// Copyright 2018 Google Inc. All Rights Reserved.
//
// 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.

// +build go1.8

package pubsub

import (
	"log"
	"sync"

	"go.opencensus.io/plugin/ocgrpc"
	"go.opencensus.io/stats"
	"go.opencensus.io/stats/view"
	"go.opencensus.io/tag"
	"golang.org/x/net/context"
	"google.golang.org/api/option"
	"google.golang.org/grpc"
)

func openCensusOptions() []option.ClientOption {
	return []option.ClientOption{
		option.WithGRPCDialOption(grpc.WithStatsHandler(&ocgrpc.ClientHandler{})),
	}
}

var subscriptionKey tag.Key

func init() {
	var err error
	if subscriptionKey, err = tag.NewKey("subscription"); err != nil {
		log.Fatal("cannot create 'subscription' key")
	}
}

var (
	// PullCount is a measure of the number of messages pulled.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	PullCount *stats.Int64Measure

	// AckCount is a measure of the number of messages acked.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	AckCount *stats.Int64Measure

	// NackCount is a measure of the number of messages nacked.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	NackCount *stats.Int64Measure

	// ModAckCount is a measure of the number of messages whose ack-deadline was modified.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	ModAckCount *stats.Int64Measure

	// StreamOpenCount is a measure of the number of times a streaming-pull stream was opened.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	StreamOpenCount *stats.Int64Measure

	// StreamRetryCount is a measure of the number of times a streaming-pull operation was retried.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	StreamRetryCount *stats.Int64Measure

	// StreamRequestCount is a measure of the number of requests sent on a streaming-pull stream.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	StreamRequestCount *stats.Int64Measure

	// StreamRequestCount is a measure of the number of responses received on a streaming-pull stream.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	StreamResponseCount *stats.Int64Measure

	// PullCountView is a cumulative sum of PullCount.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	PullCountView *view.View

	// AckCountView is a cumulative sum of AckCount.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	AckCountView *view.View

	// NackCountView is a cumulative sum of NackCount.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	NackCountView *view.View

	// ModAckCountView is a cumulative sum of ModAckCount.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	ModAckCountView *view.View

	// StreamOpenCountView is a cumulative sum of StreamOpenCount.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	StreamOpenCountView *view.View

	// StreamRetryCountView is a cumulative sum of StreamRetryCount.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	StreamRetryCountView *view.View

	// StreamRequestCountView is a cumulative sum of StreamRequestCount.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	StreamRequestCountView *view.View

	// StreamResponseCountView is a cumulative sum of StreamResponseCount.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	StreamResponseCountView *view.View
)

const statsPrefix = "cloud.google.com/go/pubsub/"

func init() {
	PullCount = mustNewMeasure("pull_count", "Number of PubSub messages pulled")
	AckCount = mustNewMeasure("ack_count", "Number of PubSub messages acked")
	NackCount = mustNewMeasure("nack_count", "Number of PubSub messages nacked")
	ModAckCount = mustNewMeasure("mod_ack_count", "Number of ack-deadlines modified")
	StreamOpenCount = mustNewMeasure("stream_open_count", "Number of calls opening a new streaming pull")
	StreamRetryCount = mustNewMeasure("stream_retry_count", "Number of retries of a stream send or receive")
	StreamRequestCount = mustNewMeasure("stream_request_count", "Number gRPC StreamingPull request messages sent")
	StreamResponseCount = mustNewMeasure("stream_response_count", "Number of gRPC StreamingPull response messages received")

	PullCountView = mustNewView(PullCount)
	AckCountView = mustNewView(AckCount)
	NackCountView = mustNewView(NackCount)
	ModAckCountView = mustNewView(ModAckCount)
	StreamOpenCountView = mustNewView(StreamOpenCount)
	StreamRetryCountView = mustNewView(StreamRetryCount)
	StreamRequestCountView = mustNewView(StreamRequestCount)
	StreamResponseCountView = mustNewView(StreamResponseCount)
}

func mustNewMeasure(name, desc string) *stats.Int64Measure {
	const unitCount = "1"
	name = statsPrefix + name
	m, err := stats.Int64(name, desc, unitCount)
	if err != nil {
		log.Fatalf("creating %q: %v", name, err)
	}
	return m
}

func mustNewView(m *stats.Int64Measure) *view.View {
	v, err := view.New(m.Name(), "cumulative "+m.Description(),
		[]tag.Key{subscriptionKey}, m, view.Sum())
	if err != nil {
		log.Fatalf("creating view for %q: %v", m.Name(), err)
	}
	return v
}

var logOnce sync.Once

func withSubscriptionKey(ctx context.Context, subName string) context.Context {
	ctx, err := tag.New(ctx, tag.Upsert(subscriptionKey, subName))
	if err != nil {
		logOnce.Do(func() {
			log.Printf("pubsub: error creating tag map: %v", err)
		})
	}
	return ctx
}

func recordStat(ctx context.Context, m *stats.Int64Measure, n int64) {
	stats.Record(ctx, m.M(n))
}