// 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 trace

import (
	"sync"
	"sync/atomic"

	export "go.opentelemetry.io/otel/sdk/export/trace"
)

// SpanProcessor is interface to add hooks to start and end method invocations.
type SpanProcessor interface {

	// OnStart method is invoked when span is started. It is a synchronous call
	// and hence should not block.
	OnStart(sd *export.SpanData)

	// OnEnd method is invoked when span is finished. It is a synchronous call
	// and hence should not block.
	OnEnd(sd *export.SpanData)

	// Shutdown is invoked when SDK shutsdown. Use this call to cleanup any processor
	// data. No calls to OnStart and OnEnd method is invoked after Shutdown call is
	// made. It should not be blocked indefinitely.
	Shutdown()
}

type spanProcessorMap map[SpanProcessor]*sync.Once

var (
	mu             sync.Mutex
	spanProcessors atomic.Value
)

// RegisterSpanProcessor adds to the list of SpanProcessors that will receive sampled
// trace spans.
func RegisterSpanProcessor(e SpanProcessor) {
	mu.Lock()
	defer mu.Unlock()
	new := make(spanProcessorMap)
	if old, ok := spanProcessors.Load().(spanProcessorMap); ok {
		for k, v := range old {
			new[k] = v
		}
	}
	new[e] = &sync.Once{}
	spanProcessors.Store(new)
}

// UnregisterSpanProcessor removes from the list of SpanProcessors the SpanProcessor that was
// registered with the given name.
func UnregisterSpanProcessor(s SpanProcessor) {
	mu.Lock()
	defer mu.Unlock()
	new := make(spanProcessorMap)
	if old, ok := spanProcessors.Load().(spanProcessorMap); ok {
		for k, v := range old {
			new[k] = v
		}
	}
	if stopOnce, ok := new[s]; ok && stopOnce != nil {
		stopOnce.Do(func() {
			s.Shutdown()
		})
	}
	delete(new, s)
	spanProcessors.Store(new)
}