// 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 (
	"go.opentelemetry.io/otel/api/core"
)

const (
	alwaysOffSamplerDescription = "AlwaysOffSampler"
)

var alwaysOffSamplerDecision = Decision{Sampled: false}

type alwaysOffSampler struct{}

// ShouldSample implements Sampler interface.
// It always returns a Decision with Sampled value set to false
// and with Attributes set to an empty slice.
func (ns alwaysOffSampler) ShouldSample(
	_ core.SpanContext,
	_ bool,
	_ core.TraceID,
	_ core.SpanID,
	_ string,
	_ SpanKind,
	_ []core.KeyValue,
	_ []Link,
) Decision {
	return alwaysOffSamplerDecision
}

// Description implements Sampler interface.
// It returns the description of this sampler.
func (ns alwaysOffSampler) Description() string {
	return alwaysOffSamplerDescription
}

var _ Sampler = alwaysOffSampler{}

func AlwaysOffSampler() Sampler {
	return alwaysOffSampler{}
}