/**
 * @fileoverview Exactly-once input delivery — Session.shouldApplyInput dedup.
 *
 * Guards the server half of the reliable-input-delivery feature: the web client
 * tags each input frame with a stable clientId + a monotonic per-session seq and
 * redelivers anything it hasn't seen ACKed (a half-open socket silently drops
 * frames on a flaky link). shouldApplyInput must apply each (clientId, seq)
 * exactly once so a redelivery can never type the prompt twice — while still
 * applying untagged input (curl/legacy) unconditionally at the call sites.
 *
 * See docs/reliable-input-delivery.md.
 */
import { describe, it, expect } from 'vitest';
import { Session } from '../src/session.js';

function makeSession(): Session {
  // workingDir is the only required field; no PTY is spawned until start(),
  // and TmuxManager no-ops under VITEST — so this is a cheap, side-effect-free
  // instance for exercising the pure dedup bookkeeping.
  return new Session({ workingDir: '/tmp' });
}

describe('Session.shouldApplyInput (exactly-once input dedup)', () => {
  it('applies a fresh (clientId, seq) exactly once', () => {
    const s = makeSession();
    expect(s.shouldApplyInput('clientA', 1)).toBe(true);
    // Same seq redelivered (lost ACK) — must NOT apply again.
    expect(s.shouldApplyInput('clientA', 1)).toBe(false);
  });

  it('applies strictly increasing seqs and rejects stale ones', () => {
    const s = makeSession();
    expect(s.shouldApplyInput('c', 1)).toBe(true);
    expect(s.shouldApplyInput('c', 2)).toBe(true);
    expect(s.shouldApplyInput('c', 3)).toBe(true);
    // Out-of-order / replayed lower seqs are duplicates.
    expect(s.shouldApplyInput('c', 2)).toBe(false);
    expect(s.shouldApplyInput('c', 1)).toBe(false);
    // The next genuinely-new seq still applies.
    expect(s.shouldApplyInput('c', 4)).toBe(true);
  });

  it('tracks each client independently', () => {
    const s = makeSession();
    expect(s.shouldApplyInput('a', 5)).toBe(true);
    // A different client at seq 1 is not shadowed by client a's higher seq.
    expect(s.shouldApplyInput('b', 1)).toBe(true);
    expect(s.shouldApplyInput('b', 1)).toBe(false);
    expect(s.shouldApplyInput('a', 6)).toBe(true);
  });

  it('tolerates a seq gap (skips never collapse a new seq to a duplicate)', () => {
    const s = makeSession();
    expect(s.shouldApplyInput('c', 1)).toBe(true);
    // Client jumped seq (e.g. resumed after a reload that kept the counter).
    expect(s.shouldApplyInput('c', 100)).toBe(true);
    expect(s.shouldApplyInput('c', 100)).toBe(false);
    expect(s.shouldApplyInput('c', 50)).toBe(false);
    expect(s.shouldApplyInput('c', 101)).toBe(true);
  });

  it('keeps recent clients dedup-correct past the eviction bound', () => {
    const s = makeSession();
    // Far exceed MAX_INPUT_DEDUP_CLIENTS (256) with one-shot clients, then prove
    // a freshly-active client is still deduped correctly (MRU eviction).
    for (let i = 0; i < 400; i++) {
      expect(s.shouldApplyInput(`oneshot-${i}`, 1)).toBe(true);
    }
    expect(s.shouldApplyInput('recent', 1)).toBe(true);
    expect(s.shouldApplyInput('recent', 1)).toBe(false);
    expect(s.shouldApplyInput('recent', 2)).toBe(true);
  });
});

describe('Session.lastInputSeq (the watermark a stuck client needs)', () => {
  it('reports 0 for a client it has never seen', () => {
    expect(makeSession().lastInputSeq('c-new')).toBe(0);
  });

  it('reports the highest seq applied for that client', () => {
    const s = makeSession();
    s.shouldApplyInput('c-1', 7);
    expect(s.lastInputSeq('c-1')).toBe(7);
  });

  it('is what a rolled-back client must clear to be heard again', () => {
    // The failure this exists for: the client's seq counter persists on a
    // DEBOUNCED write, so a tab killed between a send and that write comes back
    // counting from below the watermark. Every later keystroke then lands at or
    // under it and is rejected — silently, because a rejected frame is ACKed too.
    const s = makeSession();
    for (let i = 1; i <= 40; i++) s.shouldApplyInput('c-1', i);
    // Restored counter starts over at 1: dropped, and every subsequent one too.
    expect(s.shouldApplyInput('c-1', 1)).toBe(false);
    expect(s.shouldApplyInput('c-1', 2)).toBe(false);
    // The watermark it is handed back is exactly what makes it recoverable.
    const watermark = s.lastInputSeq('c-1');
    expect(watermark).toBe(40);
    expect(s.shouldApplyInput('c-1', watermark + 1)).toBe(true);
  });

  it('does not resurrect a seq that forgetInputSeq rolled back', () => {
    const s = makeSession();
    s.shouldApplyInput('c-1', 5);
    s.forgetInputSeq('c-1', 5);
    expect(s.lastInputSeq('c-1')).toBe(4);
    expect(s.shouldApplyInput('c-1', 5)).toBe(true);
  });
});