/*
 * Copyright 2003-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.codehaus.groovy.runtime.typehandling;

import java.math.BigDecimal;
import java.math.BigInteger;


/**
 * Stateless objects used to perform math on the various Number subclasses.
 * Instances are required so that polymorphic calls work properly, but each
 * subclass creates a singleton instance to minimize garbage.  All methods
 * must be thread-safe.
 * 
 * The design goals of this class are as follows:
 * <ol>
 * <li>Support a 'least surprising' math model to scripting language users.  This
 * means that exact, or decimal math should be used for default calculations.  This
 * scheme assumes that by default, groovy literals with decimal points are instantiated
 * as BigDecimal objects rather than binary floating points (Float, Double). 
 * <li>Do not force the appearance of exactness on a number that is by definition not 
 * guaranteed to be exact.  In particular this means that if an operand in a NumberMath 
 * operation is a binary floating point number, ensure that the result remains a binary floating point 
 * number (i.e. never automatically promote a binary floating point number to a BigDecimal).  
 * This has the effect of preserving the expectations of binary floating point users and helps performance.
 * <li>Provide an implementation that is as close as practical to the Java 1.5 BigDecimal math model 
 * which implements precision based floating point decimal math (ANSI X3.274-1996 and 
 * ANSI X3.274-1996/AM 1-2000 (section 7.4).  
 * </ol>
 * 
 * @author Steve Goetze
 */
public abstract class NumberMath {
		
	public static Number abs(Number number) {
		return getMath(number).absImpl(number);
	}
	
	public static Number add(Number left, Number right) {
		return getMath(left, right).addImpl(left,right);
	}
	
	public static Number subtract(Number left, Number right) {
		return getMath(left,right).subtractImpl(left,right);
	}
	
	public static Number multiply(Number left, Number right) {
		return getMath(left,right).multiplyImpl(left,right);
	}
	
	public static Number divide(Number left, Number right) {
		return getMath(left,right).divideImpl(left,right);
 	}
 	 
	public static int compareTo(Number left, Number right) {
		return getMath(left,right).compareToImpl(left, right);
	}
	
    public static Number or(Number left, Number right) {
        return getMath(left,right).orImpl(left, right);
    }
    
    public static Number and(Number left, Number right) {
        return getMath(left,right).andImpl(left, right);
    }
    
    public static Number xor(Number left, Number right) {
        return getMath(left,right).xorImpl(left, right);
    }
    
	public static Number intdiv(Number left, Number right) {
		return getMath(left,right).intdivImpl(left,right);
 	}

	public static Number mod(Number left, Number right) {
        return getMath(left,right).modImpl(left, right);
    }

    /**
     * For this operation, consider the operands independently.  Throw an exception if the right operand
     * (shift distance) is not an integral type.  For the left operand (shift value) also require an integral
     * type, but do NOT promote from Integer to Long.  This is consistent with Java, and makes sense for the
     * shift operators.
     */
    public static Number leftShift(Number left, Number right) {
		if (isFloatingPoint(right) || isBigDecimal(right)) {
	        throw new UnsupportedOperationException("Shift distance must be an integral type, but " +  right + " (" + right.getClass().getName() + ") was supplied");
		}
    	return getMath(left).leftShiftImpl(left,right);
    }
    
    /**
     * For this operation, consider the operands independently.  Throw an exception if the right operand
     * (shift distance) is not an integral type.  For the left operand (shift value) also require an integral
     * type, but do NOT promote from Integer to Long.  This is consistent with Java, and makes sense for the
     * shift operators.
     */
    public static Number rightShift(Number left, Number right) {
		if (isFloatingPoint(right) || isBigDecimal(right)) {
	        throw new UnsupportedOperationException("Shift distance must be an integral type, but " +  right + " (" + right.getClass().getName() + ") was supplied");
		}
    	return getMath(left).rightShiftImpl(left,right);
    }
    
    /**
     * For this operation, consider the operands independently.  Throw an exception if the right operand
     * (shift distance) is not an integral type.  For the left operand (shift value) also require an integral
     * type, but do NOT promote from Integer to Long.  This is consistent with Java, and makes sense for the
     * shift operators.
     */
    public static Number rightShiftUnsigned(Number left, Number right) {
		if (isFloatingPoint(right) || isBigDecimal(right)) {
	        throw new UnsupportedOperationException("Shift distance must be an integral type, but " +  right + " (" + right.getClass().getName() + ") was supplied");
		}
    	return getMath(left).rightShiftUnsignedImpl(left,right);
    }
    
    public static Number unaryMinus(Number left) {
        return getMath(left).unaryMinusImpl(left);
    }
    
    public static boolean isFloatingPoint(Number number) {
		return number instanceof Double || number instanceof Float;
	}

	public static boolean isInteger(Number number) {
		return number instanceof Integer;
	}

	public static boolean isLong(Number number) {
		return number instanceof Long;
	}

	public static boolean isBigDecimal(Number number) {
		return number instanceof BigDecimal;
	}

	public static boolean isBigInteger(Number number) {
		return number instanceof BigInteger;
	}

	public static BigDecimal toBigDecimal(Number n) {
		return (n instanceof BigDecimal ? (BigDecimal) n : new BigDecimal(n.toString()));
	}
				
	public static BigInteger toBigInteger(Number n) {
		return (n instanceof BigInteger ? (BigInteger) n : new BigInteger(n.toString()));
	}
					
	/**
	 * Determine which NumberMath instance to use, given the supplied operands.  This method implements
	 * the type promotion rules discussed in the documentation.  Note that by the time this method is
	 * called, any Byte, Character or Short operands will have been promoted to Integer.  For reference,
	 * here is the promotion matrix:
	 *    bD bI  D  F  L  I
	 * bD bD bD  D  D bD bD
	 * bI bD bI  D  D bI bI
	 *  D  D  D  D  D  D  D
	 *  F  D  D  D  D  D  D
	 *  L bD bI  D  D  L  L
	 *  I bD bI  D  D  L  I
	 * 
	 * Note that for division, if either operand isFloatingPoint, the result will be floating.  Otherwise,
	 * the result is BigDecimal
	 */
	private static NumberMath getMath(Number left, Number right) {
		if (isFloatingPoint(left) || isFloatingPoint(right)) {
			return FloatingPointMath.INSTANCE;
		}
		else if (isBigDecimal(left) || isBigDecimal(right)) {
			return BigDecimalMath.INSTANCE;
		}
		else if (isBigInteger(left) || isBigInteger(right)) {
			return BigIntegerMath.INSTANCE;
		}
		else if (isLong(left) || isLong(right)){
			return LongMath.INSTANCE;
		}
		return IntegerMath.INSTANCE;
	}

	private static NumberMath getMath(Number number) {
		if (isInteger(number)) {
			return IntegerMath.INSTANCE;
		}
		else if (isLong(number)) {
			return LongMath.INSTANCE;
		}
		else if (isFloatingPoint(number)) {
			return FloatingPointMath.INSTANCE;
		}			
		else if (isBigDecimal(number)) {
			return BigDecimalMath.INSTANCE;
		}
		else if (isBigInteger(number)) {
			return BigIntegerMath.INSTANCE;
		}
		else {
			throw new IllegalArgumentException("An unexpected Number subclass was supplied.");
		}
	}
	
	//Subclasses implement according to the type promotion hierarchy rules
	protected abstract Number absImpl(Number number);
	protected abstract Number addImpl(Number left, Number right);
	protected abstract Number subtractImpl(Number left, Number right);
	protected abstract Number multiplyImpl(Number left, Number right);
	protected abstract Number divideImpl(Number left, Number right);
	protected abstract int compareToImpl(Number left, Number right);
    protected abstract Number unaryMinusImpl(Number left);


    protected Number orImpl(Number left, Number right) {
        throw createUnsupportedException("or()", left);
    }
    
    protected Number andImpl(Number left, Number right) {
        throw createUnsupportedException("and()", left);
    }

    protected Number xorImpl(Number left, Number right) {
        throw createUnsupportedException("xor()", left);
    }
    
    protected Number modImpl(Number left, Number right) {
        throw createUnsupportedException("mod()", left);
    }
    
    protected Number intdivImpl(Number left, Number right) {
        throw createUnsupportedException("intdiv()", left);
    }
    
    protected Number leftShiftImpl(Number left, Number right) {
        throw createUnsupportedException("leftShift()", left);
    }

    protected Number rightShiftImpl(Number left, Number right) {
        throw createUnsupportedException("rightShift()", left);
    }

    protected Number rightShiftUnsignedImpl(Number left, Number right) {
        throw createUnsupportedException("rightShiftUnsigned()", left);
    }

    protected UnsupportedOperationException createUnsupportedException(String operation, Number left) {
        return new UnsupportedOperationException("Cannot use " + operation + " on this number type: " + left.getClass().getName() + " with value: " + left);
    }
}