#! /usr/bin/gawk -f
# Last edited on 2009-12-12 00:01:40 by stolfi

# GAWK library ment to be included in other GAWk programs with "-f"

function   date_time_init() 
{
  # To be called before any other proc of this package.

  split("", days_before); # Days in year before 1st of each month, leap years.
  days_before[ 1] =   0;
  days_before[ 2] =  31;
  days_before[ 3] =  60;
  days_before[ 4] =  91;
  days_before[ 5] = 121;
  days_before[ 6] = 152;
  days_before[ 7] = 182;
  days_before[ 8] = 213;
  days_before[ 9] = 244;
  days_before[10] = 274;
  days_before[11] = 305;
  days_before[12] = 335;
  
  # check_date_conversion();
      
}

function time_from_date(yz,yr,mo,da,  tt)
{ 
  # Day count since Jan 01, Year {yz}.
  
  # First assume that all years are leap years:
  tt = (yr-yz)*366 + days_before[mo] + (da-1);
  tt = unleap_year_adjust(yz,tt);
  return tt;
}

function date_from_time(yz,tt,  tx,yr,mo,da)
{ 
  # Convert day count back to date in format "{YEAR} {MONTH} {DAY}".
  
  # Adjust {tt} by inserting a feb/29 in eevry non-leap year:
  tx = unleap_year_unadjust(yz,tt);
  
  # Now split {tt} assuming all years are leap years:
  yr = yz + int(tx/366);
  tx = tx % 366;
  mo = 1;
  while ((mo < 12) && (tx >= days_before[mo+1])) { mo++; }
  da = tx - days_before[mo] + 1;
  # Consistency check:
  tz = time_from_date(yz,yr,mo,da);
  if (tz != tt)
    { data_error(("date bug [" tt " --> " yr "-" mo "-" da "]"), lin); }
  return sprintf("%04d %02d %02d", yr, mo, da);
}

function unleap_year_adjust(yz,tt,   k,yk,tk)
{
  # The leap years were ..., 2000, 2004, 2008, 2012, ...
  # Slow but at least it works.
  for (k = 30; k >= 0; k--)
    { yk = yz + k;
      if ((yk % 4) != 0)
        { # Compute and exclude 29 feb:
          tk = k*366 + 31 + 28;
          if (tt == tk) { data_error(("invalid date [" tt " --> " yr "-" mo "-" da "]"), lin); }
          if (tt > tk) { tt--; }
        }
    }
  return tt;
}

function unleap_year_unadjust(yz,tt,   k,yk,tk)
{
  # The leap years were ..., 2000, 2004, 2008, 2012, ...
  # Slow but at least it works.
  for (k = 0; k <= 30; k++)
    { yk = yz + k;
      if ((yk % 4) != 0) 
        { # Compute and include dummy 29 feb:
          tk = k*366 + 31 + 28;
          if (tt >= tk) { tt++; }
        }
    }
  return tt;
}

function date_time_sanity_check(yz,  yr,mo,da,du,tt,dt1,dt2,tk)
{
  # Testing date conversion
  printf "\n" > "/dev/stderr";
  tk = 0;
  for (yr = yz; yr < yz + 10; yr++)
    { printf "--- %s ---\n", yr > "/dev/stderr";
      for (mo = 1; mo <= 12; mo++) 
        { # Compute month's duration {du}:
          du = 31;
          if (mo == 2)
            { du = 28 + (yr % 4 == 0); }
          else if ((mo == 4) || (mo == 6) || (mo == 9) || (mo == 11))
            { du = 30; }
          
          for (da = 1; da <= du; da++)
            { 
              tt = time_from_date(yz,yr,mo,da);
              dt1 = sprintf("%04d %02d %02d", yr, mo, da)
              dt2 = date_from_time(yz,tt);
              printf "%s --> %8d --> %s\n", dt1, tt, dt2 > "/dev/stderr";
              if (tk != tt) 
                { data_error(("date bug [" tk "] [" tt "]"), lin); }
              if (dt1 != dt2) 
                { data_error(("date bug [" dt1 "] [" dt2 "]"), lin); }
              tk++;
            }
        }
    }
}