import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:kouyu_english/core/app_state.dart';
import 'package:kouyu_english/core/courses/course_pack.dart';
import 'package:kouyu_english/core/courses/courses.dart';
import 'package:kouyu_english/core/models.dart';
import 'package:kouyu_english/features/words/words_page.dart';

/// Learning engine 3.5: the recognition-only layer — one success to 「认识」,
/// a second one at least seven days later to 「熟悉」, a monthly spot check
/// after that, and a miss that only ever drops back to 「认识」.
/// Calendar days from today to the day the word is next due.
///
/// A miss schedules by wall clock (tomorrow morning), not by adding 24 hours,
/// so measuring the gap as a duration answers 0 for a test run in the evening.
/// Counting days on the calendar is what the ladder actually means.
int gapDays(DateTime? due) {
  final today = DateTime.now();
  return DateTime(due!.year, due.month, due.day)
      .difference(DateTime(today.year, today.month, today.day))
      .inDays;
}

void main() {
  setUp(() {
    registerSavedWord('t-ready', en: 'ready', zh: '准备好', level: 'A0');
    registerSavedWord('t-later', en: 'later', zh: '晚点', level: 'A0');
    registerSavedWord('t-busy', en: 'busy', zh: '忙', level: 'A0');
    registerSavedWord('t-tired', en: 'tired', zh: '累', level: 'A0');
    registerSavedWord('t-early', en: 'early', zh: '早', level: 'A0');
  });

  test('a met word starts as 新学 with nothing scheduled', () {
    final state = AppState();
    state.meetWord('t-ready');
    final word = state.wordKnowledge['t-ready']!;
    expect(word.status, WordStatus.newWord);
    expect(word.dueAt, isNull);
    expect(state.unaskedWords, contains('t-ready'));
  });

  test('one success reaches 认识 and comes back the next day', () {
    final state = AppState();
    state.meetWord('t-ready');
    state.recordWordRecognition('t-ready', correct: true);
    final word = state.wordKnowledge['t-ready']!;
    expect(word.status, WordStatus.recognized);
    expect(word.step, 1);
    expect(gapDays(word.dueAt), 1);
    expect(state.dueWords, isEmpty);
  });

  test('each success in a row stretches the gap', () {
    final state = AppState();
    state.meetWord('t-ready');
    for (final expected in [1, 3, 7, 15, 30, 60, 120, 120]) {
      state.recordWordRecognition('t-ready', correct: true);
      expect(gapDays(state.wordKnowledge['t-ready']!.dueAt), expected);
    }
  });

  test('successes in a row are not enough for 熟悉 without the days', () {
    final state = AppState();
    state.meetWord('t-ready');
    for (var i = 0; i < 5; i++) {
      state.recordWordRecognition('t-ready', correct: true);
    }
    // Five rungs climbed inside one minute: the calendar has not moved.
    expect(state.wordKnowledge['t-ready']!.status, WordStatus.recognized);
  });

  test('the fourth success a week on reaches 熟悉', () {
    final state = AppState();
    state.wordKnowledge['t-ready'] = WordKnowledge(
      id: 't-ready',
      status: WordStatus.recognized,
      recognizedAt: DateTime.now().subtract(const Duration(days: 8)),
      dueAt: DateTime.now().subtract(const Duration(hours: 1)),
      step: 3,
    );
    state.recordWordRecognition('t-ready', correct: true);
    final word = state.wordKnowledge['t-ready']!;
    expect(word.status, WordStatus.familiar);
    expect(gapDays(word.dueAt), 15);
  });

  test('a miss drops 熟悉 back to 认识 and asks again tomorrow', () {
    final state = AppState();
    state.wordKnowledge['t-ready'] = WordKnowledge(
      id: 't-ready',
      status: WordStatus.familiar,
      recognizedAt: DateTime.now().subtract(const Duration(days: 40)),
      dueAt: DateTime.now(),
    );
    state.recordWordRecognition('t-ready', correct: false);
    final word = state.wordKnowledge['t-ready']!;
    expect(word.status, WordStatus.recognized);
    expect(word.misses, 1);
    expect(word.step, 0, reason: 'a miss goes back to the first rung');
    expect(gapDays(word.dueAt), 1);
    expect(state.shakyWords, contains('t-ready'));
  });

  test('a miss never touches the core mastery of an item', () {
    final state = AppState();
    state.meetWord('t-ready');
    state.recordWordRecognition('t-ready', correct: false);
    expect(state.mastery, isEmpty);
    expect(state.reviewQueue, isEmpty);
    expect(state.knownItemCount, 0);
  });

  test('a recovered word has to wait another week for 熟悉', () {
    final state = AppState();
    state.wordKnowledge['t-ready'] = WordKnowledge(
      id: 't-ready',
      status: WordStatus.familiar,
      recognizedAt: DateTime.now().subtract(const Duration(days: 40)),
      dueAt: DateTime.now(),
    );
    state.recordWordRecognition('t-ready', correct: false);
    state.recordWordRecognition('t-ready', correct: true);
    final word = state.wordKnowledge['t-ready']!;
    expect(word.status, WordStatus.recognized);
    expect(word.step, 1, reason: 'the ladder is climbed again from the bottom');
    expect(gapDays(word.dueAt), 1);
  });

  test('a snapshot written before the ladder lands on a sensible rung', () {
    final state = AppState();
    state.restoreForTest({
      'wordKnowledge': [
        {
          'id': 't-ready',
          'status': 'familiar',
          'recognizedAt': DateTime.now()
              .subtract(const Duration(days: 40))
              .toIso8601String(),
          'dueAt': DateTime.now().toIso8601String(),
          'misses': 0,
        },
        {'id': 't-busy', 'status': 'recognized', 'misses': 1},
        {'id': 't-later', 'status': 'newWord', 'misses': 0},
      ],
    });
    expect(state.wordKnowledge['t-ready']!.step, 4);
    expect(state.wordKnowledge['t-busy']!.step, 1);
    expect(state.wordKnowledge['t-later']!.step, 0);
  });

  test('a question shows the word and offers the meaning among others', () {
    final question = receptiveQuestion('t-ready')!;
    expect(question.shown, 'ready');
    expect(question.options, contains('准备好'));
    expect(question.options.length, greaterThanOrEqualTo(2));
    expect(question.options.toSet().length, question.options.length);
  });

  test('a re-ask after a miss uses another set of wrong meanings', () {
    final first = receptiveQuestion('t-ready', variant: 0)!;
    final second = receptiveQuestion('t-ready', variant: 1)!;
    expect(first.options.toSet(), isNot(second.options.toSet()));
  });

  test('word questions take no more than a third of the review budget', () {
    final state = AppState();
    state.dailyMinutes = 20;
    expect(state.wordBudgetSeconds * 3, lessThanOrEqualTo(state.reviewBudgetSeconds));
    for (var i = 0; i < 60; i++) {
      state.wordKnowledge['t-ready$i'] = WordKnowledge(
        id: 't-ready$i',
        status: WordStatus.newWord,
      );
      registerSavedWord('t-ready$i', en: 'w$i', zh: '意思$i', level: 'A0');
    }
    expect(state.todayWordPlan.length, state.wordPlanSize);
    expect(state.wordPlanSize, lessThan(60));
  });

  test('a saved lookup word is recognition-only, not a checkpoint task', () {
    final state = AppState();
    state.addSavedWord(
      const VocabularyItem(
        id: 'saved-ready',
        word: 'ready',
        meaning: '准备好',
        example: '',
        exampleMeaning: '',
      ),
    );
    expect(state.reviewQueue, isEmpty);
    expect(state.mastery, isEmpty);
    expect(state.wordStatus('saved-ready'), WordStatus.newWord);
    expect(isReceptiveWord('saved-ready'), isTrue);
    expect(state.wordsByUnit[''], contains('saved-ready'));
  });

  test('word progress survives a save and reload', () async {
    final state = AppState();
    state.addSavedWord(
      const VocabularyItem(
        id: 'saved-later',
        word: 'later',
        meaning: '晚点',
        example: '',
        exampleMeaning: '',
      ),
    );
    state.recordWordRecognition('saved-later', correct: true);

    final restored = AppState()..restoreForTest(state.snapshotForTest());
    expect(restored.wordStatus('saved-later'), WordStatus.recognized);
    expect(restored.savedWords['saved-later']?.en, 'later');
    expect(wordEnglish('saved-later'), 'later');
  });

  test('finishing a unit puts its receptive words on the word page', () {
    registerReceptiveWord(
      const ReceptiveWord(id: 'u-repeat', en: 'repeat', zh: '重复'),
      level: 'A0',
      unit: 'a0-01',
    );
    final state = AppState();
    state.meetWordsOfUnit('a0-01');
    expect(state.wordsByUnit['a0-01'], contains('u-repeat'));
    expect(state.wordStatus('u-repeat'), WordStatus.newWord);
    // Meeting a word is exposure, so nothing is scheduled by itself.
    expect(state.dueWords, isEmpty);
  });

  testWidgets('the word page asks a word and records the answer', (
    tester,
  ) async {
    final state = AppState();
    state.meetWord('t-ready');
    await tester.pumpWidget(MaterialApp(home: WordsPage(state: state)));

    expect(find.text('ready'), findsOneWidget);
    await tester.tap(find.text('开始认词'));
    await tester.pumpAndSettle();

    final question = state.todayWordPlan.first;
    expect(question.id, 't-ready');
    await tester.tap(find.widgetWithText(OutlinedButton, '准备好'));
    await tester.pumpAndSettle();

    expect(state.wordStatus('t-ready'), WordStatus.recognized);
    expect(find.text('对了。'), findsOneWidget);
  });

  test('a word is introduced in writing, then heard, then recalled', () {
    final state = AppState();
    state.meetWord('t-ready');
    // Nothing to hold on to yet, so the first sight of a word is spelled out.
    expect(state.wordAskMode('t-ready'), WordAskMode.read);
    for (final expected in [
      WordAskMode.listen,
      WordAskMode.recall,
      WordAskMode.read,
      WordAskMode.listen,
      WordAskMode.recall,
    ]) {
      state.recordWordRecognition('t-ready', correct: true);
      expect(state.wordAskMode('t-ready'), expected);
    }
  });

  test('a recall question asks for the word and offers spellings', () {
    final question = receptiveQuestion('t-ready', mode: WordAskMode.recall)!;
    expect(question.shown, '准备好');
    expect(question.answer, 'ready');
    expect(question.options, contains('ready'));
    expect(question.options, hasLength(3));
    for (final option in question.options) {
      // Options are spellings; a meaning among them would give the answer away.
      expect(option, matches(RegExp(r'^[a-zA-Z ]+$')), reason: option);
    }
  });

  test('no two options mean the same thing', () {
    // A second word glossed 「准备好」 would make both spellings right.
    registerSavedWord('t-set', en: 'set', zh: '准备好', level: 'A0');
    final question = receptiveQuestion('t-ready', mode: WordAskMode.recall)!;
    expect(question.options, isNot(contains('set')));
  });

  test('the day after a miss shows the spelling again', () {
    final state = AppState();
    state.meetWord('t-ready');
    state.recordWordRecognition('t-ready', correct: true);
    expect(state.wordAskMode('t-ready'), WordAskMode.listen);
    state.recordWordRecognition('t-ready', correct: false);
    // A miss is no time to take the spelling away on top of it.
    expect(state.wordAskMode('t-ready'), WordAskMode.read);
  });

  test('a round carries the mode each word is due for', () {
    final state = AppState();
    state.meetWord('t-ready');
    state.meetWord('t-later');
    state.recordWordRecognition('t-later', correct: true);
    state.wordKnowledge['t-later'] = state.wordKnowledge['t-later']!.copyWith(
      dueAt: DateTime.now().subtract(const Duration(hours: 1)),
    );
    final modes = {
      for (final question in state.wordSession()) question.id: question.mode,
    };
    expect(modes['t-ready'], WordAskMode.read);
    expect(modes['t-later'], WordAskMode.listen);
  });

  testWidgets('a listening question withholds the spelling until answered', (
    tester,
  ) async {
    final state = AppState();
    state.meetWord('t-ready');
    state.recordWordRecognition('t-ready', correct: true);
    state.wordKnowledge['t-ready'] = state.wordKnowledge['t-ready']!.copyWith(
      dueAt: DateTime.now().subtract(const Duration(hours: 1)),
    );
    await tester.pumpWidget(MaterialApp(home: WordsPage(state: state)));
    await tester.tap(find.text('开始认词'));
    await tester.pumpAndSettle();

    expect(find.text('听词 · 1 / 1'), findsOneWidget);
    // Showing 'ready' here would turn the question back into a reading one.
    // The list behind the quiz is gone, so this is the whole screen.
    expect(find.text('ready'), findsNothing);
    expect(find.text('· · ·'), findsOneWidget);
    expect(find.byIcon(Icons.replay_outlined), findsOneWidget);

    await tester.tap(find.widgetWithText(OutlinedButton, '准备好'));
    await tester.pumpAndSettle();

    // Now it is worth seeing: this is where the sound meets the spelling.
    expect(find.text('ready'), findsOneWidget);
    expect(state.wordKnowledge['t-ready']!.step, 2);
  });

  testWidgets('a recall question asks from the meaning, with nothing to play', (
    tester,
  ) async {
    final state = AppState();
    state.meetWord('t-ready');
    state.recordWordRecognition('t-ready', correct: true);
    state.recordWordRecognition('t-ready', correct: true);
    expect(state.wordAskMode('t-ready'), WordAskMode.recall);
    state.wordKnowledge['t-ready'] = state.wordKnowledge['t-ready']!.copyWith(
      dueAt: DateTime.now().subtract(const Duration(hours: 1)),
    );
    await tester.pumpWidget(MaterialApp(home: WordsPage(state: state)));
    await tester.tap(find.text('开始认词'));
    await tester.pumpAndSettle();

    expect(find.text('想词 · 1 / 1'), findsOneWidget);
    // The prompt is the meaning, and it is the only Chinese on screen: the
    // options are spellings.
    expect(find.text('准备好'), findsOneWidget);
    // Playing the word here would simply read out the answer.
    expect(find.byIcon(Icons.volume_up_outlined), findsNothing);

    await tester.tap(find.widgetWithText(OutlinedButton, 'ready'));
    await tester.pumpAndSettle();

    // Once the answer is in: the prompt turns into the spelling, which now
    // stands beside the option that was picked, and the word can be played.
    expect(find.text('ready'), findsNWidgets(2));
    expect(find.byIcon(Icons.volume_up_outlined), findsOneWidget);
    expect(state.wordKnowledge['t-ready']!.step, 3);
  });

  testWidgets('a wrong pick tells the learner the meaning', (tester) async {
    final state = AppState();
    state.meetWord('t-ready');
    await tester.pumpWidget(MaterialApp(home: WordsPage(state: state)));
    await tester.tap(find.text('开始认词'));
    await tester.pumpAndSettle();

    final wrong = state.todayWordPlan.first.options.firstWhere(
      (option) => option != '准备好',
    );
    await tester.tap(find.widgetWithText(OutlinedButton, wrong));
    await tester.pumpAndSettle();

    expect(state.wordKnowledge['t-ready']!.misses, 1);
    expect(find.textContaining('准备好'), findsWidgets);
  });
}