#include <limits.h>
#include <pthread.h>

#include "suma.h"

enum { NTHREADS = 8 };

typedef struct {
  int *a;
  int n;
  Set start;
  Set end;
  Set found;
} BuscarArgs;

static Set total_combinaciones(int n) {
  if (n >= (int)(sizeof(Set) * CHAR_BIT))
    return ~(Set)0;
  return ((Set)1 << n) - 1;
}

static Set buscar_rango(int a[], int n, Set start, Set end) {
  if (start == 0 || start > end)
    return 0;

  Set k = start;
  while (1) {
    long long sum = 0;

    for (int i = 0; i < n; i++) {
      if (k & ((Set)1 << i))
        sum += a[i];
    }

    if (sum == 0)
      return k;

    if (k == end)
      break;
    k++;
  }

  return 0;
}

static void *buscar_thread(void *ptr) {
  BuscarArgs *args = ptr;
  args->found = buscar_rango(args->a, args->n, args->start, args->end);
  return NULL;
}

Set buscar(int a[], int n) {
  Set comb = total_combinaciones(n);
  Set base = comb / NTHREADS;
  Set extra = comb % NTHREADS;
  Set next = 1;
  pthread_t tids[NTHREADS];
  BuscarArgs args[NTHREADS];
  int created = 0;

  for (int t = 0; t < NTHREADS; t++) {
    Set len = base + (Set)(t < (int)extra);

    args[t].a = a;
    args[t].n = n;
    args[t].start = next;
    args[t].end = (len == 0) ? next - 1
                             : (t == NTHREADS - 1 ? comb : next + len - 1);
    args[t].found = 0;

    if (len != 0)
      next = args[t].end + 1;

    if (pthread_create(&tids[t], NULL, buscar_thread, &args[t]) != 0) {
      for (int i = 0; i < created; i++)
        pthread_join(tids[i], NULL);
      return buscar_rango(a, n, 1, comb);
    }
    created++;
  }

  Set best = 0;
  for (int t = 0; t < NTHREADS; t++) {
    pthread_join(tids[t], NULL);
    if (args[t].found != 0 && (best == 0 || args[t].found < best))
      best = args[t].found;
  }

  return best;
}