/*
 *
 * Created: 29.03.2018
 *
 * Authors:
 *
 * Assembled from the code released on Stackoverflow by:
 *   Dennis (instructable.com/member/nqtronix)    |
 * https://stackoverflow.com/questions/23032002/c-c-how-to-get-integer-unix-timestamp-of-build-time-not-string
 * and
 *   Alexis Wilke                                 |
 * https://stackoverflow.com/questions/10538444/do-you-know-of-a-c-macro-to-compute-unix-time-and-date
 *
 * Assembled by Jean Rabault
 *
 * UNIX_TIMESTAMP gives the UNIX timestamp (unsigned long integer of seconds
 * since 1st Jan 1970) of compilation from macros using the compiler defined
 * __TIME__ macro. This should include Gregorian calendar leap days, in
 * particular the 29ths of February, 100 and 400 years modulo leaps.
 *
 * Careful: __TIME__ is the local time of the computer, NOT the UTC time in
 * general!
 *
 */

#ifndef COMPILE_TIME_H_
#define COMPILE_TIME_H_

// Some definitions for calculation
#define SEC_PER_MIN 60UL
#define SEC_PER_HOUR 3600UL
#define SEC_PER_DAY 86400UL
#define SEC_PER_YEAR (SEC_PER_DAY * 365)

// extracts 1..4 characters from a string and interprets it as a decimal value
#define CONV_STR2DEC_1(str, i) (str[i] > '0' ? str[i] - '0' : 0)
#define CONV_STR2DEC_2(str, i) (CONV_STR2DEC_1(str, i) * 10 + str[i + 1] - '0')
#define CONV_STR2DEC_3(str, i) (CONV_STR2DEC_2(str, i) * 10 + str[i + 2] - '0')
#define CONV_STR2DEC_4(str, i) (CONV_STR2DEC_3(str, i) * 10 + str[i + 3] - '0')

// Custom "glue logic" to convert the month name to a usable number
#define GET_MONTH(str, i)                                         \
  (str[i] == 'J' && str[i + 1] == 'a' && str[i + 2] == 'n'   ? 1  \
   : str[i] == 'F' && str[i + 1] == 'e' && str[i + 2] == 'b' ? 2  \
   : str[i] == 'M' && str[i + 1] == 'a' && str[i + 2] == 'r' ? 3  \
   : str[i] == 'A' && str[i + 1] == 'p' && str[i + 2] == 'r' ? 4  \
   : str[i] == 'M' && str[i + 1] == 'a' && str[i + 2] == 'y' ? 5  \
   : str[i] == 'J' && str[i + 1] == 'u' && str[i + 2] == 'n' ? 6  \
   : str[i] == 'J' && str[i + 1] == 'u' && str[i + 2] == 'l' ? 7  \
   : str[i] == 'A' && str[i + 1] == 'u' && str[i + 2] == 'g' ? 8  \
   : str[i] == 'S' && str[i + 1] == 'e' && str[i + 2] == 'p' ? 9  \
   : str[i] == 'O' && str[i + 1] == 'c' && str[i + 2] == 't' ? 10 \
   : str[i] == 'N' && str[i + 1] == 'o' && str[i + 2] == 'v' ? 11 \
   : str[i] == 'D' && str[i + 1] == 'e' && str[i + 2] == 'c' ? 12 \
                                                             : 0)

// extract the information from the time string given by __TIME__ and __DATE__
#define __TIME_SECONDS__ CONV_STR2DEC_2(__TIME__, 6)
#define __TIME_MINUTES__ CONV_STR2DEC_2(__TIME__, 3)
#define __TIME_HOURS__ CONV_STR2DEC_2(__TIME__, 0)
#define __TIME_DAYS__ CONV_STR2DEC_2(__DATE__, 4)
#define __TIME_MONTH__ GET_MONTH(__DATE__, 0)
#define __TIME_YEARS__ CONV_STR2DEC_4(__DATE__, 7)

// Days in February
#define _UNIX_TIMESTAMP_FDAY(year) \
  (((year) % 400) == 0UL ? 29UL    \
                         : (((year) % 100) == 0UL ? 28UL : (((year) % 4) == 0UL ? 29UL : 28UL)))

// Days in the year
#define _UNIX_TIMESTAMP_YDAY(year, month, day)                                             \
  (/* January */ day /* February */ + (month >= 2 ? 31UL : 0UL) /* March */ +              \
   (month >= 3 ? _UNIX_TIMESTAMP_FDAY(year) : 0UL) /* April */ +                           \
   (month >= 4 ? 31UL : 0UL) /* May */ + (month >= 5 ? 30UL : 0UL) /* June */ +            \
   (month >= 6 ? 31UL : 0UL) /* July */ + (month >= 7 ? 30UL : 0UL) /* August */ +         \
   (month >= 8 ? 31UL : 0UL) /* September */ + (month >= 9 ? 31UL : 0UL) /* October */ +   \
   (month >= 10 ? 30UL : 0UL) /* November */ + (month >= 11 ? 31UL : 0UL) /* December */ + \
   (month >= 12 ? 30UL : 0UL))

// get the UNIX timestamp from a digits representation
#define _UNIX_TIMESTAMP(year, month, day, hour, minute, second)                              \
  (/* time */ second + minute * SEC_PER_MIN + hour * SEC_PER_HOUR +                          \
   /* year day (month + day) */ (_UNIX_TIMESTAMP_YDAY(year, month, day) - 1) * SEC_PER_DAY + \
   /* year */ (year - 1970UL) * SEC_PER_YEAR + ((year - 1969UL) / 4UL) * SEC_PER_DAY -       \
   ((year - 1901UL) / 100UL) * SEC_PER_DAY + ((year - 1601UL) / 400UL) * SEC_PER_DAY)

// the UNIX timestamp
#define UNIX_TIMESTAMP                                                            \
  (_UNIX_TIMESTAMP(__TIME_YEARS__, __TIME_MONTH__, __TIME_DAYS__, __TIME_HOURS__, \
                   __TIME_MINUTES__, __TIME_SECONDS__))

#endif