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package jscl.math.operator;

import jscl.math.*;
import jscl.math.function.Pow;
import jscl.mathml.MathML;
import jscl.text.ParserUtils;

import javax.annotation.Nonnull;

public class Factorial extends PostfixFunction {

	public static final String NAME = "!";

	public Factorial(Generic expression) {
		super(NAME, new Generic[]{expression});
	}

	private Factorial(Generic[] parameter) {
		super(NAME, ParserUtils.copyOf(parameter, 1));
	}

	@Override
	public int getMinParameters() {
		return 1;
	}

	public Generic selfExpand() {
		return expressionValue();
	}

	@Override
	public Generic selfNumeric() {
		final Generic parameter = parameters[0];
		if (parameter.isInteger()) {
			int n = parameter.integerValue().intValue();
			if (n < 0) {
				//return expressionValue();
				throw new ArithmeticException("Cannot take factorial from negative integer!");
			}

			Generic result = JsclInteger.valueOf(1);
			for (int i = 0; i < n; i++) {
				ParserUtils.checkInterruption();
				result = result.multiply(JsclInteger.valueOf(i + 1));
			}

			if (result instanceof JsclInteger) {
				return new NumericWrapper(((JsclInteger) result));
			} else {
				throw new NotIntegerException();
			}

		} else {
			throw new NotIntegerException();
		}
	}

	public void toMathML(MathML element, Object data) {
		int exponent = data instanceof Integer ? (Integer) data : 1;
		if (exponent == 1) bodyToMathML(element);
		else {
			MathML e1 = element.element("msup");
			bodyToMathML(e1);
			MathML e2 = element.element("mn");
			e2.appendChild(element.text(String.valueOf(exponent)));
			e1.appendChild(e2);
			element.appendChild(e1);
		}
	}

	@Nonnull
	@Override
	public Operator newInstance(@Nonnull Generic[] parameters) {
		return new Factorial(parameters);
	}

	void bodyToMathML(MathML element) {
		MathML e1 = element.element("mrow");
		try {
			JsclInteger en = parameters[0].integerValue();
			en.toMathML(e1, null);
		} catch (NotIntegerException e) {
			try {
				Variable v = parameters[0].variableValue();
				if (v instanceof Pow) {
					GenericVariable.valueOf(parameters[0]).toMathML(e1, null);
				} else v.toMathML(e1, null);
			} catch (NotVariableException e2) {
				GenericVariable.valueOf(parameters[0]).toMathML(e1, null);
			}
		}
		MathML e2 = element.element("mo");
		e2.appendChild(element.text("!"));
		e1.appendChild(e2);
		element.appendChild(e1);
	}

	@Nonnull
	public Variable newInstance() {
		return new Factorial((Generic) null);
	}
}