import EventEmitter from 'events';
import { exportStore } from '../../../src/static/js/utils/helpers';

// The dispatcher is an external module dependency used by exportStore; mock it to observe registrations
jest.mock('../../../src/static/js/utils/dispatcher', () => ({
    dispatcher: {
        register: jest.fn(),
    },
}));

import { dispatcher } from '../../../src/static/js/utils/dispatcher';

/**
 * Behaviors covered:
 * 1. Binds the provided handler method to store instance context.
 * 2. Registers the bound callback exactly once with the dispatcher.
 * 3. Returns the same store instance that was provided.
 * 4. Invoking the registered callback forwards payload to the handler with correct this.
 * 5. Type-safety assumption: only function keys are accepted as handler (runtime sanity via mock class).
 */

describe('utils/helpers', () => {
    describe('exportStore', () => {
        class TestStore extends (EventEmitter as { new (): EventEmitter }) {
            public calls: unknown[] = [];
            public handler(payload: unknown) {
                // Assert `this` is the store instance when called via bound function
                this.calls.push({ self: this, payload });
            }
            public otherHandler(payload: unknown) {
                this.calls.push({ self: this, payload, type: 'other' });
            }
        }

        beforeEach(() => {
            jest.clearAllMocks();
        });

        test('Returns the same store instance and registers exactly once', () => {
            const store = new TestStore();
            const returned = exportStore(store as unknown as EventEmitter, 'handler' as any);
            expect(returned).toBe(store);
            expect(dispatcher.register).toHaveBeenCalledTimes(1);
            expect(typeof (dispatcher.register as jest.Mock).mock.calls[0][0]).toBe('function');
        });

        test('Binds the handler to the store instance context', () => {
            const store = new TestStore();
            exportStore(store as unknown as EventEmitter, 'handler' as any);

            const registered = (dispatcher.register as jest.Mock).mock.calls[0][0] as (p: unknown) => void;
            const payload = { a: 1 };
            registered(payload);

            expect(store.calls).toHaveLength(1);
            const { self, payload: received } = store.calls[0] as any;
            expect(self).toBe(store);
            expect(received).toBe(payload);
        });

        test('Forwards any payload through the registered callback to the handler', () => {
            const store = new TestStore();
            exportStore(store as unknown as EventEmitter, 'otherHandler' as any);

            const registered = (dispatcher.register as jest.Mock).mock.calls[0][0] as (p: unknown) => void;
            registered(null);
            registered(42);
            registered({ x: 'y' });

            expect(store.calls.map((c: any) => c.payload)).toEqual([null, 42, { x: 'y' }]);
        });

        test('Supports different handler keys of the same store', () => {
            const store = new TestStore();
            exportStore(store as unknown as EventEmitter, 'handler' as any);
            exportStore(store as unknown as EventEmitter, 'otherHandler' as any);

            expect(dispatcher.register).toHaveBeenCalledTimes(2);
            const cb1 = (dispatcher.register as jest.Mock).mock.calls[0][0] as (p: unknown) => void;
            const cb2 = (dispatcher.register as jest.Mock).mock.calls[1][0] as (p: unknown) => void;

            cb1('a');
            cb2('b');

            expect(store.calls).toHaveLength(2);
            expect(store.calls[0]).toMatchObject({ payload: 'a' });
            expect(store.calls[1]).toMatchObject({ payload: 'b', type: 'other' });
        });

        test('Runtime guard scenario: non-existing handler results in TypeError on bind access', () => {
            const store = new TestStore();
            // @ts-expect-error intentionally passing wrong key to simulate runtime misuse
            expect(() => exportStore(store as unknown as EventEmitter, 'notAHandler')).toThrow();
        });
    });
});