Merge pull request #1362 from alphagov/letter-delivery-estimates

Add function to estimate letter delivery date

app/__init__.py

@@ -7,7 +7,6 @@ from time import monotonic
 
 import dateutil
 import itertools
-import pytz
 import ago
 from flask import (
     Flask,
@@ -55,6 +54,8 @@ from app.notify_client.organisations_client import OrganisationsClient
 from app.notify_client.models import AnonymousUser
 from app.notify_client.letter_jobs_client import LetterJobsClient
 
+from app.utils import gmt_timezones
+
 login_manager = LoginManager()
 csrf = CsrfProtect()
 
@@ -212,12 +213,6 @@ def syntax_highlight_json(code):
     return Markup(highlight(code, JavascriptLexer(), HtmlFormatter(noclasses=True)))
 
 
-def gmt_timezones(date):
-    date = dateutil.parser.parse(date)
-    forced_utc = date.replace(tzinfo=pytz.utc)
-    return forced_utc.astimezone(pytz.timezone('Europe/London'))
-
-
 def format_datetime(date):
     return '{} at {}'.format(
         format_date(date),

app/utils.py

@@ -1,10 +1,13 @@
 import re
 import csv
+import pytz
 from io import StringIO
 from os import path
 from functools import wraps
 import unicodedata
+from collections import namedtuple
 from datetime import datetime, timedelta, timezone
+from dateutil import parser
 
 import dateutil
 import ago
@@ -324,3 +327,40 @@ def get_time_left(created_at):
 
 def email_or_sms_not_enabled(template_type, permissions):
     return (template_type in ['email', 'sms']) and (template_type not in permissions)
+
+
+def get_letter_timings(upload_time):
+
+    LetterTimings = namedtuple(
+        'LetterTimings',
+        'printed_by, is_printed, earliest_delivery, latest_delivery'
+    )
+
+    # shift anything after 5pm to the next day
+    processing_day = gmt_timezones(upload_time) + timedelta(hours=(7))
+
+    print_day, earliest_delivery, latest_delivery = (
+        processing_day + timedelta(days=days)
+        for days in {
+            'Wednesday': (1, 3, 5),
+            'Thursday': (1, 4, 5),
+            'Friday': (3, 5, 6),
+            'Saturday': (2, 4, 5),
+        }.get(processing_day.strftime('%A'), (1, 3, 4))
+    )
+
+    printed_by = print_day.astimezone(pytz.timezone('Europe/London')).replace(hour=15, minute=0)
+    now = datetime.utcnow().replace(tzinfo=pytz.timezone('Europe/London'))
+
+    return LetterTimings(
+        printed_by=printed_by,
+        is_printed=(now > printed_by),
+        earliest_delivery=earliest_delivery,
+        latest_delivery=latest_delivery,
+    )
+
+
+def gmt_timezones(date):
+    date = dateutil.parser.parse(date)
+    forced_utc = date.replace(tzinfo=pytz.utc)
+    return forced_utc.astimezone(pytz.timezone('Europe/London'))