java/com/google/gerrit/extensions/conditions/BooleanCondition.java - gerrit - Git at Google

 // 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);
   }
 }
	// 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);
	}
	}