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/**
 * Copyright (C) 2009 Jesse Wilson
 *
 * 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.publicobject.io;

import java.io.RandomAccessFile;
import java.io.File;
import java.io.IOException;

/**
 * Adapts a text file as a character sequence so that it can be directly manipulated by regular
 * expressions and other character utilities. The file may be at most 2 GB in size and encoded with
 * {@code ISO-8859-1}; otherwise behaviour is undefined.
 *
 * @author jessewilson@google.com (Jesse Wilson)
 */
public final class FileCharSequence implements CharSequence {

  private final RandomAccessFile randomAccess;
  private final long start;
  private final long end;

  public FileCharSequence(File file) throws IOException {
    randomAccess = new RandomAccessFile(file, "r");
    start = 0;
    end = randomAccess.length();
  }

  private FileCharSequence(FileCharSequence prototype, long start, long end) {
    this.randomAccess = prototype.randomAccess;
    this.start = start;
    this.end = end;
  }

  public int length() {
    return (int) (end - start);
  }

  public char charAt(int index) {
    try {
      randomAccess.seek(start + index);
      return (char) randomAccess.read();
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
  }

  public CharSequence subSequence(int start, int end) {
    return new FileCharSequence(this, this.start + start, this.start + end);
  }

  public void close() throws IOException {
    randomAccess.close();
  }

  @Override
  public String toString() {
    try {
      byte[] bytes = new byte[length()];
      randomAccess.seek(start);
      randomAccess.readFully(bytes);
      return new String(bytes, "ISO-8859-1");
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
  }
}