package org.matheclipse.core.reflection.system;

import org.matheclipse.core.eval.exception.Validate;
import org.matheclipse.core.eval.interfaces.AbstractFunctionEvaluator;
import org.matheclipse.core.expression.F;
import org.matheclipse.core.generic.ITernaryComparator.COMPARE_RESULT;
import org.matheclipse.core.interfaces.IAST;
import org.matheclipse.core.interfaces.IExpr;
import org.matheclipse.core.list.algorithms.EvaluationSupport;

public class Max extends AbstractFunctionEvaluator {
	public Max() {
	}

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

		IAST list = ast;
		IAST resultList = list.copyHead();
		if (EvaluationSupport.flatten(F.List, list, resultList)) {
			list = resultList;
		}
		// IExpr max = F.Times(F.CN1, ExprFactory.Infinity);
		IExpr max1;
		IExpr max2;
		max1 = list.arg1();
		IAST f = list.copyHead();
		COMPARE_RESULT comp;
		for (int i = 2; i < list.size(); i++) {
			max2 = list.get(i);
			comp = Less.CONST.prepareCompare(max1, max2);

			if (comp == COMPARE_RESULT.TRUE) {
				max1 = max2;
			} else {
				if (comp == COMPARE_RESULT.UNDEFINED) {
					// undetermined
					if (max1.isNumber()) {
						f.add(max2);
					} else {
						f.add(max1);
						max1 = max2;
					}
				}
			}
		}
		if (f.size() > 1) {
			f.add(1, max1);
			if (f.equals(list)) {
				return null;
			}
			return f;
		} else {
			return max1;
		}
	}

}