// Copyright 2015 The Bazel Authors. All rights reserved.
//
// 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 com.google.devtools.build.lib.analysis.util;

import static com.google.common.truth.Truth.assertThat;
import static com.google.common.truth.Truth.assertWithMessage;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
import com.google.devtools.build.lib.actions.Action;
import com.google.devtools.build.lib.actions.ActionKeyContext;
import com.google.devtools.build.lib.actions.Actions;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.EnumSet;
import java.util.List;
import javax.annotation.CheckReturnValue;

/**
 * Test helper for testing {@link Action} implementations.
 */
public class ActionTester {

  /** A generator for action instances. */
  public interface ActionCombinationFactory<E extends Enum<E>> {

    /**
     * Returns a new action instance. The parameter {@code attributesToFlip} is used to vary the
     * parameters used to create the action. Implementations should do something like this: <code>
     * <pre>
     * private enum KeyAttributes { ATTR_1, ATTR_2, ATTR_3, ATTR_4 }
     * return new MyAction(owner, inputs, outputs, configuration,
     *     attributesToFlip.contains(ATTR_0) ? a1 : a2,
     *     attributesToFlip.contains(ATTR_1) ? b1 : b2,
     *     attributesToFlip.contains(ATTR_2) ? c1 : c2,
     *     attributesToFlip.contains(ATTR_3) ? d1 : d2);
     * </pre>
     * </code>
     *
     * <p>To reduce the combinatorial complexity of testing an action class, all elements that are
     * only used to change the executed command line should go into a single parameter, and the key
     * computation should take the generated command line into account.
     *
     * <p>Furthermore, when called with identical parameters, this method should return different
     * instances (i.e. according to {@code ==}), but they should have the same key.
     *
     * @param attributesToFlip
     */
    Action generate(ImmutableSet<E> attributesToFlip) throws Exception;
  }

  private final ActionKeyContext actionKeyContext;
  private final List<Action> actions = new ArrayList<>();

  public ActionTester(ActionKeyContext actionKeyContext) {
    this.actionKeyContext = actionKeyContext;
  }

  public ActionTester() {
    this(new ActionKeyContext());
  }

  /**
   * Creates all possible combinations of actions given a set of flags which can be either on or
   * off. This requires that all combinations result in different actions, i.e., all flags must be
   * orthogonal. The generated actions are added to a local list for a subsequent call to {@link
   * #runTest}. This method can be called multiple times to generate different sets of actions.
   */
  @CheckReturnValue
  public <E extends Enum<E>> ActionTester combinations(
      Class<E> attributeClass, ActionCombinationFactory<E> factory) throws Exception {
    int attributesCount = attributeClass.getEnumConstants().length;
    Preconditions.checkArgument(
        attributesCount <= 30,
        "Maximum attribute count is 30, more will overflow the max array size.");
    Preconditions.checkArgument(attributesCount > 0, "Minimum attribute count is 1");
    int count = (int) Math.pow(2, attributesCount);
    Action firstAction = null;
    for (int i = 0; i < count; i++) {
      Action action = factory.generate(makeEnumSetInitializedTo(attributeClass, i));
      actions.add(action);
      // Check that creating the same action twice results in equal actions.
      assertThat(
              Actions.canBeShared(
                  actionKeyContext,
                  action,
                  factory.generate(makeEnumSetInitializedTo(attributeClass, i))))
          .isTrue();
      if (i == 0) {
        firstAction = action;
      }
    }
    // Check that the count is correct.
    assertThat(
            Actions.canBeShared(
                actionKeyContext,
                firstAction,
                factory.generate(makeEnumSetInitializedTo(attributeClass, count))))
        .isTrue();
    return this;
  }

  /** Checks that all actions are different. */
  public void runTest() throws Exception {
    assertThat(actions).isNotEmpty();
    for (int i = 0; i < actions.size(); i++) {
      for (int j = i + 1; j < actions.size(); j++) {
        assertWithMessage(i + " and " + j)
            .that(Actions.canBeShared(actionKeyContext, actions.get(i), actions.get(j)))
            .isFalse();
      }
    }
  }

  /**
   * Tests that different actions have different keys. The attributeCount should specify how many
   * different permutations the {@link ActionCombinationFactory} should generate.
   */
  public static <E extends Enum<E>> void runTest(
      Class<E> attributeClass,
      ActionCombinationFactory<E> factory,
      ActionKeyContext actionKeyContext)
      throws Exception {
    new ActionTester(actionKeyContext).combinations(attributeClass, factory).runTest();
  }

  private static <E extends Enum<E>> ImmutableSet<E> makeEnumSetInitializedTo(
      Class<E> attributeClass, int seed) {
    EnumSet<E> result = EnumSet.<E>noneOf(attributeClass);
    BitSet b = BitSet.valueOf(new long[] {seed});
    E[] attributes = attributeClass.getEnumConstants();
    for (int i = 0; i < attributes.length; i++) {
      if (b.get(i)) {
        result.add(attributes[i]);
      }
    }
    return Sets.immutableEnumSet(result);
  }
}