/*
 * Licensed to Elasticsearch B.V. under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch B.V. licenses this file to you 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 co.elastic.apm.agent.impl.sampling;

import co.elastic.apm.agent.impl.transaction.Id;
import co.elastic.apm.agent.impl.transaction.TraceState;

/**
 * This is a implementation of {@link Sampler} which always returns the same sampling decision.
 */
public class ConstantSampler implements Sampler {

    private static final Sampler TRUE = new ConstantSampler(true);
    private static final Sampler FALSE = new ConstantSampler(false);

    private final boolean decision;
    private final double rate;

    private final String traceStateHeader;

    private ConstantSampler(boolean decision) {
        this.decision = decision;
        this.rate = decision ? 1.0d : 0.0d;
        this.traceStateHeader = TraceState.getHeaderValue(rate);
    }

    public static Sampler of(boolean decision) {
        if (decision) {
            return TRUE;
        } else {
            return FALSE;
        }
    }

    @Override
    public boolean isSampled(Id traceId) {
        return decision;
    }

    @Override
    public double getSampleRate() {
        return rate;
    }

    @Override
    public String getTraceStateHeader() {
        return traceStateHeader;
    }
}
