4.0.0 Beta 1

src/settings/context.js

@@ -0,0 +1,287 @@
+'use strict';
+
+// ============================================================================
+// Settings Contexts
+// ============================================================================
+
+import {EventEmitter} from 'utilities/events';
+import {has, get as getter, array_equals} from 'utilities/object';
+
+
+/**
+ * The SettingsContext class provides a context through which to read
+ * settings values in addition to emitting events when settings values
+ * are changed.
+ * @extends EventEmitter
+ */
+export default class SettingsContext extends EventEmitter {
+	constructor(manager, context) {
+		super();
+
+		if ( manager instanceof SettingsContext ) {
+			this.parent = manager;
+			this.manager = manager.manager;
+
+			this.parent.on('context_changed', this._rebuildContext, this);
+
+		} else {
+			this.parent = null;
+			this.manager = manager;
+		}
+
+		this.manager.__contexts.push(this);
+		this._context = context || {};
+
+		this.__cache = new Map;
+		this.__meta = new Map;
+		this.__profiles = [];
+		this.order = [];
+
+		this._rebuildContext();
+	}
+
+	destroy() {
+		if ( this.parent )
+			this.parent.off('context_changed', this._rebuildContext, this);
+
+		for(const profile of this.__profiles)
+			profile.off('changed', this._onChanged, this);
+
+		const contexts = this.manager.__contexts,
+			idx = contexts.indexOf(this);
+
+		if ( idx !== -1 )
+			contexts.splice(idx, 1);
+	}
+
+
+	// ========================================================================
+	// State Construction
+	// ========================================================================
+
+	_rebuildContext() {
+		this.__context = this.parent ?
+			Object.assign({}, this.parent._context, this._context) :
+			this._context;
+
+		// Make sure we re-build the cache. Dependency hell.
+		if ( ! this.selectProfiles() )
+			this.rebuildCache();
+
+		this.emit('context_changed');
+	}
+
+
+	selectProfiles() {
+		const new_profiles = [],
+			order = this.order = [];
+		for(const profile of this.manager.__profiles)
+			if ( profile.matches(this.__context) ) {
+				new_profiles.push(profile);
+				order.push(profile.id);
+			}
+
+		if ( array_equals(this.__profiles, new_profiles) )
+			return false;
+
+		const changed_ids = new Set;
+
+		for(const profile of this.__profiles)
+			if ( ! new_profiles.includes(profile) ) {
+				profile.off('changed', this._onChanged, this);
+				changed_ids.add(profile.id);
+			}
+
+		for(const profile of new_profiles)
+			if ( ! this.__profiles.includes(profile) ) {
+				profile.on('changed', this._onChanged, this);
+				changed_ids.add(profile.id);
+			}
+
+		this.__profiles = new_profiles;
+		this.emit('profiles_changed');
+		this.rebuildCache(changed_ids);
+		return true;
+	}
+
+
+	rebuildCache() {
+		const old_cache = this.__cache,
+			old_meta = this.__meta,
+			meta = this.__meta = new Map;
+
+		this.__cache = new Map;
+
+		// TODO: Limit the values we recalculate to ones affected by the change
+		// that happened to the profiles. This is harder because of setting
+		// dependencies.
+
+		for(const [key, old_value] of old_cache) {
+			const new_value = this.get(key),
+				new_m = meta.get(key),
+				old_m = old_meta.get(key),
+				new_uses = new_m ? new_m.uses : null,
+				old_uses = old_m ? old_m.uses : null;
+
+			if ( new_value !== old_value ) {
+				this.emit('changed', key, new_value, old_value);
+				this.emit(`changed:${key}`, new_value, old_value);
+			}
+
+			if ( new_uses !== old_uses ) {
+				this.emit('uses_changed', key, new_uses, old_uses);
+				this.emit(`uses_changed:${key}`, new_uses, old_uses);
+			}
+		}
+	}
+
+
+	// ========================================================================
+	// Context Control
+	// ========================================================================
+
+	context(context) {
+		return new SettingsContext(this, context);
+	}
+
+
+	updateContext(context) {
+		let changed = false;
+
+		for(const key in context)
+			if ( has(context, key) && context[key] !== this._context[key] ) {
+				this._context[key] = context[key];
+				changed = true;
+			}
+
+		if ( changed )
+			this._rebuildContext();
+	}
+
+
+	setContext(context) {
+		this._context = context;
+		this._rebuildContext();
+	}
+
+
+	// ========================================================================
+	// Data Access
+	// ========================================================================
+
+	_onChanged(key) {
+		this._update(key, key, []);
+	}
+
+	_update(key, initial, visited) {
+		if ( ! this.__cache.has(key) )
+			return;
+
+		else if ( visited.includes(key) )
+			throw new Error(`cyclic dependent chain when updating setting "${initial}"`);
+
+		visited.push(key);
+
+		const old_value = this.__cache.get(key),
+			old_meta = this.__meta.get(key),
+			new_value = this._get(key, key, []),
+			new_meta = this.__meta.get(key),
+
+			old_uses = old_meta ? old_meta.uses : null,
+			new_uses = new_meta ? new_meta.uses : null;
+
+		if ( old_uses !== new_uses ) {
+			this.emit('uses_changed', key, new_uses, old_uses);
+			this.emit(`uses_changed:${key}`, new_uses, old_uses);
+		}
+
+		if ( old_value === new_value )
+			return;
+
+		this.emit('changed', key, new_value, old_value);
+		this.emit(`changed:${key}`, new_value, old_value);
+
+		const definition = this.manager.definitions.get(key);
+		if ( definition && definition.required_by )
+			for(const req_key of definition.required_by)
+				if ( ! req_key.startsWith('context.') )
+					this._update(req_key, initial, Array.from(visited));
+	}
+
+
+	_get(key, initial, visited) {
+		if ( visited.includes(key) )
+			throw new Error(`cyclic dependency when resolving setting "${initial}"`);
+
+		visited.push(key);
+
+		const definition = this.manager.definitions.get(key),
+			raw_value = this._getRaw(key),
+			meta = {
+				uses: raw_value ? raw_value[1].id : null
+			};
+
+		let value = raw_value ? raw_value[0] : undefined;
+
+		if ( definition ) {
+			if ( Array.isArray(definition) )
+				throw new Error(`non-existent setting "${key}" required when resolving setting "${initial}"`);
+
+			if ( meta.uses === null ) {
+				const def_default = definition.default;
+				if ( typeof def_default === 'function' )
+					value = def_default(this);
+				else
+					value = def_default;
+			}
+
+			if ( definition.requires )
+				for(const req_key of definition.requires)
+					if ( ! req_key.startsWith('context.') && ! this.__cache.has(req_key) )
+						this._get(req_key, initial, Array.from(visited));
+
+			if ( definition.process )
+				value = definition.process(this, value, meta);
+		}
+
+		this.__cache.set(key, value);
+		this.__meta.set(key, meta);
+		return value;
+	}
+
+
+	_getRaw(key) {
+		for(const profile of this.__profiles)
+			if ( profile.has(key) )
+				return [profile.get(key), profile]
+	}
+
+
+	// ========================================================================
+	// Data Access
+	// ========================================================================
+
+	update(key) {
+		this._update(key, key, []);
+	}
+
+	get(key) {
+		if ( key.startsWith('context.') )
+			return getter(key.slice(8), this.__context);
+
+		if ( this.__cache.has(key) )
+			return this.__cache.get(key);
+
+		return this._get(key, key, []);
+	}
+
+	uses(key) {
+		if ( key.startsWith('context.') )
+			return null;
+
+		if ( ! this.__meta.has(key) )
+			this._get(key, key, []);
+
+		return this.__meta.get(key).uses;
+	}
+}