/**
 * @fileoverview Regression tests for the buffer-load flush path: what becomes of
 * the live terminal events queued while a buffer load runs, once the load ends.
 *
 * Two rules, each from a real bug.
 *
 * COD-144: newly launched Shell sessions rendered BLANK until a tab-switch. The
 * load path (`selectSession` → `_beginBufferLoad`/`_finishBufferLoad`) queues
 * live events while `_isLoadingBuffer` is true and used to DISCARD the queue on
 * completion. Right for a buffer built from the server's byte history (the
 * queued output is already in it, so replaying it duplicates Ink redraws),
 * wrong for a brand-new shell whose fetch resolves BEFORE the PTY emits its
 * prompt: the prompt arrived only as a queued event and was thrown away. A
 * caller that knows the load painted nothing passes `{ flushQueued: true }`
 * and the queue is REPLAYED through `batchTerminalWrite()` after
 * `_isLoadingBuffer` is cleared, so the events write through normally.
 *
 * #436: a tmux pane capture is current only as of the instant `capture-pane`
 * ran, so everything the CLI printed between the capture and the end of the
 * chunked write was queued and dropped, and its next partial redraw landed on
 * a frame the terminal never received. Queue entries now carry their arrival
 * time and `_finishBufferLoad` takes a `since` cutoff, so a capture load
 * replays exactly the tail that arrived after the response headers. All four
 * fetch-and-write paths take that policy from one helper,
 * `_bufferLoadFinishOpts`, and a static scan below pins each of them to it,
 * because the same fix had already been written into one path out of four,
 * twice. A path that replays and then restores a scroll position re-takes the
 * sticky-scroll baseline (`_syncStickyScrollBaseline`), pinned the same way.
 *
 * Loaded via `vm` with a stubbed context (no jsdom — jsdom is broken on this
 * box; see connection-indicator.test.ts). We extract the REAL
 * `_beginBufferLoad`/`_finishBufferLoad` mixin methods from terminal-ui.js by
 * running it against a fake `CodemanApp` and capturing `CodemanApp.prototype`,
 * then copy them onto a minimal stub whose `batchTerminalWrite` is a spy. This
 * exercises the real flush/discard logic without a full xterm fake.
 */
import { readFileSync } from 'node:fs';
import { performance } from 'node:perf_hooks';
import { resolve } from 'node:path';
import vm from 'node:vm';
import { describe, expect, it, vi } from 'vitest';

/** Run terminal-ui.js in a vm against a fake CodemanApp and return the captured prototype mixin. */
function loadTerminalMixin(): Record<string, unknown> {
  const source = readFileSync(resolve(import.meta.dirname, '../src/web/public/terminal-ui.js'), 'utf8');
  const FakeCodemanApp = function () {} as unknown as { prototype: Record<string, unknown> };
  const context = vm.createContext({
    console,
    performance,
    setTimeout,
    clearTimeout,
    setInterval: vi.fn(),
    clearInterval: vi.fn(),
    requestAnimationFrame: vi.fn(),
    CodemanApp: FakeCodemanApp,
    // terminal-ui.js IIFE is invoked with `window`; it reads/writes a few globals.
    window: { addEventListener: vi.fn(), removeEventListener: vi.fn() },
    document: { addEventListener: vi.fn() },
  });
  vm.runInContext(source, context);
  return FakeCodemanApp.prototype;
}

const mixin = loadTerminalMixin();

type BufferLoadApp = {
  _bufferLoadSeq: number;
  _bufferLoadOwner: string | null;
  _isLoadingBuffer: boolean;
  _loadBufferQueue: { at: number; data: string }[] | null;
  batchTerminalWrite: (data: string) => void;
  _beginBufferLoad: (owner?: string) => string;
  _finishBufferLoad: (owner?: string, opts?: { flushQueued?: boolean; since?: number }) => boolean;
};

/**
 * Minimal stub carrying the buffer-load state plus the REAL begin/finish methods.
 * `batchTerminalWrite` is a spy so flushed events are observable without a real
 * xterm terminal. The real `batchTerminalWrite` would queue while loading, but
 * the flush runs AFTER `_isLoadingBuffer` is cleared, so a spy is faithful here.
 */
function makeApp() {
  const writes: string[] = [];
  const app: BufferLoadApp = {
    _bufferLoadSeq: 0,
    _bufferLoadOwner: null,
    _isLoadingBuffer: false,
    _loadBufferQueue: null,
    batchTerminalWrite: vi.fn((data: string) => {
      writes.push(data);
    }),
    _beginBufferLoad: mixin._beginBufferLoad as BufferLoadApp['_beginBufferLoad'],
    _finishBufferLoad: mixin._finishBufferLoad as BufferLoadApp['_finishBufferLoad'],
  };
  return { app, writes };
}

/**
 * A stub carrying the REAL `batchTerminalWrite` on top of the real begin/finish
 * methods, so a replay samples the sticky-scroll baseline exactly as it does in
 * the browser. The terminal is a fake whose `buffer.active` the test moves by
 * hand, which is what a caller's `scrollToLine` does to a real one.
 */
function makeScrollApp() {
  const buffer = { viewportY: 0, baseY: 100 };
  const app = {
    buffer,
    terminal: { buffer: { active: buffer } },
    sessions: new Map(),
    activeSessionId: null,
    pendingWrites: [] as string[],
    writeFrameScheduled: false,
    _wasAtBottomBeforeWrite: false,
    _bufferLoadSeq: 0,
    _bufferLoadOwner: null as string | null,
    _isLoadingBuffer: false,
    _loadBufferQueue: null as { at: number; data: string }[] | null,
    _scheduleTerminalWriteFlush: vi.fn(),
    batchTerminalWrite: mixin.batchTerminalWrite as (data: string) => void,
    isTerminalAtBottom: mixin.isTerminalAtBottom as () => boolean,
    _syncStickyScrollBaseline: mixin._syncStickyScrollBaseline as () => void,
    _beginBufferLoad: mixin._beginBufferLoad as BufferLoadApp['_beginBufferLoad'],
    _finishBufferLoad: mixin._finishBufferLoad as BufferLoadApp['_finishBufferLoad'],
  };
  return app;
}

/**
 * Slice one class method out of app.js, from its header to the next method's.
 *
 * Bounding the slice matters: the two methods checked below are not followed by
 * a JSDoc block, so a scan for the next comment would run on into unrelated
 * code and match its scroll calls instead of theirs.
 */
function methodBody(source: string, method: string): string {
  const start = source.search(new RegExp(`^ {2}(?:async )?${method}\\(`, 'm'));
  expect(start, `${method} not found in app.js`).toBeGreaterThan(-1);
  const next = /^ {2}(?:async )?[A-Za-z_$][\w$]*\(/m.exec(source.slice(start + 1));
  return next ? source.slice(start, start + 1 + next.index) : source.slice(start);
}

/**
 * Simulate a live SSE event arriving while a buffer load is in progress.
 * Mirrors batchTerminalWrite's queue branch, which stamps each entry with its
 * arrival time so a flush can replay only the tail (see the `since` tests).
 */
function pushWhileLoading(app: BufferLoadApp, data: string, at = performance.now()) {
  if (app._isLoadingBuffer && app._loadBufferQueue) app._loadBufferQueue.push({ at, data });
}

describe('buffer-load flush (COD-144)', () => {
  it('finish WITHOUT flushQueued discards the queue (de-dup preserved for established sessions)', () => {
    const { app, writes } = makeApp();
    const owner = app._beginBufferLoad('load-1');
    pushWhileLoading(app, 'chunk-a');
    pushWhileLoading(app, 'chunk-b');

    const ok = app._finishBufferLoad(owner); // default: discard
    expect(ok).toBe(true);
    expect(app._isLoadingBuffer).toBe(false);
    expect(app._loadBufferQueue).toBeNull();
    // Queued events were NOT replayed.
    expect(app.batchTerminalWrite).not.toHaveBeenCalled();
    expect(writes).toEqual([]);
  });

  it('finish WITH { flushQueued: true } replays queued events in order, exactly once each', () => {
    const { app, writes } = makeApp();
    const owner = app._beginBufferLoad('load-2');
    pushWhileLoading(app, 'prompt-1');
    pushWhileLoading(app, 'prompt-2');

    const ok = app._finishBufferLoad(owner, { flushQueued: true });
    expect(ok).toBe(true);
    expect(app._isLoadingBuffer).toBe(false);
    expect(app._loadBufferQueue).toBeNull();
    // Both chunks replayed, IN ORDER, exactly once each.
    expect(writes).toEqual(['prompt-1', 'prompt-2']);
    expect(app.batchTerminalWrite).toHaveBeenCalledTimes(2);
    expect(app.batchTerminalWrite).toHaveBeenNthCalledWith(1, 'prompt-1');
    expect(app.batchTerminalWrite).toHaveBeenNthCalledWith(2, 'prompt-2');
  });

  it('flushed events are not re-queued (the queue is null when batchTerminalWrite runs)', () => {
    const { app } = makeApp();
    const owner = app._beginBufferLoad('load-3');
    pushWhileLoading(app, 'only');

    // Spy that, like the real method, would re-queue if loading were still active.
    let reQueued = false;
    app.batchTerminalWrite = vi.fn((data: string) => {
      if (app._isLoadingBuffer && app._loadBufferQueue) {
        app._loadBufferQueue.push(data);
        reQueued = true;
      }
    });

    app._finishBufferLoad(owner, { flushQueued: true });
    expect(reQueued).toBe(false);
    expect(app._isLoadingBuffer).toBe(false);
    expect(app._loadBufferQueue).toBeNull();
  });

  it('owner mismatch returns false and does NOT flush or clear state', () => {
    const { app, writes } = makeApp();
    app._beginBufferLoad('real-owner');
    pushWhileLoading(app, 'queued');

    const ok = app._finishBufferLoad('wrong-owner', { flushQueued: true });
    expect(ok).toBe(false);
    // State untouched — still loading, queue intact, nothing replayed.
    expect(app._isLoadingBuffer).toBe(true);
    expect(app._bufferLoadOwner).toBe('real-owner');
    expect(app._loadBufferQueue).toEqual([{ at: expect.any(Number), data: 'queued' }]);
    expect(app.batchTerminalWrite).not.toHaveBeenCalled();
    expect(writes).toEqual([]);
  });

  // ── The tmux-capture tail: `since` ──
  //
  // A pane capture is a point-in-time frame taken part-way through the fetch, so
  // it holds what arrived BEFORE the capture and nothing after. selectSession
  // passes the response's arrival time as `since`, which splits the queue at
  // exactly that line: pre-capture events are already painted and must stay
  // dropped, post-capture events exist nowhere else and must be replayed.

  it('flushes only the entries at or after `since`', () => {
    const { app, writes } = makeApp();
    const owner = app._beginBufferLoad('load-since');
    pushWhileLoading(app, 'already-in-the-capture', 100);
    pushWhileLoading(app, 'arrived-at-the-headers', 200);
    pushWhileLoading(app, 'arrived-after-the-headers', 300);

    app._finishBufferLoad(owner, { flushQueued: true, since: 200 });

    // The pre-capture event stays dropped; the boundary entry counts as after.
    expect(writes).toEqual(['arrived-at-the-headers', 'arrived-after-the-headers']);
  });

  it('flushQueued without `since` still replays the whole queue', () => {
    // The COD-144 path: a brand-new session's first prompt predates the
    // response, so cutting the queue would drop the only content it has.
    const { app, writes } = makeApp();
    const owner = app._beginBufferLoad('load-no-since');
    pushWhileLoading(app, 'prompt', 10);
    pushWhileLoading(app, 'more', 20);

    app._finishBufferLoad(owner, { flushQueued: true });

    expect(writes).toEqual(['prompt', 'more']);
  });

  it('a `since` past every entry flushes nothing', () => {
    const { app, writes } = makeApp();
    const owner = app._beginBufferLoad('load-since-late');
    pushWhileLoading(app, 'old', 10);

    app._finishBufferLoad(owner, { flushQueued: true, since: 999 });

    expect(writes).toEqual([]);
    expect(app.batchTerminalWrite).not.toHaveBeenCalled();
  });

  // ── Re-entering one load ──
  //
  // `selectSession` opens the load before its fetch, and `chunkedTerminalWrite`
  // opens it again under the SAME owner when it starts writing. A reset on that
  // second call would silently throw away everything queued during the fetch,
  // which on the capture path is output no buffer holds.

  it('re-entering the same load keeps what the queue already holds', () => {
    const { app, writes } = makeApp();
    const owner = app._beginBufferLoad('load-reenter');
    pushWhileLoading(app, 'arrived-during-the-fetch', 100);

    // chunkedTerminalWrite re-opens the load it was handed.
    app._beginBufferLoad(owner);
    pushWhileLoading(app, 'arrived-during-the-write', 200);

    app._finishBufferLoad(owner, { flushQueued: true, since: 50 });

    expect(writes).toEqual(['arrived-during-the-fetch', 'arrived-during-the-write']);
  });

  it('a genuinely different load still starts with an empty queue', () => {
    const { app, writes } = makeApp();
    app._beginBufferLoad('load-first');
    pushWhileLoading(app, 'belongs-to-the-abandoned-load', 100);

    // A tab switch starts a new load under a new owner. Its events are not ours.
    const second = app._beginBufferLoad('load-second');
    pushWhileLoading(app, 'belongs-to-this-load', 200);

    app._finishBufferLoad(second, { flushQueued: true, since: 0 });

    expect(writes).toEqual(['belongs-to-this-load']);
  });

  // ── The sticky-scroll baseline across a replay ──
  //
  // `batchTerminalWrite` samples `_wasAtBottomBeforeWrite` before queueing, and
  // `flushPendingWrites` scrolls to the bottom off that sample. The replay runs
  // inside `chunkedTerminalWrite` before its promise resolves, with the terminal
  // freshly reset and rewritten, so the sample is always true. A caller that
  // then restores the reader's position would have that restore undone.

  it('the replay latches the baseline true, and the viewport restore re-takes it', () => {
    const app = makeScrollApp();
    const owner = app._beginBufferLoad('load-scroll');
    pushWhileLoading(app as unknown as BufferLoadApp, 'output-after-the-capture', 100);

    // The load ends with the terminal reset and rewritten, so it reads as bottom.
    app.buffer.viewportY = app.buffer.baseY;
    app._finishBufferLoad(owner, { flushQueued: true, since: 0 });
    expect(app._wasAtBottomBeforeWrite).toBe(true);

    // The caller now puts the reader back where they were reading.
    app.buffer.viewportY = 40;
    app._syncStickyScrollBaseline();

    // The next flush must leave them there.
    expect(app._wasAtBottomBeforeWrite).toBe(false);
  });

  it('a restore that lands back at the bottom keeps sticky scroll armed', () => {
    const app = makeScrollApp();
    const owner = app._beginBufferLoad('load-scroll-bottom');
    pushWhileLoading(app as unknown as BufferLoadApp, 'output-after-the-capture', 100);

    app.buffer.viewportY = app.buffer.baseY;
    app._finishBufferLoad(owner, { flushQueued: true, since: 0 });
    app._syncStickyScrollBaseline();

    // A reader who was already at the bottom still wants to be carried along.
    expect(app._wasAtBottomBeforeWrite).toBe(true);
  });

  it('both callers that restore a scroll position re-take the baseline', () => {
    // The wiring lives in app.js, outside this file's vm harness. Without it the
    // two methods below restore the viewport and the next flush undoes it.
    const source = readFileSync(resolve(import.meta.dirname, '../src/web/public/app.js'), 'utf8');

    for (const method of ['_onSessionNeedsRefresh', '_maybeRefetchFullHistory']) {
      const body = methodBody(source, method);
      const restoreAt = body.lastIndexOf('scrollToLine(');
      const syncAt = body.indexOf('this._syncStickyScrollBaseline()');
      expect(restoreAt, `${method} no longer restores a scroll position`).toBeGreaterThan(-1);
      expect(syncAt, `${method} never re-takes the baseline`).toBeGreaterThan(-1);
      expect(syncAt, `${method} re-takes the baseline before its restore`).toBeGreaterThan(restoreAt);
    }
  });

  it('every path that fetches a terminal buffer and writes it asks the shared helper', () => {
    // Drift guard. The first version of this fix covered one of the four paths,
    // and a later pass found it still covering one of four. Nothing else in the
    // gate stops a fifth path, or an inlined `{ flushQueued: true }`, from
    // splitting the policy up again; the browser suite that would notice does
    // not run in CI.
    const source = readFileSync(resolve(import.meta.dirname, '../src/web/public/app.js'), 'utf8');

    for (const method of [
      'selectSession',
      '_onSessionNeedsRefresh',
      '_onSessionClearTerminal',
      '_maybeRefetchFullHistory',
    ]) {
      expect(methodBody(source, method), `${method} decides the flush policy itself`).toContain(
        'this._bufferLoadFinishOpts('
      );
    }
  });

  it('empty queue + flushQueued is a no-op (no throw, no writes)', () => {
    const { app, writes } = makeApp();
    const owner = app._beginBufferLoad('load-empty');
    // No events queued.

    expect(() => app._finishBufferLoad(owner, { flushQueued: true })).not.toThrow();
    expect(app._isLoadingBuffer).toBe(false);
    expect(app._loadBufferQueue).toBeNull();
    expect(app.batchTerminalWrite).not.toHaveBeenCalled();
    expect(writes).toEqual([]);
  });
});