/*******************************************************************************
 * Copyright (c) 2004, 2007 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
/*
 * Created on Sep 2, 2003
 *
 * To change the template for this generated file go to
 * Window&gt;Preferences&gt;Java&gt;Code Generation&gt;Code and Comments
 */
package org.eclipse.wst.jsdt.web.ui.internal.text;

import java.io.IOException;

import org.eclipse.jface.text.BadLocationException;
import org.eclipse.jface.text.IDocument;
import org.eclipse.wst.jsdt.web.ui.internal.derived.SingleCharReader;

/**
*

* Provisional API: This class/interface is part of an interim API that is still under development and expected to
* change significantly before reaching stability. It is being made available at this early stage to solicit feedback
* from pioneering adopters on the understanding that any code that uses this API will almost certainly be broken
* (repeatedly) as the API evolves.
*/
class JsCodeReader extends SingleCharReader {
	/** The EOF character */
	public static final int EOF = -1;
	private int fCachedLineNumber = -1;
	private int fCachedLineOffset = -1;
	private IDocument fDocument;
	private int fEnd = -1;
	private boolean fForward = false;
	private int fOffset;
	private boolean fSkipComments = false;
	private boolean fSkipStrings = false;
	
	public JsCodeReader() {}
	
	/*
	 * @see Reader#close()
	 */
	
	public void close() throws IOException {
		fDocument = null;
	}
	
	public void configureBackwardReader(IDocument document, int offset, boolean skipComments, boolean skipStrings) throws IOException {
		fDocument = document;
		fOffset = offset;
		fSkipComments = skipComments;
		fSkipStrings = skipStrings;
		fForward = false;
		try {
			fCachedLineNumber = fDocument.getLineOfOffset(fOffset);
		} catch (BadLocationException x) {
			throw new IOException(x.getMessage());
		}
	}
	
	public void configureForwardReader(IDocument document, int offset, int length, boolean skipComments, boolean skipStrings) throws IOException {
		fDocument = document;
		fOffset = offset;
		fSkipComments = skipComments;
		fSkipStrings = skipStrings;
		fForward = true;
		fEnd = Math.min(fDocument.getLength(), fOffset + length);
	}
	
	/**
	 * Returns the offset of the last read character. Should only be called
	 * after read has been called.
	 */
	public int getOffset() {
		return fForward ? fOffset - 1 : fOffset;
	}
	
	private void gotoCommentEnd() throws BadLocationException {
		while (fOffset < fEnd) {
			char current = fDocument.getChar(fOffset++);
			if (current == '*') {
				if (fOffset < fEnd && fDocument.getChar(fOffset) == '/') {
					++fOffset;
					return;
				}
			}
		}
	}
	
	private void gotoCommentStart() throws BadLocationException {
		while (0 < fOffset) {
			char current = fDocument.getChar(fOffset--);
			if (current == '*' && 0 <= fOffset && fDocument.getChar(fOffset) == '/') {
				return;
			}
		}
	}
	
	private void gotoLineEnd() throws BadLocationException {
		int line = fDocument.getLineOfOffset(fOffset);
		fOffset = fDocument.getLineOffset(line + 1);
	}
	
	private void gotoStringEnd(char delimiter) throws BadLocationException {
		while (fOffset < fEnd) {
			char current = fDocument.getChar(fOffset++);
			if (current == '\\') {
				// ignore escaped characters
				++fOffset;
			} else if (current == delimiter) {
				return;
			}
		}
	}
	
	private void gotoStringStart(char delimiter) throws BadLocationException {
		while (0 < fOffset) {
			char current = fDocument.getChar(fOffset);
			if (current == delimiter) {
				if (!(0 <= fOffset && fDocument.getChar(fOffset - 1) == '\\')) {
					return;
				}
			}
			--fOffset;
		}
	}
	
	private void handleSingleLineComment() throws BadLocationException {
		int line = fDocument.getLineOfOffset(fOffset);
		if (line < fCachedLineNumber) {
			fCachedLineNumber = line;
			fCachedLineOffset = fDocument.getLineOffset(line);
			int offset = fOffset;
			while (fCachedLineOffset < offset) {
				char current = fDocument.getChar(offset--);
				if (current == '/' && fCachedLineOffset <= offset && fDocument.getChar(offset) == '/') {
					fOffset = offset;
					return;
				}
			}
		}
	}
	
	/*
	 * @see SingleCharReader#read()
	 */
	
	public int read() throws IOException {
		try {
			return fForward ? readForwards() : readBackwards();
		} catch (BadLocationException x) {
			throw new IOException(x.getMessage());
		}
	}
	
	private int readBackwards() throws BadLocationException {
		while (0 < fOffset) {
			--fOffset;
			handleSingleLineComment();
			char current = fDocument.getChar(fOffset);
			switch (current) {
				case '/':
					if (fSkipComments && fOffset > 1) {
						char next = fDocument.getChar(fOffset - 1);
						if (next == '*') {
							// a comment ends, advance to the comment start
							fOffset -= 2;
							gotoCommentStart();
							continue;
						}
					}
					return current;
				case '"':
				case '\'':
					if (fSkipStrings) {
						--fOffset;
						gotoStringStart(current);
						continue;
					}
					return current;
			}
			return current;
		}
		return JsCodeReader.EOF;
	}
	
	private int readForwards() throws BadLocationException {
		while (fOffset < fEnd) {
			char current = fDocument.getChar(fOffset++);
			switch (current) {
				case '/':
					if (fSkipComments && fOffset < fEnd) {
						char next = fDocument.getChar(fOffset);
						if (next == '*') {
							// a comment starts, advance to the comment end
							++fOffset;
							gotoCommentEnd();
							continue;
						} else if (next == '/') {
							// '//'-comment starts, advance to the line end
							gotoLineEnd();
							continue;
						}
					}
					return current;
				case '"':
				case '\'':
					if (fSkipStrings) {
						gotoStringEnd(current);
						continue;
					}
					return current;
			}
			return current;
		}
		return JsCodeReader.EOF;
	}
}