path: root/BJC-Utils2/src/main/java/bjc/utils/parserutils/ShuntingYard.java

package bjc.utils.parserutils;

import bjc.utils.funcdata.FunctionalList;
import bjc.utils.funcdata.FunctionalMap;
import bjc.utils.funcdata.IList;
import bjc.utils.funcdata.IMap;
import bjc.utils.funcutils.StringUtils;

import java.util.Deque;
import java.util.LinkedList;
import java.util.function.Consumer;
import java.util.function.Function;

/**
 * Utility to run the shunting yard algorithm on a bunch of tokens.
 *
 * @author ben
 *
 * @param <TokenType>
 *                The type of tokens being shunted.
 */
public class ShuntingYard<TokenType> {
	/**
	 * A enum representing the fundamental operator types.
	 *
	 * @author ben
	 *
	 */
	public static enum Operator implements IPrecedent {
		/**
		 * Represents addition.
		 */
		ADD(1),
		/**
		 * Represents subtraction.
		 */
		SUBTRACT(2),

		/**
		 * Represents multiplication.
		 */
		MULTIPLY(3),
		/**
		 * Represents division.
		 */
		DIVIDE(4);

		private final int precedence;

		private Operator(int prec) {
			precedence = prec;
		}

		@Override
		public int getPrecedence() {
			return precedence;
		}
	}

	private final class TokenShunter implements Consumer<String> {
		private IList<TokenType>		output;
		private Deque<String>			stack;
		private Function<String, TokenType>	transformer;

		public TokenShunter(IList<TokenType> outpt, Deque<String> stack,
				Function<String, TokenType> transformer) {
			this.output = outpt;
			this.stack = stack;
			this.transformer = transformer;
		}

		@Override
		public void accept(String token) {
			// Handle operators
			if(operators.containsKey(token)) {
				// Pop operators while there isn't a higher
				// precedence one
				while(!stack.isEmpty() && isHigherPrec(token, stack.peek())) {
					output.add(transformer.apply(stack.pop()));
				}

				// Put this operator onto the stack
				stack.push(token);
			} else if(StringUtils.containsOnly(token, "\\(")) {
				// Handle groups of parenthesis for multiple
				// nesting levels
				stack.push(token);
			} else if(StringUtils.containsOnly(token, "\\)")) {
				// Handle groups of parenthesis for multiple
				// nesting levels
				String swappedToken = token.replace(')', '(');

				// Remove tokens up to a matching parenthesis
				while(!stack.peek().equals(swappedToken)) {
					output.add(transformer.apply(stack.pop()));
				}

				// Remove the parenthesis
				stack.pop();
			} else {
				// Just add the transformed token
				output.add(transformer.apply(token));
			}
		}
	}

	/*
	 * Holds all the shuntable operations.
	 */
	private IMap<String, IPrecedent> operators;

	/**
	 * Create a new shunting yard with a default set of operators.
	 *
	 * @param configureBasics
	 *                Whether or not basic math operators should be
	 *                provided.
	 */
	public ShuntingYard(boolean configureBasics) {
		operators = new FunctionalMap<>();

		// Add basic operators if we're configured to do so
		if(configureBasics) {
			operators.put("+", Operator.ADD);
			operators.put("-", Operator.SUBTRACT);
			operators.put("*", Operator.MULTIPLY);
			operators.put("/", Operator.DIVIDE);
		}
	}

	/**
	 * Add an operator to the list of shuntable operators.
	 *
	 * @param operator
	 *                The token representing the operator.
	 * 
	 * @param precedence
	 *                The precedence of the operator to add.
	 */
	public void addOp(String operator, int precedence) {
		/*
		 * Create the precedence marker
		 */
		IPrecedent prec = IPrecedent.newSimplePrecedent(precedence);

		this.addOp(operator, prec);
	}

	/**
	 * Add an operator to the list of shuntable operators.
	 *
	 * @param operator
	 *                The token representing the operator.
	 * 
	 * @param precedence
	 *                The precedence of the operator.
	 */
	public void addOp(String operator, IPrecedent precedence) {
		/*
		 * Complain about trying to add an incorrect operator
		 */
		if(operator == null)
			throw new NullPointerException("Operator must not be null");
		else if(precedence == null) throw new NullPointerException("Precedence must not be null");

		/*
		 * Add the operator to the ones we handle
		 */
		operators.put(operator, precedence);
	}

	private boolean isHigherPrec(String left, String right) {
		// Check if the right operator exists
		boolean exists = operators.containsKey(right);

		// If it doesn't, the left is higher precedence.
		if(!exists) return false;

		// Get the precedence of operators
		int rightPrecedence = operators.get(right).getPrecedence();
		int leftPrecedence = operators.get(left).getPrecedence();

		// Evaluate what we were asked
		return rightPrecedence >= leftPrecedence;
	}

	/**
	 * Transform a string of tokens from infix notation to postfix.
	 *
	 * @param input
	 *                The string to transform.
	 * 
	 * @param transformer
	 *                The function to use to transform strings to tokens.
	 * 
	 * @return A list of tokens in postfix notation.
	 */
	public IList<TokenType> postfix(IList<String> input, Function<String, TokenType> transformer) {
		// Check our input
		if(input == null)
			throw new NullPointerException("Input must not be null");
		else if(transformer == null) throw new NullPointerException("Transformer must not be null");

		// Here's what we're handing back
		IList<TokenType> output = new FunctionalList<>();

		// The stack to put operators on
		Deque<String> stack = new LinkedList<>();

		// Shunt the tokens
		input.forEach(new TokenShunter(output, stack, transformer));

		// Transform any resulting tokens
		stack.forEach(token -> {
			output.add(transformer.apply(token));
		});

		return output;
	}

	/**
	 * Remove an operator from the list of shuntable operators.
	 *
	 * @param operator
	 *                The token representing the operator. If null, remove
	 *                all operators.
	 */
	public void removeOp(String operator) {
		// Check if we want to remove all operators
		if(operator == null) {
			operators = new FunctionalMap<>();
		} else {
			operators.remove(operator);
		}
	}
}