/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.sysds.runtime.util;

import java.util.Arrays;

import org.apache.sysds.runtime.matrix.data.MatrixBlock;

/**
 * Utilities for sorting, primarily used for SparseRows.
 * 
 */
public class SortUtils 
{
	public static boolean isSorted(int start, int end, int[] indexes) {
		boolean ret = true;
		for( int i=start+1; i<end && ret; i++ )
			ret &= (indexes[i-1]<indexes[i]);
		return ret;
	}

	public static boolean isSorted(int start, int end, double[] values) {
		boolean ret = true;
		for( int i=start+1; i<end && ret; i++ )
			ret &= (values[i-1]<values[i]);
		return ret;
	}
	
	public static boolean isSorted(MatrixBlock in) {
		return in.isInSparseFormat() ? false : !in.isAllocated() ? true :
			isSorted(0, in.getNumRows()*in.getNumColumns(), in.getDenseBlockValues());
	}
	
	public static int compare(double[] d1, double[] d2) {
		if( d1 == null || d2 == null )
			throw new RuntimeException("Invalid invocation w/ null parameter.");
		int ret = Long.compare(d1.length, d2.length);
		if( ret != 0 ) return ret;
		for(int i=0; i<d1.length; i++) {
			ret = Double.compare(d1[i], d2[i]);
			if( ret != 0 ) return ret;
		}
		return 0;
	}
	
	/**
	 * In-place sort of two arrays, only indexes is used for comparison and values
	 * of same position are sorted accordingly. 
	 * 
     * @param start starting index
     * @param end ending index
     * @param indexes array of indexes to sort by
     * @param values double array of values to sort
     */
    public static void sortByIndex(int start, int end, int[] indexes, double[] values) 
    {
        int tempIx;
        double tempVal;
        
        int length = end - start;
        if (length < 7) {
            for (int i = start + 1; i < end; i++) {
                for (int j = i; j > start && indexes[j - 1] > indexes[j]; j--) {
                    tempIx = indexes[j];
                    indexes[j] = indexes[j - 1];
                    indexes[j - 1] = tempIx;
                    tempVal = values[j];
                    values[j] = values[j - 1];
                    values[j - 1] = tempVal;
                }
            }
            return;
        }
        int middle = (start + end) / 2;
        if (length > 7) {
            int bottom = start;
            int top = end - 1;
            if (length > 40) {
                length /= 8;
                bottom = med3(indexes, bottom, bottom + length, bottom
                        + (2 * length));
                middle = med3(indexes, middle - length, middle, middle + length);
                top = med3(indexes, top - (2 * length), top - length, top);
            }
            middle = med3(indexes, bottom, middle, top);
        }
        int partionValue = indexes[middle];
        int a, b, c, d;
        a = b = start;
        c = d = end - 1;
        while (true) {
            while (b <= c && indexes[b] <= partionValue) {
                if (indexes[b] == partionValue) {
                    tempIx = indexes[a];
                    indexes[a] = indexes[b];
                    indexes[b] = tempIx;
                    tempVal = values[a];
                    values[a++] = values[b];
                    values[b] = tempVal;
                }
                b++;
            }
            while (c >= b && indexes[c] >= partionValue) {
                if (indexes[c] == partionValue) {
                    tempIx = indexes[c];
                    indexes[c] = indexes[d];
                    indexes[d] = tempIx;
                    tempVal = values[c];
                    values[c] = values[d];
                    values[d--] = tempVal;
                }
                c--;
            }
            if (b > c) {
                break;
            }
            tempIx = indexes[b];
            indexes[b] = indexes[c];
            indexes[c] = tempIx;
            tempVal = values[b];
            values[b++] = values[c];
            values[c--] = tempVal;
        }
        length = a - start < b - a ? a - start : b - a;
        int l = start;
        int h = b - length;
        while (length-- > 0) {
            tempIx = indexes[l];
            indexes[l] = indexes[h];
            indexes[h] = tempIx;
            tempVal = values[l];
            values[l++] = values[h];
            values[h++] = tempVal;
        }
        length = d - c < end - 1 - d ? d - c : end - 1 - d;
        l = b;
        h = end - length;
        while (length-- > 0) {
            tempIx = indexes[l];
            indexes[l] = indexes[h];
            indexes[h] = tempIx;
            tempVal = values[l];
            values[l++] = values[h];
            values[h++] = tempVal;
        }
        if ((length = b - a) > 0) {
            sortByIndex(start, start + length, indexes, values);
        }
        if ((length = d - c) > 0) {
            sortByIndex(end - length, end, indexes, values);
        }
    }
    
    
    /**
	 * In-place sort of three arrays, only first indexes is used for comparison and second
	 * indexes as well as values of same position are sorted accordingly. 
	 * 
     * @param start starting index
     * @param end ending index
     * @param indexes ?
     * @param indexes2 ?
     * @param values ?
     */
    public static void sortByIndex(int start, int end, int[] indexes, int[] indexes2, double[] values) 
    {
        int tempIx;
        int tempIx2;
        double tempVal;
        
        int length = end - start;
        if (length < 7) {
            for (int i = start + 1; i < end; i++) {
                for (int j = i; j > start && indexes[j - 1] > indexes[j]; j--) {
                    tempIx = indexes[j];
                    indexes[j] = indexes[j - 1];
                    indexes[j - 1] = tempIx;
                    tempIx2 = indexes2[j];
                    indexes2[j] = indexes2[j - 1];
                    indexes2[j - 1] = tempIx2;
                    tempVal = values[j];
                    values[j] = values[j - 1];
                    values[j - 1] = tempVal;        
                }
            }
            return;
        }
        int middle = (start + end) / 2;
        if (length > 7) {
            int bottom = start;
            int top = end - 1;
            if (length > 40) {
                length /= 8;
                bottom = med3(indexes, bottom, bottom + length, bottom
                        + (2 * length));
                middle = med3(indexes, middle - length, middle, middle + length);
                top = med3(indexes, top - (2 * length), top - length, top);
            }
            middle = med3(indexes, bottom, middle, top);
        }
        int partionValue = indexes[middle];
        int a, b, c, d;
        a = b = start;
        c = d = end - 1;
        while (true) {
            while (b <= c && indexes[b] <= partionValue) {
                if (indexes[b] == partionValue) {
                    tempIx = indexes[a];
                    indexes[a] = indexes[b];
                    indexes[b] = tempIx;
                    tempIx2 = indexes2[a];
                    indexes2[a] = indexes2[b];
                    indexes2[b] = tempIx2;
                    tempVal = values[a];
                    values[a++] = values[b];
                    values[b] = tempVal;
                }
                b++;
            }
            while (c >= b && indexes[c] >= partionValue) {
                if (indexes[c] == partionValue) {
                    tempIx = indexes[c];
                    indexes[c] = indexes[d];
                    indexes[d] = tempIx;
                    tempIx2 = indexes2[c];
                    indexes2[c] = indexes2[d];
                    indexes2[d] = tempIx2;
                    tempVal = values[c];
                    values[c] = values[d];
                    values[d--] = tempVal;
                }
                c--;
            }
            if (b > c) {
                break;
            }
            tempIx = indexes[b];
            indexes[b] = indexes[c];
            indexes[c] = tempIx;
            tempIx2 = indexes2[b];
            indexes2[b] = indexes2[c];
            indexes2[c] = tempIx2;
            tempVal = values[b];
            values[b++] = values[c];
            values[c--] = tempVal;
        }
        length = a - start < b - a ? a - start : b - a;
        int l = start;
        int h = b - length;
        while (length-- > 0) {
            tempIx = indexes[l];
            indexes[l] = indexes[h];
            indexes[h] = tempIx;
            tempIx2 = indexes2[l];
            indexes2[l] = indexes2[h];
            indexes2[h] = tempIx2;
            tempVal = values[l];
            values[l++] = values[h];
            values[h++] = tempVal;
        }
        length = d - c < end - 1 - d ? d - c : end - 1 - d;
        l = b;
        h = end - length;
        while (length-- > 0) {
            tempIx = indexes[l];
            indexes[l] = indexes[h];
            indexes[h] = tempIx;
            tempIx2 = indexes2[l];
            indexes2[l] = indexes2[h];
            indexes2[h] = tempIx2;
            tempVal = values[l];
            values[l++] = values[h];
            values[h++] = tempVal;
        }
        if ((length = b - a) > 0) {
            sortByIndex(start, start + length, indexes, indexes2, values);
        }
        if ((length = d - c) > 0) {
            sortByIndex(end - length, end, indexes, indexes2, values);
        }
    }

    public static void sortByValue(int start, int end, double[] values, int[] indexes) 
    {
        double tempVal;
        int tempIx;
        
        int length = end - start;
        if (length < 7) {
            for (int i = start + 1; i < end; i++) {
                for (int j = i; j > start && values[j - 1] > values[j]; j--) {
                    tempVal = values[j];
                    values[j] = values[j - 1];
                    values[j - 1] = tempVal;
                    tempIx = indexes[j];
                    indexes[j] = indexes[j - 1];
                    indexes[j - 1] = tempIx;
                }
            }
            return;
        }
        int middle = (start + end) / 2;
        if (length > 7) {
            int bottom = start;
            int top = end - 1;
            if (length > 40) {
                length /= 8;
                bottom = med3(values, bottom, bottom + length, bottom
                        + (2 * length));
                middle = med3(values, middle - length, middle, middle + length);
                top = med3(values, top - (2 * length), top - length, top);
            }
            middle = med3(values, bottom, middle, top);
        }
        double partionValue = values[middle];
        int a, b, c, d;
        a = b = start;
        c = d = end - 1;
        while (true) {
            while (b <= c && values[b] <= partionValue) {
                if (values[b] == partionValue) {
                    tempVal = values[a];
                    values[a] = values[b];
                    values[b] = tempVal;
                    tempIx = indexes[a];
                    indexes[a++] = indexes[b];
                    indexes[b] = tempIx;
                }
                b++;
            }
            while (c >= b && values[c] >= partionValue) {
                if (values[c] == partionValue) {
                    tempVal = values[c];
                    values[c] = values[d];
                    values[d] = tempVal;
                    tempIx = indexes[c];
                    indexes[c] = indexes[d];
                    indexes[d--] = tempIx;
                }
                c--;
            }
            if (b > c) {
                break;
            }
            tempVal = values[b];
            values[b] = values[c];
            values[c] = tempVal;
            tempIx = indexes[b];
            indexes[b++] = indexes[c];
            indexes[c--] = tempIx;
        }
        length = a - start < b - a ? a - start : b - a;
        int l = start;
        int h = b - length;
        while (length-- > 0) {
            tempVal = values[l];
            values[l] = values[h];
            values[h] = tempVal;
            tempIx = indexes[l];
            indexes[l++] = indexes[h];
            indexes[h++] = tempIx;
        }
        length = d - c < end - 1 - d ? d - c : end - 1 - d;
        l = b;
        h = end - length;
        while (length-- > 0) {
            tempVal = values[l];
            values[l] = values[h];
            values[h] = tempVal;
            tempIx = indexes[l];
            indexes[l++] = indexes[h];
            indexes[h++] = tempIx;
        }
        if ((length = b - a) > 0) {
            sortByValue(start, start + length, values, indexes);
        }
        if ((length = d - c) > 0) {
            sortByValue(end - length, end, values, indexes);
        }
    }
    
    
    
	/**
	 * In-place sort of two arrays, only indexes is used for comparison and values
	 * of same position are sorted accordingly. 
	 * 
     * @param start start index
     * @param end end index
     * @param values double array of values to sort
     * @param indexes int array of indexes to sort by
     */
    public static void sortByValueStable(int start, int end, double[] values, int[] indexes) 
    {    

    	sortByValue(start, end, values, indexes);
    	
    	// Maintain the stability of the index order.
		for( int i=0; i<values.length-1; i++ ) {
			double tmp = values[i];
			//determine run of equal values
			int len = 0;
			while( i+len+1<values.length && tmp==values[i+len+1] )
				len++;
			//unstable sort of run indexes (equal value guaranteed)
			if( len>0 ) {
				Arrays.sort(indexes, i, i+len+1);
				i += len; //skip processed run
			}
		}
    }

    private static int med3(int[] array, int a, int b, int c) 
    {
        int x = array[a], y = array[b], z = array[c];
        return x < y ? (y < z ? b : (x < z ? c : a)) : (y > z ? b : (x > z ? c
                : a));
    }

    private static int med3(double[] array, int a, int b, int c) 
    {
        double x = array[a], y = array[b], z = array[c];
        return x < y ? (y < z ? b : (x < z ? c : a)) : (y > z ? b : (x > z ? c
                : a));
    }
}