/**
 * Copyright 2019, OpenCensus 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.
 */
import * as webTypes from '@opencensus/web-types';
import { NoHeadersPropagation } from '../propagation/no_headers_propagation';
import { AlwaysSampler } from '../sampler/sampler';
import { Span } from './span';
/** TracerBase represents a tracer */
export declare class TracerBase implements webTypes.TracerBase {
    /**
     * A sampler used to make trace sample decisions. In the case of
     * opencensus-web, ultimate sampling decisions will likely be made by the
     * server or agent/collector. So this defaults to sampling every trace.
     */
    sampler: AlwaysSampler;
    /** An object to log information to. Logs to the JS console by default. */
    logger: webTypes.Logger;
    /** Trace context header propagation behavior. */
    propagation: NoHeadersPropagation;
    /** Event listeners for spans managed by the tracer. */
    eventListeners: webTypes.SpanEventListener[];
    /**
     * Active status from tracer instance - this is always true for
     * opencensus-web for code simplicity purposes.
     */
    active: boolean;
    /**
     * Trace parameter configuration. Not used by OpenCensus Web, but
     * kept for interface compatibility with @opencensus/web-types.
     */
    readonly activeTraceParams: {};
    /** A configuration for starting the tracer */
    private config;
    /**
     * Starts the tracer. This makes the tracer active and sets `logger` and
     * `propagation` based on the given config. The `samplingRate` property of
     * `config` is currently ignored.
     */
    start(config: webTypes.TracerConfig): this;
    /** Stops the tracer. This is a no-op with opencensus-web. */
    stop(): this;
    /**
     * Start a new RootSpan to currentRootSpan. Currently no sampling decisions are propagated or made here.
     * @param options Options for tracer instance
     * @param fn Callback function
     * @returns The callback return
     */
    startRootSpan<T>(options: webTypes.TraceOptions, fn: (root: Span) => T): T;
    /** Notifies listeners of the span start. */
    onStartSpan(root: webTypes.Span): void;
    /** Notifies listeners of the span end. */
    onEndSpan(root: webTypes.Span): void;
    registerSpanEventListener(listener: webTypes.SpanEventListener): void;
    unregisterSpanEventListener(listener: webTypes.SpanEventListener): void;
    /**
     * Start a new Span.
     * @param name SpanOptions object.
     * @returns The new Span instance started
     */
    startChildSpan(options?: webTypes.SpanOptions): Span;
    /** Sets the current root span. */
    setCurrentRootSpan(root: webTypes.Span): void;
}