import edu.rice.hj.api.HjMetrics;
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
 *
 * 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 ArraySumLoop n on the command line
 *
 * To obtain abstract performance metrics, select the appropriate compiler option.
 *
 * 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 ArraySumLoop {

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

        // Setup metrics
        System.setProperty(HjSystemProperty.abstractMetrics.propertyKey(), "true");
        initializeHabanero();

        System.setProperty("arraysum.work.strategy", "bit");
        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(n, X);

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

        // Print out the metrics data
        finalizeHabanero();
        final HjMetrics actualMetrics = abstractMetrics();
        AbstractMetricsManager.dumpStatistics(actualMetrics);

    }

    /**
     * Reduces the array down into a single sum, mutating input array with partial sums.
     * The final result is stored in the first element of the array
     * @param n - the number of elements in the array
     * @param x - the array to sum (is mutated in the function)
     */
    protected static void computeSumReduction(final int n, final int[] x) {
        // Parallel reduction
	//TODO: insert appropriate Async and Finish calls below to parallelize the reduction
        for (int step = 1; step < n; step *= 2) {
            int size = ArraySumUtil.ceilDiv(n, 2 * step);
            final int sstep = step;
            for (int i = 0; i < size; i++) {
                final int ii = i;
                // if condition ensures that algorithm works correctly when X.length is not a power of 2
                final int rightIndex = (2 * ii + 1) * sstep;
                final int leftIndex = 2 * ii * sstep;
                if (rightIndex < x.length) {
		    x[leftIndex] = ArraySumUtil.doOperation(x, leftIndex, rightIndex);
                }
            }

        }

    }

}