// Copyright 2019, 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 global

import (
	"sync/atomic"

	"go.opentelemetry.io/otel/api/metric"
	"go.opentelemetry.io/otel/api/trace"
)

type (
	traceProvider struct {
		tp trace.Provider
	}

	meterProvider struct {
		mp metric.Provider
	}
)

var (
	globalTracer atomic.Value
	globalMeter  atomic.Value
)

// TraceProvider returns the registered global trace provider.
// If none is registered then an instance of trace.NoopProvider is returned.
// Use the trace provider to create a named tracer. E.g.
//     tracer := global.TraceProvider().GetTracer("example.com/foo")
func TraceProvider() trace.Provider {
	if gp := globalTracer.Load(); gp != nil {
		return gp.(traceProvider).tp
	}
	return trace.NoopProvider{}
}

// SetTraceProvider registers `tp` as the global trace provider.
func SetTraceProvider(tp trace.Provider) {
	globalTracer.Store(traceProvider{tp: tp})
}

// MeterProvider returns the registered global meter provider.
// If none is registered then an instance of metric.NoopProvider is returned.
// Use the trace provider to create a named meter. E.g.
//     meter := global.MeterProvider().GetMeter("example.com/foo")
func MeterProvider() metric.Provider {
	if gp := globalMeter.Load(); gp != nil {
		return gp.(meterProvider).mp
	}
	return metric.NoopProvider{}
}

// SetMeterProvider registers `mp` as the global meter provider.
func SetMeterProvider(mp metric.Provider) {
	globalMeter.Store(meterProvider{mp: mp})
}