const db = require('../db/db');

/* ══════════════════════════════════════════════════════════════════════
   COURSE TEMPLATES
   ══════════════════════════════════════════════════════════════════════ */

/* ── GET /api/templates/courses ──────────────────────────────────────── */
function listCourseTemplates(req, res) {
  const uid = req.user.id;
  const { my, subject } = req.query;

  let where;
  const args = [];

  if (my) {
    where = 'WHERE ct.created_by = ?';
    args.push(uid);
  } else if (subject) {
    where = 'WHERE (ct.is_public = 1 OR ct.created_by = ?) AND ct.subject_slug = ?';
    args.push(uid, subject);
  } else {
    where = 'WHERE ct.is_public = 1 OR ct.created_by = ?';
    args.push(uid);
  }

  const rows = db.prepare(`
    SELECT ct.*, u.name AS creator_name
    FROM course_templates ct
    LEFT JOIN users u ON ct.created_by = u.id
    ${where}
    ORDER BY ct.created_at DESC
  `).all(...args);

  res.json(rows.map(r => ({
    id:          r.id,
    title:       r.title,
    description: r.description || '',
    category:    r.category,
    subjectSlug: r.subject_slug,
    structure:   safeJSON(r.structure, {}),
    isPublic:    r.is_public === 1,
    createdBy:   r.created_by,
    creatorName: r.creator_name || '',
    createdAt:   r.created_at,
  })));
}

/* ── POST /api/templates/courses ─────────────────────────────────────── */
function saveCourseTemplate(req, res) {
  const uid = req.user.id;
  const { title, description, category, subject_slug, courseId } = req.body;
  if (!title) return res.status(400).json({ error: 'title required' });

  let structure = {};

  if (courseId) {
    // Snapshot course structure
    const course = db.prepare('SELECT * FROM courses WHERE id = ?').get(courseId);
    if (!course) return res.status(404).json({ error: 'Course not found' });

    const sections = db.prepare(
      'SELECT * FROM course_sections WHERE course_id = ? ORDER BY order_index, id'
    ).all(courseId);

    const lessons = db.prepare(
      'SELECT * FROM lessons WHERE course_id = ? ORDER BY order_index, id'
    ).all(courseId);

    const sectionArr = sections.map(s => {
      const sectionLessons = lessons.filter(l => l.section_id === s.id);
      return {
        title: s.title,
        lessons: sectionLessons.map(l => ({
          title: l.title,
          blocks: db.prepare(
            'SELECT type, data FROM lesson_blocks WHERE lesson_id = ? ORDER BY order_index, id'
          ).all(l.id).map(b => ({ type: b.type, data: safeJSON(b.data, {}) })),
        })),
      };
    });

    // Lessons without a section
    const unsectioned = lessons.filter(l => !l.section_id);
    if (unsectioned.length) {
      sectionArr.unshift({
        title: null,
        lessons: unsectioned.map(l => ({
          title: l.title,
          blocks: db.prepare(
            'SELECT type, data FROM lesson_blocks WHERE lesson_id = ? ORDER BY order_index, id'
          ).all(l.id).map(b => ({ type: b.type, data: safeJSON(b.data, {}) })),
        })),
      });
    }

    structure = { sections: sectionArr };
  }

  const r = db.prepare(`
    INSERT INTO course_templates (title, description, category, subject_slug, structure, is_public, created_by)
    VALUES (?, ?, ?, ?, ?, 1, ?)
  `).run(
    title.trim(),
    description || null,
    category || 'general',
    subject_slug || null,
    JSON.stringify(structure),
    uid
  );

  res.status(201).json({ id: r.lastInsertRowid });
}

/* ── POST /api/templates/courses/:id/create ──────────────────────────── */
function createFromCourseTemplate(req, res) {
  const tpl = db.prepare('SELECT * FROM course_templates WHERE id = ?').get(req.params.id);
  if (!tpl) return res.status(404).json({ error: 'Template not found' });

  const { title, subjectSlug } = req.body;
  const structure = safeJSON(tpl.structure, {});
  const sections  = structure.sections || [];

  let newCourseId;
  db.transaction(() => {
    const cr = db.prepare(`
      INSERT INTO courses (subject_slug, title, description, cover_emoji, order_index, is_published, created_by)
      VALUES (?, ?, ?, '', 0, 0, ?)
    `).run(
      subjectSlug || tpl.subject_slug || 'other',
      title || tpl.title,
      tpl.description || null,
      req.user.id
    );
    newCourseId = cr.lastInsertRowid;

    let lessonOrder = 0;
    for (const sec of sections) {
      let sectionId = null;
      if (sec.title) {
        const sr = db.prepare(
          'INSERT INTO course_sections (course_id, title, order_index) VALUES (?, ?, ?)'
        ).run(newCourseId, sec.title, lessonOrder);
        sectionId = sr.lastInsertRowid;
      }

      for (const lesson of (sec.lessons || [])) {
        const lr = db.prepare(
          'INSERT INTO lessons (course_id, title, order_index, section_id) VALUES (?, ?, ?, ?)'
        ).run(newCourseId, lesson.title, lessonOrder++, sectionId);
        const newLid = lr.lastInsertRowid;

        (lesson.blocks || []).forEach((b, i) => {
          db.prepare(
            'INSERT INTO lesson_blocks (lesson_id, type, order_index, data) VALUES (?, ?, ?, ?)'
          ).run(newLid, b.type, i, JSON.stringify(b.data || {}));
        });
      }
    }
  })();

  res.status(201).json({ id: newCourseId });
}

/* ── DELETE /api/templates/courses/:id ────────────────────────────────── */
function deleteCourseTemplate(req, res) {
  const tpl = db.prepare('SELECT * FROM course_templates WHERE id = ?').get(req.params.id);
  if (!tpl) return res.status(404).json({ error: 'Template not found' });
  if (tpl.created_by !== req.user.id && req.user.role !== 'admin')
    return res.status(403).json({ error: 'Forbidden' });

  db.prepare('DELETE FROM course_templates WHERE id = ?').run(tpl.id);
  res.json({ ok: true });
}


/* ══════════════════════════════════════════════════════════════════════
   LESSON TEMPLATES
   ══════════════════════════════════════════════════════════════════════ */

/* ── GET /api/templates/lessons ──────────────────────────────────────── */
function listLessonTemplates(req, res) {
  const uid = req.user.id;
  const { my, category } = req.query;

  let where;
  const args = [];

  if (my) {
    where = 'WHERE lt.created_by = ?';
    args.push(uid);
  } else if (category) {
    where = 'WHERE (lt.is_public = 1 OR lt.created_by = ?) AND lt.category = ?';
    args.push(uid, category);
  } else {
    where = 'WHERE lt.is_public = 1 OR lt.created_by = ?';
    args.push(uid);
  }

  const rows = db.prepare(`
    SELECT lt.*, u.name AS creator_name
    FROM lesson_templates lt
    LEFT JOIN users u ON lt.created_by = u.id
    ${where}
    ORDER BY lt.created_at DESC
  `).all(...args);

  res.json(rows.map(r => ({
    id:          r.id,
    title:       r.title,
    category:    r.category,
    subjectSlug: r.subject_slug,
    blocks:      safeJSON(r.blocks, []),
    isPublic:    r.is_public === 1,
    createdBy:   r.created_by,
    creatorName: r.creator_name || '',
    createdAt:   r.created_at,
  })));
}

/* ── POST /api/templates/lessons ─────────────────────────────────────── */
function saveLessonTemplate(req, res) {
  const uid = req.user.id;
  const { title, category, subject_slug, lessonId } = req.body;
  if (!title) return res.status(400).json({ error: 'title required' });

  let blocksJSON = '[]';

  if (lessonId) {
    const lesson = db.prepare('SELECT id FROM lessons WHERE id = ?').get(lessonId);
    if (!lesson) return res.status(404).json({ error: 'Lesson not found' });

    const rawBlocks = db.prepare(
      'SELECT type, data FROM lesson_blocks WHERE lesson_id = ? ORDER BY order_index, id'
    ).all(lesson.id);

    blocksJSON = JSON.stringify(rawBlocks.map(b => ({
      type: b.type,
      data: safeJSON(b.data, {}),
    })));
  }

  const r = db.prepare(`
    INSERT INTO lesson_templates (title, category, subject_slug, blocks, is_public, created_by)
    VALUES (?, ?, ?, ?, 1, ?)
  `).run(
    title.trim(),
    category || 'general',
    subject_slug || null,
    blocksJSON,
    uid
  );

  res.status(201).json({ id: r.lastInsertRowid });
}

/* ── POST /api/templates/lessons/:id/create ──────────────────────────── */
function createFromLessonTemplate(req, res) {
  const tpl = db.prepare('SELECT * FROM lesson_templates WHERE id = ?').get(req.params.id);
  if (!tpl) return res.status(404).json({ error: 'Template not found' });

  const { courseId, sectionId, title } = req.body;
  if (!courseId) return res.status(400).json({ error: 'courseId required' });

  const course = db.prepare('SELECT id FROM courses WHERE id = ?').get(courseId);
  if (!course) return res.status(404).json({ error: 'Course not found' });

  const tplBlocks = safeJSON(tpl.blocks, []);

  let newLessonId;
  db.transaction(() => {
    // Get max order_index
    const maxOrd = db.prepare(
      'SELECT MAX(order_index) AS mx FROM lessons WHERE course_id = ?'
    ).get(courseId);

    const lr = db.prepare(
      'INSERT INTO lessons (course_id, title, order_index, section_id) VALUES (?, ?, ?, ?)'
    ).run(courseId, title || tpl.title, (maxOrd?.mx ?? -1) + 1, sectionId || null);
    newLessonId = lr.lastInsertRowid;

    tplBlocks.forEach((b, i) => {
      db.prepare(
        'INSERT INTO lesson_blocks (lesson_id, type, order_index, data) VALUES (?, ?, ?, ?)'
      ).run(newLessonId, b.type, i, JSON.stringify(b.data || {}));
    });
  })();

  res.status(201).json({ id: newLessonId });
}

/* ── DELETE /api/templates/lessons/:id ────────────────────────────────── */
function deleteLessonTemplate(req, res) {
  const tpl = db.prepare('SELECT * FROM lesson_templates WHERE id = ?').get(req.params.id);
  if (!tpl) return res.status(404).json({ error: 'Template not found' });
  if (tpl.created_by !== req.user.id && req.user.role !== 'admin')
    return res.status(403).json({ error: 'Forbidden' });

  db.prepare('DELETE FROM lesson_templates WHERE id = ?').run(tpl.id);
  res.json({ ok: true });
}


/* ── helpers ─────────────────────────────────────────────────────────── */
function safeJSON(str, fallback) {
  try { return JSON.parse(str); } catch { return fallback; }
}

module.exports = {
  listCourseTemplates,
  saveCourseTemplate,
  createFromCourseTemplate,
  deleteCourseTemplate,
  listLessonTemplates,
  saveLessonTemplate,
  createFromLessonTemplate,
  deleteLessonTemplate,
};