/*
 * Copyright 2019 The Knative 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 source

import (
	"context"
	"strconv"

	"go.opencensus.io/stats/view"
	"knative.dev/pkg/metrics"

	"go.opencensus.io/stats"
	"go.opencensus.io/tag"
	"knative.dev/pkg/metrics/metricskey"
)

var (
	// eventCountM is a counter which records the number of events sent by the source.
	eventCountM = stats.Int64(
		"event_count",
		"Number of events sent",
		stats.UnitDimensionless,
	)

	// Create the tag keys that will be used to add tags to our measurements.
	// Tag keys must conform to the restrictions described in
	// go.opencensus.io/tag/validate.go. Currently those restrictions are:
	// - length between 1 and 255 inclusive
	// - characters are printable US-ASCII
	namespaceKey           = tag.MustNewKey(metricskey.LabelNamespaceName)
	eventSourceKey         = tag.MustNewKey(metricskey.LabelEventSource)
	eventTypeKey           = tag.MustNewKey(metricskey.LabelEventType)
	sourceNameKey          = tag.MustNewKey(metricskey.LabelSourceName)
	sourceResourceGroupKey = tag.MustNewKey(metricskey.LabelSourceResourceGroup)
	responseCodeKey        = tag.MustNewKey(metricskey.LabelResponseCode)
	responseCodeClassKey   = tag.MustNewKey(metricskey.LabelResponseCodeClass)
)

type ReportArgs struct {
	Namespace     string
	EventType     string
	EventSource   string
	Name          string
	ResourceGroup string
}

func init() {
	register()
}

// StatsReporter defines the interface for sending source metrics.
type StatsReporter interface {
	// ReportEventCount captures the event count. It records one per call.
	ReportEventCount(args *ReportArgs, responseCode int) error
}

var _ StatsReporter = (*reporter)(nil)

// reporter holds cached metric objects to report source metrics.
type reporter struct {
	ctx context.Context
}

// NewStatsReporter creates a reporter that collects and reports source metrics.
func NewStatsReporter() (StatsReporter, error) {
	ctx, err := tag.New(
		context.Background(),
	)
	if err != nil {
		return nil, err
	}
	return &reporter{ctx: ctx}, nil
}

func (r *reporter) ReportEventCount(args *ReportArgs, responseCode int) error {
	ctx, err := r.generateTag(args, responseCode)
	if err != nil {
		return err
	}
	metrics.Record(ctx, eventCountM.M(1))
	return nil
}

func (r *reporter) generateTag(args *ReportArgs, responseCode int) (context.Context, error) {
	return tag.New(
		r.ctx,
		tag.Insert(namespaceKey, args.Namespace),
		tag.Insert(eventSourceKey, args.EventSource),
		tag.Insert(eventTypeKey, args.EventType),
		tag.Insert(sourceNameKey, args.Name),
		tag.Insert(sourceResourceGroupKey, args.ResourceGroup),
		tag.Insert(responseCodeKey, strconv.Itoa(responseCode)),
		tag.Insert(responseCodeClassKey, metrics.ResponseCodeClass(responseCode)))
}

func register() {
	tagKeys := []tag.Key{
		namespaceKey,
		eventSourceKey,
		eventTypeKey,
		sourceNameKey,
		sourceResourceGroupKey,
		responseCodeKey,
		responseCodeClassKey}

	// Create view to see our measurements.
	if err := view.Register(
		&view.View{
			Description: eventCountM.Description(),
			Measure:     eventCountM,
			Aggregation: view.Count(),
			TagKeys:     tagKeys,
		},
	); err != nil {
		panic(err)
	}
}