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/*
 * Copyright (C) 2013 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.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndexes;

import java.io.IOException;
import java.io.Reader;
import java.nio.CharBuffer;

/**
 * A {@link Reader} that reads the characters in a {@link CharSequence}. Like {@code StringReader},
 * but works with any {@link CharSequence}.
 *
 * @author Colin Decker
 */
// TODO(user): make this public? as a type, or a method in CharStreams?
final class CharSequenceReader extends Reader {

  private CharSequence seq;
  private int pos;
  private int mark;

  /**
   * Creates a new reader wrapping the given character sequence.
   */
  public CharSequenceReader(CharSequence seq) {
    this.seq = checkNotNull(seq);
  }

  private void checkOpen() throws IOException {
    if (seq == null) {
      throw new IOException("reader closed");
    }
  }

  private boolean hasRemaining() {
    return remaining() > 0;
  }

  private int remaining() {
    return seq.length() - pos;
  }

  @Override
  public synchronized int read(CharBuffer target) throws IOException {
    checkNotNull(target);
    checkOpen();
    if (!hasRemaining()) {
      return -1;
    }
    int charsToRead = Math.min(target.remaining(), remaining());
    for (int i = 0; i < charsToRead; i++) {
      target.put(seq.charAt(pos++));
    }
    return charsToRead;
  }

  @Override
  public synchronized int read() throws IOException {
    checkOpen();
    return hasRemaining() ? seq.charAt(pos++) : -1;
  }

  @Override
  public synchronized int read(char[] cbuf, int off, int len) throws IOException {
    checkPositionIndexes(off, off + len, cbuf.length);
    checkOpen();
    if (!hasRemaining()) {
      return -1;
    }
    int charsToRead = Math.min(len, remaining());
    for (int i = 0; i < charsToRead; i++) {
      cbuf[off + i] = seq.charAt(pos++);
    }
    return charsToRead;
  }

  @Override
  public synchronized long skip(long n) throws IOException {
    checkArgument(n >= 0, "n (%s) may not be negative", n);
    checkOpen();
    int charsToSkip = (int) Math.min(remaining(), n); // safe because remaining is an int
    pos += charsToSkip;
    return charsToSkip;
  }

  @Override
  public synchronized boolean ready() throws IOException {
    checkOpen();
    return true;
  }

  @Override
  public boolean markSupported() {
    return true;
  }

  @Override
  public synchronized void mark(int readAheadLimit) throws IOException {
    checkArgument(readAheadLimit >= 0, "readAheadLimit (%s) may not be negative", readAheadLimit);
    checkOpen();
    mark = pos;
  }

  @Override
  public synchronized void reset() throws IOException {
    checkOpen();
    pos = mark;
  }

  @Override
  public synchronized void close() throws IOException {
    seq = null;
  }
}