// Copyright The OpenTelemetry 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 main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"sync"
	"time"

	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/exporters/prometheus"
	"go.opentelemetry.io/otel/metric"
	"go.opentelemetry.io/otel/metric/global"
	"go.opentelemetry.io/otel/sdk/metric/aggregator/histogram"
	controller "go.opentelemetry.io/otel/sdk/metric/controller/basic"
	"go.opentelemetry.io/otel/sdk/metric/export/aggregation"
	processor "go.opentelemetry.io/otel/sdk/metric/processor/basic"
	selector "go.opentelemetry.io/otel/sdk/metric/selector/simple"
)

var (
	lemonsKey = attribute.Key("ex.com/lemons")
)

func initMeter() {
	config := prometheus.Config{
		DefaultHistogramBoundaries: []float64{1, 2, 5, 10, 20, 50},
	}
	c := controller.New(
		processor.NewFactory(
			selector.NewWithHistogramDistribution(
				histogram.WithExplicitBoundaries(config.DefaultHistogramBoundaries),
			),
			aggregation.CumulativeTemporalitySelector(),
			processor.WithMemory(true),
		),
	)
	exporter, err := prometheus.New(config, c)
	if err != nil {
		log.Panicf("failed to initialize prometheus exporter %v", err)
	}
	global.SetMeterProvider(exporter.MeterProvider())

	http.HandleFunc("/", exporter.ServeHTTP)
	go func() {
		_ = http.ListenAndServe(":2222", nil)
	}()

	fmt.Println("Prometheus server running on :2222")
}

func main() {
	initMeter()

	meter := global.Meter("ex.com/basic")
	observerLock := new(sync.RWMutex)
	observerValueToReport := new(float64)
	observerLabelsToReport := new([]attribute.KeyValue)
	cb := func(_ context.Context, result metric.Float64ObserverResult) {
		(*observerLock).RLock()
		value := *observerValueToReport
		labels := *observerLabelsToReport
		(*observerLock).RUnlock()
		result.Observe(value, labels...)
	}
	_ = metric.Must(meter).NewFloat64GaugeObserver("ex.com.one", cb,
		metric.WithDescription("A GaugeObserver set to 1.0"),
	)

	histogram := metric.Must(meter).NewFloat64Histogram("ex.com.two")
	counter := metric.Must(meter).NewFloat64Counter("ex.com.three")

	commonLabels := []attribute.KeyValue{lemonsKey.Int(10), attribute.String("A", "1"), attribute.String("B", "2"), attribute.String("C", "3")}
	notSoCommonLabels := []attribute.KeyValue{lemonsKey.Int(13)}

	ctx := context.Background()

	(*observerLock).Lock()
	*observerValueToReport = 1.0
	*observerLabelsToReport = commonLabels
	(*observerLock).Unlock()
	meter.RecordBatch(
		ctx,
		commonLabels,
		histogram.Measurement(2.0),
		counter.Measurement(12.0),
	)

	time.Sleep(5 * time.Second)

	(*observerLock).Lock()
	*observerValueToReport = 1.0
	*observerLabelsToReport = notSoCommonLabels
	(*observerLock).Unlock()
	meter.RecordBatch(
		ctx,
		notSoCommonLabels,
		histogram.Measurement(2.0),
		counter.Measurement(22.0),
	)

	time.Sleep(5 * time.Second)

	(*observerLock).Lock()
	*observerValueToReport = 13.0
	*observerLabelsToReport = commonLabels
	(*observerLock).Unlock()
	meter.RecordBatch(
		ctx,
		commonLabels,
		histogram.Measurement(12.0),
		counter.Measurement(13.0),
	)

	fmt.Println("Example finished updating, please visit :2222")

	select {}
}