com.google.gerrit.extensions.conditions.BooleanCondition Maven / Gradle / Ivy
// 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.ImmutableList;
import com.google.common.collect.Iterables;
/** 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 ImmutableList children(Class type) {
return ImmutableList.of();
}
@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);
}
}