#!/usr/bin/env node
/**
 * Splits slash-separated alternatives in grammar exercise answers into separate exercise variants.
 *
 * Default: dry-run (no writes)
 * Use --apply to persist.
 *
 * Optional filters:
 *   --course-id=<id>
 *   --lesson-id=<id>
 */

import { Op } from 'sequelize';
import { sequelize } from '../utils/sequelize.js';
import VocabCourseLesson from '../models/community/vocab_course_lesson.js';
import VocabGrammarExercise from '../models/community/vocab_grammar_exercise.js';

const GAP_FILL_MAX_VARIANTS = 8;

function parseArgs(argv) {
  const args = {
    apply: false,
    courseId: null,
    lessonId: null,
  };

  argv.forEach((arg) => {
    if (arg === '--apply') {
      args.apply = true;
      return;
    }
    if (arg.startsWith('--course-id=')) {
      const value = Number(arg.split('=')[1]);
      if (Number.isFinite(value) && value > 0) args.courseId = value;
      return;
    }
    if (arg.startsWith('--lesson-id=')) {
      const value = Number(arg.split('=')[1]);
      if (Number.isFinite(value) && value > 0) args.lessonId = value;
    }
  });

  return args;
}

function normalizeText(value) {
  return String(value || '').trim().replace(/\s+/g, ' ');
}

function splitAlternatives(value) {
  const text = normalizeText(value);
  if (!text) return [];
  const parts = text
    .split(/\s+\/\s+/)
    .map((part) => normalizeText(part))
    .filter(Boolean);
  return parts.length >= 2 ? parts : [text];
}

function parseJsonLike(value) {
  if (!value) return {};
  if (typeof value === 'string') {
    try {
      return JSON.parse(value);
    } catch (_) {
      return {};
    }
  }
  if (typeof value === 'object') return value;
  return {};
}

function buildCartesianProduct(arrays) {
  let out = [[]];
  for (const arr of arrays) {
    const next = [];
    out.forEach((prefix) => {
      arr.forEach((value) => {
        next.push([...prefix, value]);
      });
    });
    out = next;
  }
  return out;
}

function buildExerciseVariants(exercise) {
  const questionData = parseJsonLike(exercise.questionData);
  const answerData = parseJsonLike(exercise.answerData);
  const type = String(questionData?.type || answerData?.type || '').trim();

  const base = {
    lessonId: exercise.lessonId,
    exerciseTypeId: exercise.exerciseTypeId,
    title: exercise.title,
    instruction: exercise.instruction,
    explanation: exercise.explanation,
    createdByUserId: exercise.createdByUserId,
    createdAt: exercise.createdAt,
  };

  if (type === 'transformation') {
    const correctAnswer = normalizeText(answerData?.correctAnswer || answerData?.correct || '');
    const alternatives = splitAlternatives(correctAnswer);
    if (alternatives.length <= 1) {
      return { changed: false, skipped: false, variants: [{ ...base, questionData, answerData }] };
    }
    return {
      changed: true,
      skipped: false,
      variants: alternatives.map((alt) => ({
        ...base,
        questionData,
        answerData: {
          ...answerData,
          correctAnswer: alt
        }
      }))
    };
  }

  if (type === 'multiple_choice') {
    const options = Array.isArray(questionData?.options) ? questionData.options.slice() : [];
    const correctIndex = Number(answerData?.correctAnswer);
    if (!Number.isFinite(correctIndex) || correctIndex < 0 || correctIndex >= options.length) {
      return { changed: false, skipped: false, variants: [{ ...base, questionData, answerData }] };
    }
    const correctOption = normalizeText(options[correctIndex]);
    const alternatives = splitAlternatives(correctOption);
    if (alternatives.length <= 1) {
      return { changed: false, skipped: false, variants: [{ ...base, questionData, answerData }] };
    }
    return {
      changed: true,
      skipped: false,
      variants: alternatives.map((alt) => {
        const nextOptions = options.slice();
        nextOptions[correctIndex] = alt;
        return {
          ...base,
          questionData: {
            ...questionData,
            options: nextOptions
          },
          answerData
        };
      })
    };
  }

  if (type === 'gap_fill') {
    const answers = Array.isArray(answerData?.answers) ? answerData.answers : [];
    if (!answers.length) {
      return { changed: false, skipped: false, variants: [{ ...base, questionData, answerData }] };
    }
    const splitAnswers = answers.map((answer) => splitAlternatives(answer));
    const hasAlternatives = splitAnswers.some((entry) => entry.length > 1);
    if (!hasAlternatives) {
      return { changed: false, skipped: false, variants: [{ ...base, questionData, answerData }] };
    }

    const variantCount = splitAnswers.reduce((acc, parts) => acc * parts.length, 1);
    if (variantCount > GAP_FILL_MAX_VARIANTS) {
      return { changed: false, skipped: true, variants: [{ ...base, questionData, answerData }] };
    }

    const combos = buildCartesianProduct(splitAnswers);
    return {
      changed: true,
      skipped: false,
      variants: combos.map((combo) => ({
        ...base,
        questionData,
        answerData: {
          ...answerData,
          answers: combo
        }
      }))
    };
  }

  return { changed: false, skipped: false, variants: [{ ...base, questionData, answerData }] };
}

async function main() {
  const args = parseArgs(process.argv.slice(2));
  const lessonWhere = {};
  if (args.courseId) lessonWhere.courseId = args.courseId;
  if (args.lessonId) lessonWhere.id = args.lessonId;

  const lessons = await VocabCourseLesson.findAll({
    where: Object.keys(lessonWhere).length ? lessonWhere : undefined,
    attributes: ['id', 'courseId', 'lessonNumber', 'title'],
    order: [['courseId', 'ASC'], ['lessonNumber', 'ASC']],
  });

  const lessonIds = lessons.map((lesson) => lesson.id);
  const byLesson = new Map(lessons.map((lesson) => [lesson.id, lesson]));

  const exercises = lessonIds.length
    ? await VocabGrammarExercise.findAll({
      where: {
        lessonId: {
          [Op.in]: lessonIds
        }
      },
      attributes: [
        'id',
        'lessonId',
        'exerciseTypeId',
        'exerciseNumber',
        'title',
        'instruction',
        'questionData',
        'answerData',
        'explanation',
        'createdByUserId',
        'createdAt'
      ],
      order: [['lessonId', 'ASC'], ['exerciseNumber', 'ASC'], ['id', 'ASC']]
    })
    : [];

  const grouped = new Map();
  exercises.forEach((exercise) => {
    const list = grouped.get(exercise.lessonId) || [];
    list.push(exercise);
    grouped.set(exercise.lessonId, list);
  });

  let affectedLessons = 0;
  let changedExercises = 0;
  let createdVariants = 0;
  let skippedComplex = 0;

  console.log(`Gefundene Lektionen: ${lessons.length}`);
  console.log(`Gefundene Übungen: ${exercises.length}`);
  console.log(`Modus: ${args.apply ? 'APPLY (schreibt Änderungen)' : 'DRY-RUN (keine Änderungen)'}`);

  for (const lesson of lessons) {
    const source = grouped.get(lesson.id) || [];
    if (!source.length) continue;

    let lessonChangedExercises = 0;
    let lessonSkipped = 0;
    const rebuilt = [];

    source.forEach((exercise) => {
      const variantResult = buildExerciseVariants(exercise);
      if (variantResult.changed) {
        lessonChangedExercises += 1;
        createdVariants += Math.max(0, variantResult.variants.length - 1);
      }
      if (variantResult.skipped) lessonSkipped += 1;
      rebuilt.push(...variantResult.variants);
    });

    if (lessonChangedExercises === 0) {
      skippedComplex += lessonSkipped;
      continue;
    }

    affectedLessons += 1;
    changedExercises += lessonChangedExercises;
    skippedComplex += lessonSkipped;

    console.log(
      `- Kurs ${lesson.courseId}, Lektion #${lesson.lessonNumber} (${lesson.id}) "${lesson.title}": `
      + `${source.length} -> ${rebuilt.length} Übungen`
      + `, geändert: ${lessonChangedExercises}`
      + (lessonSkipped > 0 ? `, übersprungen (komplex): ${lessonSkipped}` : '')
    );

    if (args.apply) {
      await sequelize.transaction(async (transaction) => {
        await VocabGrammarExercise.destroy({
          where: { lessonId: lesson.id },
          transaction
        });

        if (rebuilt.length) {
          const payload = rebuilt.map((entry, index) => ({
            lessonId: lesson.id,
            exerciseTypeId: entry.exerciseTypeId,
            exerciseNumber: index + 1,
            title: entry.title,
            instruction: entry.instruction,
            questionData: entry.questionData,
            answerData: entry.answerData,
            explanation: entry.explanation,
            createdByUserId: entry.createdByUserId,
            createdAt: entry.createdAt
          }));
          await VocabGrammarExercise.bulkCreate(payload, { transaction });
        }
      });
    }
  }

  console.log('');
  console.log(`Betroffene Lektionen: ${affectedLessons}`);
  console.log(`Geänderte Übungen: ${changedExercises}`);
  console.log(`Zusätzliche Varianten erzeugt: ${createdVariants}`);
  console.log(`Komplexe Fälle übersprungen: ${skippedComplex}`);
}

main()
  .then(async () => {
    await sequelize.close();
  })
  .catch(async (error) => {
    console.error('Fehler beim Normalisieren der Übungsantworten:', error);
    await sequelize.close();
    process.exit(1);
  });