package edu.rice.hj.example.comp322.assignments.hw2;

import edu.rice.hj.api.SuspendableException;

import static edu.rice.hj.Module1.asyncNb;
import static edu.rice.hj.Module1.finish;

/**
 * This file is a skeleton for your GeneralizedReduce implementation. You can assume that each client includes a call to
 * perf.doWork(1) for each call to the combine() method. This abstraction assumes that each call to combine() takes 1
 * unit of time, and ignores the cost all other computations. You should aim for maximum parallelism with respect to
 * this abstraction. All code should include basic documentation for each method in this class.
 * <p>
 * Though you will need to extend this file for your homework submission, do not alter the declarations below in any
 * way, other than filling in the "..." code regions.
 *
 * @author Vivek Sarkar (vsarkar@rice.edu)
 */
public class GeneralizedReduceSol<T> {

    private final GeneralizedReduceApp<T> app;

    /**
     * <p>Constructor for GeneralizedReduceSol.</p>
     *
     * @param a a {@link edu.rice.hj.example.comp322.assignments.hw2.GeneralizedReduceApp} object.
     */
    public GeneralizedReduceSol(final GeneralizedReduceApp<T> a) {
        app = a;
    }

    /**
     * <p>run.</p>
     *
     * @param inArray an array of T objects.
     * @return a T object.
     */
    public T run(final T[] inArray) throws SuspendableException {

        for (int strideOut = 1; strideOut < inArray.length; strideOut *= 2) {
            final int size = (inArray.length + (2 * strideOut) - 1) / (2 * strideOut);
            final int stride = strideOut;
            finish(() -> {
                for (int indexOut = 0; indexOut < size; indexOut++) {
                    final int index = indexOut;
                    asyncNb(() -> {
                        final int index1 = 2 * index * stride;
                        final int index2 = (2 * index + 1) * stride;
                        if (index2 < inArray.length) {
                            inArray[index1] = app.combine(inArray[index1], inArray[index2]);
                        }
                    });
                }
            });
        }
        return app.combine(app.init(), inArray[0]);
    }
}