/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.lucene.analysis;


import org.apache.lucene.analysis.tokenattributes.FlagsAttribute;
import org.apache.lucene.analysis.tokenattributes.PackedTokenAttributeImpl;
import org.apache.lucene.analysis.tokenattributes.PayloadAttribute;
import org.apache.lucene.util.AttributeFactory;
import org.apache.lucene.util.AttributeImpl;
import org.apache.lucene.util.AttributeReflector;
import org.apache.lucene.util.BytesRef;

/** 
  A Token is an occurrence of a term from the text of a field.  It consists of
  a term's text, the start and end offset of the term in the text of the field,
  and a type string.
  <p>
  The start and end offsets permit applications to re-associate a token with
  its source text, e.g., to display highlighted query terms in a document
  browser, or to show matching text fragments in a <a href="http://en.wikipedia.org/wiki/Key_Word_in_Context">KWIC</a>
  display, etc.
  <p>
  The type is a string, assigned by a lexical analyzer
  (a.k.a. tokenizer), naming the lexical or syntactic class that the token
  belongs to.  For example an end of sentence marker token might be implemented
  with type "eos".  The default token type is "word".  
  <p>
  A Token can optionally have metadata (a.k.a. payload) in the form of a variable
  length byte array. Use {@link org.apache.lucene.index.PostingsEnum#getPayload()} to retrieve the
  payloads from the index.
 
  A few things to note:
  <ul>
  <li>clear() initializes all of the fields to default values. This was changed in contrast to Lucene 2.4, but should affect no one.</li>
  <li>Because <code>TokenStreams</code> can be chained, one cannot assume that the <code>Token's</code> current type is correct.</li>
  <li>The startOffset and endOffset represent the start and offset in the source text, so be careful in adjusting them.</li>
  <li>When caching a reusable token, clone it. When injecting a cached token into a stream that can be reset, clone it again.</li>
  </ul>
*/
public class Token extends PackedTokenAttributeImpl implements FlagsAttribute, PayloadAttribute {

  private int flags;
  private BytesRef payload;

  /** Constructs a Token will null text. */
  public Token() {
  }

  /** Constructs a Token with the given term text, start
   *  and end offsets.  The type defaults to "word."
   *  <b>NOTE:</b> for better indexing speed you should
   *  instead use the char[] termBuffer methods to set the
   *  term text.
   *  @param text term text
   *  @param start start offset in the source text
   *  @param end end offset in the source text
   */
  public Token(CharSequence text, int start, int end) {
    append(text);
    setOffset(start, end);
  }

  /** Constructs a Token with the given term text, position increment, start and end offsets */
  public Token(CharSequence text, int posInc, int start, int end) {
    append(text);
    setOffset(start, end);
    setPositionIncrement(posInc);
  }

  public Token(CharSequence text, int posInc, int start, int end, int posLength) {
    append(text);
    setOffset(start, end);
    setPositionIncrement(posInc);
    setPositionLength(posLength);
  }

  /**
   * {@inheritDoc}
   * @see FlagsAttribute
   */
  @Override
  public int getFlags() {
    return flags;
  }

  /**
   * {@inheritDoc}
   * @see FlagsAttribute
   */
  @Override
  public void setFlags(int flags) {
    this.flags = flags;
  }

  /**
   * {@inheritDoc}
   * @see PayloadAttribute
   */
  @Override
  public BytesRef getPayload() {
    return this.payload;
  }

  /**
   * {@inheritDoc}
   * @see PayloadAttribute
   */
  @Override
  public void setPayload(BytesRef payload) {
    this.payload = payload;
  }
  
  /** Resets the term text, payload, flags, positionIncrement, positionLength,
   * startOffset, endOffset and token type to default.
   */
  @Override
  public void clear() {
    super.clear();
    flags = 0;
    payload = null;
  }

  @Override
  public boolean equals(Object obj) {
    if (obj == this)
      return true;

    if (obj instanceof Token) {
      final Token other = (Token) obj;
      return (
        flags == other.flags &&
        (payload == null ? other.payload == null : payload.equals(other.payload)) &&
        super.equals(obj)
      );
    } else
      return false;
  }

  @Override
  public int hashCode() {
    int code = super.hashCode();
    code = code * 31 + flags;
    if (payload != null) {
      code = code * 31 + payload.hashCode();
    }
    return code;
  }

  @Override
  public Token clone() {
    final Token t = (Token) super.clone();
    if (payload != null) {
      t.payload = BytesRef.deepCopyOf(payload);
    }
    return t;
  }

  /**
   * Copy the prototype token's fields into this one. Note: Payloads are shared.
   * @param prototype source Token to copy fields from
   */
  public void reinit(Token prototype) {
    // this is a bad hack to emulate no cloning of payload!
    prototype.copyToWithoutPayloadClone(this);
  }

  private void copyToWithoutPayloadClone(AttributeImpl target) {
    super.copyTo(target);
    ((FlagsAttribute) target).setFlags(flags);
    ((PayloadAttribute) target).setPayload(payload);
  }

  @Override
  public void copyTo(AttributeImpl target) {
    super.copyTo(target);
    ((FlagsAttribute) target).setFlags(flags);
    ((PayloadAttribute) target).setPayload((payload == null) ? null : BytesRef.deepCopyOf(payload));
  }

  @Override
  public void reflectWith(AttributeReflector reflector) {
    super.reflectWith(reflector);
    reflector.reflect(FlagsAttribute.class, "flags", flags);
    reflector.reflect(PayloadAttribute.class, "payload", payload);
  }

  /** Convenience factory that returns <code>Token</code> as implementation for the basic
   * attributes and return the default impl (with &quot;Impl&quot; appended) for all other
   * attributes.
   * @since 3.0
   */
  public static final AttributeFactory TOKEN_ATTRIBUTE_FACTORY =
      AttributeFactory.getStaticImplementation(AttributeFactory.DEFAULT_ATTRIBUTE_FACTORY, Token.class);
}