#!/usr/bin/env python
"""
dtu - A Collecton of Datetime Utilities.
License: GPL 2; share and enjoy!
Author: Sean B. Palmer, inamidst.com
"""

import sys, re, datetime

# Utility functions

r_date = re.compile(r'(\d{4})-(\d{2})-(\d{2})')
def date(s): 
   m = r_date.match(s)
   if not m: 
      raise "ParseError", "Invalid date: %s" % s
   intify = lambda s: int(s.lstrip('0'))
   year, month, day = tuple(map(intify, m.groups()))
   return datetime.datetime(year=year, month=month, day=day)

def datenow(): 
   try: return datetime.datetime.now()
   except ValueError: 
      import time
      t = time.gmtime()
      parts = {'year': int(time.strftime('%Y', t)), 
               'month': int(time.strftime('%m', t)), 
               'day': int(time.strftime('%d', t)), 
               'hour': int(time.strftime('%H', t)), 
               'minute': int(time.strftime('%M', t)), 
               'second': int(time.strftime('%S', t))}
      print >> sys.stderr, "Warning: problem generating datenow."
      return datetime.datetime(**parts)

def delta(s): 
   s = ['0', '0'] + s.split(':')
   secs = int(s.pop().lstrip('0') or '0')
   mins = int(s.pop().lstrip('0') or '0')
   hours = int(s.pop().lstrip('0') or '0')
   return datetime.timedelta(hours=hours, minutes=mins, seconds=secs)

def format(t): 
   fmt = '%Y-%m-%d'
   if t.hour: 
      fmt += ' %H:%M'
      if t.second: fmt += ':%S'
   return t.strftime(fmt)

# Main commands
commands = {}

def diff(then, now=None): 
   """diff <then> <now>? - Return the interval between then and now."""
   if now is None: 
      now = datenow()
   else: now = date(now)

   then = date(then)
   if then < now: 
      return '-' + str(now - then)
   else: return str(then - now)
commands['diff'] = diff

def hop(step, times=None, now=None): 
   """hop <step> <rpt>? <now>? - Give rpt hops from now given step."""
   # @@ Whoo! Lamest documentation evvah!
   if now is None: 
      now = datenow()
   else: now = date(now)
   if times is None: 
      times = 1
   else: times = abs(int(times) or 1)

   if step.startswith('+') or step.startswith('-'): 
      step = int(step)
      step = datetime.timedelta(days=step)
   else: step = delta(step)

   result = []
   for i in xrange(times): 
      now = now + step
      if times > 1: 
         result.append(str(i + 1) + ') ' + format(now))
      else: result.append(format(now))
   return "\n".join(result)
commands['hop'] = hop

def info(t): 
   """info <date> - Give information about date."""
   t = date(t)
   result = [t.strftime('%d %B: a %A. Day #%j in the year.')]
   return "\n".join(result)
commands['info'] = info

def help(command=None): 
   """help <command>? - Provide help on a command."""
   if command is None: 
      return documentation()

   if commands.has_key(command): 
      return commands[command].__doc__
   elif command == 'help': 
      return help.__doc__
   else: return "Can't provide help for command %r." % command
commands['help'] = help

def documentation(): 
   result = [__doc__]
   result.append("Valid commands: ")
   for command in commands.keys(): 
      result.append("   " + commands[command].__doc__)
   return "\n".join(result).lstrip()

def main(args=None): 
   if args is None: 
      args = sys.argv[1:]

   if (len(args) < 2): 
      print >> sys.stderr, documentation()
      sys.exit(1)
   if not commands.has_key(args[0]): 
      print >> sys.stderr, "Unknown command: %s" % args[0]
      print >> sys.stderr, "Try ./%s help" % sys.argv[0]
      sys.exit(1)
   else: print commands[args[0]](*args[1:])

if __name__=="__main__": 
   main()