#include "internal.h"

static const char *month_names[] = {
  "Jan", "Feb", "Mar", "Apr", "May", "Jun",
  "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};

// Convert month to the month number. Return -1 on error, or month number
static int get_month_index(const char *s) {
  int i;

  for (i = 0; i < (int) ARRAY_SIZE(month_names); i++)
    if (!strcmp(s, month_names[i]))
      return i;

  return -1;
}

static int num_leap_years(int year) {
  return year / 4 - year / 100 + year / 400;
}

// Parse UTC date-time string, and return the corresponding time_t value.
static time_t parse_date_string(const char *datetime) {
  static const unsigned short days_before_month[] = {
    0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
  };
  char month_str[32];
  int second, minute, hour, day, month, year, leap_days, days;
  time_t result = (time_t) 0;

  if (((sscanf(datetime, "%d/%3s/%d %d:%d:%d",
               &day, month_str, &year, &hour, &minute, &second) == 6) ||
       (sscanf(datetime, "%d %3s %d %d:%d:%d",
               &day, month_str, &year, &hour, &minute, &second) == 6) ||
       (sscanf(datetime, "%*3s, %d %3s %d %d:%d:%d",
               &day, month_str, &year, &hour, &minute, &second) == 6) ||
       (sscanf(datetime, "%d-%3s-%d %d:%d:%d",
               &day, month_str, &year, &hour, &minute, &second) == 6)) &&
      year > 1970 &&
      (month = get_month_index(month_str)) != -1) {
    leap_days = num_leap_years(year) - num_leap_years(1970);
    year -= 1970;
    days = year * 365 + days_before_month[month] + (day - 1) + leap_days;
    result = days * 24 * 3600 + hour * 3600 + minute * 60 + second;
  }

  return result;
}