#! /bin/sh

DC=dc
#DC="sed -nf /cygdrive/e/Projects/bag/scripts/dc.sed"

if [ "x$1" = x ]; then
  year=`date "+%Y"`
else
  year=$1
fi

leap=`echo $year | sed -n 's/00$//
  # Test divisibility by 4
  /[02468][048]$/d
  /[13579][26]$/! s/.*/29/p' `

# Transform year into a dc script that computes
#   stacktop = stacktop-1
#   z = stacktop / 100
#   stacktop + stacktop / 4 - z + z/4 + 1
# And prints stacktop % 7, 12 times
sed1='s,$, 1-dd100/sz4/+lz-lz4/+1+d7/7*-pppppppppppp,'

# Make the real calendar
sed2='
  # Add the blanks to the first line, depending on the week-day
  1!g
  /^[1-6]/ s/$/    /
  /^[2-6]/ s/$/    /
  /^[3-6]/ s/$/    /
  /^[4-6]/ s/$/    /
  /^[5-6]/ s/$/    /
  /^6/     s/$/    /
  s/^[0-6]//

  # Then add the days
  s/$/  1   2   3   4   5   6   7   8   9  10  11  12  13  14 /
  s/$/ 15  16  17  18  19  20  21  22  23  24  25  26  27  28  29 /

  # Pick the number of days in the month
  2 s/ '"$leap"' $//
  2!s/$/ 30  31 /
  4 s/ 31 //
  6 s/ 31 //
  9 s/ 31 //
  11 s/ 31 //

  # Provide a little sugar
  =
  i\
Sun Mon Tue Wed Thu Fri Sat
  a\

  # Split the calendar in 27-character lines
  s/\([^\n]\{27\}\) /\1\
/g
  
  # Save the blanks in the last line, so that they we use
  # them for the next month, and print the last line
  h
  s/.*\n//
  s/./ /g
  x
'

# Go!
echo $year | sed "$sed1" | $DC | sed "$sed2"