiddleware.InternalServerError(err)
	}
	if errJson := apimiddleware.ProcessMiddlewareResponseFields(data); errJson != nil {
		return errJson
	}
	dataJson, errJson := apimiddleware.SerializeMiddlewareResponseIntoJson(data)
	if errJson != nil {
		return errJson
	}

	w.Header().Set("Content-Type", "text/event-stream")

	if _, err := w.Write([]byte("event: ")); err != nil {
		return apimiddleware.InternalServerError(err)
	}
	if _, err := w.Write(msg.Event); err != nil {
		return apimiddleware.InternalServerError(err)
	}
	if _, err := w.Write([]byte("\ndata: ")); err != nil {
		return apimiddleware.InternalServerError(err)
	}
	if _, err := w.Write(dataJson); err != nil {
		return apimiddleware.InternalServerError(err)
	}
	if _, err := w.Write([]byte("\n\n")); err != nil {
		return apimiddleware.InternalServerError(err)
	}

	return nil
}

func flushEvent(w http.ResponseWriter) apimiddleware.ErrorJson {
	flusher, ok := w.(http.Flusher)
	if !ok {
		return &apimiddleware.DefaultErrorJson{Message: fmt.Sprintf("Flush not supported in %T", w), Code: http.StatusInternalServerError}
	}
	flusher.Flush()
	return nil
}