Add the API code to know when the last save was.

docs/changelog.txt

@@ -77,11 +77,13 @@ Template for new versions:
 - ``Units::isUnitInBox``, ``Units::getUnitsInBox``: add versions accepting pos arguments
 - ``Units::getVisibleName``: when acting on a unit without an impersonated identity, returns the unit's name structure instead of the associated histfig's name structure
 - ``Translation::generateName``: generates in-game names, mirroring DF's internal logic
+- ``Persistence::getUnsavedSeconds``: returns the number of seconds since last save or last load
 
 ## Lua
 - ``dfhack.units.isUnitInBox``, ``dfhack.units.getUnitsInBox``: add versions accepting pos arguments
 - ``widgets.FilteredList``: search keys for list items can now be functions that return a string
 - ``dfhack.translation.generateName``: Lua API for ``Translation::generateName``
+- ``dfhack.persistent.getUnsavedSeconds``: Lua API for ``Persistence::getUnsavedSeconds``
 
 ## Removed
 - ``dfhack.TranslateName`` has been renamed to ``dfhack.translation.translateName``

docs/dev/Lua API.rst

@@ -771,6 +771,10 @@ arbitrary Lua tables.
   Same semantics as for the ``Site`` functions, but will associated the data
   with the global world context.
 
+* ``dfhack.persistent.getUnsavedSeconds()``
+
+  Returns the number of seconds since last save or load of a save.
+
 The data is kept in memory, so no I/O occurs when getting or saving keys. It is
 all written to a json file in the game save directory when the game is saved.
 

library/LuaApi.cpp

@@ -353,13 +353,19 @@ static int dfhack_persistent_delete_world_data(lua_State *L) {
     return delete_site_data(L, get_world_data);
 }
 
+static int dfhack_persistent_get_unsaved_seconds(lua_State *L) {
+    lua_pushinteger(L, Persistence::getUnsavedSeconds());
+    return 1;
+}
+
 static const luaL_Reg dfhack_persistent_funcs[] = {
     { "getSiteDataString", dfhack_persistent_get_site_data_string },
     { "saveSiteDataString", dfhack_persistent_save_site_data_string },
     { "deleteSiteData", dfhack_persistent_delete_site_data },
     { "getWorldDataString", dfhack_persistent_get_world_data_string },
     { "saveWorldDataString", dfhack_persistent_save_world_data_string },
     { "deleteWorldData", dfhack_persistent_delete_world_data },
+    { "getUnsavedSeconds", dfhack_persistent_get_unsaved_seconds },
     { NULL, NULL }
 };
 

library/include/modules/Persistence.h

@@ -213,5 +213,7 @@ namespace DFHack
         // Fills the vector with references to each persistent item with a key that is
         // equal to the given key.
         DFHACK_EXPORT void getAllByKey(std::vector<PersistentDataItem> &vec, int entity_id, const std::string &key);
+        // Returns the number of seconds since the current savegame was saved or loaded.
+        DFHACK_EXPORT uint32_t getUnsavedSeconds();
     }
 }

library/modules/Persistence.cpp

@@ -49,6 +49,8 @@ using namespace DFHack;
 static std::unordered_map<int, std::multimap<std::string, std::shared_ptr<Persistence::DataEntry>>> store;
 static std::unordered_map<size_t, std::shared_ptr<Persistence::DataEntry>> entry_cache;
 
+static uint32_t lastLoadSaveTickCount = 0;
+
 size_t next_entry_id = 0;   // goes more positive
 int next_fake_df_id = -101; // goes more negative
 
@@ -189,13 +191,20 @@ static std::string getSaveFilePath(const std::string &world, const std::string &
     return getSavePath(world) + "/dfhack-" + filterSaveFileName(name) + ".dat";
 }
 
+struct LastLoadSaveTickCountUpdater {
+    ~LastLoadSaveTickCountUpdater() {
+        lastLoadSaveTickCount = Core::getInstance().p->getTickCount();
+    }
+};
+
 void Persistence::Internal::save(color_ostream& out) {
     Core &core = Core::getInstance();
 
     if (!core.isWorldLoaded())
         return;
 
     CoreSuspender suspend;
+    LastLoadSaveTickCountUpdater tickCountUpdater;
 
     // write status
     {
@@ -237,6 +246,7 @@ void Persistence::Internal::save(color_ostream& out) {
         color_ostream_wrapper wrapper(file);
         Lua::CallLuaModuleFunction(wrapper, "script-manager", "print_timers");
     }
+
 }
 
 static bool get_entity_id(const std::string & fname, int & entity_id) {
@@ -283,6 +293,7 @@ static bool load_file(const std::string & path, int entity_id) {
 
 void Persistence::Internal::load(color_ostream& out) {
     CoreSuspender suspend;
+    LastLoadSaveTickCountUpdater tickCountUpdater;
 
     clear(out);
 
@@ -417,3 +428,8 @@ void Persistence::getAllByKey(std::vector<PersistentDataItem> &vec, int entity_i
     for (auto it = range.first; it != range.second; ++it)
         vec.emplace_back(it->second);
 }
+
+uint32_t Persistence::getUnsavedSeconds() {
+    uint32_t durMS =  Core::getInstance().p->getTickCount() - lastLoadSaveTickCount;
+    return durMS / 1000;
+}