import '../models.dart';
import 'answer_rules.dart';

/// One stage-assessment task, from the level's `assessment` JSON. Choice
/// tasks carry `choices` and `answerIndex`; open tasks (writing, speaking)
/// carry an `accept` rule in the language of `answer_rules.dart` and the
/// `guide` shown after a wrong answer.
class AssessmentTask {
  const AssessmentTask({
    required this.id,
    required this.skill,
    required this.prompt,
    this.audio,
    this.choices = const [],
    this.answerIndex,
    this.accept = const [],
    this.guide = '',
  });

  factory AssessmentTask.fromJson(Map<String, dynamic> json) => AssessmentTask(
    id: json['id'] as String,
    skill: AssessmentSkill.values.byName(json['skill'] as String),
    prompt: json['prompt'] as String? ?? '',
    audio: json['audio'] as String?,
    choices: [for (final choice in json['choices'] as List? ?? const []) '$choice'],
    answerIndex: json['answerIndex'] as int?,
    accept: [
      for (final group in json['accept'] as List? ?? const [])
        [for (final term in group as List) '$term'],
    ],
    guide: json['guide'] as String? ?? '',
  );

  final String id;
  final AssessmentSkill skill;
  final String prompt;
  final String? audio;
  final List<String> choices;
  final int? answerIndex;
  final List<List<String>> accept;
  final String guide;
}

extension AssessmentSkillLabel on AssessmentSkill {
  String get label => switch (this) {
    AssessmentSkill.listening => '听力',
    AssessmentSkill.speaking => '口语',
    AssessmentSkill.reading => '阅读',
    AssessmentSkill.writing => '写作',
  };
}

/// A stage-assessment pack. A replacement pack ([replaces] set) assesses the
/// same abilities as its original with different people, places and values,
/// and its results count toward the original.
class AssessmentPack {
  const AssessmentPack({
    required this.id,
    required this.level,
    required this.tasks,
    this.replaces,
  });

  factory AssessmentPack.fromJson(Map<String, dynamic> json) => AssessmentPack(
    id: json['id'] as String,
    level: json['level'] as String? ?? '',
    replaces: json['replaces'] as String?,
    tasks: [
      for (final task in json['tasks'] as List? ?? const [])
        AssessmentTask.fromJson(task as Map<String, dynamic>),
    ],
  );

  final String id;
  final String level;
  final String? replaces;
  final List<AssessmentTask> tasks;

  List<AssessmentTask> forSkill(AssessmentSkill skill) =>
      tasks.where((task) => task.skill == skill).toList();
}

/// Every loaded assessment pack, in file order; filled by `CourseRepository`.
final List<AssessmentPack> assessmentPacks = <AssessmentPack>[];

/// The A0 stage assessments, in the order they unlock.
List<AssessmentPack> get a0AssessmentPacks => [
  for (final pack in assessmentPacks)
    if (pack.level == 'A0' && pack.replaces == null) pack,
];

/// The A0 replacement packs.
List<AssessmentPack> get a0ReplacementPacks => [
  for (final pack in assessmentPacks)
    if (pack.level == 'A0' && pack.replaces != null) pack,
];

/// The replacement pack of [packId], if it has one.
AssessmentPack? replacementFor(String packId) =>
    assessmentPacks.where((pack) => pack.replaces == packId).firstOrNull;

/// The pack whose results [packId] counts toward: the original of a
/// replacement pack, otherwise [packId] itself.
String canonicalAssessmentPackId(String packId) =>
    assessmentPacks
        .where((pack) => pack.id == packId)
        .firstOrNull
        ?.replaces ??
    packId;

/// Local check of an open task with the same rule engine as the lessons: it
/// accepts variable names and places, but requires the communicative
/// information the task names.
bool checkOpenAssessmentAnswer(AssessmentTask task, String input) =>
    task.accept.isNotEmpty && matchesRule(input, task.accept);

/// What a correct answer to [task] looks like, shown when reviewing a
/// wrong answer after the assessment. [answer] is what the learner gave.
String assessmentAnswerGuide(AssessmentTask task, String answer) {
  final index = task.answerIndex;
  if (index != null && index >= 0 && index < task.choices.length) {
    final correct = task.choices[index];
    if (task.skill == AssessmentSkill.listening && answer == correct) {
      return '正确答案：$correct（选对了，但作答前没有播放音频，所以不计分）';
    }
    return '正确答案：$correct';
  }
  if (task.guide.isNotEmpty) return task.guide;
  return task.skill == AssessmentSkill.writing
      ? '需要写一个完整的英文句子。'
      : '需要用完整英文回答题目要求。';
}