EliminateUnitsFromZeroNumericValues.java

/*
 * Copyright 2009 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.passes;

import com.google.common.collect.ImmutableSet;
import com.google.common.css.compiler.ast.CssCompilerPass;
import com.google.common.css.compiler.ast.CssNumericNode;
import com.google.common.css.compiler.ast.CssValueNode;
import com.google.common.css.compiler.ast.DefaultTreeVisitor;
import com.google.common.css.compiler.ast.MutatingVisitController;

import java.util.logging.Logger;

/**
 * A compiler pass that eliminates useless units from 0.
 *
 * <p>It is only allowed to eliminate units from relative or absolute length
 * units. See:
 * <a href="http://www.w3.org/TR/1998/WD-css2-19980128/syndata.html#length-units">
 * CSS 2 length units</a> and
 * <a href="http://www.w3.org/TR/css3-values/#lengths">CSS 3 length units</a>
 *
 * @author oana@google.com (Oana Florescu)
 * @author fbenz@google.com (Florian Benz)
 */
public class EliminateUnitsFromZeroNumericValues extends DefaultTreeVisitor
    implements CssCompilerPass {
  private static final ImmutableSet<String> REMOVABLE_LENGTH_UNITS =
      ImmutableSet.of("em", "ex", "px", "gd", "rem", "vw", "vh", "vm", "ch",
          "in", "cm", "mm", "pt", "pc");

  private static final Logger logger = Logger.getLogger(
      EliminateUnitsFromZeroNumericValues.class.getName());

  private final MutatingVisitController visitController;

  public EliminateUnitsFromZeroNumericValues(
      MutatingVisitController visitController) {
    this.visitController = visitController;
  }

  @Override
  public boolean enterValueNode(CssValueNode node) {
    if (node instanceof CssNumericNode) {
      CssNumericNode numericNode = (CssNumericNode) node;
      String numericValue = numericNode.getNumericPart();
      try {
        float value = Float.parseFloat(numericValue);
        if (value == 0.0) {
          if (REMOVABLE_LENGTH_UNITS.contains(numericNode.getUnit())) {
            numericNode.setUnit("");
          }
          numericNode.setNumericPart("0");
        } else {
          // Removes the 0s at the left of the dot.
          int stripFront = 0;
          while (numericValue.charAt(stripFront) == '0') {
            stripFront++; 
          }

          int stripBack = numericValue.length() - 1;
          if (numericValue.indexOf(".") >= 0) {
            // Remove the 0s at the right of the dot.
            while (numericValue.charAt(stripBack) == '0') {
              stripBack--;
            }
            // Maybe remove the dot.
            if (numericValue.charAt(stripBack) == '.') {
              stripBack--;
            }
            numericValue = numericValue.substring(stripFront, stripBack + 1);
          }
          numericNode.setNumericPart(numericValue);
        }
      } catch (NumberFormatException e) {
        logger.warning("Numeric part of the numeric value node could not be "
            + "parsed: " + node.toString()
            + ((node.getSourceCodeLocation() != null) ?
                "@" + node.getSourceCodeLocation().getLineNumber() : ""));
      }
    }
    return true;
  }

  @Override
  public void runPass() {
    visitController.startVisit(this);
  }
}