/*

Copyright 2010, Google Inc.
All rights reserved.

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    * Redistributions of source code must retain the above copyright
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    * Redistributions in binary form must reproduce the above
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contributors may be used to endorse or promote products derived from
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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*/

package com.google.refine.expr.functions.math;

import java.util.Properties;

import com.google.refine.expr.EvalError;
import com.google.refine.grel.ControlFunctionRegistry;
import com.google.refine.grel.Function;

public class FactN implements Function {

    @Override
    public Object call(Properties bindings, Object[] args) {
        if (args.length != 2) {
            return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects two numbers");
        }
        if (args[0] == null || !(args[0] instanceof Number)) {
            return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects the first parameter to be a number");
        }
        if (args[1] == null || !(args[1] instanceof Number)) {
            return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects the second parameter to be a number");
        }

        return FactN.factorial(((Number) args[0]).intValue(), ((Number) args[1]).intValue());

    }

    /*
     * Calculates the factorial of an integer, i, for a decreasing step of n.
     * e.g. A double factorial would have a step of 2.
     * Returns 1 for zero and negative integers.
     */
    public static long factorial(long i, long step){
        if (i < 0) {
            throw new IllegalArgumentException("Can't compute the factorial of a negative number");
        } else if(i <= 1) {
            return 1;
        } else {
            long result = i * FactN.factorial(i - step, step);
            if (result < 0) {
                throw new ArithmeticException("Integer overflow computing factorial");
            }
            return result;
        }
    }

    @Override
    public String getDescription() {
        return "Returns the factorial of a number";
    }
    
    @Override
    public String getParams() {
        return "number i";
    }
    
    @Override
    public String getReturns() {
        return "number";
    }
}