import {
    describe,
    it,
    expect,
    vi,
    beforeEach,
    afterEach,
    type MockInstance
} from 'vitest';
import { handle } from './hooks.server';

// `BACKEND_URL` is read at module load time, so the values used in the
// asserts below assume the test env didn't set it. `?? 'http://localhost:8080'`
// is the default.
const DEFAULT_BACKEND = 'http://localhost:8080';

function makeEvent(path: string, init?: RequestInit) {
    const url = new URL(`http://app.example.com${path}`);
    const request = new Request(url, init);
    return { url, request } as Parameters<typeof handle>[0]['event'];
}

describe('hooks.server proxy', () => {
    let fetchSpy: MockInstance<typeof globalThis.fetch>;

    beforeEach(() => {
        fetchSpy = vi.spyOn(globalThis, 'fetch');
    });
    afterEach(() => {
        vi.restoreAllMocks();
    });

    it('forwards /api/* requests to the backend, preserving status', async () => {
        fetchSpy.mockResolvedValueOnce(
            new Response(JSON.stringify({ status: 'ok' }), {
                status: 200,
                headers: { 'content-type': 'application/json' }
            })
        );
        const resolve = vi.fn();

        const event = makeEvent('/api/v1/health');
        const resp = await handle({ event, resolve });

        expect(resolve).not.toHaveBeenCalled();
        expect(fetchSpy).toHaveBeenCalledTimes(1);
        expect(fetchSpy.mock.calls[0][0]).toBe(`${DEFAULT_BACKEND}/api/v1/health`);
        expect(resp.status).toBe(200);
        expect(await resp.json()).toEqual({ status: 'ok' });
    });

    it('passes through the query string', async () => {
        fetchSpy.mockResolvedValueOnce(new Response('[]', { status: 200 }));
        const resolve = vi.fn();
        await handle({
            event: makeEvent('/api/v1/mangas?search=narto&limit=10'),
            resolve
        });
        expect(fetchSpy.mock.calls[0][0]).toBe(
            `${DEFAULT_BACKEND}/api/v1/mangas?search=narto&limit=10`
        );
    });

    it('strips the host header so the backend sees its own origin', async () => {
        fetchSpy.mockResolvedValueOnce(new Response('[]', { status: 200 }));
        const resolve = vi.fn();
        await handle({
            event: makeEvent('/api/v1/health', {
                headers: { host: 'app.example.com', cookie: 'mangalord_session=abc' }
            }),
            resolve
        });
        const init = fetchSpy.mock.calls[0][1] as RequestInit;
        const headers = init.headers as Headers;
        expect(headers.get('host')).toBeNull();
        // Cookies must still be forwarded — that's how the session reaches axum.
        expect(headers.get('cookie')).toBe('mangalord_session=abc');
    });

    it('forwards request bodies on POST', async () => {
        fetchSpy.mockResolvedValueOnce(new Response('{}', { status: 201 }));
        const resolve = vi.fn();
        await handle({
            event: makeEvent('/api/v1/auth/login', {
                method: 'POST',
                headers: { 'content-type': 'application/json' },
                body: JSON.stringify({ username: 'alice', password: 'hunter2hunter2' })
            }),
            resolve
        });
        const init = fetchSpy.mock.calls[0][1] as RequestInit;
        expect(init.method).toBe('POST');
        expect(init.body).toBeDefined();
    });

    it('delegates non-/api requests to SvelteKit', async () => {
        const resolve = vi.fn().mockResolvedValue(new Response('page', { status: 200 }));

        await handle({ event: makeEvent('/manga/abc'), resolve });

        expect(fetchSpy).not.toHaveBeenCalled();
        expect(resolve).toHaveBeenCalledTimes(1);
    });

    it('returns 502 with the standard error envelope when the upstream is unreachable', async () => {
        // Silence the console.error the handler emits on failure so
        // the test output stays clean.
        const errSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
        fetchSpy.mockRejectedValueOnce(new TypeError('fetch failed'));

        const resolve = vi.fn();
        const resp = await handle({ event: makeEvent('/api/v1/health'), resolve });

        expect(resolve).not.toHaveBeenCalled();
        expect(resp.status).toBe(502);
        expect(resp.headers.get('content-type')).toContain('application/json');
        const body = await resp.json();
        expect(body.error.code).toBe('upstream_unavailable');
        expect(errSpy).toHaveBeenCalled();
    });

    it('strips every hop-by-hop header listed in RFC 7230 §6.1', async () => {
        // Defence in depth: axum doesn't emit these, but a future
        // middleware that did would otherwise leak per-connection
        // state across the proxy boundary.
        fetchSpy.mockResolvedValueOnce(new Response('[]', { status: 200 }));
        const resolve = vi.fn();
        await handle({
            event: makeEvent('/api/v1/health', {
                headers: {
                    host: 'app.example.com',
                    'content-length': '0',
                    connection: 'keep-alive',
                    'keep-alive': 'timeout=5',
                    'proxy-authenticate': 'Basic realm=x',
                    'proxy-authorization': 'Basic xyz',
                    te: 'trailers',
                    trailer: 'Expires',
                    'transfer-encoding': 'chunked',
                    upgrade: 'websocket',
                    // A non-hop-by-hop header to ensure non-targets
                    // aren't accidentally stripped.
                    'x-custom': 'pass-through'
                }
            }),
            resolve
        });
        const init = fetchSpy.mock.calls[0][1] as RequestInit;
        const headers = init.headers as Headers;
        for (const h of [
            'host',
            'content-length',
            'connection',
            'keep-alive',
            'proxy-authenticate',
            'proxy-authorization',
            'te',
            'trailer',
            'transfer-encoding',
            'upgrade'
        ]) {
            expect(headers.get(h), `${h} should be stripped`).toBeNull();
        }
        expect(headers.get('x-custom')).toBe('pass-through');
    });

    it('aborts and returns 502 when the upstream stalls past the timeout', async () => {
        const errSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
        // Simulate an aborted fetch (AbortController.abort() raises a
        // DOMException with name 'AbortError' on Node's fetch). The
        // handler should treat it as the same upstream_unavailable
        // 502 it uses for any other network failure.
        const abortErr = new DOMException('aborted', 'AbortError');
        fetchSpy.mockRejectedValueOnce(abortErr);

        const resolve = vi.fn();
        const resp = await handle({ event: makeEvent('/api/v1/slow'), resolve });
        expect(resp.status).toBe(502);
        const body = await resp.json();
        expect(body.error.code).toBe('upstream_unavailable');
        expect(errSpy).toHaveBeenCalled();
    });

    it('attaches an AbortSignal to the upstream fetch so it can time out', async () => {
        fetchSpy.mockResolvedValueOnce(new Response('[]', { status: 200 }));
        const resolve = vi.fn();
        await handle({ event: makeEvent('/api/v1/health'), resolve });
        const init = fetchSpy.mock.calls[0][1] as RequestInit;
        expect(init.signal).toBeInstanceOf(AbortSignal);
        // The signal hasn't fired (handler returned in time), but its
        // presence is the contract this test is pinning.
        expect(init.signal?.aborted).toBe(false);
    });
});