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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() {}
+
+ /** @return evaluate 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 <T> Iterable<T> children(Class<T> 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.
+ *
+ * <p><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
+ * </code>
+ *
+ * <p>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}.
+ *
+ * <p>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 <T> Iterable<T> children(Class<T> 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 <T> Iterable<T> children(Class<T> 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 <T> Iterable<T> children(Class<T> 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 <T> Iterable<T> children(Class<T> 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<? extends BooleanCondition> 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);
+ }
+}
generated by cgit v1.2.3 (git 2.25.1) at 2024-06-14 03:18:59 +0000