/*******************************************************************************
 * Copyright (c) 2002, 2016 QNX Software Systems 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:
 *     QNX Software Systems - Initial API and implementation
 *******************************************************************************/

package org.eclipse.cdt.make.internal.ui.text.makefile;

import org.eclipse.jface.text.rules.ICharacterScanner;
import org.eclipse.jface.text.rules.IPredicateRule;
import org.eclipse.jface.text.rules.IToken;

class MacroDefinitionRule implements IPredicateRule {
	private static final int INIT_STATE = 0;
	private static final int VAR_STATE = 1;
	private static final int END_VAR_STATE = 2;
	private static final int EQUAL_STATE = 3;
	private static final int FINISH_STATE = 4;
	private static final int ERROR_STATE = 5;

	private IToken token;
	private StringBuilder buffer = new StringBuilder();
	protected IToken defaultToken;

	public MacroDefinitionRule(IToken token, IToken defaultToken) {
		this.token = token;
		this.defaultToken = defaultToken;
	}

	@Override
	public IToken getSuccessToken() {
		return token;
	}

	@Override
	public IToken evaluate(ICharacterScanner scanner, boolean resume) {
		buffer.setLength(0);
		int state = INIT_STATE;

		if (resume)
			scanToBeginOfLine(scanner);

		for (int c = scanner.read(); c != ICharacterScanner.EOF; c = scanner.read()) {
			switch (state) {
				case INIT_STATE :
					if (c != '\n' && Character.isWhitespace((char) c)) {
						break;
					}
					if (isValidCharacter(c)) {
						state = VAR_STATE;
					} else {
						state = ERROR_STATE;
					}
					break;
				case VAR_STATE :
					if (isValidCharacter(c)) {
						break;
					}
				//$FALL-THROUGH$
				case END_VAR_STATE :
					if (c != '\n' && Character.isWhitespace((char) c)) {
						state = END_VAR_STATE;
					} else if (c == ':' || c == '+' || c == '?') {
						state = EQUAL_STATE;
					} else if (c == '=') {
						state = FINISH_STATE;
					} else {
						state = ERROR_STATE;
					}
					break;
				case EQUAL_STATE :
					if (c == '=') {
						state = FINISH_STATE;
					} else {
						state = ERROR_STATE;
					}
					break;
				case FINISH_STATE :
					break;
				default :
					break;
			}
			if (state >= FINISH_STATE) {
				break;
			}
			buffer.append((char) c);
		}

		scanner.unread();

		if (state == FINISH_STATE) {
			//scanToEndOfLine(scanner);
			return token;
		}

		if (defaultToken.isUndefined())
			unreadBuffer(scanner);

		return defaultToken;

	}

	@Override
	public IToken evaluate(ICharacterScanner scanner) {
		return evaluate(scanner, false);
	}

	/**
	 * Returns the characters in the buffer to the scanner.
	 *
	 * @param scanner the scanner to be used
	 */
	protected void unreadBuffer(ICharacterScanner scanner) {
		for (int i = buffer.length() - 1; i >= 0; i--) {
			scanner.unread();
		}
	}

	@SuppressWarnings("unused")
	private void scanToEndOfLine(ICharacterScanner scanner) {
		int c;
		char[][] delimiters = scanner.getLegalLineDelimiters();
		while ((c = scanner.read()) != ICharacterScanner.EOF) {
			// Check for end of line since it can be used to terminate the pattern.
			for (int i = 0; i < delimiters.length; i++) {
				if (c == delimiters[i][0] && sequenceDetected(scanner, delimiters[i])) {
					return;
				}
			}
		}
	}

	private void scanToBeginOfLine(ICharacterScanner scanner) {
		while(scanner.getColumn() != 0) {
			scanner.unread();
		}
	}

	private boolean sequenceDetected(ICharacterScanner scanner, char[] sequence) {
		for (int i = 1; i < sequence.length; i++) {
			int c = scanner.read();
			if (c == ICharacterScanner.EOF) {
				return true;
			} else if (c != sequence[i]) {
				// Non-matching character detected, rewind the scanner back to the start.
				for (; i > 0; i--) {
					scanner.unread();
				}
				return false;
			}
		}

		return true;
	}

	protected boolean isValidCharacter(int c) {
		// From GNUMakefile manual:
		// A variable name may be any sequence of characters not containing �:�, �#�, �=�, or leading or trailing whitespace.
		// However, variable names containing characters other than letters, numbers, and underscores should be avoided,
		// as they may be given special meanings in the future, and with some shells they cannot be passed through the environment to a sub-make
		return !Character.isWhitespace(c) && c != ':' && c != '#' && c != '=';
	}

}