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package org.mybatis.generator.internal.util;

import java.lang.reflect.Array;

/**
 * This class is from javapractices.com:
 * 
 * http://www.javapractices.com/Topic28.cjp
 * 
 * Collected methods which allow easy implementation of hashCode.
 * 
 * Example use case:
 * 
 *  * public int hashCode() {
 *     int result = HashCodeUtil.SEED;
 *     //collect the contributions of various fields
 *     result = HashCodeUtil.hash(result, fPrimitive);
 *     result = HashCodeUtil.hash(result, fObject);
 *     result = HashCodeUtil.hash(result, fArray);
 *     return result;
 * }
 * 
 */
public final class HashCodeUtil {

    /**
     * An initial value for a hashCode, to which is added
     * contributions from fields. Using a non-zero value decreases collisons of
     * hashCode values.
     */
    public static final int SEED = 23;

    /**
     * booleans.
     *
     * @param aSeed aSeed
     * @param aBoolean aBoolean
     * @return hash
     */
    public static int hash(int aSeed, boolean aBoolean) {
        return firstTerm(aSeed) + (aBoolean ? 1 : 0);
    }

    /**
     * chars.
     * @param aSeed aSeed
     * @param aChar aChar
     * @return hash
     */
    public static int hash(int aSeed, char aChar) {
        return firstTerm(aSeed) + aChar;
    }

    /**
     * ints.
     * @param aSeed aSeed
     * @param aInt aInt
     * @return hash
     */
    public static int hash(int aSeed, int aInt) {
        /*
         * Implementation Note Note that byte and short are handled by this
         * method, through implicit conversion.
         */
        return firstTerm(aSeed) + aInt;
    }

    /**
     * longs.
     * @param aSeed aSeed
     * @param aLong aLong
     * @return hash
     */
    public static int hash(int aSeed, long aLong) {
        return firstTerm(aSeed) + (int) (aLong ^ (aLong >>> 32));
    }

    /**
     * floats.
     * @param aSeed aSeed
     * @param aFloat aFloat
     * @return hash
     */
    public static int hash(int aSeed, float aFloat) {
        return hash(aSeed, Float.floatToIntBits(aFloat));
    }

    /**
     * doubles.
     * @param aSeed aSeed
     * @param aDouble aDouble
     * @return hash
     */
    public static int hash(int aSeed, double aDouble) {
        return hash(aSeed, Double.doubleToLongBits(aDouble));
    }

    /**
     * aObject is a possibly-null object field, and possibly an
     * array.
     *
     * If aObject is an array, then each element may be a primitive
     * or a possibly-null object.
     *
     * @param aSeed aSeed
     * @param aObject aObject
     * @return hash
     */
    public static int hash(int aSeed, Object aObject) {
        int result = aSeed;
        if (aObject == null) {
            result = hash(result, 0);
        } else if (!isArray(aObject)) {
            result = hash(result, aObject.hashCode());
        } else {
            int length = Array.getLength(aObject);
            for (int idx = 0; idx < length; ++idx) {
                Object item = Array.get(aObject, idx);
                // recursive call!
                result = hash(result, item);
            }
        }
        return result;
    }

    // / PRIVATE ///
    private static final int fODD_PRIME_NUMBER = 37;

    private static int firstTerm(int aSeed) {
        return fODD_PRIME_NUMBER * aSeed;
    }

    private static boolean isArray(Object aObject) {
        return aObject.getClass().isArray();
    }
}