datematch.py

'''
Copyright 2013 Paul Sidnell

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
'''

import re
from datetime import datetime, timedelta

def hunt_for_day (now, dow, forward, match_today = False):
    direction = -1
    start = 1
    if forward:
        direction = 1
    if match_today:
        start = 0
    for days in range (start, 8):
        next_date = now + timedelta(days=days*direction)
        next_dow = next_date.strftime ('%A').lower()
        if next_dow.startswith (dow):
            return next_date
    return None

def find_first_of_month (now):
    year = now.year
    month = now.month
    return datetime.strptime(str(year) + '-' + str(month) + '-01', '%Y-%m-%d')

def find_next_month (now):
    in_next_month = find_first_of_month (now) + timedelta(days=33)
    return find_first_of_month (in_next_month)

def find_prev_month (now):
    in_last_month = find_first_of_month (now) + timedelta(days=-1)
    return find_first_of_month (in_last_month)

def find_end_of_month (now):
    first_of_this_month = find_first_of_month (now)
    first_of_next_month = find_next_month (first_of_this_month)
    return first_of_next_month - timedelta (days=1)
    
def hunt_for_month (now, month_to_find, forward, match_this_month = False):
    month = None
    if not match_this_month:
        if forward:
            month = find_next_month (now)
        else:
            month = find_prev_month (now)
    else:
        month = find_first_of_month (now)
        
    for i in range (0, 12):
        i = i # stop warning
        month_name = month.strftime ('%B').lower()
        if month_name.startswith (month_to_find):
            return month
        if forward:
            month = find_next_month (month)
        else:
            month = find_prev_month (month)
    return None

def find_monday_this_week (now):
    return hunt_for_day (now, 'mo', False, match_today=True)

def find_monday_next_week (now):
    return hunt_for_day (now, 'mo', True, match_today=False)

def find_january_this_year (now):
    year = now.year
    return datetime.strptime(str(year) + '-01-01', '%Y-%m-%d')

def date_from_string (now, date_str):
    if date_str == "today":
        return now
    elif date_str == 'yesterday':
        return now + timedelta(days=-1)
    elif date_str == 'tomorrow':
        return now + timedelta(days=1)
    elif re.match ('^next (mo|tu|we|th|fr|sa|su)', date_str) != None:
        dow = date_str[4:].strip ()
        next_monday = find_monday_next_week (now)
        return hunt_for_day (next_monday, dow, True, match_today=True)
    elif re.match ('^last (mo|tu|we|th|fr|sa|su)', date_str) != None:
        dow = date_str[4:].strip ()
        this_monday = find_monday_this_week (now)
        return hunt_for_day (this_monday, dow, False)
    elif re.match ('^(mo|tu|we|th|fr|sa|su)', date_str) != None:
        dow = date_str.strip ()
        monday = find_monday_this_week (now)
        return hunt_for_day (monday, dow, True, match_today=True)
    elif re.match ('^(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)', date_str) != None:
        month = date_str.strip ()
        jan = find_january_this_year (now)
        return hunt_for_month (jan, month, True, match_this_month=True)
    elif re.match ('^next (jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)', date_str) != None:
        month_str = date_str[4:].strip ()
        jan = find_january_this_year (now)
        month = hunt_for_month (jan, month_str, True, match_this_month=True).month
        year = now.year
        return datetime.strptime(str(year + 1) + '-' + str(month) + '-01', '%Y-%m-%d')
    elif re.match ('^last (jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)', date_str) != None:
        month_str = date_str[4:].strip ()
        jan = find_january_this_year (now)
        return hunt_for_month (jan, month_str, False, match_this_month=False)
    elif re.match ('^[0-9][0-9][0-9][0-9]-[01][0-9]-[0-3][0-9]$', date_str) != None:
        return datetime.strptime(date_str, '%Y-%m-%d')
    else:
        return None
    
def tidy_space_separated_fields (string):
    # eliminate multiple spaces
    elements = str.split (string)
    return ' '.join(elements)

def process_date_specifier (now, date_spec):
    date_spec = tidy_space_separated_fields (date_spec).lower()
    
    if date_spec == '' or date_spec == 'none':
        return (None, None)
    if date_spec == '' or date_spec == 'any':
        # This is a bit of a hack
        return (datetime.strptime ('1900-01-01', '%Y-%m-%d'), datetime.strptime ('9000-01-01', '%Y-%m-%d'))
    
    match_date = date_from_string (now, date_spec)
    if match_date != None:
        # We've found a single stand alone date, not a range.
        # But if it's a month we want to convert it into a range
        
        if re.match ('(next |last )?(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)', date_spec) != None:
            return (match_date, find_end_of_month (match_date))
        else:    
            return (match_date, match_date)
    
    if date_spec == 'this week':
        mon = find_monday_this_week (now)
        sun = hunt_for_day (now, 'sun', True, match_today=True)
        return (mon, sun)
    elif date_spec == 'next week':
        mon = find_monday_this_week (now) + timedelta(days=7)
        sun = hunt_for_day (now, 'sun', True, match_today=True) + timedelta(days=7)
        return (mon, sun)
    elif date_spec == 'last week':
        mon = find_monday_this_week (now) - timedelta(days=7)
        sun = hunt_for_day (now, 'sun', True, match_today=True) - timedelta(days=7)
        return (mon, sun)
    elif date_spec.startswith ('from '):
        date_str = date_spec[4:].strip()
        start =  date_from_string (now, date_str)
        return (start, None)
    elif date_spec.startswith ('to '):
        date_str = date_spec[2:].strip()
        end =  date_from_string (now, date_str)
        if re.match ('.*(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)', date_str) != None:
            end = find_end_of_month (end)
        return (None, end)
    elif re.search (' to ', date_spec) != None:
        elements = str.split (date_spec, ' to ')
        elements = [x.strip() for x in elements if len (x) > 0]
        start = date_from_string(now, elements[0])
        end = date_from_string(now, elements[1])
        if re.match ('.*(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)', elements[1]) != None:
            end = find_end_of_month (end)
        return (start, end)
    else:
        raise Exception ('I don\'t think "' + date_spec + '" is any kind of date specification I recognise')