// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0

package otlpreceiver // import "go.opentelemetry.io/collector/receiver/otlpreceiver"

import (
	"fmt"
	"io"
	"mime"
	"net/http"
	"strconv"
	"time"

	"google.golang.org/grpc/status"

	"go.opentelemetry.io/collector/internal/statusutil"
	"go.opentelemetry.io/collector/receiver/otlpreceiver/internal/errors"
	"go.opentelemetry.io/collector/receiver/otlpreceiver/internal/logs"
	"go.opentelemetry.io/collector/receiver/otlpreceiver/internal/metrics"
	"go.opentelemetry.io/collector/receiver/otlpreceiver/internal/profiles"
	"go.opentelemetry.io/collector/receiver/otlpreceiver/internal/trace"
)

// Pre-computed status with code=Internal to be used in case of a marshaling error.
var fallbackMsg = []byte(`{"code": 13, "message": "failed to marshal error message"}`)

const fallbackContentType = "application/json"

func handleTraces(resp http.ResponseWriter, req *http.Request, tracesReceiver *trace.Receiver) {
	enc, ok := readContentType(resp, req)
	if !ok {
		return
	}

	body, ok := readAndCloseBody(resp, req, enc)
	if !ok {
		return
	}

	otlpReq, err := enc.unmarshalTracesRequest(body)
	if err != nil {
		writeError(resp, enc, err, http.StatusBadRequest)
		return
	}

	otlpResp, err := tracesReceiver.Export(req.Context(), otlpReq)
	if err != nil {
		writeError(resp, enc, err, http.StatusInternalServerError)
		return
	}

	msg, err := enc.marshalTracesResponse(otlpResp)
	if err != nil {
		writeError(resp, enc, err, http.StatusInternalServerError)
		return
	}
	writeResponse(resp, enc.contentType(), http.StatusOK, msg)
}

func handleMetrics(resp http.ResponseWriter, req *http.Request, metricsReceiver *metrics.Receiver) {
	enc, ok := readContentType(resp, req)
	if !ok {
		return
	}

	body, ok := readAndCloseBody(resp, req, enc)
	if !ok {
		return
	}

	otlpReq, err := enc.unmarshalMetricsRequest(body)
	if err != nil {
		writeError(resp, enc, err, http.StatusBadRequest)
		return
	}

	otlpResp, err := metricsReceiver.Export(req.Context(), otlpReq)
	if err != nil {
		writeError(resp, enc, err, http.StatusInternalServerError)
		return
	}

	msg, err := enc.marshalMetricsResponse(otlpResp)
	if err != nil {
		writeError(resp, enc, err, http.StatusInternalServerError)
		return
	}
	writeResponse(resp, enc.contentType(), http.StatusOK, msg)
}

func handleLogs(resp http.ResponseWriter, req *http.Request, logsReceiver *logs.Receiver) {
	enc, ok := readContentType(resp, req)
	if !ok {
		return
	}

	body, ok := readAndCloseBody(resp, req, enc)
	if !ok {
		return
	}

	otlpReq, err := enc.unmarshalLogsRequest(body)
	if err != nil {
		writeError(resp, enc, err, http.StatusBadRequest)
		return
	}

	otlpResp, err := logsReceiver.Export(req.Context(), otlpReq)
	if err != nil {
		writeError(resp, enc, err, http.StatusInternalServerError)
		return
	}

	msg, err := enc.marshalLogsResponse(otlpResp)
	if err != nil {
		writeError(resp, enc, err, http.StatusInternalServerError)
		return
	}
	writeResponse(resp, enc.contentType(), http.StatusOK, msg)
}

func handleProfiles(resp http.ResponseWriter, req *http.Request, profilesReceiver *profiles.Receiver) {
	enc, ok := readContentType(resp, req)
	if !ok {
		return
	}

	body, ok := readAndCloseBody(resp, req, enc)
	if !ok {
		return
	}

	otlpReq, err := enc.unmarshalProfilesRequest(body)
	if err != nil {
		writeError(resp, enc, err, http.StatusBadRequest)
		return
	}

	otlpResp, err := profilesReceiver.Export(req.Context(), otlpReq)
	if err != nil {
		writeError(resp, enc, err, http.StatusInternalServerError)
		return
	}

	msg, err := enc.marshalProfilesResponse(otlpResp)
	if err != nil {
		writeError(resp, enc, err, http.StatusInternalServerError)
		return
	}
	writeResponse(resp, enc.contentType(), http.StatusOK, msg)
}

func readContentType(resp http.ResponseWriter, req *http.Request) (encoder, bool) {
	if req.Method != http.MethodPost {
		handleUnmatchedMethod(resp)
		return nil, false
	}

	switch getMimeTypeFromContentType(req.Header.Get("Content-Type")) {
	case pbContentType:
		return pbEncoder, true
	case jsonContentType:
		return jsEncoder, true
	default:
		handleUnmatchedContentType(resp)
		return nil, false
	}
}

func readAndCloseBody(resp http.ResponseWriter, req *http.Request, enc encoder) ([]byte, bool) {
	body, err := io.ReadAll(req.Body)
	if err != nil {
		writeError(resp, enc, err, http.StatusBadRequest)
		return nil, false
	}
	if err = req.Body.Close(); err != nil {
		writeError(resp, enc, err, http.StatusBadRequest)
		return nil, false
	}
	return body, true
}

// writeError encodes the HTTP error inside a rpc.Status message as required by the OTLP protocol.
func writeError(w http.ResponseWriter, encoder encoder, err error, statusCode int) {
	s, ok := status.FromError(err)
	if ok {
		statusCode = errors.GetHTTPStatusCodeFromStatus(s)
	} else {
		s = statusutil.NewStatusFromMsgAndHTTPCode(err.Error(), statusCode)
	}
	writeStatusResponse(w, encoder, statusCode, s)
}

// errorHandler encodes the HTTP error message inside a rpc.Status message as required
// by the OTLP protocol.
func errorHandler(w http.ResponseWriter, r *http.Request, errMsg string, statusCode int) {
	s := statusutil.NewStatusFromMsgAndHTTPCode(errMsg, statusCode)
	contentType := r.Header.Get("Content-Type")
	if contentType == "" {
		contentType = fallbackContentType
	}
	switch getMimeTypeFromContentType(contentType) {
	case pbContentType:
		writeStatusResponse(w, pbEncoder, statusCode, s)
		return
	case jsonContentType:
		writeStatusResponse(w, jsEncoder, statusCode, s)
		return
	}
	writeResponse(w, fallbackContentType, http.StatusInternalServerError, fallbackMsg)
}

func writeStatusResponse(w http.ResponseWriter, enc encoder, statusCode int, st *status.Status) {
	// https://github.com/open-telemetry/opentelemetry-proto/blob/main/docs/specification.md#otlphttp-throttling
	if statusCode == http.StatusTooManyRequests || statusCode == http.StatusServiceUnavailable {
		retryInfo := statusutil.GetRetryInfo(st)
		// Check if server returned throttling information.
		if retryInfo != nil {
			// We are throttled. Wait before retrying as requested by the server.
			// The value of Retry-After field can be either an HTTP-date or a number of
			// seconds to delay after the response is received. See https://datatracker.ietf.org/doc/html/rfc7231#section-7.1.3
			//
			// Retry-After = HTTP-date / delay-seconds
			//
			// Use delay-seconds since is easier to format as well as does not require clock synchronization.
			w.Header().Set("Retry-After", strconv.FormatInt(int64(retryInfo.GetRetryDelay().AsDuration()/time.Second), 10))
		}
	}
	msg, err := enc.marshalStatus(st.Proto())
	if err != nil {
		writeResponse(w, fallbackContentType, http.StatusInternalServerError, fallbackMsg)
		return
	}

	writeResponse(w, enc.contentType(), statusCode, msg)
}

func writeResponse(w http.ResponseWriter, contentType string, statusCode int, msg []byte) {
	w.Header().Set("Content-Type", contentType)
	w.WriteHeader(statusCode)
	// Nothing we can do with the error if we cannot write to the response.
	_, _ = w.Write(msg)
}

func getMimeTypeFromContentType(contentType string) string {
	mediatype, _, err := mime.ParseMediaType(contentType)
	if err != nil {
		return ""
	}
	return mediatype
}

func handleUnmatchedMethod(resp http.ResponseWriter) {
	hst := http.StatusMethodNotAllowed
	writeResponse(resp, "text/plain", hst, fmt.Appendf(nil, "%v method not allowed, supported: [POST]", hst))
}

func handleUnmatchedContentType(resp http.ResponseWriter) {
	hst := http.StatusUnsupportedMediaType
	writeResponse(resp, "text/plain", hst, fmt.Appendf(nil, "%v unsupported media type, supported: [%s, %s]", hst, jsonContentType, pbContentType))
}