SubMiner/src/core/services/subtitle-prefetch.test.ts

import assert from 'node:assert/strict';
import test from 'node:test';
import {
  computePriorityWindow,
  createSubtitlePrefetchService,
} from './subtitle-prefetch';
import type { SubtitleCue } from './subtitle-cue-parser';
import type { SubtitleData } from '../../types';

function makeCues(count: number, startOffset = 0): SubtitleCue[] {
  return Array.from({ length: count }, (_, i) => ({
    startTime: startOffset + i * 5,
    endTime: startOffset + i * 5 + 4,
    text: `line-${i}`,
  }));
}

test('computePriorityWindow returns next N cues from current position', () => {
  const cues = makeCues(20);
  const window = computePriorityWindow(cues, 12.0, 5);

  assert.equal(window.length, 5);
  // Position 12.0 is during cue index 2 (start=10, end=14). Priority window starts from index 3.
  assert.equal(window[0]!.text, 'line-3');
  assert.equal(window[4]!.text, 'line-7');
});

test('computePriorityWindow clamps to remaining cues at end of file', () => {
  const cues = makeCues(5);
  const window = computePriorityWindow(cues, 18.0, 10);

  // Position 18.0 is during cue 3 (start=15). Only cue 4 is ahead.
  assert.equal(window.length, 1);
  assert.equal(window[0]!.text, 'line-4');
});

test('computePriorityWindow returns empty when past all cues', () => {
  const cues = makeCues(3);
  const window = computePriorityWindow(cues, 999.0, 10);
  assert.equal(window.length, 0);
});

test('computePriorityWindow at position 0 returns first N cues', () => {
  const cues = makeCues(20);
  const window = computePriorityWindow(cues, 0, 5);

  assert.equal(window.length, 5);
  assert.equal(window[0]!.text, 'line-0');
});

function flushMicrotasks(): Promise<void> {
  return new Promise((resolve) => setTimeout(resolve, 0));
}

test('prefetch service tokenizes priority window cues and caches them', async () => {
  const cues = makeCues(20);
  const cached: Map<string, SubtitleData> = new Map();
  let tokenizeCalls = 0;

  const service = createSubtitlePrefetchService({
    cues,
    tokenizeSubtitle: async (text) => {
      tokenizeCalls += 1;
      return { text, tokens: [] };
    },
    preCacheTokenization: (text, data) => {
      cached.set(text, data);
    },
    isCacheFull: () => false,
    priorityWindowSize: 3,
  });

  service.start(0);
  // Allow all async tokenization to complete
  for (let i = 0; i < 25; i += 1) {
    await flushMicrotasks();
  }
  service.stop();

  // Priority window (first 3) should be cached
  assert.ok(cached.has('line-0'));
  assert.ok(cached.has('line-1'));
  assert.ok(cached.has('line-2'));
});

test('prefetch service stops when cache is full', async () => {
  const cues = makeCues(20);
  let tokenizeCalls = 0;
  let cacheSize = 0;

  const service = createSubtitlePrefetchService({
    cues,
    tokenizeSubtitle: async (text) => {
      tokenizeCalls += 1;
      return { text, tokens: [] };
    },
    preCacheTokenization: () => {
      cacheSize += 1;
    },
    isCacheFull: () => cacheSize >= 5,
    priorityWindowSize: 3,
  });

  service.start(0);
  for (let i = 0; i < 30; i += 1) {
    await flushMicrotasks();
  }
  service.stop();

  // Should have stopped at 5 (cache full), not tokenized all 20
  assert.ok(tokenizeCalls <= 6, `Expected <= 6 tokenize calls, got ${tokenizeCalls}`);
});

test('prefetch service can be stopped mid-flight', async () => {
  const cues = makeCues(100);
  let tokenizeCalls = 0;

  const service = createSubtitlePrefetchService({
    cues,
    tokenizeSubtitle: async (text) => {
      tokenizeCalls += 1;
      return { text, tokens: [] };
    },
    preCacheTokenization: () => {},
    isCacheFull: () => false,
    priorityWindowSize: 3,
  });

  service.start(0);
  await flushMicrotasks();
  await flushMicrotasks();
  service.stop();
  const callsAtStop = tokenizeCalls;

  // Wait more to confirm no further calls
  for (let i = 0; i < 10; i += 1) {
    await flushMicrotasks();
  }

  assert.equal(tokenizeCalls, callsAtStop, 'No further tokenize calls after stop');
  assert.ok(tokenizeCalls < 100, 'Should not have tokenized all cues');
});