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// Copyright (C) 2017 The Android Open Source Project
//
// 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.gerrit.extensions.conditions;

import com.google.common.collect.Iterables;
import java.util.Collections;

/** Delayed evaluation of a boolean condition. */
public abstract class BooleanCondition {
  public static final BooleanCondition TRUE = new Value(true);
  public static final BooleanCondition FALSE = new Value(false);

  public static BooleanCondition valueOf(boolean a) {
    return a ? TRUE : FALSE;
  }

  public static BooleanCondition and(BooleanCondition a, BooleanCondition b) {
    return a == FALSE || b == FALSE ? FALSE : new And(a, b);
  }

  public static BooleanCondition and(boolean a, BooleanCondition b) {
    return and(valueOf(a), b);
  }

  public static BooleanCondition or(BooleanCondition a, BooleanCondition b) {
    return a == TRUE || b == TRUE ? TRUE : new Or(a, b);
  }

  public static BooleanCondition or(boolean a, BooleanCondition b) {
    return or(valueOf(a), b);
  }

  public static BooleanCondition not(BooleanCondition bc) {
    return bc == TRUE ? FALSE : bc == FALSE ? TRUE : new Not(bc);
  }

  BooleanCondition() {}

  /** Evaluates the condition and return its value. */
  public abstract boolean value();

  /**
   * Recursively collect all children of type {@code type}.
   *
   * @param type implementation type of the conditions to collect and return.
   * @return non-null, unmodifiable iteration of children of type {@code type}.
   */
  public abstract  Iterable children(Class type);

  /**
   * Reduce evaluation tree by cutting off branches that evaluate trivially and replacing them with
   * a leave note corresponding to the value the branch evaluated to.
   *
   * 

* *

{@code
   * Example 1 (T=True, F=False, C=non-trivial check):
   *      OR
   *     /  \    =>    T
   *    C   T
   * Example 2 (cuts off a not-trivial check):
   *      AND
   *     /  \    =>    F
   *    C   F
   * Example 3:
   *      AND
   *     /  \    =>    F
   *    T   F
   * }
* *

There is no guarantee that the resulting tree is minimal. The only guarantee made is that * branches that evaluate trivially will be cut off and replaced by primitive values. */ public abstract BooleanCondition reduce(); /** * Check if the condition evaluates to either {@code true} or {@code false} without providing * additional information to the evaluation tree, e.g. through checks to a remote service such as * {@code PermissionBackend}. * *

In this case, the tree can be reduced to skip all non-trivial checks resulting in a * performance gain. */ protected abstract boolean evaluatesTrivially(); private static final class And extends BooleanCondition { private final BooleanCondition a; private final BooleanCondition b; And(BooleanCondition a, BooleanCondition b) { this.a = a; this.b = b; } @Override public boolean value() { if (evaluatesTriviallyToExpectedValue(a, false) || evaluatesTriviallyToExpectedValue(b, false)) { return false; } return a.value() && b.value(); } @Override public Iterable children(Class type) { return Iterables.concat(a.children(type), b.children(type)); } @Override public BooleanCondition reduce() { if (evaluatesTrivially()) { return Value.valueOf(value()); } return new And(a.reduce(), b.reduce()); } @Override public int hashCode() { return a.hashCode() * 31 + b.hashCode(); } @Override public boolean equals(Object other) { if (other instanceof And) { And o = (And) other; return a.equals(o.a) && b.equals(o.b); } return false; } @Override public String toString() { return "(" + maybeTrim(a, getClass()) + " && " + maybeTrim(a, getClass()) + ")"; } @Override protected boolean evaluatesTrivially() { return evaluatesTriviallyToExpectedValue(a, false) || evaluatesTriviallyToExpectedValue(b, false) || (a.evaluatesTrivially() && b.evaluatesTrivially()); } } private static final class Or extends BooleanCondition { private final BooleanCondition a; private final BooleanCondition b; Or(BooleanCondition a, BooleanCondition b) { this.a = a; this.b = b; } @Override public boolean value() { if (evaluatesTriviallyToExpectedValue(a, true) || evaluatesTriviallyToExpectedValue(b, true)) { return true; } return a.value() || b.value(); } @Override public Iterable children(Class type) { return Iterables.concat(a.children(type), b.children(type)); } @Override public BooleanCondition reduce() { if (evaluatesTrivially()) { return Value.valueOf(value()); } return new Or(a.reduce(), b.reduce()); } @Override public int hashCode() { return a.hashCode() * 31 + b.hashCode(); } @Override public boolean equals(Object other) { if (other instanceof Or) { Or o = (Or) other; return a.equals(o.a) && b.equals(o.b); } return false; } @Override public String toString() { return "(" + maybeTrim(a, getClass()) + " || " + maybeTrim(a, getClass()) + ")"; } @Override protected boolean evaluatesTrivially() { return evaluatesTriviallyToExpectedValue(a, true) || evaluatesTriviallyToExpectedValue(b, true) || (a.evaluatesTrivially() && b.evaluatesTrivially()); } } private static final class Not extends BooleanCondition { private final BooleanCondition cond; Not(BooleanCondition bc) { cond = bc; } @Override public boolean value() { return !cond.value(); } @Override public Iterable children(Class type) { return cond.children(type); } @Override public BooleanCondition reduce() { if (evaluatesTrivially()) { return Value.valueOf(value()); } return this; } @Override public int hashCode() { return cond.hashCode() * 31; } @Override public boolean equals(Object other) { return other instanceof Not ? cond.equals(((Not) other).cond) : false; } @Override public String toString() { return "!" + cond; } @Override protected boolean evaluatesTrivially() { return cond.evaluatesTrivially(); } } private static final class Value extends BooleanCondition { private final boolean value; Value(boolean v) { value = v; } @Override public boolean value() { return value; } @Override public Iterable children(Class type) { return Collections.emptyList(); } @Override public BooleanCondition reduce() { return this; } @Override public int hashCode() { return value ? 1 : 0; } @Override public boolean equals(Object other) { return other instanceof Value ? value == ((Value) other).value : false; } @Override public String toString() { return Boolean.toString(value); } @Override protected boolean evaluatesTrivially() { return true; } } /** * Helper for use in toString methods. Remove leading '(' and trailing ')' if the type is the same * as the parent. */ static String maybeTrim(BooleanCondition cond, Class type) { String s = cond.toString(); if (cond.getClass() == type && s.length() > 2 && s.charAt(0) == '(' && s.charAt(s.length() - 1) == ')') { s = s.substring(1, s.length() - 1); } return s; } private static boolean evaluatesTriviallyToExpectedValue( BooleanCondition cond, boolean expectedValue) { return cond.evaluatesTrivially() && (cond.value() == expectedValue); } }





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