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Less compiler in Java, based on less.js
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/**
 * Copyright (c) 2014 SQUARESPACE, 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.squarespace.less.model;

import java.util.ArrayList;
import java.util.List;

import com.squarespace.less.LessException;
import com.squarespace.less.core.Buffer;
import com.squarespace.less.core.CharClass;
import com.squarespace.less.core.LessUtils;
import com.squarespace.less.exec.ExecEnv;


/**
 * Represents a comma-separated list of Selector nodes that forms
 * the header of a {@link Ruleset}.
 */
public class Selectors extends BaseNode {

  /**
   * Indicates whether one or more of the selectors requires evaluation.
   */
  private static final int FLAG_EVALUATE = 0x01;

  /**
   * Indicates that at least one of the child selectors is "mixin-friendly".
   */
  private static final int FLAG_HAS_MIXIN_PATH = 0x02;

  /**
   * Indicates at least one of the child selectors has an extend list.
   */
  private static final int FLAG_HAS_EXTEND = 0x04;

  /**
   * List of {@link Selector} nodes in this set.
   */
  protected List selectors;

  /**
   * Guard expression attached to the child selector.
   */
  protected Guard guard;

  /**
   * Set of flag bits for this selector group.
   */
  protected int flags;

  /**
   * Constructs an empty selector set.
   */
  public Selectors() {
  }

  /**
   * Constructs a selector set with the given starting selectors.
   */
  public Selectors(List selectors) {
    this.selectors = selectors;
  }

  /**
   * Indicates whether this selector set is empty.
   */
  public boolean isEmpty() {
    return selectors == null ? true : selectors.isEmpty();
  }

  /**
   * Adds a selector to the set.
   */
  public void add(Selector selector) {
    selectors = LessUtils.initList(selectors, 2);
    selectors.add(selector);
    if (guard == null) {
      this.guard = selector.guard();
    }
    if (selector.needsEval()) {
      flags |= FLAG_EVALUATE;
    }
    if (selector.hasMixinPath()) {
      flags |= FLAG_HAS_MIXIN_PATH;
    }
    if (selector.hasExtend()) {
      flags |= FLAG_HAS_EXTEND;
    }
  }

  /**
   * Copy this selector group, its guard and flags.
   */
  public Selectors copy() {
    Selectors result = new Selectors(new ArrayList<>(selectors));
    result.guard = guard;
    result.flags = flags;
    return result;
  }

  /**
   * Returns the list of selectors in the set.
   */
  public List selectors() {
    return LessUtils.safeList(selectors);
  }

  /**
   * Returns the guard expression for this selector set.
   */
  public Guard guard() {
    return guard;
  }

  /**
   * Indicates that at least one of the child selectors is "mixin-friendly".
   */
  public boolean hasMixinPath() {
    return (flags & FLAG_HAS_MIXIN_PATH) != 0;
  }

  /**
   * Indicates that at least one of the child selectors has an extend list.
   */
  public boolean hasExtend() {
    return (flags & FLAG_HAS_EXTEND) != 0;
  }

  /**
   * See {@link Node#needsEval()}
   */
  @Override
  public boolean needsEval() {
    return (flags & FLAG_EVALUATE) != 0;
  }

  /**
   * See {@link Node#eval(ExecEnv)}
   */
  @Override
  public Node eval(ExecEnv env) throws LessException {
    if (!needsEval()) {
      return this;
    }

    Selectors result = new Selectors();
    for (Selector selector : selectors) {
      result.add((Selector)selector.eval(env));
    }
    return result;
  }

  /**
   * See {@link Node#type()}
   */
  @Override
  public NodeType type() {
    return NodeType.SELECTORS;
  }

  /**
   * See {@link Node#repr(Buffer)}
   */
  @Override
  public void repr(Buffer buf) {
    int size = selectors.size();
    boolean emitted = false;
    for (int i = 0; i < size; i++) {
      if (emitted) {
        buf.append(',');
        if (!buf.compress()) {
          buf.append('\n').indent();
        }
      }
      Selector selector = selectors.get(i);
      if (selector != null) {
        emitted = true;
        reprSelector(buf, selector);
      }
    }
  }

  /**
   * Renders the {@link Node#repr()} for the selector.
   */
  public static void reprSelector(Buffer buf, Selector selector) {
    List parts = selector.parts();
    int size = parts.size();
    int last = size - 1;
    for (int i = 0; i < size; i++) {
      reprSelectorPart(buf, parts.get(i), i == 0, i == last);
    }
    ExtendList extendList = selector.extendList();
    if (extendList != null) {
      extendList.repr(buf);
    }
  }

  /**
   * Renders the {@link SelectorPart}'s {@link Node#repr()} to the buffer.
   */
  public static void reprSelectorPart(Buffer buf, SelectorPart part, boolean isFirst, boolean isLast) {
    if (part instanceof Combinator) {
      CombinatorType type = ((Combinator)part).combinatorType();
      boolean isDescendant = type == CombinatorType.DESC;
      if (isFirst) {
        if (!isDescendant) {
          buf.append(type.repr());
        }
      } else {
        if (!buf.compress() && !isDescendant) {
          buf.append(' ');
        }
        if (!isDescendant || !CharClass.whitespace(buf.prevChar())) {
          buf.append(type.repr());
        }
      }
      if (!buf.compress() && !isLast && !CharClass.whitespace(buf.prevChar())) {
        buf.append(' ');
      }
    } else {
      part.repr(buf);
    }
  }

  /**
   * See {@link Node#modelRepr(Buffer)}
   */
  @Override
  public void modelRepr(Buffer buf) {
    typeRepr(buf);
    posRepr(buf);
    buf.append('\n');
    buf.incrIndent();
    ReprUtils.modelRepr(buf, "\n", true, selectors);
    buf.decrIndent();
  }

  @Override
  public boolean equals(Object obj) {
    return (obj instanceof Selectors) ? LessUtils.safeEquals(selectors, ((Selectors)obj).selectors) : false;
  }

  @Override
  public int hashCode() {
    return super.hashCode();
  }

}