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/**
 * Copyright 2022 the original author or 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
 *
 * https://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 io.micrometer.tracing;

import java.util.ArrayDeque;

/**
 * Represents a {@link Span} stored in thread local.
 *
 * @author Marcin Grzejszczak
 * @since 1.0.0
 */
public class ThreadLocalSpan {

    private final ThreadLocal> currentSpanInScopeStack = new ThreadLocal<>();

    private final Tracer tracer;

    /**
     * Creates a new instance of {@link ThreadLocalSpan}.
     * @param tracer tracer
     */
    public ThreadLocalSpan(Tracer tracer) {
        this.tracer = tracer;
    }

    /**
     * Sets given span and scope.
     * @param span - span to be put in scope
     */
    public void set(Span span) {
        Tracer.SpanInScope spanInScope = this.tracer.withSpan(span);
        SpanAndScope newSpanAndScope = new SpanAndScope(span, spanInScope);
        getCurrentSpanInScopeStack().addFirst(newSpanAndScope);
    }

    /**
     * Returns the currently stored span and scope.
     * @return span and scope
     */
    public SpanAndScope get() {
        return getCurrentSpanInScopeStack().peekFirst();
    }

    /**
     * Removes the current span from thread local and brings back the previous span to the
     * current thread local.
     * @return removed span of {@code null} if there was none
     */
    public SpanAndScope remove() {
        SpanAndScope spanAndScope = getCurrentSpanInScopeStack().pollFirst();
        if (spanAndScope == null) {
            return null;
        }
        if (spanAndScope.getScope() != null) {
            spanAndScope.getScope().close();
        }
        return spanAndScope;
    }

    private ArrayDeque getCurrentSpanInScopeStack() {
        ArrayDeque stack = this.currentSpanInScopeStack.get();
        if (stack == null) {
            stack = new ArrayDeque<>();
            this.currentSpanInScopeStack.set(stack);
        }
        return stack;
    }

}