com.google.common.css.compiler.ast.CssBooleanExpressionNode Maven / Gradle / Ivy
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Closure Stylesheets is an extension to CSS that adds variables, functions,
conditionals, and mixins to standard CSS. The tool also supports
minification, linting, RTL flipping, and CSS class renaming.
/*
* Copyright 2008 Google Inc.
*
* 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.common.css.compiler.ast;
import com.google.common.base.Preconditions;
import com.google.common.css.SourceCodeLocation;
import javax.annotation.Nullable;
/**
* A node representing a boolean expression to evaluate.
*/
/* TODO(user): It might be better for each operator to have a list of
operands, not just the left and right operand. Thus, A || B || C would be
represented as a single operator node and a list of three constant nodes
(similar to what the old tree structure does, but with explicit lists).
This might make the code larger but has the potential of faster
compilation (important for Gmail). This structure might also ease
constructing a canonical form of the expression and simplifying
expressions (such as EXPR || !EXPR).
*/
public class CssBooleanExpressionNode extends CssValueNode {
/**
* Boolean expression node types. The types are given in the order of their
* precedence, "!" having the highest priority.
*/
public enum Type {
CONSTANT(null),
NOT("!"),
AND("&&"),
OR("||");
public static final String TRUE_CONSTANT = "TRUE";
public static final String FALSE_CONSTANT = "FALSE";
private final String operatorString;
Type(@Nullable String operatorString) {
this.operatorString = operatorString;
}
public String getOperatorString() {
return operatorString;
}
public boolean isConstant() {
return this == CONSTANT;
}
public boolean isOperator() {
return !isConstant();
}
public boolean isBinaryOperator() {
Preconditions.checkArgument(this.isOperator());
return this != NOT;
}
public boolean isUnaryOperator() {
Preconditions.checkArgument(this.isOperator());
return this == NOT;
}
/**
* Lower numbers are lower priority.
*
* @return priority
*/
public int getPriority() {
return -this.ordinal();
}
/**
* For debugging only.
*/
@Override
public String toString() {
return getOperatorString();
}
}
private final Type type;
private final CssBooleanExpressionNode left;
private final CssBooleanExpressionNode right;
/**
* Constructor for a boolean expression node.
*
* @param type Type of node
* @param value Value of node
* @param left Left expression node
* @param right Right expression node
* @param sourceCodeLocation The location of the source code
*/
public CssBooleanExpressionNode(Type type, String value,
@Nullable CssBooleanExpressionNode left,
@Nullable CssBooleanExpressionNode right,
@Nullable SourceCodeLocation sourceCodeLocation) {
super(value, sourceCodeLocation);
this.type = type;
this.left = left;
this.right = right;
becomeParentForNode(this.left);
becomeParentForNode(this.right);
Preconditions.checkArgument(isValidExpressionTree());
}
/**
* Constructor for a boolean expression node.
*
* @param type Type of node
* @param value Value of node
* @param left Left expression node
* @param sourceCodeLocation The location of the source code
*/
// TODO(oana): Maybe we want to change the constructor to build the right
// child instead of the left ona for the unary operators.
public CssBooleanExpressionNode(Type type, String value,
@Nullable CssBooleanExpressionNode left,
@Nullable SourceCodeLocation sourceCodeLocation) {
this(type, value, left, null, sourceCodeLocation);
}
/**
* Constructor for a boolean expression node.
*
* @param type type
* @param value value
* @param sourceCodeLocation sourceCodeLocation
*/
public CssBooleanExpressionNode(Type type, String value,
@Nullable SourceCodeLocation sourceCodeLocation) {
this(type, value, null, null, sourceCodeLocation);
}
/**
* Constructor for a boolean expression node.
*
* @param type Type of node
* @param value Value of node
*/
public CssBooleanExpressionNode(Type type, String value) {
this(type, value, null, null, null);
}
/**
* Copy constructor.
*
* @param node node
*/
public CssBooleanExpressionNode(CssBooleanExpressionNode node) {
super(node);
this.type = node.getType();
if (node.getLeft() != null) {
this.left = new CssBooleanExpressionNode(node.getLeft());
becomeParentForNode(this.left);
} else {
this.left = null;
}
if (node.getRight() != null) {
this.right = new CssBooleanExpressionNode(node.getRight());
becomeParentForNode(this.right);
} else {
this.right = null;
}
}
@Override
public CssBooleanExpressionNode deepCopy() {
return new CssBooleanExpressionNode(this);
}
public Type getType() {
return type;
}
public CssBooleanExpressionNode getLeft() {
return left;
}
public CssBooleanExpressionNode getRight() {
return right;
}
/**
* Checks if the expression tree is valid.
*
* @return isValid
*/
public boolean isValidExpressionTree() {
if (getType().isConstant()) {
return true;
} else if (!getType().isOperator()) {
return getLeft() == null && getRight() == null;
} else if (getType().isBinaryOperator()) {
return getLeft() != null && getRight() != null;
} else if (getType().isUnaryOperator()) {
return getLeft() != null && getRight() == null;
} else {
// assert false
return false;
}
}
/**
* For debugging only.
*/
private void appendChildExpression(StringBuilder sb,
CssBooleanExpressionNode child) {
if (child.getType().getPriority() >= getType().getPriority()) {
sb.append(child);
} else {
sb.append("(").append(child).append(")");
}
}
/**
* For debugging only.
*/
@Override
public String toString() {
if (!getType().isOperator()) {
return getValue();
} else if (getType().isBinaryOperator()) {
StringBuilder sb = new StringBuilder();
appendChildExpression(sb, getLeft());
sb.append(" ").append(this.getType().getOperatorString()).append(" ");
appendChildExpression(sb, getRight());
return sb.toString();
} else if (getType().isUnaryOperator()) {
StringBuilder sb = new StringBuilder();
sb.append(this.getType().getOperatorString());
appendChildExpression(sb, getLeft());
return sb.toString();
} else {
return "";
}
}
}