Extract natural language and locale specific dates in content

Previously we just extracted dates in YYYY-MM-DD format from content
for date filterings during search.

Use dateparser to extract dates across locales and natural language

This should improve notes returned as context when chat searches
knowledge base with date filters

Fallback to regex for date parsing from content if dateparser fails

- Limit natural date extractor capabilities to improve performance
  - Assume language is english
    Language detection otherwise takes a REALLY long time
  - Do not extract unix timestamps, timezone
    - This isn't required, as just using date and approximating dates as UTC

src/khoj/search_filter/date_filter.py

@@ -6,10 +6,12 @@ from math import inf
 from typing import List
 
 import dateparser as dtparse
+from dateparser.search import search_dates
+from dateparser_data.settings import default_parsers
 from dateutil.relativedelta import relativedelta
 
 from khoj.search_filter.base_filter import BaseFilter
-from khoj.utils.helpers import LRU, timer
+from khoj.utils.helpers import LRU, merge_dicts, timer
 
 logger = logging.getLogger(__name__)
 
@@ -21,17 +23,40 @@ class DateFilter(BaseFilter):
     # - dt>="last week"
     # - dt:"2 years ago"
     date_regex = r"dt([:><=]{1,2})[\"'](.*?)[\"']"
-    raw_date_regex = r"\d{4}-\d{2}-\d{2}"
+    raw_date_regex = r"\d{4}[-/]\d{2}[-/]\d{2}"
 
     def __init__(self, entry_key="compiled"):
         self.entry_key = entry_key
         self.date_to_entry_ids = defaultdict(set)
         self.cache = LRU()
+        self.dtparser_settings = {
+            "PREFER_DAY_OF_MONTH": "first",
+            "DATE_ORDER": "YMD",  # Prefer YMD and DMY over MDY when parsing ambiguous dates
+        }
 
     def extract_dates(self, content):
-        pattern_matched_dates = re.findall(self.raw_date_regex, content)
+        "Extract all natural and structured dates across formats and locales from content"
+        excluded_parsers = ["relative-time"]
+        dtparser_settings = merge_dicts(
+            {
+                # Exclude relative dates for date extraction from content as very ambiguous
+                "PARSERS": [parser for parser in default_parsers if parser not in excluded_parsers],
+                "RETURN_AS_TIMEZONE_AWARE": False,
+            },
+            self.dtparser_settings,
+        )
+        try:
+            valid_dates = [
+                dt_item[1] for dt_item in search_dates(content, settings=dtparser_settings, languages=["en"]) or []
+            ]
+            return valid_dates
+        except Exception as e:
+            logger.warning(
+                f"Failed to extract natural dates from content with error: {e}. Fallback to regex based extraction."
+            )
 
-        # Filter down to valid dates
+        # Fallback to extracting YYYY-MM-DD format dates from content
+        pattern_matched_dates = re.findall(self.raw_date_regex, content)
         valid_dates = []
         for date_str in pattern_matched_dates:
             try:
@@ -120,18 +145,13 @@ class DateFilter(BaseFilter):
         # clean date string to handle future date parsing by date parser
         future_strings = ["later", "from now", "from today"]
         prefer_dates_from = {True: "future", False: "past"}[any([True for fstr in future_strings if fstr in date_str])]
-        clean_date_str = re.sub("|".join(future_strings), "", date_str)
+        dtquery_settings = {"RELATIVE_BASE": relative_base or datetime.now(), "PREFER_DATES_FROM": prefer_dates_from}
+        dtparser_settings = merge_dicts(dtquery_settings, self.dtparser_settings)
 
         # parse date passed in query date filter
+        clean_date_str = re.sub("|".join(future_strings), "", date_str)
         try:
-            parsed_date = dtparse.parse(
-                clean_date_str,
-                settings={
-                    "RELATIVE_BASE": relative_base or datetime.now(),
-                    "PREFER_DAY_OF_MONTH": "first",
-                    "PREFER_DATES_FROM": prefer_dates_from,
-                },
-            )
+            parsed_date = dtparse.parse(clean_date_str, settings=dtparser_settings)
         except Exception as e:
             logger.error(f"Failed to parse date string: {date_str} with error: {e}")
             return None