/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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 org.apache.beam.sdk.annotations;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


/**
 * Signifies that a public API (public class, method or field) is subject to incompatible changes,
 * or even removal, in a future release.
 *
 * <p>Note that the presence of this annotation implies nothing about the quality or performance of
 * the API in question, only the fact that the API or behavior may change in any way.
 */
@Retention(RetentionPolicy.CLASS)
@Target({
  ElementType.ANNOTATION_TYPE,
  ElementType.CONSTRUCTOR,
  ElementType.FIELD,
  ElementType.METHOD,
  ElementType.TYPE
})
@Documented
public @interface Experimental {
  Kind value() default Kind.UNSPECIFIED;

  /**
   * An enumeration of various kinds of experimental APIs.
   */
  enum Kind {
    /** Generic group of experimental APIs. This is the default value. */
    UNSPECIFIED,

    /** Sources and sinks related experimental APIs. */
    SOURCE_SINK,

    /** Auto-scaling related experimental APIs. */
    AUTOSCALING,

    /** Trigger-related experimental APIs. */
    TRIGGER,

    /** Experimental APIs for Coder binary format identifiers. */
    CODER_ENCODING_ID,

    /** State-related experimental APIs. */
    STATE,

    /** Timer-related experimental APIs. */
    TIMERS,

    /** Experimental APIs related to customizing the output time for computed values. */
    OUTPUT_TIME,

    /**
     * <a href="https://s.apache.org/splittable-do-fn">Splittable DoFn</a>.
     * Do not use: API is unstable and runner support is incomplete.
     */
    SPLITTABLE_DO_FN,

    /** Metrics-related experimental APIs. */
    METRICS,

    /**
     * {@link org.apache.beam.sdk.io.FileSystem} and {@link org.apache.beam.sdk.io.fs.ResourceId}
     * related APIs.
     */
    FILESYSTEM,

    /** Experimental feature related to alternative, unnested encodings for coders. */
    CODER_CONTEXT,

    /** Experimental runner APIs. Should not be used by pipeline authors. */
    CORE_RUNNERS_ONLY,

    /** Experimental feature related to making the encoded element type available from a Coder. */
    CODER_TYPE_ENCODING
  }
}