#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include <string.h>
#include <pthread.h>

// this code is left uncommented as it is self explanatory or the same as the
// parallel version
bool allow_print;

void printSquare(double **array, unsigned long dimension) {
  unsigned long i, j;
  for (i = 0; i < dimension; i++) {
    for (j = 0; j < dimension; j++) printf("%f ", array[i][j]);
    printf("\n");
  }
}

long double time_seconds(struct timespec begin, struct timespec end) {
  long long sec_diff = end.tv_sec - begin.tv_sec;
  long long nsec_diff = end.tv_nsec - begin.tv_nsec;
  long long as_ns = sec_diff * 1000000000L + nsec_diff;
  return (long double) as_ns / 1000000000.0;
}

unsigned long solveArray(double **array, unsigned long dimension, 
    double precision) {
  unsigned long i, j, k;
  bool solved;
  struct timespec begin, end;
  k = 0;

  clock_gettime(CLOCK_MONOTONIC, &begin);
  while (1) {
    k++;
    solved = true;
    for (i = 1; i < dimension - 1; i++) {
      for (j = 1; j < dimension - 1; j++) {
        double previous = array[i][j];
        double avg = (array[i][j - 1] + array[i][j + 1] + array[i - 1][j] + 
            array[i + 1][j]) / 4.0;
        array[i][j] = avg;
        if (solved == true && fabs(avg - previous) > precision) {
          solved = false;
        }
      }
    }
    if (solved == true) {
      clock_gettime(CLOCK_MONOTONIC, &end);
      if (allow_print) printf("time taken: %Lf\n", time_seconds(begin, end));
      return k;
    }
  }
}

double **constructBigArray(double top, double bottom, double left, 
    double right, long unsigned int n) {
  long unsigned int i, j, k;
  double **arr = (double **) malloc(n * sizeof(double *));
  for (k = 0; k < n; k++) {
    arr[k] = (double *) malloc(n * sizeof(double));
  }
  for (i = 0; i < n; i++) {
    for (j = 0; j < n; j++) {
      if (i == 0) {
        if (j == 0 || j == n - 1) arr[i][j] = 0;
        else arr[i][j] = top;
      } else if (i == n - 1) {
        if (j == 0 || j == n - 1) arr[i][j] = 0;
        else arr[i][j] = bottom;
      } else if (j == 0) {
        arr[i][j] = left;
      } else if (j == n - 1) {
        arr[i][j] = right;
      } else {
        arr[i][j] = 0;
      }
    }
  }
  return arr;
}

typedef struct arg_data {
  double precision;
  unsigned long dimension;
  double top_start;
  double bottom_start;
  double left_start;
  double right_start;
} ARG_DATA_T;

int argsContain(const char *val, char **arr, int size) {
  int i;
  for (i = 0; i < size; i++) {
    if (strcmp(arr[i], val) == 0)
      return i;
  }
  return -1;
}

ARG_DATA_T *parseArgs(int argc, char **argv) {
  int tmp;
  ARG_DATA_T *args = (ARG_DATA_T *) malloc(sizeof(ARG_DATA_T));
  allow_print = true;
  if ((tmp = argsContain("-p", argv, argc)) >= 0 || 
      (tmp = argsContain("--precision", argv, argc)) >= 0) {
    args->precision = strtod(argv[tmp + 1], NULL);
  } else {
    args->precision = 0.00001;
  }
  if ((tmp = argsContain("-d", argv, argc)) >= 0 
      || (tmp = argsContain("--dimension", argv, argc)) >= 0) {
    args->dimension = (unsigned long) strtol(argv[tmp + 1], NULL, 10);
  } else {
    args->dimension = 10;
  }
  if ((tmp = argsContain("-t", argv, argc)) >= 0 
      || (tmp = argsContain("--top", argv, argc)) >= 0) {
    args->top_start = strtod(argv[tmp + 1], NULL);
  } else {
    args->top_start = 1;
  }
  if ((tmp = argsContain("-l", argv, argc)) >= 0 
      || (tmp = argsContain("--left", argv, argc)) >= 0) {
    args->left_start = strtod(argv[tmp + 1], NULL);
  } else {
    args->left_start = 2;
  }
  if ((tmp = argsContain("-r", argv, argc)) >= 0 
      || (tmp = argsContain("--right", argv, argc)) >= 0) {
    args->right_start = strtod(argv[tmp + 1], NULL);
  } else {
    args->right_start = 4;
  }
  if ((tmp = argsContain("-b", argv, argc)) >= 0 
      || (tmp = argsContain("--bottom", argv, argc)) >= 0) {
    args->bottom_start = strtod(argv[tmp + 1], NULL);
  } else {
    args->bottom_start = 3;
  }
  if ((tmp = argsContain("-q", argv, argc)) > 0 ||
      (tmp = argsContain("--quiet", argv, argc)) >= 0) {
    allow_print = false;
  }
  if (argsContain("-h", argv, argc) >= 0 
      || argsContain("--help", argv, argc) >= 0) {
    printf("Usage: %s [-p N] [-d N] [-t N] [-l N] [-r N] [-b N]\n",
        argv[0]);
    printf("Constructs a 2D array of doubles, with values from arguments "
        "of size dimension^2 and performs relaxation method"
        " to given precision.\n");
    printf("Options:\n");
    printf("-p/--precision: A double value to specify precision. "
        "Default: 0.0001\n");
    printf("-d/--dimension: A long value to specify width and height of "
        "grid. Default: 10\n");
    printf("-t/--top: A double indicating the values along the top of the "
        "array. Default: 1.0\n");
    printf("-l/--left: A double indicating the values along the left side"
        " of the array. Default: 2.0\n");
    printf("-b/--bottom: A double indicating the values along the bottom "
        "of the array. Default: 3.0\n");
    printf("-r/--right: A double indicating the values along the right "
        "side of the array. Default: 4.0\n");
    printf("-q/--quiet: Disables all printing except the result.\n");
    exit(0);
  }
  return args;
}


int main(int argc, char **argv) {
  unsigned long iter;
  ARG_DATA_T *args;

  args = parseArgs(argc, argv);

  double **array = constructBigArray(args->top_start, args->bottom_start, 
      args->left_start, args->right_start, args->dimension);

  iter = solveArray(array, args->dimension, args->precision);
  if (allow_print) printf("completed with iters: %lu\n", iter);
  printSquare(array, args->dimension);

}