From de1b79d705385c543cebeb1127c56abed4d4615e Mon Sep 17 00:00:00 2001
From: Igor Chubin <igor@chub.in>
Date: Sat, 7 Sep 2019 15:12:10 +0200
Subject: [PATCH] lru cache for formatted answers (fixes #346)

---
 lib/cache.py    | 50 +++++++++++++++++++++++++++++++++++++++++++++++++
 lib/spark.py    |  5 ++---
 lib/wttr_srv.py | 15 ++++++++++++++-
 3 files changed, 66 insertions(+), 4 deletions(-)
 create mode 100644 lib/cache.py

diff --git a/lib/cache.py b/lib/cache.py
new file mode 100644
index 0000000..8f923b4
--- /dev/null
+++ b/lib/cache.py
@@ -0,0 +1,50 @@
+"""
+LRU-Cache implementation for formatted (`format=`) answers
+"""
+
+import datetime
+import re
+import time
+import pylru
+import pytz
+
+CACHE_SIZE = 10000
+CACHE = pylru.lrucache(CACHE_SIZE)
+
+def _update_answer(answer):
+    def _now_in_tz(timezone):
+        return datetime.datetime.now(pytz.timezone(timezone)).strftime("%H:%M:%S%z")
+
+    if "%{{NOW(" in answer:
+        answer = re.sub(r"%{{NOW\(([^}]*)\)}}", lambda x: _now_in_tz(x.group(1)), answer)
+
+    return answer
+
+def get_signature(user_agent, query_string, client_ip_address, lang):
+    """
+    Get cache signature based on `user_agent`, `url_string`,
+    `lang`, and `client_ip_address`
+    """
+
+    timestamp = int(time.time()) / 1000
+    signature = "%s:%s:%s:%s:%s" % \
+        (user_agent, query_string, client_ip_address, lang, timestamp)
+    return signature
+
+def get(signature):
+    """
+    If `update_answer` is not True, return answer as it is
+    stored in the cache. Otherwise update it, using
+    the `_update_answer` function.
+    """
+
+    if signature in CACHE:
+        return _update_answer(CACHE[signature])
+    return None
+
+def store(signature, value):
+    """
+    Store in cache `value` for `signature`
+    """
+    CACHE[signature] = value
+    return _update_answer(value)
diff --git a/lib/spark.py b/lib/spark.py
index 019e715..47c935d 100644
--- a/lib/spark.py
+++ b/lib/spark.py
@@ -481,13 +481,12 @@ def textual_information(data_parsed, geo_data, config):
     output.append('Timezone: %s' % timezone)
 
     tmp_output = []
-    tmp_output.append('  Now:    %s'
-                      % datetime.datetime.now(pytz.timezone(timezone)).strftime("%H:%M:%S%z"))
+    tmp_output.append('  Now:    %%{{NOW(%s)}}' % timezone)
     tmp_output.append('Dawn:    %s'
                       % str(sun['dawn'].strftime("%H:%M:%S")))
     tmp_output.append('Sunrise: %s'
                       % str(sun['sunrise'].strftime("%H:%M:%S")))
-    tmp_output.append('  Noon:   %s'
+    tmp_output.append('  Zenith: %s'
                       % str(sun['noon'].strftime("%H:%M:%S     ")))
     tmp_output.append('Sunset:  %s'
                       % str(sun['sunset'].strftime("%H:%M:%S")))
diff --git a/lib/wttr_srv.py b/lib/wttr_srv.py
index 7c64387..e389e6d 100644
--- a/lib/wttr_srv.py
+++ b/lib/wttr_srv.py
@@ -25,6 +25,8 @@ from limits import Limits
 from wttr import get_wetter, get_moon
 from wttr_line import wttr_line
 
+import cache
+
 if not os.path.exists(os.path.dirname(LOG_FILE)):
     os.makedirs(os.path.dirname(LOG_FILE))
 logging.basicConfig(filename=LOG_FILE, level=logging.DEBUG, format='%(asctime)s %(message)s')
@@ -211,6 +213,12 @@ def wttr(location, request):
     html_output = get_output_format(request, query)
     user_agent = request.headers.get('User-Agent', '').lower()
 
+    # generating cache signature
+    cache_signature = cache.get_signature(user_agent, request.url, ip_addr, lang)
+    answer = cache.get(cache_signature)
+    if answer:
+        return _wrap_response(answer, html_output)
+
     if location in PLAIN_TEXT_PAGES:
         help_ = show_text_file(location, lang)
         if html_output:
@@ -242,8 +250,13 @@ def wttr(location, request):
     # We are ready to return the answer
     try:
         if fmt or 'format' in query:
+            response_text = wttr_line(
+                location, override_location_name, full_address, query, lang, fmt)
+            fmt = fmt or query.get('format')
+            response_text = cache.store(cache_signature, response_text)
+
             return _wrap_response(
-                wttr_line(location, override_location_name, full_address, query, lang, fmt),
+                response_text,
                 html_output)
 
         if png_filename: