From 70ac35b2a5b0640e6ebc6ceacd04ae7fdd32ad95 Mon Sep 17 00:00:00 2001
From: Debanjum Singh Solanky <debanjum@gmail.com>
Date: Thu, 14 Jul 2022 18:20:09 +0400
Subject: [PATCH] Compute Date Range to filter entries to, from Comparators,
 Dates in Query

---
 src/search_filter/date_filter.py | 44 ++++++++++++++++++++++++++++++++
 tests/test_date_filter.py        | 14 +++++++++-
 2 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/src/search_filter/date_filter.py b/src/search_filter/date_filter.py
index fe7ee5e5..b1c2cadc 100644
--- a/src/search_filter/date_filter.py
+++ b/src/search_filter/date_filter.py
@@ -45,6 +45,50 @@ def date_filter(query, entries, embeddings):
 
     return query, entries, embeddings
 
+
+def extract_date_range(query):
+    # find date range filter in query
+    date_range_match = re.search(date_range_regex, query)
+    if not date_range_match or date_range_match.groups() == (None, None, None, None):
+        return None
+
+    # extract, parse natural dates ranges from date range filter passed in query
+    # e.g today maps to (start_of_day, start_of_tomorrow)
+    query_dtranges = []
+    for date_str in date_range_match.groups()[1::2]:
+        if date_str and parse(date_str):
+            dt_start, dt_end = parse(date_str)
+            query_dtranges.append((dt_start.timestamp(), dt_end.timestamp()))
+
+    date_comparators = [date_cmp for date_cmp in date_range_match.groups()[0::2] if date_cmp]
+
+    # Combine dates with their comparators to form date range intervals
+    # For e.g
+    #   >=yesterday maps to [start_of_yesterday, inf)
+    #   <tomorrow maps to [0, start_of_tomorrow)
+    # Then combine above intervals (via AND/intersect)
+    # In the above example, this gives us [start_of_yesterday, start_of_tomorrow)
+    # This is the effective date range to filter entries by
+    # ---
+    effective_date_range = [0, inf]
+    for ((dtrange_start, dtrange_end), cmp) in zip(query_dtranges, date_comparators):
+        if cmp == '>' and dtrange_end < effective_date_range[1]:
+            effective_date_range[0] = dtrange_end
+        elif cmp == '<' and dtrange_start > effective_date_range[0]:
+            effective_date_range[1] = dtrange_start
+        elif cmp == '>=' and dtrange_end < effective_date_range[1]:
+            effective_date_range[0] = dtrange_start
+        elif cmp == '<=' and dtrange_start > effective_date_range[0]:
+            effective_date_range[1] = dtrange_end
+        elif cmp == '=' or cmp == ':' or cmp == '==':
+            effective_date_range = [dtrange_start, dtrange_end]
+
+    if effective_date_range == [0, inf]:
+        return None
+    else:
+        return effective_date_range
+
+
 def parse(date_str, relative_base=None):
     "Parse date string passed in date filter of query to datetime object"
     # clean date string to handle future date parsing by date parser
diff --git a/tests/test_date_filter.py b/tests/test_date_filter.py
index 8abec3af..76dad113 100644
--- a/tests/test_date_filter.py
+++ b/tests/test_date_filter.py
@@ -1,10 +1,22 @@
 # Standard Packages
 import re
-from datetime import timedelta, datetime
+from datetime import datetime
+from math import inf
 
 # Application Packages
 from src.search_filter import date_filter
 
+
+def test_extract_date_range():
+    assert date_filter.extract_date_range('head dt>"2020-01-04" dt<"2020-01-07" tail') == [datetime(2020, 1, 5, 0, 0, 0).timestamp(), datetime(2020, 1, 7, 0, 0, 0).timestamp()]
+    assert date_filter.extract_date_range('head dt<="2020-01-01"') == [0, datetime(2020, 1, 2, 0, 0, 0).timestamp()]
+    assert date_filter.extract_date_range('head dt>="2020-01-01"') == [datetime(2020, 1, 1, 0, 0, 0).timestamp(), inf]
+    assert date_filter.extract_date_range('head dt:"2020-01-01"') == [datetime(2020, 1, 1, 0, 0, 0).timestamp(), datetime(2020, 1, 2, 0, 0, 0).timestamp()]
+
+    # No date filter specified in query
+    assert date_filter.extract_date_range('head tail') == None
+
+
 def test_parse():
     test_now = datetime(1984, 4, 1, 21, 21, 21)