feat: introduce intersection calculation of charts

packages/backend/src/services/chart/charts/test-intersection.ts

@@ -0,0 +1,32 @@
+import autobind from 'autobind-decorator';
+import Chart, { KVs } from '../core';
+import { name, schema } from './entities/test-intersection';
+
+/**
+ * For testing
+ */
+// eslint-disable-next-line import/no-default-export
+export default class TestIntersectionChart extends Chart<typeof schema> {
+	constructor() {
+		super(name, schema);
+	}
+
+	@autobind
+	protected async queryCurrentState(): Promise<Partial<KVs<typeof schema>>> {
+		return {};
+	}
+
+	@autobind
+	public async addA(key: string): Promise<void> {
+		await this.commit({
+			a: [key],
+		});
+	}
+
+	@autobind
+	public async addB(key: string): Promise<void> {
+		await this.commit({
+			b: [key],
+		});
+	}
+}