package org.matheclipse.core.reflection.system;

import org.matheclipse.core.eval.exception.Validate;
import org.matheclipse.core.eval.interfaces.IFunctionEvaluator;
import org.matheclipse.core.expression.F;
import org.matheclipse.core.interfaces.IAST;
import org.matheclipse.core.interfaces.IExpr;
import org.matheclipse.core.interfaces.IRational;
import org.matheclipse.core.interfaces.ISymbol;

/**
 * Get the denominator part of an expression
 * 
 * See Wikipedia:
 * Fraction (mathematics)
 * 
 * @see org.matheclipse.core.reflection.system.Numerator
 */
public class Denominator implements IFunctionEvaluator {

	static ISymbol[] NUMERATOR_SYMBOLS = { F.Csc, F.Cot, F.Sec };
	static ISymbol[] DENOMINATOR_SYMBOLS = { F.Sin, F.Tan, F.Cos };

	public Denominator() {
	}

	public IExpr evaluate(final IAST ast) {
		Validate.checkSize(ast, 2);

		IExpr expr = ast.arg1();
		if (expr.isRational()) {
			return ((IRational) expr).getDenominator();
		}
		IExpr[] parts = Apart.getFractionalParts(expr);
		return parts[1];
	}

	public IExpr numericEval(final IAST functionList) {
		return evaluate(functionList);
	}

	public void setUp(final ISymbol symbol) {
		symbol.setAttributes(ISymbol.LISTABLE);
	}

	/**
	 * Get the "denominator form" of the given function. Example:
	 * Csc[x] gives Sin[x].
	 * 
	 * @param function
	 *          the function which should be transformed to "denominator
	 *          form"
	 * @return
	 */
	public static IAST getDenominatorForm(IAST function) {
		if (function.size() == 2) {
			for (int i = 0; i < Denominator.NUMERATOR_SYMBOLS.length; i++) {
				ISymbol sym = Denominator.NUMERATOR_SYMBOLS[i];
				if (function.head().equals(sym)) {
					return F.$(Denominator.DENOMINATOR_SYMBOLS[i], function.arg1());
				}
			}
		}
		return null;
	}

}