6 files changed, 77 insertions, 18 deletions

diff --git a/src/fios.cpp b/src/fios.cpp
index c59bcfb21..0491c1e51 100644
--- a/src/fios.cpp
+++ b/src/fios.cpp
@@ -22,6 +22,7 @@
 #include <sys/stat.h>
 #include <functional>
 #include <optional>
+#include <charconv>
 
 #ifndef _WIN32
 # include <unistd.h>
@@ -745,3 +746,59 @@ void ScanScenarios()
 {
 	_scanner.Scan(true);
 }
+
+/**
+ * Constructs FiosNumberedSaveName. Initial number is the most recent save, or -1 if not found.
+ * @param prefix The prefix to use to generate a filename.
+*/
+FiosNumberedSaveName::FiosNumberedSaveName(const std::string &prefix) : prefix(prefix), number(-1)
+{
+	static std::optional<std::string> _autosave_path;
+	if (!_autosave_path) _autosave_path = FioFindDirectory(AUTOSAVE_DIR);
+
+	static std::string _prefix; ///< Static as the lambda needs access to it.
+
+	/* Callback for FiosFileScanner. */
+	static fios_getlist_callback_proc *proc = [](SaveLoadOperation fop, const std::string &file, const char *ext, char *title, const char *last) {
+		if (strcasecmp(ext, ".sav") == 0 && StrStartsWith(file, _prefix)) return FIOS_TYPE_FILE;
+		return FIOS_TYPE_INVALID;
+	};
+
+	/* Prefix to check in the callback. */
+	_prefix = *_autosave_path + this->prefix;
+
+	/* Get the save list. */
+	FileList list;
+	FiosFileScanner scanner(SLO_SAVE, proc, list);
+	scanner.Scan(".sav", _autosave_path->c_str(), false);
+
+	/* Find the number for the most recent save, if any. */
+	if (list.begin() != list.end()) {
+		SortingBits order = _savegame_sort_order;
+		_savegame_sort_order = SORT_BY_DATE | SORT_DESCENDING;
+		std::sort(list.begin(), list.end());
+		_savegame_sort_order = order;
+
+		std::string_view name = list.begin()->title;
+		std::from_chars(name.data() + this->prefix.size(), name.data() + name.size(), this->number);
+	}
+}
+
+/**
+ * Generate a savegame name and number according to _settings_client.gui.max_num_autosaves.
+ * @return A filename in format "<prefix><number>.sav".
+*/
+std::string FiosNumberedSaveName::Filename()
+{
+	if (++this->number >= _settings_client.gui.max_num_autosaves) this->number = 0;
+	return fmt::format("{}{}.sav", this->prefix, this->number);
+}
+
+/**
+ * Generate an extension for a savegame name.
+ * @return An extension in format "-<prefix>.sav".
+*/
+std::string FiosNumberedSaveName::Extension()
+{
+	return fmt::format("-{}.sav", this->prefix);
+}
diff --git a/src/fios.h b/src/fios.h
index 34504d5e0..c0e516297 100644
--- a/src/fios.h
+++ b/src/fios.h
@@ -125,4 +125,16 @@ std::string FiosMakeSavegameName(const char *name);
 
 FiosType FiosGetSavegameListCallback(SaveLoadOperation fop, const std::string &file, const char *ext, char *title, const char *last);
 
+/**
+ * A savegame name automatically numbered.
+ */
+struct FiosNumberedSaveName {
+	FiosNumberedSaveName(const std::string &prefix);
+	std::string Filename();
+	std::string Extension();
+private:
+	std::string prefix;
+	int number;
+};
+
 #endif /* FIOS_H */
diff --git a/src/network/network_client.cpp b/src/network/network_client.cpp
index 9f08062f3..d38437cc1 100644
--- a/src/network/network_client.cpp
+++ b/src/network/network_client.cpp
@@ -132,8 +132,8 @@ struct PacketReader : LoadFilter {
  */
 void ClientNetworkEmergencySave()
 {
-	static int _netsave_ctr = 0;
-	DoAutoOrNetsave(_netsave_ctr, true);
+	static FiosNumberedSaveName _netsave_ctr("netsave");
+	DoAutoOrNetsave(_netsave_ctr);
 }
 
 
diff --git a/src/openttd.cpp b/src/openttd.cpp
index 711df58c4..0ea1fa75d 100644
--- a/src/openttd.cpp
+++ b/src/openttd.cpp
@@ -1393,7 +1393,7 @@ void StateGameLoop()
  */
 static void DoAutosave()
 {
-	static int _autosave_ctr = 0;
+	static FiosNumberedSaveName _autosave_ctr("autosave");
 	DoAutoOrNetsave(_autosave_ctr);
 }
 
diff --git a/src/saveload/saveload.cpp b/src/saveload/saveload.cpp
index d771bf526..c8a1a0d29 100644
--- a/src/saveload/saveload.cpp
+++ b/src/saveload/saveload.cpp
@@ -3328,26 +3328,15 @@ SaveOrLoadResult SaveOrLoad(const std::string &filename, SaveLoadOperation fop,
  * @param counter A reference to the counter variable to be used for rotating the file name.
  * @param netsave Indicates if this is a regular autosave or a netsave.
  */
-void DoAutoOrNetsave(int &counter, bool netsave)
+void DoAutoOrNetsave(FiosNumberedSaveName &counter)
 {
 	char buf[MAX_PATH];
 
 	if (_settings_client.gui.keep_all_autosave) {
 		GenerateDefaultSaveName(buf, lastof(buf));
-		if (!netsave) {
-			strecat(buf, ".sav", lastof(buf));
-		} else {
-			strecat(buf, "-netsave.sav", lastof(buf));
-		}
+		strecat(buf, counter.Extension().c_str(), lastof(buf));
 	} else {
-		/* Generate a savegame name and number according to _settings_client.gui.max_num_autosaves. */
-		if (!netsave) {
-			seprintf(buf, lastof(buf), "autosave%d.sav", counter);
-		} else {
-			seprintf(buf, lastof(buf), "netsave%d.sav", counter);
-		}
-
-		if (++counter >= _settings_client.gui.max_num_autosaves) counter = 0;
+		strecpy(buf, counter.Filename().c_str(), lastof(buf));
 	}
 
 	Debug(sl, 2, "Autosaving to '{}'", buf);
diff --git a/src/saveload/saveload.h b/src/saveload/saveload.h
index d79bc1416..3047cbfd8 100644
--- a/src/saveload/saveload.h
+++ b/src/saveload/saveload.h
@@ -11,6 +11,7 @@
 #define SAVELOAD_H
 
 #include "../fileio_type.h"
+#include "../fios.h"
 #include "../strings_type.h"
 #include "../core/span_type.hpp"
 #include <optional>
@@ -381,7 +382,7 @@ void WaitTillSaved();
 void ProcessAsyncSaveFinish();
 void DoExitSave();
 
-void DoAutoOrNetsave(int &counter, bool netsave = false);
+void DoAutoOrNetsave(FiosNumberedSaveName &counter);
 
 SaveOrLoadResult SaveWithFilter(struct SaveFilter *writer, bool threaded);
 SaveOrLoadResult LoadWithFilter(struct LoadFilter *reader);