closes #1 cache pages when retrieved

src/app.py

@@ -1,16 +1,28 @@
 from flask import Flask
 import requests
 import re
+import redis
+import time
 
 app = Flask(__name__)
 CHEMGUIDE_BASE="https://chemguide.co.uk/"
+PAGE_CACHE_DURATION = 3600 # cache pages for an hour before retrieving again
+db = redis.Redis(host='db', port=6379, db=0)
 
-@app.route('/')
-@app.route('/<path:path>')
-def path(path='/'):
+class PathKeyType():
+    Data = 1
+    Date = 2
+
+def pathkey(path, type):
+    if type == PathKeyType.Data:
+        return f"{path}:data"
+    elif type == PathKeyType.Date:
+        return f"{path}:date"
+
+def set_cache(path):
     r = requests.get(CHEMGUIDE_BASE + '/' + path)
     try:
-        return re.sub(
+        data =  re.sub(
                     r'<table .* width="480"',
                     '<table style="max-width: 60em; margin: 0 auto; font-size: 16px;"',
                     re.sub(
@@ -41,7 +53,24 @@ def path(path='/'):
                     )
                 )
     except UnicodeDecodeError:
-        return r.content
+        data =  r.content
+
+    db.set(pathkey(path, PathKeyType.Data), data)
+    db.set(pathkey(path, PathKeyType.Date), time.time())
+
+def get_page(path):
+    date = db.get(pathkey(path, PathKeyType.Date))
+    if date is not None:
+        if float(str(date, 'utf-8')) + PAGE_CACHE_DURATION < time.time():
+            set_cache(path)
+    else:
+        set_cache(path)
+    return db.get(pathkey(path, PathKeyType.Data))
+
+@app.route('/')
+@app.route('/<path:path>')
+def path(path='/'):
+    return get_page(path)
 
 if __name__ == '__main__':
     app.run(host='0.0.0.0', debug=True)