Refactoring with a MapStore

A great deal of the complexity of the current code is that we must chain
2 reactive values (one in the map "GameScene.MapPlayersByKey" and one in
the snapshot store).

The new generic MapStore class can be used to listen to stores inside a map.
When the store inside the map, or the map itself is modified, the
resulting store is updated.

front/tests/Stores/Utils/MapStoreTest.ts

@@ -0,0 +1,97 @@
+import "jasmine";
+import {MapStore} from "../../../src/Stores/Utils/MapStore";
+import type {Readable, Writable} from "svelte/store";
+import {get, writable} from "svelte/store";
+
+describe("Main store", () => {
+    it("Set / delete / clear triggers main store updates", () => {
+        const mapStore = new MapStore<string, string>();
+
+        let triggered = false;
+
+        mapStore.subscribe((map) => {
+            triggered = true;
+            expect(map).toBe(mapStore);
+        })
+
+        expect(triggered).toBeTrue();
+        triggered = false;
+        mapStore.set('foo', 'bar');
+        expect(triggered).toBeTrue();
+
+        triggered = false;
+        mapStore.delete('baz');
+        expect(triggered).toBe(false);
+        mapStore.delete('foo');
+        expect(triggered).toBe(true);
+
+        triggered = false;
+        mapStore.clear();
+        expect(triggered).toBe(true);
+    });
+
+    it("generates stores for keys with getStore", () => {
+
+        const mapStore = new MapStore<string, string>();
+
+        let valueReceivedInStoreForFoo: string|undefined;
+        let valueReceivedInStoreForBar: string|undefined;
+
+        mapStore.set('foo', 'someValue');
+
+        mapStore.getStore('foo').subscribe((value) => {
+            valueReceivedInStoreForFoo = value;
+        });
+        const unsubscribeBar = mapStore.getStore('bar').subscribe((value) => {
+            valueReceivedInStoreForBar = value;
+        });
+
+        expect(valueReceivedInStoreForFoo).toBe('someValue');
+        expect(valueReceivedInStoreForBar).toBe(undefined);
+        mapStore.set('foo', 'someOtherValue');
+        expect(valueReceivedInStoreForFoo).toBe('someOtherValue');
+        mapStore.delete('foo');
+        expect(valueReceivedInStoreForFoo).toBe(undefined);
+        mapStore.set('bar', 'baz');
+        expect(valueReceivedInStoreForBar).toBe('baz');
+        mapStore.clear();
+        expect(valueReceivedInStoreForBar).toBe(undefined);
+        unsubscribeBar();
+        mapStore.set('bar', 'fiz');
+        expect(valueReceivedInStoreForBar).toBe(undefined);
+    });
+
+    it("generates stores with getStoreByAccessor", () => {
+        const mapStore = new MapStore<string, {
+            foo: string,
+            store: Writable<string>
+        }>();
+
+        const fooStore = mapStore.getNestedStore('foo', (value) => {
+            return value.store;
+        });
+
+        mapStore.set('foo', {
+            foo: 'bar',
+            store: writable('init')
+        });
+
+        expect(get(fooStore)).toBe('init');
+
+        mapStore.get('foo')?.store.set('newVal');
+
+        expect(get(fooStore)).toBe('newVal');
+
+        mapStore.set('foo', {
+            foo: 'bar',
+            store: writable('anotherVal')
+        });
+
+        expect(get(fooStore)).toBe('anotherVal');
+
+        mapStore.delete('foo');
+
+        expect(get(fooStore)).toBeUndefined();
+
+    });
+});