/*
 * Copyright (c) 2003, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package java.lang;

import java.io.IOException;
import java.nio.CharBuffer;
import java.util.Objects;

/**
 * A {@code Readable} is a source of characters. Characters from
 * a {@code Readable} are made available to callers of the read
 * method via a {@link java.nio.CharBuffer CharBuffer}.
 *
 * @since 1.5
 */
public interface Readable {

    /**
     * Attempts to read characters into the specified character buffer.
     * The buffer is used as a repository of characters as-is: the only
     * changes made are the results of a put operation. No flipping or
     * rewinding of the buffer is performed.
     *
     * @param cb the buffer to read characters into
     * @return The number of {@code char} values added to the buffer,
     *                 or -1 if this source of characters is at its end
     * @throws IOException if an I/O error occurs
     * @throws NullPointerException if cb is null
     * @throws java.nio.ReadOnlyBufferException if cb is a read only buffer
     */
    public int read(java.nio.CharBuffer cb) throws IOException;

    /**
     * Reads all characters from this source and writes the characters to
     * the given appendable in the order that they are read. On return, the
     * source of characters will be at its end.
     * <p>
     * This method may block indefinitely reading from the readable, or
     * writing to the appendable. Where this source or the appendable is
     * {@link AutoCloseable closeable}, then the behavior when either are
     * <i>asynchronously closed</i>, or the thread interrupted during the transfer,
     * is highly readable and appendable specific, and therefore not specified.
     * <p>
     * If an I/O error occurs reading from the readable or writing to the
     * appendable, then it may do so after some characters have been read or
     * written. Consequently the readable may not be at end of its data and
     * one, or both participants may be in an inconsistent state. That in mind
     * all additional measures required by one or both participants in order to
     * eventually free their internal resources have to be taken by the caller
     * of this method.
     *
     * @param  out the appendable, non-null
     * @return the number of characters transferred
     * @throws IOException if an I/O error occurs when reading or writing
     * @throws NullPointerException if {@code out} is {@code null}
     *
     * @since 10
     */
    public default long transferTo(Appendable out) throws IOException {
        Objects.requireNonNull(out, "out");
        long transferred = 0;
        CharBuffer buffer = CharBuffer.allocate(8192);
        int read;
        while ((read = this.read(buffer)) >= 0) {
            buffer.rewind();
            out.append(buffer, 0, read);
            transferred += read;
        }
        return transferred;
    }
}