validDate

#!/bin/bash

function exceededDaysInMonth
{
  case $(echo $1 | tr '[:upper:]' '[:lower:]') in
    jan* ) days=31 ;;
    feb* ) days=28 ;;
    mar* ) days=31 ;;
    apr* ) days=30 ;;
    may* ) days=31 ;;
    jun* ) days=30 ;;
    jul* ) days=31 ;;
    aug* ) days=31 ;;
    sep* ) days=30 ;;
    oct* ) days=31 ;;
    nov* ) days=30 ;;
    dec* ) days=31 ;;
    * ) echo "$(basename $0): Unknown month $1" >&2
      exit 1
  esac

  if [ $2 -lt 1 -o $2 -gt $days ]
  then
    return 1
  else
    return 0
  fi 
}

function isLeapYear
{
  #return 0 if it is a leap year
  # 1 otherwise
  year=$1
  if [ $((year%4)) -ne 0 ]; then
    return 1
  elif [ $((year%400)) -eq 0 ]; then
    return 0
  elif [ $((year%100)) -eq 0 ];then
    return 1
  else
    return 0
  fi
}

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

newdate=$(normdate "$@")
if [ $? -eq 1 ]
then
  exit 1
fi

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

if ! exceededDaysInMonth $month $day; then
  if [ "$month" = "Feb" -a "$day" -eq 29 ]; then
    if ! isLeapYear $year; then
      echo "$(basename $0): Not a leap year, so Feb doesn't have 29 days" >&2
      exit 1
    fi
  else
    echo "$(basename $0): bad day value, $month does not have $day days" >&2
    exit 1
  fi
fi

echo "valid date: $newdate"
exit 0