/*
    * Copyright (C) 2007 The Guava Authors
    *
    * 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.google.common.io;
  
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.annotations.Beta;
  
  import java.io.IOException;
  import java.io.Reader;
  import java.nio.CharBuffer;
  import java.util.LinkedList;
  import java.util.Queue;
  
  /**
   * A class for reading lines of text. Provides the same functionality
   * as {@link java.io.BufferedReader#readLine()} but for all {@link Readable}
   * objects, not just instances of {@link Reader}.
   *
   * @author Chris Nokleberg
   * @since 1.0
   */
  @Beta
  public final class LineReader {
    private final Readable readable;
    private final Reader reader;
    private final char[] buf = new char[0x1000]; // 4K
    private final CharBuffer cbuf = CharBuffer.wrap(buf);
  
    private final Queue<String> lines = new LinkedList<String>();
    private final LineBuffer lineBuf = new LineBuffer() {
      @Override protected void handleLine(String line, String end) {
        lines.add(line);
      }
    };
  
    /**
     * Creates a new instance that will read lines from the given
     * {@code Readable} object.
     */
    public LineReader(Readable readable) {
      this.readable = checkNotNull(readable);
      this.reader = (readable instanceof Reader) ? (Reader) readable : null;
    }
  
    /**
     * Reads a line of text. A line is considered to be terminated by any
     * one of a line feed ({@code '\n'}), a carriage return
     * ({@code '\r'}), or a carriage return followed immediately by a linefeed
     * ({@code "\r\n"}).
     *
     * @return a {@code String} containing the contents of the line, not
     *     including any line-termination characters, or {@code null} if the
     *     end of the stream has been reached.
     * @throws IOException if an I/O error occurs
     */
    public String readLine() throws IOException {
      while (lines.peek() == null) {
        cbuf.clear();
        // The default implementation of Reader#read(CharBuffer) allocates a
        // temporary char[], so we call Reader#read(char[], int, int) instead.
        int read = (reader != null)
            ? reader.read(buf, 0, buf.length)
            : readable.read(cbuf);
        if (read == -1) {
          lineBuf.finish();
          break;
        }
        lineBuf.add(buf, 0, read);
      }
      return lines.poll();
    }
  }