// 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"
	"time"

	"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/model/histogram"
	"github.com/prometheus/prometheus/model/labels"
	"github.com/prometheus/prometheus/model/timestamp"
	"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
}

const maxAheadTime = 10 * time.Minute

// 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) http.Handler {
	h := &writeHandler{
		logger:     logger,
		appendable: appendable,

		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) {
	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
	}

	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), errors.Is(err, storage.ErrTooOldSample):
		// 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 AppendExemplar'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

	timeLimitApp := &timeLimitAppender{
		Appender: h.appendable.Appender(ctx),
		maxTime:  timestamp.FromTime(time.Now().Add(maxAheadTime)),
	}

	defer func() {
		if err != nil {
			_ = timeLimitApp.Rollback()
			return
		}
		err = timeLimitApp.Commit()
	}()

	b := labels.NewScratchBuilder(0)
	var exemplarErr error

	for _, ts := range req.Timeseries {
		labels := LabelProtosToLabels(&b, ts.Labels)
		if !labels.IsValid() {
			level.Warn(h.logger).Log("msg", "Invalid metric names or labels", "got", labels.String())
			samplesWithInvalidLabels++
			continue
		}
		var ref storage.SeriesRef
		for _, s := range ts.Samples {
			ref, err = timeLimitApp.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
			}
		}

		for _, ep := range ts.Exemplars {
			e := exemplarProtoToExemplar(&b, ep)

			_, exemplarErr = timeLimitApp.AppendExemplar(0, labels, e)
			exemplarErr = h.checkAppendExemplarError(exemplarErr, e, &outOfOrderExemplarErrs)
			if exemplarErr != 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", exemplarErr)
			}
		}

		for _, hp := range ts.Histograms {
			if hp.IsFloatHistogram() {
				fhs := FloatHistogramProtoToFloatHistogram(hp)
				_, err = timeLimitApp.AppendHistogram(0, labels, hp.Timestamp, nil, fhs)
			} else {
				hs := HistogramProtoToHistogram(hp)
				_, err = timeLimitApp.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
			}
		}
	}

	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
}

// 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
	}

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

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

	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)
}

type timeLimitAppender struct {
	storage.Appender

	maxTime int64
}

func (app *timeLimitAppender) Append(ref storage.SeriesRef, lset labels.Labels, t int64, v float64) (storage.SeriesRef, error) {
	if t > app.maxTime {
		return 0, fmt.Errorf("%w: timestamp is too far in the future", storage.ErrOutOfBounds)
	}

	ref, err := app.Appender.Append(ref, lset, t, v)
	if err != nil {
		return 0, err
	}
	return ref, nil
}

func (app *timeLimitAppender) AppendHistogram(ref storage.SeriesRef, l labels.Labels, t int64, h *histogram.Histogram, fh *histogram.FloatHistogram) (storage.SeriesRef, error) {
	if t > app.maxTime {
		return 0, fmt.Errorf("%w: timestamp is too far in the future", storage.ErrOutOfBounds)
	}

	ref, err := app.Appender.AppendHistogram(ref, l, t, h, fh)
	if err != nil {
		return 0, err
	}
	return ref, nil
}

func (app *timeLimitAppender) AppendExemplar(ref storage.SeriesRef, l labels.Labels, e exemplar.Exemplar) (storage.SeriesRef, error) {
	if e.Ts > app.maxTime {
		return 0, fmt.Errorf("%w: timestamp is too far in the future", storage.ErrOutOfBounds)
	}

	ref, err := app.Appender.AppendExemplar(ref, l, e)
	if err != nil {
		return 0, err
	}
	return ref, nil
}