package edu.rice.hj.example.comp322.labs.lab2;

import edu.rice.hj.api.HjMetrics;
import edu.rice.hj.api.SuspendableException;
import edu.rice.hj.runtime.config.HjSystemProperty;
import edu.rice.hj.runtime.metrics.AbstractMetricsManager;

import static edu.rice.hj.Module1.*;

/**
 * ArraySum1.hj --- Parallel iterative example program for computing the sum of an array
 * <p>
 * This example program creates an array of n random int's, and computes their sum in parallel. The default value of n
 * is 8, but any array size can be provided as argv[0] by going into the run configuration and putting it in the program
 * arguments field on intelliJ, or by typing java ArraySumRecursive n on the command line
 * <p>
 * To obtain abstract performance metrics, select the appropriate compiler option.
 * <p>
 * NOTE: this example program is for illustrative purposes, and is not intended to be used as a performance benchmark.
 *
 * @author Vivek Sarkar (vsarkar@rice.edu)
 */
public class ArraySumRecursive {

    /**
     * Main method, runs the ArraySum
     *
     * @param args - the input parameters
     */
    public static void main(final String[] args) {

        // Setup metrics
        HjSystemProperty.abstractMetrics.set(true);
        launchHabaneroApp(() -> {

            final String strategyStr = System.getProperty("arraysum.work.strategy");
            System.out.println("Strategy: " + strategyStr);

            final int n = ArraySumUtil.readLengthArgument(args);
            final int[] X = ArraySumUtil.initialize(n);
            final int expectedResult = ArraySumUtil.expectedResult(X);

            computeSumReduction(X, 0, n);

            // Output
            System.out.println("Sum of " + n + " elements = " + X[0] + " (should be " + expectedResult + ")");

        }, () -> {
            // Print out the metrics data
            final HjMetrics actualMetrics = abstractMetrics();
            AbstractMetricsManager.dumpStatistics(actualMetrics);
        });

    }

    /**
     * Method that computes the sum of the elements in an array between two indices, a start index and an end index.
     * Mutates the array that is given as input, final result of the sum is stored in at the index listed as the start
     * index
     *
     * @param x          - the array to sum (is mutated)
     * @param startIndex - the leftmost index to be considered in the sum of the array. Is also where the result will be
     *                   stored
     * @param endIndex   -the rightmost index to be considered in the sum of the array.
     */
    protected static void computeSumReduction(final int[] x, final int startIndex, final int endIndex) throws SuspendableException {

        if (endIndex - startIndex <= 1) {
            // nothing to do
            return;
        }

        // Parallel reduction
        final int midIndex = (startIndex + endIndex) / 2;

        finish(() -> {
            async(() -> {
                computeSumReduction(x, startIndex, midIndex);
            });
            computeSumReduction(x, midIndex, endIndex);
        });
        x[startIndex] = ArraySumUtil.doOperation(x, startIndex, midIndex);

    }

}