/*
 * 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.queryparser.charstream;

import java.io.IOException;
import java.io.Reader;
import java.io.UncheckedIOException;

/**
 * An efficient implementation of JavaCC's CharStream interface.
 *
 * <p>Note that this does not do line-number counting, but instead keeps track of the character
 * position of the token in the input, as required by Lucene's {@link
 * org.apache.lucene.analysis.tokenattributes.OffsetAttribute} API.
 */
public final class FastCharStream implements CharStream {
  // See SOLR-11314
  private static final IOException READ_PAST_EOF = new IOException("Read past EOF.");

  char[] buffer = null;

  int bufferLength = 0; // end of valid chars
  int bufferPosition = 0; // next char to read

  int tokenStart = 0; // offset in buffer
  int bufferStart = 0; // position in file of buffer

  Reader input; // source of chars

  /** Constructs from a Reader. */
  public FastCharStream(Reader r) {
    input = r;
  }

  @Override
  public final char readChar() throws IOException {
    if (bufferPosition >= bufferLength) refill();
    return buffer[bufferPosition++];
  }

  private void refill() throws IOException {
    int newPosition = bufferLength - tokenStart;

    if (tokenStart == 0) { // token won't fit in buffer
      if (buffer == null) { // first time: alloc buffer
        buffer = new char[2048];
      } else if (bufferLength == buffer.length) { // grow buffer
        char[] newBuffer = new char[buffer.length * 2];
        System.arraycopy(buffer, 0, newBuffer, 0, bufferLength);
        buffer = newBuffer;
      }
    } else { // shift token to front
      System.arraycopy(buffer, tokenStart, buffer, 0, newPosition);
    }

    bufferLength = newPosition; // update state
    bufferPosition = newPosition;
    bufferStart += tokenStart;
    tokenStart = 0;

    int charsRead = // fill space in buffer
        input.read(buffer, newPosition, buffer.length - newPosition);
    if (charsRead == -1) throw READ_PAST_EOF;
    else bufferLength += charsRead;
  }

  @Override
  public final char BeginToken() throws IOException {
    tokenStart = bufferPosition;
    return readChar();
  }

  @Override
  public final void backup(int amount) {
    bufferPosition -= amount;
  }

  @Override
  public final String GetImage() {
    return new String(buffer, tokenStart, bufferPosition - tokenStart);
  }

  @Override
  public final char[] GetSuffix(int len) {
    char[] value = new char[len];
    System.arraycopy(buffer, bufferPosition - len, value, 0, len);
    return value;
  }

  @Override
  public final void Done() {
    try {
      input.close();
    } catch (IOException e) {
      throw new UncheckedIOException(e);
    }
  }

  @Override
  public final int getEndColumn() {
    return bufferStart + bufferPosition;
  }

  @Override
  public final int getEndLine() {
    return 1;
  }

  @Override
  public final int getBeginColumn() {
    return bufferStart + tokenStart;
  }

  @Override
  public final int getBeginLine() {
    return 1;
  }
}
