Add base instances for instance config inheritance

Instances can be marked as a base with instance.is_base and other
instances inherit config values from it through instance.base_id.
The controller copies base values into inheriting configs and keeps
track of inherited fields in the hidden instance.inherited_fields, so
hosts receive resolved configs and need no changes. Setting a field
stops inheriting it, `instance config inherit` undoes that.

Bases cannot be assigned to a host, are hidden from `instance list`
unless --bases is given, and cannot be deleted or unmarked while
other instances inherit from them. Chains of bases are allowed and
cycles are rejected.

Part of #200

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/controller/src/InstanceManager.ts

@@ -1,4 +1,6 @@
+import { isDeepStrictEqual } from "node:util";
 import * as lib from "@clusterio/lib";
+import { logger } from "@clusterio/lib";
 
 import type Controller from "./Controller.js";
 import type HostConnection from "./HostConnection.js";
@@ -24,6 +26,9 @@ export default class InstanceManager {
 		non_blocking_saving: false,
 	} as const;
 
+	/** Non-zero while base values are being copied into inheriting instances */
+	private _inheriting = 0;
+
 	constructor(
 		public readonly records: lib.SubscribableDatastore<InstanceRecord>,
 		private readonly _controller: Controller,
@@ -106,11 +111,190 @@ export default class InstanceManager {
 	 */
 	addInstanceHooks(instance: InstanceRecord): void {
 		instance.config.on("fieldChanged", (field: string, curr: unknown, prev: unknown) => {
+			if (field === "instance.base_id") {
+				this._rebase(instance);
+			} else if (!this._inheriting && instance.config.isInherited(field)) {
+				this._setInherited(instance, [field], false);
+			}
 			this.records.set(instance);
 			this._notifyConfigFieldChanged(instance, field, curr, prev);
+			this._propagate(instance, field, curr);
 		});
 	}
 
+	/* ------------------------------------------------------------------------- */
+	/* Inheritance                                                               */
+	/* ------------------------------------------------------------------------- */
+
+	/**
+	 * Get the instances that inherit directly from the given base.
+	 *
+	 * @param baseId - ID of the base instance.
+	 * @returns Instances with `instance.base_id` set to baseId.
+	 */
+	inheritorsOf(baseId: number): InstanceRecord[] {
+		return [...this.records.values()].filter(
+			instance => instance.config.get("instance.base_id") === baseId
+		);
+	}
+
+	/**
+	 * Check that new values for `instance.is_base` and `instance.base_id` are allowed.
+	 *
+	 * @param config - Current config of the instance.
+	 * @param isBase - New value for `instance.is_base`.
+	 * @param baseId - New value for `instance.base_id`.
+	 * @throws {module:lib.ValidationError} if the base is not a base or would create a cycle.
+	 * @throws {module:lib.ConflictError} if the instance is assigned or still has inheritors.
+	 */
+	checkInheritance(config: lib.InstanceConfig, isBase: boolean, baseId: number | null): void {
+		const instanceId = config.get("instance.id");
+		if (isBase && config.get("instance.assigned_host") !== null) {
+			throw new lib.ConflictError("Instance must be unassigned before it can be made a base");
+		}
+		if (!isBase && config.get("instance.is_base")) {
+			const count = this.inheritorsOf(instanceId).length;
+			if (count) {
+				throw new lib.ConflictError(`Instance is the base of ${count} other instance(s)`);
+			}
+		}
+		if (baseId === null) {
+			return;
+		}
+		const base = this.records.get(baseId);
+		if (!base) {
+			throw new lib.NotFoundError(`Instance with ID ${baseId} does not exist`);
+		}
+		if (!base.config.get("instance.is_base")) {
+			throw new lib.ValidationError(`Instance ${base.config.get("instance.name")} is not a base`);
+		}
+		const visited = new Set<number>();
+		for (let id: number | null = baseId; id !== null && !visited.has(id);) {
+			if (id === instanceId) {
+				throw new lib.ValidationError("Base instances cannot inherit from themselves");
+			}
+			visited.add(id);
+			id = this.records.get(id)?.config.get("instance.base_id") ?? null;
+		}
+	}
+
+	/**
+	 * Copy all inheritable values from the base set in `instance.base_id`
+	 * into a config that is not yet part of the cluster and mark them inherited.
+	 *
+	 * @param config - Config of the instance to be created.
+	 * @param keep - Fields to keep the current value of.
+	 */
+	applyBase(config: lib.InstanceConfig, keep: string[] = []): void {
+		const base = this.records.get(config.get("instance.base_id")!);
+		if (!base) {
+			return;
+		}
+		const values: Record<string, any> = {};
+		const inherited: Record<string, true> = {};
+		for (const name of Object.keys(lib.InstanceConfig.fieldDefinitions)) {
+			if (lib.InstanceConfig.isInheritable(name) && !keep.includes(name)) {
+				values[name] = structuredClone(base.config.get(name as keyof lib.InstanceConfigFields));
+				inherited[name] = true;
+			}
+		}
+		config.update(values, false);
+		config.set("instance.inherited_fields", inherited);
+	}
+
+	/**
+	 * Make a field take its value from the base instance again.
+	 *
+	 * @param instanceId - ID of the instance to update.
+	 * @param field - Name of the field to inherit.
+	 * @throws {module:lib.ValidationError} if the instance has no base or the field cannot be inherited.
+	 */
+	inheritField(instanceId: number, field: string): void {
+		const instance = this.getForRequest(instanceId);
+		const baseId = instance.config.get("instance.base_id");
+		const base = baseId !== null ? this.records.get(baseId) : undefined;
+		if (!base) {
+			throw new lib.ValidationError("Instance does not have a base");
+		}
+		if (!lib.InstanceConfig.isInheritable(field)) {
+			throw new lib.ValidationError(`Field ${field} cannot be inherited`);
+		}
+		this._setInherited(instance, [field], true);
+		this._inheriting += 1;
+		try {
+			instance.config.update({
+				[field]: structuredClone(base.config.get(field as keyof lib.InstanceConfigFields)),
+			}, true);
+		} finally {
+			this._inheriting -= 1;
+		}
+	}
+
+	/**
+	 * Stop inheriting the given fields, used when a value is explicitly set.
+	 *
+	 * @param instance - Instance the fields were set on.
+	 * @param fields - Names of fields set.
+	 */
+	overrideFields(instance: InstanceRecord, fields: string[]): void {
+		const inherited = fields.filter(field => instance.config.isInherited(field));
+		if (inherited.length) {
+			this._setInherited(instance, inherited, false);
+		}
+	}
+
+	private _setInherited(instance: InstanceRecord, fields: string[], inherited: boolean): void {
+		const value = { ...instance.config.get("instance.inherited_fields") };
+		for (const field of fields) {
+			if (inherited) {
+				value[field] = true;
+			} else {
+				delete value[field];
+			}
+		}
+		instance.config.set("instance.inherited_fields", value);
+	}
+
+	/** Recompute inherited fields after base_id changed, values equal to the base are inherited */
+	private _rebase(instance: InstanceRecord): void {
+		const baseId = instance.config.get("instance.base_id");
+		const base = baseId !== null ? this.records.get(baseId) : undefined;
+		const inherited: Record<string, true> = {};
+		if (base) {
+			for (const name of Object.keys(lib.InstanceConfig.fieldDefinitions)) {
+				const field = name as keyof lib.InstanceConfigFields;
+				if (
+					lib.InstanceConfig.isInheritable(name)
+					&& isDeepStrictEqual(instance.config.get(field), base.config.get(field))
+				) {
+					inherited[name] = true;
+				}
+			}
+		}
+		instance.config.set("instance.inherited_fields", inherited);
+	}
+
+	/** Copy a changed value from a base to the instances inheriting it */
+	private _propagate(base: InstanceRecord, field: string, value: unknown): void {
+		if (!lib.InstanceConfig.isInheritable(field)) {
+			return;
+		}
+		for (const instance of this.inheritorsOf(base.id)) {
+			if (!instance.config.isInherited(field)) {
+				continue;
+			}
+			this._inheriting += 1;
+			try {
+				instance.config.update({ [field]: structuredClone(value) as any }, true);
+			} finally {
+				this._inheriting -= 1;
+			}
+			this._controller.instanceConfigUpdated(instance).catch(err => {
+				logger.error(`Failed to send config of instance ${instance.id} to its host:\n${err.stack}`);
+			});
+		}
+	}
+
 	/* ------------------------------------------------------------------------- */
 	/* Lifecycle                                                                 */
 	/* ------------------------------------------------------------------------- */
@@ -136,13 +320,15 @@ export default class InstanceManager {
 			throw new lib.ConflictError(`Instance with ID ${instanceId} already exists`);
 		}
 
-		const controllerName = this._controller.config.get("controller.name");
-		instanceConfig.set("factorio.settings", {
-			name: `${controllerName} - ${instanceConfig.get("instance.name")}`,
-			description: `Clusterio instance for ${controllerName}`,
-			...InstanceManager.DefaultFactorioSettings,
-			...instanceConfig.get("factorio.settings"),
-		});
+		if (!instanceConfig.isInherited("factorio.settings")) {
+			const controllerName = this._controller.config.get("controller.name");
+			instanceConfig.set("factorio.settings", {
+				name: `${controllerName} - ${instanceConfig.get("instance.name")}`,
+				description: `Clusterio instance for ${controllerName}`,
+				...InstanceManager.DefaultFactorioSettings,
+				...instanceConfig.get("factorio.settings"),
+			});
+		}
 
 		const instance = new InstanceRecord(instanceConfig, "unassigned");
 		this.addInstanceHooks(instance);
@@ -186,6 +372,9 @@ export default class InstanceManager {
 		if (currentAssignedHost === hostId) {
 			return;
 		}
+		if (hostId !== null && instance.config.get("instance.is_base")) {
+			throw new lib.ValidationError("Base instances cannot be assigned to a host");
+		}
 
 		let newHostConnection: HostConnection | undefined;
 		if (hostId !== null) {
@@ -252,6 +441,10 @@ export default class InstanceManager {
 	async deleteInstance(instanceId: number): Promise<void> {
 		const instance = this.getForRequest(instanceId);
 		const hostId = instance.config.get("instance.assigned_host");
+		const inheritors = this.inheritorsOf(instanceId).length;
+		if (inheritors) {
+			throw new lib.ConflictError(`Instance is the base of ${inheritors} other instance(s)`);
+		}
 
 		if (hostId !== null) {
 			await this._controller.sendTo(