//
// Program to compute the variance of a set of numbers. 
//
// Command-line arguments are:
//    number of threads (P) -- required; number of threads to use
//    number of numbers (N) -- optional; see below
//
// If only one command-line argument is given, the program reads
//    input numbers (floating-point okay) from standard input until 
//    end-of-file is reached.
// If two command-line arguments are given, the program generates
//    N random numbers to use as input.
//
// Program output:
//    computed variance
//    elapsed time needed for computation, starting when all the
//      input numbers have been read in / generated, and ending
//      when the variance has been computed.
// 
#include <iostream>
#include <iomanip>		// has setprecision()
#include <cstdlib>		// has exit(), etc.
#include <vector>
#include <algorithm>		// has generate()
#include <numeric>		// has accumulate()
#include "timer.h"		// has timer()

// Function declarations; see definitions below for comments.
double * getStdinInput(int & count);
double * getRandomInput(const char inCount[], int & count);

// ---- Main program -------------------------------------------------

int main(int argc, char* argv[]) {

  int P;			// number of threads
  int N;			// number of input numbers
  double * nums;		// will point to array of input numbers

  if (argc < 2) {
    cerr << "Usage:  " << argv[0] << " numThreads [numNumbers]\n";
    exit(EXIT_FAILURE);
  }

  P = atoi(argv[1]);

  // Read/generate input.
  if (argc == 2) 
    nums = getStdinInput(N);
  else 
    nums = getRandomInput(argv[2], N);

  // Print some useful info.
  cout << "Computing the variance of " << N << " numbers using "
       << P << " threads\n";
  
  // Start timing.
  double startTime = timer();

  // Compute variance.
  // ==== START OF CODE TO REPLACE ====
  double avg = (accumulate(nums, nums+N, 0.0))/double(N);
#ifdef DEBUG
  cerr << "Average = " << avg << endl;
#endif
  double variance = 0.0;
  for (int i = 0; i < N; ++i) 
    variance += (nums[i] - avg)*(nums[i] - avg);
  // ==== END OF CODE TO REPLACE ====

  // Stop timing.
  double endTime = timer();

  // Print results.
  cout << "Variance times number of points = " << variance << endl;
  cout << "Time to compute (seconds) = " << setprecision(4)
       << endTime - startTime << endl;
  return EXIT_SUCCESS;
}

// ---- Function definitions -----------------------------------------

// Function to get input from standard input.
double * getStdinInput(int & count) {
  double temp;
  vector<double> vTemp;
  while (cin >> temp)
    vTemp.push_back(temp);
  count = vTemp.size();
  double * numsToReturn = new double[count];
  copy(vTemp.begin(), vTemp.end(), numsToReturn);
  return numsToReturn;
}

// Function to generate input randomly.
double * getRandomInput(const char inCount[], int & count)  {
  count = 0;
  count = atoi(inCount);
  if (count <= 0) {
    cerr << "Count is not numeric\n";
    exit(EXIT_FAILURE);
  }
  double * numsToReturn = new double[count];
  for (int i = 0; i < count; ++i)
    numsToReturn[i] = (double) rand() / (double) (RAND_MAX);
  return numsToReturn;
}