/*
 * Copyright (C) 2011 eXo Platform SAS.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */

package org.exoplatform.commons.utils;

import java.io.IOException;
import java.io.Reader;


/**
 * @author <a href="mailto:julien.viet@exoplatform.com">Julien Viet</a>
 */
public class PropertyResolverReader extends Reader {

    /** . */
    private static final int STATUS_READING = 0;

    /** . */
    private static final int STATUS_READ_DOLLAR = 1;

    /** . */
    private static final int STATUS_READING_PROPERTY = 2;

    /** . */
    private static final int STATUS_WRITING = 3;

    /** . */
    private static final int STATUS_TERMINATED = 4;

    /** . */
    private Reader delegate;

    /** . */
    private int status = STATUS_READING;

    /** . */
    private char[] buffer;

    /** . */
    private int bufferLen;

    /** . */
    private int bufferOff;

    /** . */
    private int mark;

    public PropertyResolverReader(Reader delegate) {
        this(delegate, 64);
    }

    public PropertyResolverReader(Reader delegate, int bufferSize) {
        if (delegate == null) {
            throw new NullPointerException();
        }
        if (bufferSize < 0) {
            throw new IllegalArgumentException();
        }

        //
        this.delegate = delegate;
        this.buffer = new char[bufferSize];
        this.bufferLen = 0;
        this.bufferOff = 0;
    }

    @Override
    public int read(char[] cbuf, int off, int len) throws IOException {
        final int olen = len;
        while (true) {
            switch (status) {
                case STATUS_READING: {
                    if (len > 0) {
                        if (bufferOff == bufferLen) {
                            resetBuffer();
                            fillBuffer(Math.min(len, buffer.length));
                        } else {
                            char c = buffer[bufferOff++];
                            if (c == '$') {
                                mark = bufferOff - 1;
                                status = STATUS_READ_DOLLAR;
                            } else {
                                cbuf[off++] = c;
                                len--;
                            }
                        }
                    } else {
                        return olen - len;
                    }
                    break;
                }
                case STATUS_TERMINATED: {
                    if (mark != -1 && mark < bufferOff) {
                        if (len > 0) {
                            cbuf[off++] = buffer[mark++];
                            len--;
                        } else {
                            return olen - len;
                        }
                    } else {
                        if (olen > len) {
                            return olen - len;
                        } else {
                            return -1;
                        }
                    }
                    break;
                }
                case STATUS_READ_DOLLAR: {
                    if (bufferOff == bufferLen) {
                        // For now let's read 1 ?
                        fillBuffer(1);
                    } else {
                        char c = buffer[bufferOff++];
                        if (c == '{') {
                            status = STATUS_READING_PROPERTY;
                        } else {
                            status = STATUS_WRITING;
                        }
                    }
                    break;
                }
                case STATUS_WRITING: {
                    if (mark < bufferOff) {
                        if (len > 0) {
                            cbuf[off++] = buffer[mark++];
                            len--;
                        } else {
                            return olen - len;
                        }
                    } else {
                        mark = -1;
                        status = STATUS_READING;
                    }
                    break;
                }
                case STATUS_READING_PROPERTY: {
                    if (bufferOff == bufferLen) {
                        // For now let's read 1 ?
                        fillBuffer(1);
                    } else {
                        char c = buffer[bufferOff++];
                        if (c == '}') {
                            String name = new String(buffer, mark + 2, bufferOff - mark - 2 - 1);
                            String value = resolve(name);
                            if (value == null) {
                                status = STATUS_WRITING;
                            } else {
                                mark = bufferOff - value.length();
                                if (mark < 0) {
                                    int nextBufferLen = bufferLen - mark;
                                    if (nextBufferLen > buffer.length) {
                                        char[] tmp = new char[nextBufferLen];
                                        System.arraycopy(buffer, bufferOff, tmp, bufferOff - mark, bufferLen - bufferOff);
                                        buffer = tmp;
                                    } else {
                                        System.arraycopy(buffer, bufferOff, buffer, bufferOff - mark, bufferLen - bufferOff);
                                    }
                                    bufferOff -= mark;
                                    bufferLen = nextBufferLen;
                                    mark = 0;
                                }
                                value.getChars(0, value.length(), buffer, mark);
                                status = STATUS_WRITING;
                            }
                        } else {
                            // We do nothing until we get end of stream of }
                        }
                    }
                    break;
                }
                default:
                    throw new UnsupportedOperationException();
            }
        }
    }

    /**
     * Resolves a property value, this method is called during the stream analysis. When the returned value is null, the
     * property declaration will be read by the client (i.e ${a} will be read as ${a}).
     *
     * @param name the property name
     * @return the property value
     */
    protected String resolve(String name) {
        return name;
    }

    private void resetBuffer() {
        if (bufferLen != bufferOff) {
            throw new AssertionError();
        }
        bufferOff = 0;
        bufferLen = 0;
    }

    private void fillBuffer(int amount) throws IOException {
        if (bufferLen > bufferOff) {
            throw new AssertionError();
        }
        if (amount < 0) {
            throw new IllegalArgumentException();
        }
        int space = bufferLen + amount - buffer.length;
        if (space > 0) {
            // We allocate more space
            char[] tmp = new char[buffer.length + space];
            System.arraycopy(buffer, 0, tmp, 0, buffer.length);
            buffer = tmp;
        }
        int ret = delegate.read(buffer, bufferLen, amount);
        if (ret != -1) {
            bufferLen += ret;
        } else {
            status = STATUS_TERMINATED;
        }
    }

    @Override
    public void close() throws IOException {
        delegate.close();
    }
}
