/*
 *  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 java.nio;

import java.io.IOException;
import java.util.Arrays;

/**
 * A buffer of chars.
 * <p>
 * A char buffer can be created in either one of the following ways:
 * <ul>
 * <li>{@link #allocate(int) Allocate} a new char array and create a buffer
 * based on it;</li>
 * <li>{@link #wrap(char[]) Wrap} an existing char array to create a new
 * buffer;</li>
 * <li>{@link #wrap(CharSequence) Wrap} an existing char sequence to create a
 * new buffer;</li>
 * <li>Use {@link java.nio.ByteBuffer#asCharBuffer() ByteBuffer.asCharBuffer}
 * to create a char buffer based on a byte buffer.</li>
 * </ul>
 */
public abstract class CharBuffer extends Buffer implements
        Comparable<CharBuffer>, CharSequence, Appendable, Readable {

    /**
     * Creates a char buffer based on a newly allocated char array.
     *
     * @param capacity
     *            the capacity of the new buffer.
     * @return the created char buffer.
     * @throws IllegalArgumentException
     *             if {@code capacity} is less than zero.
     */
    public static CharBuffer allocate(int capacity) {
        if (capacity < 0) {
            throw new IllegalArgumentException();
        }
        return new ReadWriteCharArrayBuffer(capacity);
    }

    /**
     * Creates a new char buffer by wrapping the given char array.
     * <p>
     * Calling this method has the same effect as
     * {@code wrap(array, 0, array.length)}.
     *
     * @param array
     *            the char array which the new buffer will be based on.
     * @return the created char buffer.
     */
    public static CharBuffer wrap(char[] array) {
        return wrap(array, 0, array.length);
    }

    /**
     * Creates a new char buffer by wrapping the given char array.
     * <p>
     * The new buffer's position will be {@code start}, limit will be
     * {@code start + charCount}, capacity will be the length of the array.
     *
     * @param array
     *            the char array which the new buffer will be based on.
     * @param start
     *            the start index, must not be negative and not greater than
     *            {@code array.length}.
     * @param charCount
     *            the length, must not be negative and not greater than
     *            {@code array.length - start}.
     * @return the created char buffer.
     * @exception IndexOutOfBoundsException
     *                if either {@code start} or {@code charCount} is invalid.
     */
    public static CharBuffer wrap(char[] array, int start, int charCount) {
        Arrays.checkOffsetAndCount(array.length, start, charCount);
        CharBuffer buf = new ReadWriteCharArrayBuffer(array);
        buf.position = start;
        buf.limit = start + charCount;
        return buf;
    }

    /**
     * Creates a new char buffer by wrapping the given char sequence.
     * <p>
     * Calling this method has the same effect as
     * {@code wrap(chseq, 0, chseq.length())}.
     *
     * @param chseq
     *            the char sequence which the new buffer will be based on.
     * @return the created char buffer.
     */
    public static CharBuffer wrap(CharSequence chseq) {
        return new CharSequenceAdapter(chseq);
    }

    /**
     * Creates a new char buffer by wrapping the given char sequence.
     * <p>
     * The new buffer's position will be {@code start}, limit will be
     * {@code end}, capacity will be the length of the char sequence. The new
     * buffer is read-only.
     *
     * @param cs
     *            the char sequence which the new buffer will be based on.
     * @param start
     *            the start index, must not be negative and not greater than
     *            {@code cs.length()}.
     * @param end
     *            the end index, must be no less than {@code start} and no
     *            greater than {@code cs.length()}.
     * @return the created char buffer.
     * @exception IndexOutOfBoundsException
     *                if either {@code start} or {@code end} is invalid.
     */
    public static CharBuffer wrap(CharSequence cs, int start, int end) {
        if (start < 0 || end < start || end > cs.length()) {
            throw new IndexOutOfBoundsException("cs.length()=" + cs.length() + ", start=" + start + ", end=" + end);
        }
        CharBuffer result = new CharSequenceAdapter(cs);
        result.position = start;
        result.limit = end;
        return result;
    }

    CharBuffer(int capacity) {
        super(1, capacity, null);
    }

    public final char[] array() {
        return protectedArray();
    }

    public final int arrayOffset() {
        return protectedArrayOffset();
    }

    /**
     * Returns a read-only buffer that shares its content with this buffer.
     * <p>
     * The returned buffer is guaranteed to be a new instance, even if this
     * buffer is read-only itself. The new buffer's position, limit, capacity
     * and mark are the same as this buffer's.
     * <p>
     * The new buffer shares its content with this buffer, which means this
     * buffer's change of content will be visible to the new buffer. The two
     * buffer's position, limit and mark are independent.
     *
     * @return a read-only version of this buffer.
     */
    public abstract CharBuffer asReadOnlyBuffer();

    /**
     * Returns the character located at the specified index in the buffer. The
     * index value is referenced from the current buffer position.
     *
     * @param index
     *            the index referenced from the current buffer position. It must
     *            not be less than zero but less than the value obtained from a
     *            call to {@code remaining()}.
     * @return the character located at the specified index (referenced from the
     *         current position) in the buffer.
     * @exception IndexOutOfBoundsException
     *                if the index is invalid.
     */
    public final char charAt(int index) {
        if (index < 0 || index >= remaining()) {
            throw new IndexOutOfBoundsException("index=" + index + ", remaining()=" + remaining());
        }
        return get(position + index);
    }

    /**
     * Compacts this char buffer.
     * <p>
     * The remaining chars will be moved to the head of the buffer,
     * starting from position zero. Then the position is set to
     * {@code remaining()}; the limit is set to capacity; the mark is cleared.
     *
     * @return this buffer.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public abstract CharBuffer compact();

    /**
     * Compare the remaining chars of this buffer to another char
     * buffer's remaining chars.
     *
     * @param otherBuffer
     *            another char buffer.
     * @return a negative value if this is less than {@code otherBuffer}; 0 if
     *         this equals to {@code otherBuffer}; a positive value if this is
     *         greater than {@code otherBuffer}.
     * @exception ClassCastException
     *                if {@code otherBuffer} is not a char buffer.
     */
    public int compareTo(CharBuffer otherBuffer) {
        int compareRemaining = (remaining() < otherBuffer.remaining()) ? remaining()
                : otherBuffer.remaining();
        int thisPos = position;
        int otherPos = otherBuffer.position;
        char thisByte, otherByte;
        while (compareRemaining > 0) {
            thisByte = get(thisPos);
            otherByte = otherBuffer.get(otherPos);
            if (thisByte != otherByte) {
                return thisByte < otherByte ? -1 : 1;
            }
            thisPos++;
            otherPos++;
            compareRemaining--;
        }
        return remaining() - otherBuffer.remaining();
    }

    /**
     * Returns a duplicated buffer that shares its content with this buffer.
     * <p>
     * The duplicated buffer's initial position, limit, capacity and mark are
     * the same as this buffer's. The duplicated buffer's read-only property and
     * byte order are the same as this buffer's, too.
     * <p>
     * The new buffer shares its content with this buffer, which means either
     * buffer's change of content will be visible to the other. The two buffer's
     * position, limit and mark are independent.
     *
     * @return a duplicated buffer that shares its content with this buffer.
     */
    public abstract CharBuffer duplicate();

    /**
     * Checks whether this char buffer is equal to another object.
     * <p>
     * If {@code other} is not a char buffer then {@code false} is returned. Two
     * char buffers are equal if and only if their remaining chars are exactly
     * the same. Position, limit, capacity and mark are not considered.
     *
     * @param other
     *            the object to compare with this char buffer.
     * @return {@code true} if this char buffer is equal to {@code other},
     *         {@code false} otherwise.
     */
    @Override
    public boolean equals(Object other) {
        if (!(other instanceof CharBuffer)) {
            return false;
        }
        CharBuffer otherBuffer = (CharBuffer) other;

        if (remaining() != otherBuffer.remaining()) {
            return false;
        }

        int myPosition = position;
        int otherPosition = otherBuffer.position;
        boolean equalSoFar = true;
        while (equalSoFar && (myPosition < limit)) {
            equalSoFar = get(myPosition++) == otherBuffer.get(otherPosition++);
        }

        return equalSoFar;
    }

    /**
     * Returns the char at the current position and increases the position by 1.
     *
     * @return the char at the current position.
     * @exception BufferUnderflowException
     *                if the position is equal or greater than limit.
     */
    public abstract char get();

    /**
     * Reads chars from the current position into the specified char array and
     * increases the position by the number of chars read.
     * <p>
     * Calling this method has the same effect as
     * {@code get(dst, 0, dst.length)}.
     *
     * @param dst
     *            the destination char array.
     * @return this buffer.
     * @exception BufferUnderflowException
     *                if {@code dst.length} is greater than {@code remaining()}.
     */
    public CharBuffer get(char[] dst) {
        return get(dst, 0, dst.length);
    }

    /**
     * Reads chars from the current position into the specified char array,
     * starting from the specified offset, and increases the position by the
     * number of chars read.
     *
     * @param dst
     *            the target char array.
     * @param dstOffset
     *            the offset of the char array, must not be negative and not
     *            greater than {@code dst.length}.
     * @param charCount
     *            The number of chars to read, must be no less than zero and no
     *            greater than {@code dst.length - dstOffset}.
     * @return this buffer.
     * @exception IndexOutOfBoundsException
     *                if either {@code dstOffset} or {@code charCount} is invalid.
     * @exception BufferUnderflowException
     *                if {@code charCount} is greater than {@code remaining()}.
     */
    public CharBuffer get(char[] dst, int dstOffset, int charCount) {
        Arrays.checkOffsetAndCount(dst.length, dstOffset, charCount);
        if (charCount > remaining()) {
            throw new BufferUnderflowException();
        }
        for (int i = dstOffset; i < dstOffset + charCount; ++i) {
            dst[i] = get();
        }
        return this;
    }

    /**
     * Returns a char at the specified index; the position is not changed.
     *
     * @param index
     *            the index, must not be negative and less than limit.
     * @return a char at the specified index.
     * @exception IndexOutOfBoundsException
     *                if index is invalid.
     */
    public abstract char get(int index);

    public final boolean hasArray() {
        return protectedHasArray();
    }

    /**
     * Calculates this buffer's hash code from the remaining chars. The
     * position, limit, capacity and mark don't affect the hash code.
     *
     * @return the hash code calculated from the remaining chars.
     */
    @Override
    public int hashCode() {
        int myPosition = position;
        int hash = 0;
        while (myPosition < limit) {
            hash = hash + get(myPosition++);
        }
        return hash;
    }

    /**
     * Indicates whether this buffer is direct. A direct buffer will try its
     * best to take advantage of native memory APIs and it may not stay in the
     * Java heap, so it is not affected by garbage collection.
     * <p>
     * A char buffer is direct if it is based on a byte buffer and the byte
     * buffer is direct.
     *
     * @return {@code true} if this buffer is direct, {@code false} otherwise.
     */
    public abstract boolean isDirect();

    /**
     * Returns the number of remaining chars.
     *
     * @return the number of remaining chars.
     */
    public final int length() {
        return remaining();
    }

    /**
     * Returns the byte order used by this buffer when converting chars from/to
     * bytes.
     * <p>
     * If this buffer is not based on a byte buffer, then this always returns
     * the platform's native byte order.
     *
     * @return the byte order used by this buffer when converting chars from/to
     *         bytes.
     */
    public abstract ByteOrder order();

    /**
     * Child class implements this method to realize {@code array()}.
     *
     * @see #array()
     */
    abstract char[] protectedArray();

    /**
     * Child class implements this method to realize {@code arrayOffset()}.
     *
     * @see #arrayOffset()
     */
    abstract int protectedArrayOffset();

    /**
     * Child class implements this method to realize {@code hasArray()}.
     *
     * @see #hasArray()
     */
    abstract boolean protectedHasArray();

    /**
     * Writes the given char to the current position and increases the position
     * by 1.
     *
     * @param c
     *            the char to write.
     * @return this buffer.
     * @exception BufferOverflowException
     *                if position is equal or greater than limit.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public abstract CharBuffer put(char c);

    /**
     * Writes chars from the given char array to the current position and
     * increases the position by the number of chars written.
     * <p>
     * Calling this method has the same effect as
     * {@code put(src, 0, src.length)}.
     *
     * @param src
     *            the source char array.
     * @return this buffer.
     * @exception BufferOverflowException
     *                if {@code remaining()} is less than {@code src.length}.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public final CharBuffer put(char[] src) {
        return put(src, 0, src.length);
    }

    /**
     * Writes chars from the given char array, starting from the specified offset,
     * to the current position and increases the position by the number of chars
     * written.
     *
     * @param src
     *            the source char array.
     * @param srcOffset
     *            the offset of char array, must not be negative and not greater
     *            than {@code src.length}.
     * @param charCount
     *            the number of chars to write, must be no less than zero and no
     *            greater than {@code src.length - srcOffset}.
     * @return this buffer.
     * @exception BufferOverflowException
     *                if {@code remaining()} is less than {@code charCount}.
     * @exception IndexOutOfBoundsException
     *                if either {@code srcOffset} or {@code charCount} is invalid.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public CharBuffer put(char[] src, int srcOffset, int charCount) {
        Arrays.checkOffsetAndCount(src.length, srcOffset, charCount);
        if (charCount > remaining()) {
            throw new BufferOverflowException();
        }
        for (int i = srcOffset; i < srcOffset + charCount; ++i) {
            put(src[i]);
        }
        return this;
    }

    /**
     * Writes all the remaining chars of the {@code src} char buffer to this
     * buffer's current position, and increases both buffers' position by the
     * number of chars copied.
     *
     * @param src
     *            the source char buffer.
     * @return this buffer.
     * @exception BufferOverflowException
     *                if {@code src.remaining()} is greater than this buffer's
     *                {@code remaining()}.
     * @exception IllegalArgumentException
     *                if {@code src} is this buffer.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public CharBuffer put(CharBuffer src) {
        if (src == this) {
            throw new IllegalArgumentException();
        }
        if (src.remaining() > remaining()) {
            throw new BufferOverflowException();
        }

        char[] contents = new char[src.remaining()];
        src.get(contents);
        put(contents);
        return this;
    }

    /**
     * Writes a char to the specified index of this buffer; the position is not
     * changed.
     *
     * @param index
     *            the index, must be no less than zero and less than the limit.
     * @param c
     *            the char to write.
     * @return this buffer.
     * @exception IndexOutOfBoundsException
     *                if index is invalid.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public abstract CharBuffer put(int index, char c);

    /**
     * Writes all chars of the given string to the current position of this
     * buffer, and increases the position by the length of string.
     * <p>
     * Calling this method has the same effect as
     * {@code put(str, 0, str.length())}.
     *
     * @param str
     *            the string to write.
     * @return this buffer.
     * @exception BufferOverflowException
     *                if {@code remaining()} is less than the length of string.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public final CharBuffer put(String str) {
        return put(str, 0, str.length());
    }

    /**
     * Writes chars of the given string to the current position of this buffer,
     * and increases the position by the number of chars written.
     *
     * @param str
     *            the string to write.
     * @param start
     *            the first char to write, must not be negative and not greater
     *            than {@code str.length()}.
     * @param end
     *            the last char to write (excluding), must be less than
     *            {@code start} and not greater than {@code str.length()}.
     * @return this buffer.
     * @exception BufferOverflowException
     *                if {@code remaining()} is less than {@code end - start}.
     * @exception IndexOutOfBoundsException
     *                if either {@code start} or {@code end} is invalid.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public CharBuffer put(String str, int start, int end) {
        if (start < 0 || end < start || end > str.length()) {
            throw new IndexOutOfBoundsException("str.length()=" + str.length() +
                    ", start=" + start + ", end=" + end);
        }
        if (end - start > remaining()) {
            throw new BufferOverflowException();
        }
        for (int i = start; i < end; i++) {
            put(str.charAt(i));
        }
        return this;
    }

    /**
     * Returns a sliced buffer that shares its content with this buffer.
     * <p>
     * The sliced buffer's capacity will be this buffer's {@code remaining()},
     * and its zero position will correspond to this buffer's current position.
     * The new buffer's position will be 0, limit will be its capacity, and its
     * mark is cleared. The new buffer's read-only property and byte order are
     * same as this buffer.
     * <p>
     * The new buffer shares its content with this buffer, which means either
     * buffer's change of content will be visible to the other. The two buffer's
     * position, limit and mark are independent.
     *
     * @return a sliced buffer that shares its content with this buffer.
     */
    public abstract CharBuffer slice();

    /**
     * Returns a new char buffer representing a sub-sequence of this buffer's
     * current remaining content.
     * <p>
     * The new buffer's position will be {@code position() + start}, limit will
     * be {@code position() + end}, capacity will be the same as this buffer.
     * The new buffer's read-only property and byte order are the same as this
     * buffer.
     * <p>
     * The new buffer shares its content with this buffer, which means either
     * buffer's change of content will be visible to the other. The two buffer's
     * position, limit and mark are independent.
     *
     * @param start
     *            the start index of the sub-sequence, referenced from the
     *            current buffer position. Must not be less than zero and not
     *            greater than the value obtained from a call to
     *            {@code remaining()}.
     * @param end
     *            the end index of the sub-sequence, referenced from the current
     *            buffer position. Must not be less than {@code start} and not
     *            be greater than the value obtained from a call to
     *            {@code remaining()}.
     * @return a new char buffer represents a sub-sequence of this buffer's
     *         current remaining content.
     * @exception IndexOutOfBoundsException
     *                if either {@code start} or {@code end} is invalid.
     */
    public abstract CharSequence subSequence(int start, int end);

    /**
     * Returns a string representing the current remaining chars of this buffer.
     */
    @Override
    public String toString() {
        StringBuilder result = new StringBuilder(limit - position);
        for (int i = position; i < limit; i++) {
            result.append(get(i));
        }
        return result.toString();
    }

    /**
     * Writes the given char to the current position and increases the position
     * by 1.
     *
     * @param c
     *            the char to write.
     * @return this buffer.
     * @exception BufferOverflowException
     *                if position is equal or greater than limit.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public CharBuffer append(char c) {
        return put(c);
    }

    /**
     * Writes all chars of the given character sequence {@code csq} to the
     * current position of this buffer, and increases the position by the length
     * of the csq.
     * <p>
     * Calling this method has the same effect as {@code append(csq.toString())}.
     * If the {@code CharSequence} is {@code null} the string "null" will be
     * written to the buffer.
     *
     * @param csq
     *            the {@code CharSequence} to write.
     * @return this buffer.
     * @exception BufferOverflowException
     *                if {@code remaining()} is less than the length of csq.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public CharBuffer append(CharSequence csq) {
        if (csq != null) {
            return put(csq.toString());
        }
        return put("null");
    }

    /**
     * Writes chars of the given {@code CharSequence} to the current position of
     * this buffer, and increases the position by the number of chars written.
     *
     * @param csq
     *            the {@code CharSequence} to write.
     * @param start
     *            the first char to write, must not be negative and not greater
     *            than {@code csq.length()}.
     * @param end
     *            the last char to write (excluding), must be less than
     *            {@code start} and not greater than {@code csq.length()}.
     * @return this buffer.
     * @exception BufferOverflowException
     *                if {@code remaining()} is less than {@code end - start}.
     * @exception IndexOutOfBoundsException
     *                if either {@code start} or {@code end} is invalid.
     * @exception ReadOnlyBufferException
     *                if no changes may be made to the contents of this buffer.
     */
    public CharBuffer append(CharSequence csq, int start, int end) {
        if (csq == null) {
            csq = "null";
        }
        CharSequence cs = csq.subSequence(start, end);
        if (cs.length() > 0) {
            return put(cs.toString());
        }
        return this;
    }

    /**
     * Reads characters from this buffer and puts them into {@code target}. The
     * number of chars that are copied is either the number of remaining chars
     * in this buffer or the number of remaining chars in {@code target},
     * whichever is smaller.
     *
     * @param target
     *            the target char buffer.
     * @throws IllegalArgumentException
     *             if {@code target} is this buffer.
     * @throws IOException
     *             if an I/O error occurs.
     * @throws ReadOnlyBufferException
     *             if no changes may be made to the contents of {@code target}.
     * @return the number of chars copied or -1 if there are no chars left to be
     *         read from this buffer.
     */
    public int read(CharBuffer target) throws IOException {
        int remaining = remaining();
        if (target == this) {
            if (remaining == 0) {
                return -1;
            }
            throw new IllegalArgumentException();
        }
        if (remaining == 0) {
            return limit > 0 && target.remaining() == 0 ? 0 : -1;
        }
        remaining = Math.min(target.remaining(), remaining);
        if (remaining > 0) {
            char[] chars = new char[remaining];
            get(chars);
            target.put(chars);
        }
        return remaining;
    }
}