// Copyright 2021 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package remote

import (
	"context"
	"errors"
	"fmt"
	"net/http"

	"github.com/prometheus/prometheus/model/labels"

	"github.com/go-kit/log"
	"github.com/go-kit/log/level"

	"github.com/prometheus/client_golang/prometheus"

	"github.com/prometheus/prometheus/model/exemplar"
	"github.com/prometheus/prometheus/prompb"
	"github.com/prometheus/prometheus/storage"
	otlptranslator "github.com/prometheus/prometheus/storage/remote/otlptranslator/prometheusremotewrite"
)

type writeHandler struct {
	logger     log.Logger
	appendable storage.Appendable

	samplesWithInvalidLabelsTotal prometheus.Counter

	// Experimental feature, new remote write proto format
	// The handler will accept the new format, but it can still accept the old one
	enableRemoteWrite11 bool
}

// NewWriteHandler creates a http.Handler that accepts remote write requests and
// writes them to the provided appendable.
func NewWriteHandler(logger log.Logger, reg prometheus.Registerer, appendable storage.Appendable, enableRemoteWrite11 bool) http.Handler {
	h := &writeHandler{
		logger:              logger,
		appendable:          appendable,
		enableRemoteWrite11: enableRemoteWrite11,

		samplesWithInvalidLabelsTotal: prometheus.NewCounter(prometheus.CounterOpts{
			Namespace: "prometheus",
			Subsystem: "api",
			Name:      "remote_write_invalid_labels_samples_total",
			Help:      "The total number of remote write samples which contains invalid labels.",
		}),
	}
	if reg != nil {
		reg.MustRegister(h.samplesWithInvalidLabelsTotal)
	}
	return h
}

func (h *writeHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	var err error
	var req *prompb.WriteRequest
	var reqWithRefs *prompb.WriteRequestWithRefs
	// TODO-RW11: Need to check headers to decide what version is and what to do
	if h.enableRemoteWrite11 {
		reqWithRefs, err = DecodeReducedWriteRequest(r.Body)
	} else {
		req, err = DecodeWriteRequest(r.Body)
	}

	if err != nil {
		level.Error(h.logger).Log("msg", "Error decoding remote write request", "err", err.Error())
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	if h.enableRemoteWrite11 {
		err = h.writeReduced(r.Context(), reqWithRefs)
	} else {
		err = h.write(r.Context(), req)
	}

	switch {
	case err == nil:
	case errors.Is(err, storage.ErrOutOfOrderSample), errors.Is(err, storage.ErrOutOfBounds), errors.Is(err, storage.ErrDuplicateSampleForTimestamp):
		// Indicated an out of order sample is a bad request to prevent retries.
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	default:
		level.Error(h.logger).Log("msg", "Error appending remote write", "err", err.Error())
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	w.WriteHeader(http.StatusNoContent)
}

// checkAppendExemplarError modifies the AppendExamplar's returned error based on the error cause.
func (h *writeHandler) checkAppendExemplarError(err error, e exemplar.Exemplar, outOfOrderErrs *int) error {
	unwrappedErr := errors.Unwrap(err)
	if unwrappedErr == nil {
		unwrappedErr = err
	}
	switch {
	case errors.Is(unwrappedErr, storage.ErrNotFound):
		return storage.ErrNotFound
	case errors.Is(unwrappedErr, storage.ErrOutOfOrderExemplar):
		*outOfOrderErrs++
		level.Debug(h.logger).Log("msg", "Out of order exemplar", "exemplar", fmt.Sprintf("%+v", e))
		return nil
	default:
		return err
	}
}

func (h *writeHandler) write(ctx context.Context, req *prompb.WriteRequest) (err error) {
	outOfOrderExemplarErrs := 0
	samplesWithInvalidLabels := 0

	app := h.appendable.Appender(ctx)
	defer func() {
		if err != nil {
			_ = app.Rollback()
			return
		}
		err = app.Commit()
	}()

	for _, ts := range req.Timeseries {
		labels := labelProtosToLabels(ts.Labels)
		if !labels.IsValid() {
			level.Warn(h.logger).Log("msg", "Invalid metric names or labels", "got", labels.String())
			samplesWithInvalidLabels++
			continue
		}
		err := h.appendSamples(app, ts.Samples, labels)
		if err != nil {
			return err
		}

		for _, ep := range ts.Exemplars {
			e := exemplarProtoToExemplar(ep)
			h.appendExemplar(app, e, labels, &outOfOrderExemplarErrs)
		}

		err = h.appendHistograms(app, ts.Histograms, labels)
		if err != nil {
			return err
		}
	}

	if outOfOrderExemplarErrs > 0 {
		_ = level.Warn(h.logger).Log("msg", "Error on ingesting out-of-order exemplars", "num_dropped", outOfOrderExemplarErrs)
	}
	if samplesWithInvalidLabels > 0 {
		h.samplesWithInvalidLabelsTotal.Add(float64(samplesWithInvalidLabels))
	}

	return nil
}

func (h *writeHandler) appendExemplar(app storage.Appender, e exemplar.Exemplar, labels labels.Labels, outOfOrderExemplarErrs *int) {
	_, err := app.AppendExemplar(0, labels, e)
	err = h.checkAppendExemplarError(err, e, outOfOrderExemplarErrs)
	if err != nil {
		// Since exemplar storage is still experimental, we don't fail the request on ingestion errors
		level.Debug(h.logger).Log("msg", "Error while adding exemplar in AddExemplar", "exemplar", fmt.Sprintf("%+v", e), "err", err)
	}
}

func (h *writeHandler) appendSamples(app storage.Appender, ss []prompb.Sample, labels labels.Labels) error {
	var ref storage.SeriesRef
	var err error
	for _, s := range ss {
		ref, err = app.Append(ref, labels, s.Timestamp, s.
			Value)
		if err != nil {
			unwrappedErr := errors.Unwrap(err)
			if unwrappedErr == nil {
				unwrappedErr = err
			}
			if errors.Is(err, storage.ErrOutOfOrderSample) || errors.Is(unwrappedErr, storage.ErrOutOfBounds) || errors.Is(unwrappedErr, storage.ErrDuplicateSampleForTimestamp) {
				level.Error(h.logger).Log("msg", "Out of order sample from remote write", "err", err.Error(), "series", labels.String(), "timestamp", s.Timestamp)
			}
			return err
		}
	}
	return nil
}

func (h *writeHandler) appendHistograms(app storage.Appender, hh []prompb.Histogram, labels labels.Labels) error {
	var err error
	for _, hp := range hh {
		if hp.IsFloatHistogram() {
			fhs := FloatHistogramProtoToFloatHistogram(hp)
			_, err = app.AppendHistogram(0, labels, hp.Timestamp, nil, fhs)
		} else {
			hs := HistogramProtoToHistogram(hp)
			_, err = app.AppendHistogram(0, labels, hp.Timestamp, hs, nil)
		}
		if err != nil {
			unwrappedErr := errors.Unwrap(err)
			if unwrappedErr == nil {
				unwrappedErr = err
			}
			// Although AppendHistogram does not currently return ErrDuplicateSampleForTimestamp there is
			// a note indicating its inclusion in the future.
			if errors.Is(unwrappedErr, storage.ErrOutOfOrderSample) || errors.Is(unwrappedErr, storage.ErrOutOfBounds) || errors.Is(unwrappedErr, storage.ErrDuplicateSampleForTimestamp) {
				level.Error(h.logger).Log("msg", "Out of order histogram from remote write", "err", err.Error(), "series", labels.String(), "timestamp", hp.Timestamp)
			}
			return err
		}
	}
	return nil
}

// NewOTLPWriteHandler creates a http.Handler that accepts OTLP write requests and
// writes them to the provided appendable.
func NewOTLPWriteHandler(logger log.Logger, appendable storage.Appendable) http.Handler {
	rwHandler := &writeHandler{
		logger:     logger,
		appendable: appendable,
	}

	return &otlpWriteHandler{
		logger:    logger,
		rwHandler: rwHandler,
	}
}

type otlpWriteHandler struct {
	logger    log.Logger
	rwHandler *writeHandler
}

func (h *otlpWriteHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	req, err := DecodeOTLPWriteRequest(r)
	if err != nil {
		level.Error(h.logger).Log("msg", "Error decoding remote write request", "err", err.Error())
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	prwMetricsMap, errs := otlptranslator.FromMetrics(req.Metrics(), otlptranslator.Settings{
		AddMetricSuffixes: true,
	})
	if errs != nil {
		level.Warn(h.logger).Log("msg", "Error translating OTLP metrics to Prometheus write request", "err", errs)
	}

	prwMetrics := make([]prompb.TimeSeries, 0, len(prwMetricsMap))

	for _, ts := range prwMetricsMap {
		prwMetrics = append(prwMetrics, *ts)
	}

	err = h.rwHandler.write(r.Context(), &prompb.WriteRequest{
		Timeseries: prwMetrics,
	})

	switch {
	case err == nil:
	case errors.Is(err, storage.ErrOutOfOrderSample), errors.Is(err, storage.ErrOutOfBounds), errors.Is(err, storage.ErrDuplicateSampleForTimestamp):
		// Indicated an out of order sample is a bad request to prevent retries.
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	default:
		level.Error(h.logger).Log("msg", "Error appending remote write", "err", err.Error())
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	w.WriteHeader(http.StatusOK)
}

func (h *writeHandler) writeReduced(ctx context.Context, req *prompb.WriteRequestWithRefs) (err error) {
	outOfOrderExemplarErrs := 0

	app := h.appendable.Appender(ctx)
	defer func() {
		if err != nil {
			_ = app.Rollback()
			return
		}
		err = app.Commit()
	}()

	for _, ts := range req.Timeseries {
		labels := labelRefProtosToLabels(req.StringSymbolTable, ts.Labels)
		// TODO(npazosmendez): ?
		// if !labels.IsValid() {
		// 	level.Warn(h.logger).Log("msg", "Invalid metric names or labels", "got", labels.String())
		// 	samplesWithInvalidLabels++
		// 	continue
		// }

		err := h.appendSamples(app, ts.Samples, labels)
		if err != nil {
			return err
		}

		for _, ep := range ts.Exemplars {
			e := exemplarRefProtoToExemplar(req.StringSymbolTable, ep)
			h.appendExemplar(app, e, labels, &outOfOrderExemplarErrs)
		}

		err = h.appendHistograms(app, ts.Histograms, labels)
		if err != nil {
			return err
		}
	}

	if outOfOrderExemplarErrs > 0 {
		_ = level.Warn(h.logger).Log("msg", "Error on ingesting out-of-order exemplars", "num_dropped", outOfOrderExemplarErrs)
	}

	return nil
}