Add player online autosave pool

Add separate autosave pool for autosaves that have had players online
since the previous autosave.

docs/configuration.md

@@ -271,6 +271,19 @@ If null a random secure password is generated and used each time the instance st
 Defaults to null.
 
 
+### player_online_autosave_slots
+
+Keeps a separate pool for autosaves where at least on player has been online since the previous autosave was done.
+This requires regular autosaving to be enabled and will rename autosaves to `_autosave_poN.zip` (where N is a slot number) whenever a player has been online for that save.
+The slot numbers start at 1, are incremented by 1 after each autosave that is renamed and reset back to 1 whenever this value is exceeded.
+Note that this value should be set to a higher value than the value of `autosave_slots` in `factorio.settings`.
+Useful for preventing the loss of all progress when nobody is around on always online servers with auto pause disabled.
+
+If 0 no autosave renaming takes place.
+
+Defaults to 5.
+
+
 ### factorio.enable_save_patching
 
 Whether to use save patching or not.

packages/lib/config/definitions.js

@@ -265,6 +265,14 @@ FactorioGroup.define({
 	type: "string",
 	optional: true,
 });
+FactorioGroup.define({
+	name: "player_online_autosave_slots",
+	description:
+		"Rename autosaves where players have been online since the previous autosave into a separate autosave " +
+		"pool with this many slots. Requires autosaves to be enabled to work. Set to 0 to disable.",
+	type: "number",
+	initial_value: 5,
+});
 FactorioGroup.define({
 	name: "enable_save_patching",
 	description: "Patch saves with Lua code. Required for Clusterio integrations, lua modules, and most plugins.",

packages/slave/src/Instance.js

@@ -283,6 +283,8 @@ class Instance extends libLink.Link {
 		 */
 		this.playersOnline = new Set();
 		this._playerCheckInterval = null;
+		this._hadPlayersOnline = false;
+		this._playerAutosaveSlot = 1;
 	}
 
 	_watchPlayerJoinsByChat() {
@@ -364,6 +366,7 @@ class Instance extends libLink.Link {
 		let stats = this.playerStats.get(name);
 		stats.lastLeaveAt = Date.now();
 		stats.onlineTimeMs += stats.lastLeaveAt - stats.lastJoinAt;
+		this._hadPlayersOnline = true;
 
 		let event = {
 			instance_id: this.id,
@@ -428,6 +431,22 @@ class Instance extends libLink.Link {
 	async _autosave(name) {
 		let stat = await fs.stat(this.path("saves", `${name}.zip`));
 		instanceFactorioAutosaveSize.labels(String(this.id)).set(stat.size);
+
+		if (
+			this.config.get("factorio.player_online_autosave_slots") > 0
+			&& (this._hadPlayersOnline || this.playersOnline.size)
+		) {
+			if (this._playerAutosaveSlot > this.config.get("factorio.player_online_autosave_slots")) {
+				this._playerAutosaveSlot = 1;
+			}
+			await fs.rename(
+				this.path("saves", `${name}.zip`),
+				this.path("saves", `_autosave_po${this._playerAutosaveSlot}.zip`),
+			);
+			this._playerAutosaveSlot += 1;
+			this._hadPlayersOnline = false;
+		}
+
 		await this.sendSaveListUpdate();
 	}
 
@@ -498,10 +517,14 @@ class Instance extends libLink.Link {
 			throw err;
 		}
 		this.playerStats = new Map(stats["players"]);
+		this._playerAutosaveSlot = stats["player_autosave_slot"] || 1;
 	}
 
 	async _saveStats() {
-		let content = JSON.stringify({ players: [...this.playerStats] }, null, 4);
+		let content = JSON.stringify({
+			players: [...this.playerStats],
+			player_autosave_slot: this._playerAutosaveSlot,
+		}, null, 4);
 		await libFileOps.safeOutputFile(this.path("instance-stats.json"), content);
 	}