/*
 * Copyright (C) 2015 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.android.voicemail.impl.mail.store.imap;

/**
 * Class representing "element"s in IMAP responses.
 *
 * <p>Class hierarchy:
 *
 * <pre>
 * ImapElement
 *   |
 *   |-- ImapElement.NONE (for 'index out of range')
 *   |
 *   |-- ImapList (isList() == true)
 *   |   |
 *   |   |-- ImapList.EMPTY
 *   |   |
 *   |   --- ImapResponse
 *   |
 *   --- ImapString (isString() == true)
 *       |
 *       |-- ImapString.EMPTY
 *       |
 *       |-- ImapSimpleString
 *       |
 *       |-- ImapMemoryLiteral
 *       |
 *       --- ImapTempFileLiteral
 * </pre>
 */
public abstract class ImapElement {
  /**
   * An element that is returned by {@link ImapList#getElementOrNone} to indicate an index is out of
   * range.
   */
  public static final ImapElement NONE =
      new ImapElement() {
        @Override
        public void destroy() {
          // Don't call super.destroy().
          // It's a shared object.  We don't want the mDestroyed to be set on this.
        }

        @Override
        public boolean isList() {
          return false;
        }

        @Override
        public boolean isString() {
          return false;
        }

        @Override
        public String toString() {
          return "[NO ELEMENT]";
        }

        @Override
        public boolean equalsForTest(ImapElement that) {
          return super.equalsForTest(that);
        }
      };

  private boolean destroyed = false;

  public abstract boolean isList();

  public abstract boolean isString();

  protected boolean isDestroyed() {
    return destroyed;
  }

  /**
   * Clean up the resources used by the instance. It's for removing a temp file used by {@link
   * ImapTempFileLiteral}.
   */
  public void destroy() {
    destroyed = true;
  }

  /** Throws {@link RuntimeException} if it's already destroyed. */
  protected final void checkNotDestroyed() {
    if (destroyed) {
      throw new RuntimeException("Already destroyed");
    }
  }

  /**
   * Return a string that represents this object; it's purely for the debug purpose. Don't mistake
   * it for {@link ImapString#getString}.
   *
   * <p>Abstract to force subclasses to implement it.
   */
  @Override
  public abstract String toString();

  /**
   * The equals implementation that is intended to be used only for unit testing. (Because it may be
   * heavy and has a special sense of "equal" for testing.)
   */
  public boolean equalsForTest(ImapElement that) {
    if (that == null) {
      return false;
    }
    return this.getClass() == that.getClass(); // Has to be the same class.
  }
}