generate ep3 map list on demand

src/Episode3.cc

@@ -802,10 +802,24 @@ Ep3DataIndex::Ep3DataIndex(const string& directory) {
       }
     }
   }
+}
 
+const string& Ep3DataIndex::get_compressed_card_definitions() const {
+  if (this->compressed_card_definitions.empty()) {
+    throw runtime_error("card definitions are not available");
+  }
+  return this->compressed_card_definitions;
+}
+
+shared_ptr<const Ep3DataIndex::CardEntry> Ep3DataIndex::get_card_definition(
+    uint32_t id) const {
+  return this->card_definitions.at(id);
+}
+
+const string& Ep3DataIndex::get_compressed_map_list() const {
+  if (this->compressed_map_list.empty()) {
     // TODO: Write a version of prs_compress that takes iovecs (or something
-  // similar) so we can eliminate all this string copying here. At least this
-  // only happens once at load time...
+    // similar) so we can eliminate all this string copying here.
     StringWriter entries_w;
     StringWriter strings_w;
 
@@ -856,23 +870,6 @@ Ep3DataIndex::Ep3DataIndex(const string& directory) {
     this->compressed_map_list = move(compressed_w.str());
     log(INFO, "Generated Episode 3 compressed map list (%zu -> %zu bytes)",
         w.size(), this->compressed_map_list.size());
-}
-
-const string& Ep3DataIndex::get_compressed_card_definitions() const {
-  if (this->compressed_card_definitions.empty()) {
-    throw runtime_error("card definitions are not available");
-  }
-  return this->compressed_card_definitions;
-}
-
-shared_ptr<const Ep3DataIndex::CardEntry> Ep3DataIndex::get_card_definition(
-    uint32_t id) const {
-  return this->card_definitions.at(id);
-}
-
-const string& Ep3DataIndex::get_compressed_map_list() const {
-  if (this->compressed_map_list.empty()) {
-    throw runtime_error("map list is not available");
   }
   return this->compressed_map_list;
 }

src/Episode3.hh

@@ -335,6 +335,10 @@ private:
   std::string compressed_card_definitions;
   std::unordered_map<uint32_t, std::shared_ptr<CardEntry>> card_definitions;
 
-  std::string compressed_map_list;
+  // The compressed map list is generated on demand from the maps map below.
+  // It's marked mutable because the logical consistency of the Ep3DataIndex
+  // object is not violated from the caller's perspective even if we don't
+  // generate the compressed map list at load time.
+  mutable std::string compressed_map_list;
   std::map<uint32_t, std::shared_ptr<MapEntry>> maps;
 };