#!/bin/bash
# valid-date--Validates a date, taking into account leap year rules.

setglobal PATH = ".:$PATH"

proc exceedsDaysInMonth
{
  # Given a month name and day number in that month, this function will 
  #   return 0 if the specified day value is less than or equal to the 
  #   max days in the month; 1 otherwise.

  match $[echo $1|tr '[:upper:]' '[:lower:]] {
    with jan*  setglobal days = '31'      with feb*  setglobal days = '28'    
    with mar*  setglobal days = '31'      with apr*  setglobal days = '30'    
    with may*  setglobal days = '31'      with jun*  setglobal days = '30'    
    with jul*  setglobal days = '31'      with aug*  setglobal days = '31'    
    with sep*  setglobal days = '30'      with oct*  setglobal days = '31'    
    with nov*  setglobal days = '30'      with dec*  setglobal days = '31'    
    with *  echo "$0: Unknown month name $1" > !2; exit 1
  }
   if test $2 -lt 1 -o $2 -gt $days  {
     return 1
   } else {
     return 0   # the day number is valid 
   } 
}

proc isLeapYear
{    
  # This function returns 0 if the specified year is a leap year; 
  #   1 otherwise.
  # The formula for checking whether a year is a leap year is: 
  #   1. Years not divisible by 4 are not leap years.
  #   2. Years divisible by 4 and by 400 are leap years.
  #   3. Years divisible by 4, not divisible by 400, and divisible by
  #   100, are not leap years.
  #   4. All other years divisible by 4 are leap years.

  setglobal year = $1
  if test "$shExpr('year % 4')" -ne 0  {
    return 1 # nope, not a leap year
  } elif test "$shExpr('year % 400')" -eq 0  {
    return 0 # yes, it's a leap year
  } elif test "$shExpr('year % 100')" -eq 0  {
    return 1
  } else {
     return 0
  } 
}

# BEGIN MAIN SCRIPT
# =================

#if [ $# -ne 3 ] ; then
#  echo "Usage: $0 month day year" >&2
#  echo "Typical input formats are August 3 1962 and 8 3 2002" >&2
#  exit 1
#fi

# Normalize date and store the return value to check for errors.

#newdate="$(normdate "$@")"
#echo $newdate
#if [ $? -eq 1 ] ; then
#  exit 1        # Error condition already reported by normdate
#fi

# Split the normalized date format, where
# first word = month, second word = day, third word = year.

#month="$(echo $newdate | cut -d\  -f1)"
#day="$(echo $newdate | cut -d\  -f2)"
#year="$(echo $newdate | cut -d\  -f3)"

# Now that we have a normalized date, let's check to see if the
#   day value is legal and valid (e.g., not Jan 36).

#if ! exceedsDaysInMonth $month "$2" ; then
#  if [ "$month" = "Feb" -a "$2" -eq "29" ] ; then
#    if ! isLeapYear $3 ; then
#      echo "$0: $3 is not a leap year, so Feb doesn't have 29 days" >&2
#      exit 1
#    fi
#  else 
#    echo "$0: bad day value: $month doesn't have $2 days" >&2
#    exit 1
#  fi
#fi

#echo "Valid date: $newdate"

#exit 0