/* 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.charset;

import java.nio.BufferOverflowException;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.util.Arrays;

/**
 * Transforms a sequence of 16-bit Java characters to a byte sequence in some encoding.
 *
 * <p>The input character sequence is a {@link java.nio.CharBuffer CharBuffer} and the
 * output byte sequence is a {@link java.nio.ByteBuffer ByteBuffer}.
 *
 * <p>Use {@link #encode(CharBuffer)} to encode an entire {@code CharBuffer} to a
 * new {@code ByteBuffer}, or {@link #encode(CharBuffer, ByteBuffer, boolean)} for more
 * control. When using the latter method, the entire operation proceeds as follows:
 * <ol>
 * <li>Invoke {@link #reset()} to reset the encoder if this instance has been used before.</li>
 * <li>Invoke {@link #encode(CharBuffer, ByteBuffer, boolean) encode} with the {@code endOfInput}
 * parameter set to false until additional input is not needed (as signaled by the return value).
 * The input buffer must be filled and the output buffer must be flushed between invocations.
 * <p>The {@link #encode(CharBuffer, ByteBuffer, boolean) encode} method will
 * convert as many characters as possible, and the process won't stop until the
 * input buffer has been exhausted, the output buffer has been filled, or an
 * error has occurred. A {@link CoderResult CoderResult} instance will be
 * returned to indicate the current state. The caller should fill the input buffer, flush
 * the output buffer, or recovering from an error and try again, accordingly.
 * </li>
 * <li>Invoke {@link #encode(CharBuffer, ByteBuffer, boolean) encode} for the last time with
 * {@code endOfInput} set to true.</li>
 * <li>Invoke {@link #flush(ByteBuffer)} to flush remaining output.</li>
 * </ol>
 *
 * <p>There are two classes of encoding error: <i>malformed input</i>
 * signifies that the input character sequence is not legal, while <i>unmappable character</i>
 * signifies that the input is legal but cannot be mapped to a byte sequence (because the charset
 * cannot represent the character, for example).
 *
 * <p>Errors can be handled in three ways. The default is to
 * {@link CodingErrorAction#REPORT report} the error to the caller. The alternatives are to
 * {@link CodingErrorAction#IGNORE ignore} the error or {@link CodingErrorAction#REPLACE replace}
 * the problematic input with the byte sequence returned by {@link #replacement}. The disposition
 * for each of the two kinds of error can be set independently using the {@link #onMalformedInput}
 * and {@link #onUnmappableCharacter} methods.
 *
 * <p>The default replacement bytes depend on the charset but can be overridden using the
 * {@link #replaceWith} method.
 *
 * <p>This class is abstract and encapsulates many common operations of the
 * encoding process for all charsets. Encoders for a specific charset should
 * extend this class and need only to implement the
 * {@link #encodeLoop(CharBuffer, ByteBuffer) encodeLoop} method for basic
 * encoding. If a subclass maintains internal state, it should also override the
 * {@link #implFlush(ByteBuffer) implFlush} and {@link #implReset() implReset} methods.
 *
 * <p>This class is not thread-safe.
 *
 * @see java.nio.charset.Charset
 * @see java.nio.charset.CharsetDecoder
 */
public abstract class CharsetEncoder {
    private static final String RESET = "RESET";
    private static final String ONGOING = "ONGOING";
    private static final String END_OF_INPUT = "END_OF_INPUT";
    private static final String FLUSHED = "FLUSHED";

    private final Charset charset;

    private final float averageBytesPerChar;
    private final float maxBytesPerChar;

    private byte[] replacementBytes;

    private String state = RESET;

    private CodingErrorAction malformedInputAction = CodingErrorAction.REPORT;
    private CodingErrorAction unmappableCharacterAction = CodingErrorAction.REPORT;

    // decoder instance for this encoder's charset, used for replacement value checking
    private CharsetDecoder decoder;

    /**
     * Constructs a new {@code CharsetEncoder} using the given parameters and
     * the replacement byte array {@code { (byte) '?' }}.
     */
    protected CharsetEncoder(Charset cs, float averageBytesPerChar, float maxBytesPerChar) {
        this(cs, averageBytesPerChar, maxBytesPerChar, new byte[] { (byte) '?' });
    }

    /**
     * Constructs a new <code>CharsetEncoder</code> using the given
     * <code>Charset</code>, replacement byte array, average number and
     * maximum number of bytes created by this encoder for one input character.
     *
     * @param cs
     *            the <code>Charset</code> to be used by this encoder.
     * @param averageBytesPerChar
     *            average number of bytes created by this encoder for one single
     *            input character, must be positive.
     * @param maxBytesPerChar
     *            maximum number of bytes which can be created by this encoder
     *            for one single input character, must be positive.
     * @param replacement
     *            the replacement byte array, cannot be null or empty, its
     *            length cannot be larger than <code>maxBytesPerChar</code>,
     *            and must be a legal replacement, which can be justified by
     *            {@link #isLegalReplacement(byte[]) isLegalReplacement}.
     * @throws IllegalArgumentException
     *             if any parameters are invalid.
     */
    protected CharsetEncoder(Charset cs, float averageBytesPerChar, float maxBytesPerChar, byte[] replacement) {
        this(cs, averageBytesPerChar, maxBytesPerChar, replacement, false);
    }

    CharsetEncoder(Charset cs, float averageBytesPerChar, float maxBytesPerChar, byte[] replacement, boolean trusted) {
        if (averageBytesPerChar <= 0 || maxBytesPerChar <= 0) {
            throw new IllegalArgumentException("averageBytesPerChar and maxBytesPerChar must both be positive");
        }
        if (averageBytesPerChar > maxBytesPerChar) {
            throw new IllegalArgumentException("averageBytesPerChar is greater than maxBytesPerChar");
        }
        this.charset = cs;
        this.averageBytesPerChar = averageBytesPerChar;
        this.maxBytesPerChar = maxBytesPerChar;
        if (trusted) {
            // The RI enforces unnecessary restrictions on the replacement bytes. We trust ICU to
            // know what it's doing. Doing so lets us support ICU's EUC-JP, SCSU, and Shift_JIS.
            this.replacementBytes = replacement;
        } else {
            replaceWith(replacement);
        }
    }

    /**
     * Returns the average number of bytes created by this encoder for a single
     * input character.
     */
    public final float averageBytesPerChar() {
        return averageBytesPerChar;
    }

    /**
     * Tests whether the given character can be encoded by this encoder.
     *
     * <p>Note that this method may change the internal state of this encoder, so
     * it should not be called when another encoding process is ongoing,
     * otherwise it will throw an <code>IllegalStateException</code>.
     *
     * @throws IllegalStateException if another encode process is ongoing.
     */
    public boolean canEncode(char c) {
        return canEncode(CharBuffer.wrap(new char[] { c }));
    }

    /**
     * Tests whether the given <code>CharSequence</code> can be encoded by this
     * encoder.
     *
     * <p>Note that this method may change the internal state of this encoder, so
     * it should not be called when another encode process is ongoing, otherwise
     * it will throw an <code>IllegalStateException</code>.
     *
     * @throws IllegalStateException if another encode process is ongoing.
     */
    public boolean canEncode(CharSequence sequence) {
        CharBuffer cb;
        if (sequence instanceof CharBuffer) {
            cb = ((CharBuffer) sequence).duplicate();
        } else {
            cb = CharBuffer.wrap(sequence);
        }

        if (state == FLUSHED) {
            reset();
        }
        if (state != RESET) {
            throw illegalStateException();
        }

        CodingErrorAction originalMalformedInputAction = malformedInputAction;
        CodingErrorAction originalUnmappableCharacterAction = unmappableCharacterAction;
        onMalformedInput(CodingErrorAction.REPORT);
        onUnmappableCharacter(CodingErrorAction.REPORT);
        try {
            encode(cb);
            return true;
        } catch (CharacterCodingException e) {
            return false;
        } finally {
            onMalformedInput(originalMalformedInputAction);
            onUnmappableCharacter(originalUnmappableCharacterAction);
            reset();
        }
    }

    /**
     * Returns the {@link Charset} which this encoder uses.
     */
    public final Charset charset() {
        return charset;
    }

    /**
     * This is a facade method for the encoding operation.
     * <p>
     * This method encodes the remaining character sequence of the given
     * character buffer into a new byte buffer. This method performs a complete
     * encoding operation, resets at first, then encodes, and flushes at last.
     * <p>
     * This method should not be invoked if another encode operation is ongoing.
     *
     * @param in
     *            the input buffer.
     * @return a new <code>ByteBuffer</code> containing the bytes produced by
     *         this encoding operation. The buffer's limit will be the position
     *         of the last byte in the buffer, and the position will be zero.
     * @throws IllegalStateException
     *             if another encoding operation is ongoing.
     * @throws MalformedInputException
     *             if an illegal input character sequence for this charset is
     *             encountered, and the action for malformed error is
     *             {@link CodingErrorAction#REPORT CodingErrorAction.REPORT}
     * @throws UnmappableCharacterException
     *             if a legal but unmappable input character sequence for this
     *             charset is encountered, and the action for unmappable
     *             character error is
     *             {@link CodingErrorAction#REPORT CodingErrorAction.REPORT}.
     *             Unmappable means the Unicode character sequence at the input
     *             buffer's current position cannot be mapped to a equivalent
     *             byte sequence.
     * @throws CharacterCodingException
     *             if other exception happened during the encode operation.
     */
    public final ByteBuffer encode(CharBuffer in) throws CharacterCodingException {
        int length = (int) (in.remaining() * averageBytesPerChar);
        ByteBuffer out = ByteBuffer.allocate(length);

        reset();

        while (state != FLUSHED) {
            CoderResult result = encode(in, out, true);
            if (result == CoderResult.OVERFLOW) {
                out = allocateMore(out);
                continue; // No point trying to flush to an already-full buffer.
            } else {
                checkCoderResult(result);
            }

            result = flush(out);
            if (result == CoderResult.OVERFLOW) {
                out = allocateMore(out);
            } else {
                checkCoderResult(result);
            }
        }

        out.flip();
        return out;
    }

    private void checkCoderResult(CoderResult result) throws CharacterCodingException {
        if (malformedInputAction == CodingErrorAction.REPORT && result.isMalformed()) {
            throw new MalformedInputException(result.length());
        } else if (unmappableCharacterAction == CodingErrorAction.REPORT && result.isUnmappable()) {
            throw new UnmappableCharacterException(result.length());
        }
    }

    private ByteBuffer allocateMore(ByteBuffer output) {
        if (output.capacity() == 0) {
            return ByteBuffer.allocate(1);
        }
        ByteBuffer result = ByteBuffer.allocate(output.capacity() * 2);
        output.flip();
        result.put(output);
        return result;
    }

    /**
     * Encodes characters starting at the current position of the given input
     * buffer, and writes the equivalent byte sequence into the given output
     * buffer from its current position.
     * <p>
     * The buffers' position will be changed with the reading and writing
     * operation, but their limits and marks will be kept intact.
     * <p>
     * A <code>CoderResult</code> instance will be returned according to
     * following rules:
     * <ul>
     * <li>A {@link CoderResult#malformedForLength(int) malformed input} result
     * indicates that some malformed input error was encountered, and the
     * erroneous characters start at the input buffer's position and their
     * number can be got by result's {@link CoderResult#length() length}. This
     * kind of result can be returned only if the malformed action is
     * {@link CodingErrorAction#REPORT CodingErrorAction.REPORT}.</li>
     * <li>{@link CoderResult#UNDERFLOW CoderResult.UNDERFLOW} indicates that
     * as many characters as possible in the input buffer have been encoded. If
     * there is no further input and no characters left in the input buffer then
     * this task is complete. If this is not the case then the client should
     * call this method again supplying some more input characters.</li>
     * <li>{@link CoderResult#OVERFLOW CoderResult.OVERFLOW} indicates that the
     * output buffer has been filled, while there are still some characters
     * remaining in the input buffer. This method should be invoked again with a
     * non-full output buffer.</li>
     * <li>A {@link CoderResult#unmappableForLength(int) unmappable character}
     * result indicates that some unmappable character error was encountered,
     * and the erroneous characters start at the input buffer's position and
     * their number can be got by result's {@link CoderResult#length() length}.
     * This kind of result can be returned only on
     * {@link CodingErrorAction#REPORT CodingErrorAction.REPORT}.</li>
     * </ul>
     * <p>
     * The <code>endOfInput</code> parameter indicates if the invoker can
     * provider further input. This parameter is true if and only if the
     * characters in the current input buffer are all inputs for this encoding
     * operation. Note that it is common and won't cause an error if the invoker
     * sets false and then has no more input available, while it may cause an
     * error if the invoker always sets true in several consecutive invocations.
     * This would make the remaining input to be treated as malformed input.
     * input.
     * <p>
     * This method invokes the
     * {@link #encodeLoop(CharBuffer, ByteBuffer) encodeLoop} method to
     * implement the basic encode logic for a specific charset.
     *
     * @param in
     *            the input buffer.
     * @param out
     *            the output buffer.
     * @param endOfInput
     *            true if all the input characters have been provided.
     * @return a <code>CoderResult</code> instance indicating the result.
     * @throws IllegalStateException
     *             if the encoding operation has already started or no more
     *             input is needed in this encoding process.
     * @throws CoderMalfunctionError
     *             If the {@link #encodeLoop(CharBuffer, ByteBuffer) encodeLoop}
     *             method threw an <code>BufferUnderflowException</code> or
     *             <code>BufferUnderflowException</code>.
     */
    public final CoderResult encode(CharBuffer in, ByteBuffer out, boolean endOfInput) {
        if (state != RESET && state != ONGOING && !(endOfInput && state == END_OF_INPUT)) {
            throw illegalStateException();
        }

        state = endOfInput ? END_OF_INPUT : ONGOING;

        while (true) {
            CoderResult result;
            try {
                result = encodeLoop(in, out);
            } catch (BufferOverflowException ex) {
                throw new CoderMalfunctionError(ex);
            } catch (BufferUnderflowException ex) {
                throw new CoderMalfunctionError(ex);
            }

            if (result == CoderResult.UNDERFLOW) {
                if (endOfInput && in.hasRemaining()) {
                    result = CoderResult.malformedForLength(in.remaining());
                } else {
                    return result;
                }
            } else if (result == CoderResult.OVERFLOW) {
                return result;
            }

            // We have a real error, so do what the appropriate action tells us what to do...
            CodingErrorAction action =
                    result.isUnmappable() ? unmappableCharacterAction : malformedInputAction;
            if (action == CodingErrorAction.REPORT) {
                return result;
            } else if (action == CodingErrorAction.REPLACE) {
                if (out.remaining() < replacementBytes.length) {
                    return CoderResult.OVERFLOW;
                }
                out.put(replacementBytes);
            }
            in.position(in.position() + result.length());
        }
    }

    /**
     * Encodes characters into bytes. This method is called by
     * {@link #encode(CharBuffer, ByteBuffer, boolean) encode}.
     * <p>
     * This method will implement the essential encoding operation, and it won't
     * stop encoding until either all the input characters are read, the output
     * buffer is filled, or some exception is encountered. Then it will
     * return a <code>CoderResult</code> object indicating the result of the
     * current encoding operation. The rule to construct the
     * <code>CoderResult</code> is the same as for
     * {@link #encode(CharBuffer, ByteBuffer, boolean) encode}. When an
     * exception is encountered in the encoding operation, most implementations
     * of this method will return a relevant result object to the
     * {@link #encode(CharBuffer, ByteBuffer, boolean) encode} method, and
     * subclasses may handle the exception and
     * implement the error action themselves.
     * <p>
     * The buffers are scanned from their current positions, and their positions
     * will be modified accordingly, while their marks and limits will be
     * intact. At most {@link CharBuffer#remaining() in.remaining()} characters
     * will be read, and {@link ByteBuffer#remaining() out.remaining()} bytes
     * will be written.
     * <p>
     * Note that some implementations may pre-scan the input buffer and return
     * <code>CoderResult.UNDERFLOW</code> until it receives sufficient input.
     * <p>
     * @param in
     *            the input buffer.
     * @param out
     *            the output buffer.
     * @return a <code>CoderResult</code> instance indicating the result.
     */
    protected abstract CoderResult encodeLoop(CharBuffer in, ByteBuffer out);

    /**
     * Flushes this encoder.
     * <p>
     * This method will call {@link #implFlush(ByteBuffer) implFlush}. Some
     * encoders may need to write some bytes to the output buffer when they have
     * read all input characters, subclasses can overridden
     * {@link #implFlush(ByteBuffer) implFlush} to perform writing action.
     * <p>
     * The maximum number of written bytes won't larger than
     * {@link ByteBuffer#remaining() out.remaining()}. If some encoder wants to
     * write more bytes than the output buffer's available remaining space, then
     * <code>CoderResult.OVERFLOW</code> will be returned, and this method
     * must be called again with a byte buffer that has free space. Otherwise
     * this method will return <code>CoderResult.UNDERFLOW</code>, which
     * means one encoding process has been completed successfully.
     * <p>
     * During the flush, the output buffer's position will be changed
     * accordingly, while its mark and limit will be intact.
     *
     * @param out
     *            the given output buffer.
     * @return <code>CoderResult.UNDERFLOW</code> or
     *         <code>CoderResult.OVERFLOW</code>.
     * @throws IllegalStateException
     *             if this encoder isn't already flushed or at end of input.
     */
    public final CoderResult flush(ByteBuffer out) {
        if (state != FLUSHED && state != END_OF_INPUT) {
            throw illegalStateException();
        }
        CoderResult result = implFlush(out);
        if (result == CoderResult.UNDERFLOW) {
            state = FLUSHED;
        }
        return result;
    }

    /**
     * Flushes this encoder. The default implementation does nothing and always
     * returns <code>CoderResult.UNDERFLOW</code>; this method can be
     * overridden if needed.
     *
     * @param out
     *            the output buffer.
     * @return <code>CoderResult.UNDERFLOW</code> or
     *         <code>CoderResult.OVERFLOW</code>.
     */
    protected CoderResult implFlush(ByteBuffer out) {
        return CoderResult.UNDERFLOW;
    }

    /**
     * Notifies that this encoder's <code>CodingErrorAction</code> specified
     * for malformed input error has been changed. The default implementation
     * does nothing; this method can be overridden if needed.
     *
     * @param newAction
     *            the new action.
     */
    protected void implOnMalformedInput(CodingErrorAction newAction) {
        // default implementation is empty
    }

    /**
     * Notifies that this encoder's <code>CodingErrorAction</code> specified
     * for unmappable character error has been changed. The default
     * implementation does nothing; this method can be overridden if needed.
     *
     * @param newAction
     *            the new action.
     */
    protected void implOnUnmappableCharacter(CodingErrorAction newAction) {
        // default implementation is empty
    }

    /**
     * Notifies that this encoder's replacement has been changed. The default
     * implementation does nothing; this method can be overridden if needed.
     *
     * @param newReplacement
     *            the new replacement string.
     */
    protected void implReplaceWith(byte[] newReplacement) {
        // default implementation is empty
    }

    /**
     * Resets this encoder's charset related state. The default implementation
     * does nothing; this method can be overridden if needed.
     */
    protected void implReset() {
        // default implementation is empty
    }

    /**
     * Tests whether the given argument is legal as this encoder's replacement byte
     * array. The given byte array is legal if and only if it can be decoded into
     * characters.
     */
    public boolean isLegalReplacement(byte[] replacement) {
        if (decoder == null) {
            decoder = charset.newDecoder();
            decoder.onMalformedInput(CodingErrorAction.REPORT);
            decoder.onUnmappableCharacter(CodingErrorAction.REPORT);
        }
        ByteBuffer in = ByteBuffer.wrap(replacement);
        CharBuffer out = CharBuffer.allocate((int) (replacement.length * decoder.maxCharsPerByte()));
        CoderResult result = decoder.decode(in, out, true);
        return !result.isError();
    }

    /**
     * Returns this encoder's <code>CodingErrorAction</code> when a malformed
     * input error occurred during the encoding process.
     */
    public CodingErrorAction malformedInputAction() {
        return malformedInputAction;
    }

    /**
     * Returns the maximum number of bytes which can be created by this encoder for
     * one input character, must be positive.
     */
    public final float maxBytesPerChar() {
        return maxBytesPerChar;
    }

    /**
     * Sets this encoder's action on malformed input error.
     *
     * This method will call the
     * {@link #implOnMalformedInput(CodingErrorAction) implOnMalformedInput}
     * method with the given new action as argument.
     *
     * @param newAction
     *            the new action on malformed input error.
     * @return this encoder.
     * @throws IllegalArgumentException
     *             if the given newAction is null.
     */
    public final CharsetEncoder onMalformedInput(CodingErrorAction newAction) {
        if (newAction == null) {
            throw new IllegalArgumentException("newAction == null");
        }
        malformedInputAction = newAction;
        implOnMalformedInput(newAction);
        return this;
    }

    /**
     * Sets this encoder's action on unmappable character error.
     *
     * This method will call the
     * {@link #implOnUnmappableCharacter(CodingErrorAction) implOnUnmappableCharacter}
     * method with the given new action as argument.
     *
     * @param newAction
     *            the new action on unmappable character error.
     * @return this encoder.
     * @throws IllegalArgumentException
     *             if the given newAction is null.
     */
    public final CharsetEncoder onUnmappableCharacter(CodingErrorAction newAction) {
        if (newAction == null) {
            throw new IllegalArgumentException("newAction == null");
        }
        unmappableCharacterAction = newAction;
        implOnUnmappableCharacter(newAction);
        return this;
    }

    /**
     * Returns the replacement byte array, which is never null or empty.
     */
    public final byte[] replacement() {
        return replacementBytes;
    }

    /**
     * Sets the new replacement value.
     *
     * This method first checks the given replacement's validity, then changes
     * the replacement value and finally calls the
     * {@link #implReplaceWith(byte[]) implReplaceWith} method with the given
     * new replacement as argument.
     *
     * @param replacement
     *            the replacement byte array, cannot be null or empty, its
     *            length cannot be larger than <code>maxBytesPerChar</code>,
     *            and it must be legal replacement, which can be justified by
     *            calling <code>isLegalReplacement(byte[] replacement)</code>.
     * @return this encoder.
     * @throws IllegalArgumentException
     *             if the given replacement cannot satisfy the requirement
     *             mentioned above.
     */
    public final CharsetEncoder replaceWith(byte[] replacement) {
        if (replacement == null) {
            throw new IllegalArgumentException("replacement == null");
        }
        if (replacement.length == 0) {
            throw new IllegalArgumentException("replacement.length == 0");
        }
        if (replacement.length > maxBytesPerChar()) {
            throw new IllegalArgumentException("replacement.length > maxBytesPerChar: " +
                    replacement.length + " > " + maxBytesPerChar());
        }
        if (!isLegalReplacement(replacement)) {
            throw new IllegalArgumentException("Bad replacement: " + Arrays.toString(replacement));
        }
        // It seems like a bug, but the RI doesn't clone, and we have tests that check we don't.
        this.replacementBytes = replacement;
        implReplaceWith(replacementBytes);
        return this;
    }

    /**
     * Resets this encoder. This method will reset the internal state and then
     * calls {@link #implReset} to reset any state related to the
     * specific charset.
     */
    public final CharsetEncoder reset() {
        state = RESET;
        implReset();
        return this;
    }

    /**
     * Returns this encoder's <code>CodingErrorAction</code> when unmappable
     * character occurred during encoding process.
     */
    public CodingErrorAction unmappableCharacterAction() {
        return unmappableCharacterAction;
    }

    private IllegalStateException illegalStateException() {
        throw new IllegalStateException("State: " + state);
    }
}