/*
 * Copyright 2018, 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.
 */

package io.opencensus.metrics.export;

import com.google.auto.value.AutoValue;
import io.opencensus.common.ExperimentalApi;
import io.opencensus.common.Function;
import javax.annotation.concurrent.Immutable;

/**
 * The actual point value for a {@link Point}.
 *
 * <p>Currently there are three types of {@link Value}:
 *
 * <ul>
 *   <li>{@code double}
 *   <li>{@code long}
 *   <li>{@link Distribution}
 * </ul>
 *
 * <p>Each {@link Point} contains exactly one of the three {@link Value} types.
 *
 * @since 0.17
 */
@ExperimentalApi
@Immutable
public abstract class Value {

  Value() {}

  /**
   * Returns a double {@link Value}.
   *
   * @param value value in double.
   * @return a double {@code Value}.
   * @since 0.17
   */
  public static Value doubleValue(double value) {
    return ValueDouble.create(value);
  }

  /**
   * Returns a long {@link Value}.
   *
   * @param value value in long.
   * @return a long {@code Value}.
   * @since 0.17
   */
  public static Value longValue(long value) {
    return ValueLong.create(value);
  }

  /**
   * Returns a {@link Distribution} {@link Value}.
   *
   * @param value value in {@link Distribution}.
   * @return a {@code Distribution} {@code Value}.
   * @since 0.17
   */
  public static Value distributionValue(Distribution value) {
    return ValueDistribution.create(value);
  }

  /**
   * Returns a {@link Summary} {@link Value}.
   *
   * @param value value in {@link Summary}.
   * @return a {@code Summary} {@code Value}.
   * @since 0.17
   */
  public static Value summaryValue(Summary value) {
    return ValueSummary.create(value);
  }

  /**
   * Applies the given match function to the underlying data type.
   *
   * @since 0.17
   */
  public abstract <T> T match(
      Function<? super Double, T> doubleFunction,
      Function<? super Long, T> longFunction,
      Function<? super Distribution, T> distributionFunction,
      Function<? super Summary, T> summaryFunction,
      Function<? super Value, T> defaultFunction);

  /** A 64-bit double-precision floating-point {@link Value}. */
  @AutoValue
  @Immutable
  abstract static class ValueDouble extends Value {

    ValueDouble() {}

    @Override
    public final <T> T match(
        Function<? super Double, T> doubleFunction,
        Function<? super Long, T> longFunction,
        Function<? super Distribution, T> distributionFunction,
        Function<? super Summary, T> summaryFunction,
        Function<? super Value, T> defaultFunction) {
      return doubleFunction.apply(getValue());
    }

    /**
     * Creates a {@link ValueDouble}.
     *
     * @param value the value in double.
     * @return a {@code ValueDouble}.
     */
    static ValueDouble create(double value) {
      return new AutoValue_Value_ValueDouble(value);
    }

    /**
     * Returns the double value.
     *
     * @return the double value.
     */
    abstract double getValue();
  }

  /** A 64-bit integer {@link Value}. */
  @AutoValue
  @Immutable
  abstract static class ValueLong extends Value {

    ValueLong() {}

    @Override
    public final <T> T match(
        Function<? super Double, T> doubleFunction,
        Function<? super Long, T> longFunction,
        Function<? super Distribution, T> distributionFunction,
        Function<? super Summary, T> summaryFunction,
        Function<? super Value, T> defaultFunction) {
      return longFunction.apply(getValue());
    }

    /**
     * Creates a {@link ValueLong}.
     *
     * @param value the value in long.
     * @return a {@code ValueLong}.
     */
    static ValueLong create(long value) {
      return new AutoValue_Value_ValueLong(value);
    }

    /**
     * Returns the long value.
     *
     * @return the long value.
     */
    abstract long getValue();
  }

  /**
   * {@link ValueDistribution} contains summary statistics for a population of values. It optionally
   * contains a histogram representing the distribution of those values across a set of buckets.
   */
  @AutoValue
  @Immutable
  abstract static class ValueDistribution extends Value {

    ValueDistribution() {}

    @Override
    public final <T> T match(
        Function<? super Double, T> doubleFunction,
        Function<? super Long, T> longFunction,
        Function<? super Distribution, T> distributionFunction,
        Function<? super Summary, T> summaryFunction,
        Function<? super Value, T> defaultFunction) {
      return distributionFunction.apply(getValue());
    }

    /**
     * Creates a {@link ValueDistribution}.
     *
     * @param value the {@link Distribution} value.
     * @return a {@code ValueDistribution}.
     */
    static ValueDistribution create(Distribution value) {
      return new AutoValue_Value_ValueDistribution(value);
    }

    /**
     * Returns the {@link Distribution} value.
     *
     * @return the {@code Distribution} value.
     */
    abstract Distribution getValue();
  }

  /**
   * {@link ValueSummary} contains a snapshot representing values calculated over an arbitrary time
   * window.
   */
  @AutoValue
  @Immutable
  abstract static class ValueSummary extends Value {

    ValueSummary() {}

    @Override
    public final <T> T match(
        Function<? super Double, T> doubleFunction,
        Function<? super Long, T> longFunction,
        Function<? super Distribution, T> distributionFunction,
        Function<? super Summary, T> summaryFunction,
        Function<? super Value, T> defaultFunction) {
      return summaryFunction.apply(getValue());
    }

    /**
     * Creates a {@link ValueSummary}.
     *
     * @param value the {@link Summary} value.
     * @return a {@code ValueSummary}.
     */
    static ValueSummary create(Summary value) {
      return new AutoValue_Value_ValueSummary(value);
    }

    /**
     * Returns the {@link Summary} value.
     *
     * @return the {@code Summary} value.
     */
    abstract Summary getValue();
  }
}