ready for testing

backend/src/overpass/caching_strategy.py

@@ -1,9 +1,9 @@
-"""Module defining the caching strategy for overpass requests."""
 import os
 import xml.etree.ElementTree as ET
 import hashlib
+import time
 
-from ..constants import OSM_CACHE_DIR
+from ..constants import OSM_CACHE_DIR, OSM_TYPES
 
 
 def get_cache_key(query: str) -> str:
@@ -13,14 +13,9 @@ def get_cache_key(query: str) -> str:
     """
     return hashlib.md5(query.encode('utf-8')).hexdigest()
 
-
 class CachingStrategyBase:
     """
     Base class for implementing caching strategies.
-
-    This class defines the structure for a caching strategy with basic methods
-    that must be implemented by subclasses. Subclasses should define how to
-    retrieve, store, and close the cache.
     """
     def get(self, key):
         """Retrieve the cached data associated with the provided key."""
@@ -30,6 +25,15 @@ class CachingStrategyBase:
         """Store data in the cache with the specified key."""
         raise NotImplementedError('Subclass should implement set')
 
+    def set_hollow(self, key, cell: tuple, osm_types: OSM_TYPES,
+                    selector: str, conditions=[], out='center'):
+        """Create a hollow (empty) cache entry with a specific key."""
+        raise NotImplementedError('Subclass should implement set_hollow')
+
+    def fill_hollow(self, key, value):
+        """Fill in the cache for an existing hollow entry."""
+        raise NotImplementedError('Subclass should implement fill_hollow')
+
     def close(self):
         """Clean up or close any resources used by the caching strategy."""
 
@@ -37,22 +41,10 @@ class CachingStrategyBase:
 class XMLCache(CachingStrategyBase):
     """
     A caching strategy that stores and retrieves data in XML format.
-
-    This class provides methods to cache data as XML files in a specified directory.
-    The directory is automatically suffixed with '_XML' to distinguish it from other
-    caching strategies. The data is stored and retrieved using XML serialization.
-
-    Args:
-        cache_dir (str): The base directory where XML cache files will be stored.
-                         Defaults to 'OSM_CACHE_DIR' with a '_XML' suffix.
-
-    Methods:
-        get(key): Retrieve cached data from a XML file associated with the given key.
-        set(key, value): Store data in a XML file with the specified key.
     """
     def __init__(self, cache_dir=OSM_CACHE_DIR):
         # Add the class name as a suffix to the directory
-        self._cache_dir = f'{cache_dir}_XML'
+        self._cache_dir = f'{cache_dir}'
         if not os.path.exists(self._cache_dir):
             os.makedirs(self._cache_dir)
 
@@ -68,7 +60,6 @@ class XMLCache(CachingStrategyBase):
                 tree = ET.parse(filename)
                 return tree.getroot()  # Return the root element of the parsed XML
             except ET.ParseError:
-                # print(f"Error parsing cached XML file: {filename}")
                 return None
         return None
 
@@ -77,25 +68,41 @@ class XMLCache(CachingStrategyBase):
         filename = self._filename(key)
         tree = ET.ElementTree(value)  # value is expected to be an ElementTree root element
         try:
-            # Write the XML data to a file
             with open(filename, 'wb') as file:
                 tree.write(file, encoding='utf-8', xml_declaration=True)
         except IOError as e:
             raise IOError(f"Error writing to cache file: {filename} - {e}") from e
 
+    def set_hollow(self, key, cell: tuple, osm_types: OSM_TYPES,
+                    selector: str, conditions=[], out='center'):
+        """Create an empty placeholder cache entry for a future fill."""
+        hollow_key = f'hollow_{key}'
+        filename = self._filename(hollow_key)
+    
+        # Create the root element <cache>
+        root = ET.Element("params")
+        # Add sub-elements with provided values
+        ET.SubElement(root, "key").text = key
+        ET.SubElement(root, "cell").text = f"({cell[0]}, {cell[1]})"
+        ET.SubElement(root, "osm_types").text = ','.join(osm_types)
+        ET.SubElement(root, "selector").text = selector
+        ET.SubElement(root, "conditions").text = ','.join(conditions) if conditions else "none"
+        ET.SubElement(root, "out").text = out
+
+        # Create an ElementTree object from the root
+        tree = ET.ElementTree(root)
+
+        # Write the XML to the file
+        with open(filename, 'wb') as file:
+            tree.write(file, encoding='utf-8', xml_declaration=True)
+
+    def close(self):
+        """Cleanup method, if needed."""
+        pass
 
 class CachingStrategy:
     """
     A class to manage different caching strategies.
-
-    This class provides an interface to switch between different caching strategies 
-    (e.g., XMLCache, JSONCache) dynamically. It allows caching data in different formats, 
-    depending on the strategy being used. By default, it uses the XMLCache strategy.
-
-    Attributes:
-    __strategy (CachingStrategyBase): The currently active caching strategy.
-    __strategies (dict): A mapping between strategy names (as strings) and their corresponding
-                         classes, allowing dynamic selection of caching strategies.
     """
     __strategy = XMLCache()  # Default caching strategy
     __strategies = {
@@ -104,37 +111,31 @@ class CachingStrategy:
 
     @classmethod
     def use(cls, strategy_name='XML', **kwargs):
-        """
-        Set the caching strategy based on the strategy_name provided.
-
-        Args:
-            strategy_name (str): The name of the caching strategy (e.g., 'XML').
-            **kwargs: Additional keyword arguments to pass when initializing the strategy.
-        """
-        # If a previous strategy exists, close it
         if cls.__strategy:
             cls.__strategy.close()
 
-        # Retrieve the strategy class based on the strategy name
         strategy_class = cls.__strategies.get(strategy_name)
-
         if not strategy_class:
             raise ValueError(f"Unknown caching strategy: {strategy_name}")
 
-        # Instantiate the new strategy with the provided arguments
         cls.__strategy = strategy_class(**kwargs)
         return cls.__strategy
 
     @classmethod
     def get(cls, key):
-        """Get data from the current strategy's cache."""
-        if not cls.__strategy:
-            raise RuntimeError("Caching strategy has not been set.")
         return cls.__strategy.get(key)
 
     @classmethod
     def set(cls, key, value):
-        """Set data in the current strategy's cache."""
-        if not cls.__strategy:
-            raise RuntimeError("Caching strategy has not been set.")
         cls.__strategy.set(key, value)
+
+    @classmethod
+    def set_hollow(cls, key, cell: tuple, osm_types: OSM_TYPES,
+                    selector: str, conditions=[], out='center'):
+        """Create a hollow cache entry."""
+        cls.__strategy.set_hollow(key, cell, osm_types, selector, conditions, out)
+
+    @classmethod
+    def fill_hollow(cls, key, value):
+        """Fill in the hollow cache entry with actual data."""
+        cls.__strategy.fill_hollow(key, value)