plantuml/src/net/sourceforge/plantuml/tim/expression/ShuntingYard.java

/* ========================================================================
 * PlantUML : a free UML diagram generator
 * ========================================================================
 *
 * (C) Copyright 2009-2020, Arnaud Roques
 *
 * Project Info:  http://plantuml.com
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 * under the terms of the GNU General Public License as published by
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 *
 * PlantUML 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.
 *
 * You should have received a copy of the GNU General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
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 * Original Author:  Arnaud Roques
 *
 */
package net.sourceforge.plantuml.tim.expression;

import java.util.ArrayDeque;
import java.util.Deque;

import net.sourceforge.plantuml.tim.EaterException;
import net.sourceforge.plantuml.tim.TVariable;

// https://en.wikipedia.org/wiki/Shunting-yard_algorithm
// https://en.cppreference.com/w/c/language/operator_precedence
public class ShuntingYard {

	final private TokenStack ouputQueue = new TokenStack();
	final private Deque<Token> operatorStack = new ArrayDeque<Token>();

	private static final boolean TRACE = false;

	private void traceMe() {
		if (TRACE == false)
			return;
		System.err.println("-------------------");
		System.err.println("operatorStack=" + operatorStack);
		System.err.println("ouputQueue=" + ouputQueue);
		System.err.println("");
	}

	public ShuntingYard(TokenIterator it, Knowledge knowledge) throws EaterException {

		while (it.hasMoreTokens()) {
			final Token token = it.nextToken();
			traceMe();
			if (TRACE)
				System.err.println("token=" + token);
			if (token.getTokenType() == TokenType.NUMBER || token.getTokenType() == TokenType.QUOTED_STRING) {
				ouputQueue.add(token);
			} else if (token.getTokenType() == TokenType.FUNCTION_NAME) {
				operatorStack.addFirst(token);
			} else if (token.getTokenType() == TokenType.PLAIN_TEXT) {
				final String name = token.getSurface();
				final TVariable variable = knowledge.getVariable(name);
				if (variable == null) {
					throw new EaterException("Unknown variable " + name);
				}
				ouputQueue.add(variable.getValue().toToken());
			} else if (token.getTokenType() == TokenType.OPERATOR) {
				while ((thereIsAFunctionAtTheTopOfTheOperatorStack(token) //
						|| thereIsAnOperatorAtTheTopOfTheOperatorStackWithGreaterPrecedence(token) //
				|| theOperatorAtTheTopOfTheOperatorStackHasEqualPrecedenceAndIsLeftAssociative(token)) //
						&& theOperatorAtTheTopOfTheOperatorStackIsNotALeftParenthesis(token)) {
					ouputQueue.add(operatorStack.removeFirst());
				}
				// push it onto the operator stack.
				operatorStack.addFirst(token);
			} else if (token.getTokenType() == TokenType.OPEN_PAREN_FUNC) {
				operatorStack.addFirst(token);
			} else if (token.getTokenType() == TokenType.OPEN_PAREN_MATH) {
				operatorStack.addFirst(token);
			} else if (token.getTokenType() == TokenType.CLOSE_PAREN_FUNC) {
				final Token first = operatorStack.removeFirst();
				ouputQueue.add(first);
			} else if (token.getTokenType() == TokenType.CLOSE_PAREN_MATH) {
				while (operatorStack.peekFirst().getTokenType() != TokenType.OPEN_PAREN_MATH) {
					ouputQueue.add(operatorStack.removeFirst());
				}
				if (operatorStack.peekFirst().getTokenType() == TokenType.OPEN_PAREN_MATH) {
					operatorStack.removeFirst();
				}
			} else if (token.getTokenType() == TokenType.COMMA) {
				while (operatorStack.peekFirst() != null
						&& operatorStack.peekFirst().getTokenType() != TokenType.OPEN_PAREN_FUNC) {
					ouputQueue.add(operatorStack.removeFirst());
				}
			} else {
				throw new UnsupportedOperationException(token.toString());
			}
		}

		while (operatorStack.isEmpty() == false) {
			final Token token = operatorStack.removeFirst();
			ouputQueue.add(token);
		}

		// System.err.println("ouputQueue=" + ouputQueue);
	}

	private boolean thereIsAFunctionAtTheTopOfTheOperatorStack(Token token) {
		final Token top = operatorStack.peekFirst();
		return top != null && top.getTokenType() == TokenType.FUNCTION_NAME;
	}

	private boolean thereIsAnOperatorAtTheTopOfTheOperatorStackWithGreaterPrecedence(Token token) {
		final Token top = operatorStack.peekFirst();
		if (top != null && top.getTokenType() == TokenType.OPERATOR
				&& top.getTokenOperator().getPrecedence() > token.getTokenOperator().getPrecedence()) {
			return true;
		}
		return false;
	}

	private boolean theOperatorAtTheTopOfTheOperatorStackHasEqualPrecedenceAndIsLeftAssociative(Token token) {
		final Token top = operatorStack.peekFirst();
		if (top != null && top.getTokenType() == TokenType.OPERATOR && top.getTokenOperator().isLeftAssociativity()
				&& top.getTokenOperator().getPrecedence() == token.getTokenOperator().getPrecedence()) {
			return true;
		}
		return false;
	}

	private boolean theOperatorAtTheTopOfTheOperatorStackIsNotALeftParenthesis(Token token) {
		final Token top = operatorStack.peekFirst();
		if (top != null && top.getTokenType() == TokenType.OPEN_PAREN_MATH) {
			return true;
		}
		return true;
	}

	public TokenStack getQueue() {
		return this.ouputQueue;
	}

}