/*
 * Copyright (c) 2011 TMate Software Ltd
 *  
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * This program 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 for more details.
 *
 * For information on how to redistribute this software under
 * the terms of a license other than GNU General Public License
 * contact TMate Software at support@svnkit.com
 */
package org.tmatesoft.hg.internal;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.util.TreeMap;

import org.tmatesoft.hg.core.Path;
import org.tmatesoft.hg.repo.HgRepository;

/**
 *
 * @author Artem Tikhomirov
 * @author TMate Software Ltd.
 */
public class KeywordFilter implements Filter {
	private final boolean isExpanding;
	private final TreeMap<String,String> keywords;
	private final int minBufferLen;

	/**
	 * 
	 * @param expand <code>true</code> to expand keywords, <code>false</code> to shrink
	 */
	private KeywordFilter(boolean expand) {
		isExpanding = expand;
		keywords = new TreeMap<String,String>();
		keywords.put("Id", "Id");
		keywords.put("Revision", "Revision");
		keywords.put("Author", "Author");
		int l = 0;
		for (String s : keywords.keySet()) {
			if (s.length() > l) {
				l = s.length();
			}
		}
		// FIXME later may implement #filter() not to read full kw value (just "$kw:"). However, limit of maxLen + 2 would keep valid.
		// for buffers less then minBufferLen, there are chances #filter() implementation would never end
		// (i.e. for input "$LongestKey"$
		minBufferLen = l + 2 + (isExpanding ? 0 : 120 /*any reasonable constant for max possible kw value length*/);
	}

	/**
	 * @param src buffer ready to be read
	 * @return buffer ready to be read and original buffer's position modified to reflect consumed bytes. IOW, if source buffer
	 * on return has remaining bytes, they are assumed not-read (not processed) and next chunk passed to filter is supposed to 
	 * start with them  
	 */
	public ByteBuffer filter(ByteBuffer src) {
		if (src.capacity() < minBufferLen) {
			throw new IllegalStateException(String.format("Need buffer of at least %d bytes to ensure filter won't hang", minBufferLen));
		}
		ByteBuffer rv = null;
		int keywordStart = -1;
		int x = src.position();
		while (x < src.limit()) {
			if (keywordStart == -1) {
				int i = indexOf(src, '$', x, false);
				if (i == -1) {
					if (rv == null) {
						return src;
					} else {
						copySlice(src, x, src.limit(), rv);
						rv.flip();
						src.position(src.limit());
						return rv;
					}
				}
				keywordStart = i;
				// fall-through
			}
			if (keywordStart >= 0) {
				int i = indexOf(src, '$', keywordStart+1, true);
				if (i == -1) {
					// end of buffer reached
					if (rv == null) {
						if (keywordStart == x) {
							// FIXME in fact, x might be equal to keywordStart and to src.position() here ('$' is first character in the buffer, 
							// and there are no other '$' not eols till the end of the buffer). This would lead to deadlock (filter won't consume any
							// bytes). To prevent this, either shall copy bytes [keywordStart..buffer.limit()) to local buffer and use it on the next invocation,
							// or add lookup of the keywords right after first '$' is found (do not wait for closing '$'). For now, large enough src buffer would be sufficient
							// not to run into such situation
							throw new IllegalStateException("Try src buffer of a greater size");
						}
						rv = ByteBuffer.allocateDirect(keywordStart - x);
					}
					// copy all from source till latest possible kw start 
					copySlice(src, x, keywordStart, rv);
					rv.flip();
					// and tell caller we've consumed only to the potential kw start
					src.position(keywordStart);
					return rv;
				} else if (src.get(i) == '$') {
					// end of keyword, or start of a new one.
					String keyword;
					if ((keyword = matchKeyword(src, keywordStart, i)) != null) {
						if (rv == null) {
							rv = ByteBuffer.allocateDirect(isExpanding ? src.capacity() * 4 : src.capacity());
						}
						copySlice(src, x, keywordStart+1, rv);
						rv.put(keyword.getBytes());
						if (isExpanding) {
							rv.put((byte) ':');
							rv.put((byte) ' ');
							expandKeywordValue(keyword, rv);
							rv.put((byte) ' ');
						}
						rv.put((byte) '$');
						keywordStart = -1;
						x = i+1;
						continue;
					} else {
						if (rv != null) {
							// we've already did some substitution, thus need to copy bytes we've scanned. 
							copySlice(src, x, i, rv);
						} // no else in attempt to avoid rv creation if no real kw would be found  
						keywordStart = i;
						x = i; // '$' at i wasn't consumed, hence x points to i, not i+1. This is to avoid problems with case: "sdfsd $ asdfs $Id$ sdf"
						continue;
					}
				} else {
					assert src.get(i) == '\n' || src.get(i) == '\r';
					// line break
					if (rv != null) {
						copySlice(src, x, i+1, rv);
					}
					x = i+1;
					keywordStart = -1; // Wasn't keyword, really
					continue; // try once again
				}
			}
		}
		if (keywordStart != -1) {
			if (rv == null) {
				// no expansion happened yet, and we have potential kw start
				rv = ByteBuffer.allocateDirect(keywordStart - src.position());
				copySlice(src, src.position(), keywordStart, rv);
			}
			src.position(keywordStart);
		}
		if (rv != null) {
			rv.flip();
			return rv;
		}
		return src;
	}
	
	/**
	 * @param keyword
	 * @param rv
	 */
	private void expandKeywordValue(String keyword, ByteBuffer rv) {
		if ("Id".equals(keyword)) {
			rv.put(identityString().getBytes());
		} else if ("Revision".equals(keyword)) {
			rv.put(revision());
		} else if ("Author".equals(keyword)) {
			rv.put(username().getBytes());
		}
	}

	private String matchKeyword(ByteBuffer src, int kwStart, int kwEnd) {
		assert kwEnd - kwStart - 1 > 0;
		assert src.get(kwStart) == src.get(kwEnd) && src.get(kwEnd) == '$';
		char[] chars = new char[kwEnd - kwStart - 1];
		int i;
		for (i = 0; i < chars.length; i++) {
			char c = (char) src.get(kwStart + 1 + i);
			if (c == ':') {
				break;
			}
			chars[i] = c;
		}
		String kw = new String(chars, 0, i);
		return keywords.get(kw);
	}
	
	// copies part of the src buffer, [from..to). doesn't modify src position
	private static void copySlice(ByteBuffer src, int from, int to, ByteBuffer dst) {
		if (to > src.limit()) {
			throw new IllegalArgumentException("Bad right boundary");
		}
		if (dst.remaining() < to - from) {
			throw new IllegalArgumentException("Not enough room in the destination buffer");
		}
		for (int i = from; i < to; i++) {
			dst.put(src.get(i));
		}
	}

	private static int indexOf(ByteBuffer b, char ch, int from, boolean newlineBreaks) {
	for (int i = from; i < b.limit(); i++) {
			byte c = b.get(i);
			if (ch == c) {
				return i;
			}
			if (newlineBreaks && (c == '\n' || c == '\r')) {
				return i;
			}
		}
		return -1;
	}

	private String identityString() {
		return "sample/file.txt, asd";
	}

	private byte[] revision() {
		return "1234567890ab".getBytes();
	}
	
	private String username() {
		/* ui.py: username()
        Searched in this order: $HGUSER, [ui] section of hgrcs, $EMAIL
        and stop searching if one of these is set.
        If not found and ui.askusername is True, ask the user, else use
        ($LOGNAME or $USER or $LNAME or $USERNAME) + "@full.hostname".
        */
		return "<Sample> sample@sample.org";
	}

	public static class Factory implements Filter.Factory {

		public Filter create(HgRepository hgRepo, Path path) {
			return new KeywordFilter(true);
		}
	}


	public static void main(String[] args) throws Exception {
		FileInputStream fis = new FileInputStream(new File("/temp/kwoutput.txt"));
		FileOutputStream fos = new FileOutputStream(new File("/temp/kwoutput2.txt"));
		ByteBuffer b = ByteBuffer.allocateDirect(256);
		KeywordFilter kwFilter = new KeywordFilter(false);
		while (fis.getChannel().read(b) != -1) {
			b.flip(); // get ready to be read
			ByteBuffer f = kwFilter.filter(b);
			fos.getChannel().write(f);
			if (b.hasRemaining()) {
				ByteBuffer remaining = b.slice();
				b.clear();
				b.put(remaining);
			} else {
				b.clear();
			}
		}
		fis.close();
		fos.flush();
		fos.close();
	}
}