/***********************************************************************************************************************************************************************
 * File Name: units.controller.js  (client)
 * Type of Program: Controller
 * Description: Standalone Unit / Lesson consumption — the junction revamp lets
 *              learners run Units and Lessons outside any Course:
 *
 *   GET  /client/units                          → INDEPENDENT units only (no course affiliation)
 *   GET  /client/lessons                        → INDEPENDENT lessons only (no unit is course-affiliated)
 *   GET  /client/units/:uuid                    → unit metadata (shared handler)
 *   GET  /client/units/:uuid/lessons            → unit + ALL lesson data (shared handler)
 *   GET  /client/units/:uuid/quiz               → the unit's quiz, no course context
 *   POST /client/units/:uuid/quiz/:quizId/submit→ graded attempt with course_id NULL
 *   GET  /client/lessons/:uuid                  → single lesson, runs independently (shared handler)
 *   POST /client/lessons/:uuid/progress         → standalone reading progress (course NULL, unit optional)
 *
 *   Access rule: a unit attached to no course is open; otherwise the user must
 *   be able to access at least one attached course. Lessons resolve through
 *   their parent units the same way.
 *
 *   Discovery rule (getUnits/getLessons only): ALL non-deleted units/lessons
 *   are listed, whether or not they're attached to a course — course_count/
 *   courses[] (published courses only) and is_locked tell the learner whether
 *   a given item is standalone or bound, and if bound, whether they already
 *   have access. This does not affect the single-item endpoints above
 *   (:uuid) — those still enforce access normally for direct links, and
 *   course-scoped consumption runs through a separate controller entirely.
 *
 * Author: Kenneth Obsequio (@lash0000)
 * Date Created: Jul. 7, 2026
 ***********************************************************************************************************************************************************************/
"use strict";

const R = require("../../utils/response.util");
const logActivity = require("../../utils/logActivity.util");
const sequelize = require("../../config/db.config");

const {
  Unit, Lesson,
  CourseUnit, UnitLesson,
  UnitQuiz, QuizQuestion, QuizOption, QuizAttempt, QuizSession,
} = require("../../models/courses/courses.associations");

const coursesCtrl = require("./courses.controller"); // canAccessUnit / canAccessLesson / shared uuid handlers
const { gradeSubmission } = require("../../utils/courses/grading.util");
const { shuffleOptions, shuffleQuestions, getAttemptStatus } = require("../../utils/courses/quiz_security.util");
const { recomputeCascade, recordWatchProgress, recordManualComplete } = require("../../services/completion_requirements.service");

const notDeleted = { deletedAt: null };

// Strip correct-answer data (same policy as course-scoped quiz endpoints)
function sanitizeQuestions(questions = []) {
  return questions.map((q) => {
    const plain = q.toJSON ? q.toJSON() : { ...q };
    if (plain.type === "multi_select") {
      plain.correct_count = (plain.options ?? []).filter((o) => o.is_correct).length;
    }
    plain.options = (plain.options ?? []).map(({ is_correct: _drop, ...o }) => o);
    delete plain.explanation;
    return plain;
  });
}

// ─── UNIT LIBRARY (learner view) ──────────────────────────────────────────────

// Client-side Units/Lessons browsing shows ALL content, bound to a course or
// not — course_count/courses[] + is_locked below tell the learner which is
// which. This does not affect course-scoped consumption (which runs through
// ClientCoursesContext/getCourse, a separate path) or direct-link access to
// UnitDetails/LessonDetails, which still enforce access normally.
exports.getUnits = async (req, res) => {
  try {
    const rows = await sequelize.query(`
      SELECT
        u.unit_id, u.uuid, u.title, u.subscription, u.description, u.duration_seconds,
        (SELECT CAST(COUNT(*) AS INTEGER) FROM unit_lessons ul
           JOIN lessons l ON l.lesson_id = ul.lesson_id AND l."deletedAt" IS NULL
          WHERE ul.unit_id = u.unit_id)                       AS lesson_count,
        (SELECT CAST(COUNT(*) AS INTEGER) FROM course_units cu
           JOIN courses c ON c.course_id = cu.course_id AND c."deletedAt" IS NULL AND c.status = 'published'
          WHERE cu.unit_id = u.unit_id)                       AS course_count,
        (SELECT quiz_id FROM unit_quizzes q
          WHERE q.unit_id = u.unit_id AND q."deletedAt" IS NULL LIMIT 1) AS quiz_id
      FROM units u
      WHERE u."deletedAt" IS NULL
      ORDER BY u.title ASC
    `, { type: sequelize.QueryTypes.SELECT });

    // Batch-fetch attached courses for every returned unit in one query, so the
    // learner-facing upsell modal can say which course(s)/tier(s) unlock a unit
    // (a unit may sit under several courses at different tiers — no single "Buy").
    const unitIds = rows.map((r) => r.unit_id);
    const courseLinkRows = unitIds.length ? await sequelize.query(`
      SELECT cu.unit_id, c.course_id, c.uuid, c.title, c.subscription
      FROM course_units cu
      JOIN courses c ON c.course_id = cu.course_id AND c."deletedAt" IS NULL AND c.status = 'published'
      WHERE cu.unit_id IN (:unitIds)
    `, { replacements: { unitIds }, type: sequelize.QueryTypes.SELECT }) : [];

    const coursesByUnit = new Map();
    for (const row of courseLinkRows) {
      const list = coursesByUnit.get(row.unit_id) ?? [];
      list.push({ course_id: row.course_id, uuid: row.uuid, title: row.title, subscription: row.subscription });
      coursesByUnit.set(row.unit_id, list);
    }

    // is_locked mirrors canAccessUnit: a unit with its own subscription or at
    // least one attached course needs an access check; a fully open standalone
    // unit (no subscription, no course links) is never locked.
    const result = [];
    for (const row of rows) {
      const is_locked = (row.subscription || Number(row.course_count) > 0)
        ? !(await coursesCtrl.canAccessUnit(req.user.user_id, row.unit_id))
        : false;
      result.push({ ...row, courses: coursesByUnit.get(row.unit_id) ?? [], is_locked });
    }

    return R.success(res, "Units retrieved.", result);
  } catch (err) {
    console.error("[CLIENT][UNITS][GET ALL]", err);
    return R.error(res, "Could not retrieve units.", 500);
  }
};

// ─── LESSON LIBRARY (learner view) ────────────────────────────────────────────
// Mirrors getUnits above — a Lesson may sit in several Units (each possibly in
// different courses), so is_locked/courses are resolved across ALL attached
// units rather than a single direct course link.

exports.getLessons = async (req, res) => {
  try {
    const rows = await sequelize.query(`
      SELECT
        l.lesson_id, l.uuid, l.title, l.description, l.duration_seconds,
        (SELECT CAST(COUNT(*) AS INTEGER) FROM unit_lessons ul
           JOIN units u ON u.unit_id = ul.unit_id AND u."deletedAt" IS NULL
          WHERE ul.lesson_id = l.lesson_id)                     AS unit_count
      FROM lessons l
      WHERE l."deletedAt" IS NULL
      ORDER BY l.title ASC
    `, { type: sequelize.QueryTypes.SELECT });

    // Batch-fetch every course reachable through any attached unit, for every
    // returned lesson, in one query — same batching style as getUnits.
    const lessonIds = rows.map((r) => r.lesson_id);
    const courseLinkRows = lessonIds.length ? await sequelize.query(`
      SELECT DISTINCT ul.lesson_id, c.course_id, c.uuid, c.title, c.subscription
      FROM unit_lessons ul
      JOIN course_units cu ON cu.unit_id = ul.unit_id
      JOIN courses c ON c.course_id = cu.course_id AND c."deletedAt" IS NULL AND c.status = 'published'
      WHERE ul.lesson_id IN (:lessonIds)
    `, { replacements: { lessonIds }, type: sequelize.QueryTypes.SELECT }) : [];

    const coursesByLesson = new Map();
    for (const row of courseLinkRows) {
      const list = coursesByLesson.get(row.lesson_id) ?? [];
      list.push({ course_id: row.course_id, uuid: row.uuid, title: row.title, subscription: row.subscription });
      coursesByLesson.set(row.lesson_id, list);
    }

    // is_locked mirrors canAccessLesson: standalone/unattached lessons are
    // open, attached lessons need at least one accessible course through
    // any attached unit.
    const result = [];
    for (const row of rows) {
      const is_locked = Number(row.unit_count) > 0
        ? !(await coursesCtrl.canAccessLesson(req.user.user_id, row.lesson_id))
        : false;
      result.push({ ...row, courses: coursesByLesson.get(row.lesson_id) ?? [], is_locked });
    }

    return R.success(res, "Lessons retrieved.", result);
  } catch (err) {
    console.error("[CLIENT][LESSONS][GET ALL]", err);
    return R.error(res, "Could not retrieve lessons.", 500);
  }
};

// ─── STANDALONE UNIT QUIZ ─────────────────────────────────────────────────────

exports.getUnitQuiz = async (req, res) => {
  try {
    const { uuid } = req.params;

    const unit = await Unit.findOne({ where: { uuid, ...notDeleted } });
    if (!unit) return R.error(res, "Unit not found.", 404);

    if (!await coursesCtrl.canAccessUnit(req.user.user_id, unit.unit_id)) {
      return R.error(res, "You do not have access to this unit.", 403);
    }

    const quiz = await UnitQuiz.findOne({
      where: { unit_id: unit.unit_id, ...notDeleted },
      attributes: [
        "quiz_id", "uuid", "title",
        "is_required", "passing_score", "max_questions", "shuffle_questions",
      ],
      include: [{
        model: QuizQuestion, as: "questions",
        where: notDeleted, required: false,
        attributes: ["question_id", "uuid", "type", "question", "order_index", "points"],
        include: [{
          model: QuizOption, as: "options",
          attributes: ["option_id", "text", "order_index", "is_correct"],
        }],
      }],
      order: [[{ model: QuizQuestion, as: "questions" }, "order_index", "ASC"]],
    });

    if (!quiz) return R.error(res, "Quiz not found.", 404);

    const plain = quiz.toJSON();
    let qs = sanitizeQuestions(plain.questions ?? []);
    if (plain.shuffle_questions) qs = shuffleQuestions(qs);
    plain.questions = shuffleOptions(qs);

    const attempts = await QuizAttempt.findAll({
      where: { quiz_id: quiz.quiz_id, user_id: req.user.user_id },
      attributes: ["attempt_id", "attempt_number", "score", "passing_score", "passed", "createdAt"],
    });

    const status = getAttemptStatus(attempts, "quiz");
    plain.attempt_count      = status.attempt_count;
    plain.has_passed         = status.has_passed;
    plain.best_attempt       = status.best_attempt;
    plain.attempts_remaining = status.attempts_remaining;
    plain.cooldown_until     = status.cooldown_until;
    plain.window_reset_at    = status.window_reset_at;
    plain.can_attempt        = status.can_attempt;

    const activeSession = await QuizSession.findOne({
      where: { quiz_id: quiz.quiz_id, user_id: req.user.user_id, status: "in_progress" },
      attributes: ["session_id", "draft_answers", "started_at", "last_saved_at"],
    });
    plain.active_session = activeSession ?? null;

    return R.success(res, "Quiz retrieved.", plain);
  } catch (err) {
    console.error("[CLIENT][UNITS][QUIZ][GET]", err);
    return R.error(res, "Could not retrieve quiz.", 500);
  }
};

exports.submitUnitQuiz = async (req, res) => {
  try {
    const { uuid, quizId } = req.params;
    const { answers = {} } = req.body;
    const user_id = req.user.user_id;

    const unit = await Unit.findOne({ where: { uuid, ...notDeleted } });
    if (!unit) return R.error(res, "Unit not found.", 404);

    if (!await coursesCtrl.canAccessUnit(user_id, unit.unit_id)) {
      return R.error(res, "You do not have access to this unit.", 403);
    }

    const quiz = await UnitQuiz.findOne({
      where: { quiz_id: quizId, unit_id: unit.unit_id, ...notDeleted },
      include: [{
        model: QuizQuestion, as: "questions",
        where: notDeleted, required: false,
        include: [{ model: QuizOption, as: "options" }],
      }],
    });
    if (!quiz) return R.error(res, "Quiz not found.", 404);

    const priorAttempts = await QuizAttempt.findAll({
      where: { quiz_id: quiz.quiz_id, user_id },
      attributes: ["attempt_id", "score", "passed", "createdAt"],
    });

    const { totalPoints, earnedPoints, score } = gradeSubmission(quiz.questions ?? [], answers);
    const passed = score >= (quiz.passing_score ?? 70);

    const attempt = await QuizAttempt.create({
      user_id,
      quiz_id:        quiz.quiz_id,
      course_id:      null, // standalone — no course context
      attempt_number: priorAttempts.length + 1,
      answers,
      total_points:   totalPoints,
      earned_points:  earnedPoints,
      score,
      passing_score:  quiz.passing_score ?? 70,
      passed,
    });

    await QuizSession.update(
      { status: "submitted" },
      { where: { quiz_id: quiz.quiz_id, user_id, status: "in_progress" } }
    );

    return R.success(res, "Quiz submitted.", {
      attempt_id:     attempt.attempt_id,
      attempt_number: attempt.attempt_number,
      score,
      passed,
      passing_score:  attempt.passing_score,
      total_points:   totalPoints,
      earned_points:  earnedPoints,
    });
  } catch (err) {
    console.error("[CLIENT][UNITS][QUIZ][SUBMIT]", err);
    return R.error(res, "Could not submit quiz.", 500);
  }
};

// ─── STANDALONE UNIT QUIZ DRAFT ───────────────────────────────────────────────
// PATCH /client/units/:uuid/quiz/:quizId/draft — mirrors the course-scoped
// saveQuizDraft in courses.controller.js; only quiz_id + user_id are needed to
// locate the session, course_id/unit_id are just extra nullable columns on it.

exports.saveUnitQuizDraft = async (req, res) => {
  try {
    const { uuid, quizId } = req.params;
    const { answers = {} } = req.body;
    const user_id = req.user.user_id;

    const unit = await Unit.findOne({ where: { uuid, ...notDeleted } });
    if (!unit) return R.error(res, "Unit not found.", 404);

    const [updatedCount] = await QuizSession.update(
      { draft_answers: answers, last_saved_at: new Date() },
      { where: { quiz_id: quizId, user_id, status: "in_progress" } }
    );

    if (updatedCount === 0) {
      await QuizSession.create({
        quiz_id:       quizId,
        user_id,
        course_id:     null,
        unit_id:       unit.unit_id,
        draft_answers: answers,
        started_at:    new Date(),
      });
    }

    return res.status(204).end();
  } catch (err) {
    console.error("[CLIENT][UNITS][QUIZ][DRAFT]", err);
    return R.error(res, "Could not save quiz draft.", 500);
  }
};

// ─── STANDALONE LESSON PROGRESS ───────────────────────────────────────────────
// POST /client/lessons/:uuid/progress   Body: { status, unit_uuid? }
// Evaluated + written via completion_requirements.service#recomputeCascade with
// courseId null, which persists to lesson_reading_progress/unit_reading_progress
// (the tables that tolerate a null course_id) instead of course_reading_progress.
// When unit_uuid is given (unit context, still no course) the parent unit is
// re-evaluated + upserted too, against any configured CompletionRequirement rows.

exports.upsertStandaloneLessonProgress = async (req, res) => {
  try {
    const { uuid } = req.params;
    const userId = req.user.user_id;
    const status = req.body.status === "completed" ? "completed" : "in_progress";
    const unitUuid = req.body.unit_uuid ?? null;

    const lesson = await Lesson.findOne({ where: { uuid, ...notDeleted }, attributes: ["lesson_id", "uuid"] });
    if (!lesson) return R.error(res, "Lesson not found.", 404);

    if (!await coursesCtrl.canAccessLesson(userId, lesson.lesson_id)) {
      return R.error(res, "You do not have access to this lesson.", 403);
    }

    let unitId = null;
    if (unitUuid) {
      const unit = await Unit.findOne({ where: { uuid: unitUuid, ...notDeleted }, attributes: ["unit_id"] });
      if (!unit) return R.error(res, "Unit not found.", 404);
      const link = await UnitLesson.findOne({ where: { unit_id: unit.unit_id, lesson_id: lesson.lesson_id } });
      if (!link) return R.error(res, "Lesson is not attached to this unit.", 404);
      unitId = unit.unit_id;
    }

    const result = await recomputeCascade(userId, {
      courseId: null,
      unitId,
      unitUuid,
      lessonId: lesson.lesson_id,
      lessonUuid: lesson.uuid,
      lessonStatus: status,
    });

    logActivity(userId, "lesson_read", {
      entityType: "lesson",
      entityId:   lesson.lesson_id,
      details:    { lesson_uuid: lesson.uuid, status, standalone: true },
    });

    return R.success(res, "Progress updated.", result, 200);
  } catch (err) {
    console.error("[CLIENT][LESSONS][STANDALONE PROGRESS]", err);
    return R.error(res, "Could not update progress.", 500);
  }
};

// ─── STANDALONE WATCH PROGRESS ─────────────────────────────────────────────────
// POST /client/lessons/:uuid/watch-progress   Body: { percent, unit_uuid?, block_id?, block_type? }
// block_id/block_type identify which block on the lesson's page sent this update — needed
// to drive watch_video/listen_audio; omit them and only watch_percent (if configured) is touched.
exports.upsertStandaloneWatchProgress = async (req, res) => {
  try {
    const { uuid } = req.params;
    const userId = req.user.user_id;
    const percent = Number(req.body.percent);
    if (!Number.isFinite(percent)) return R.error(res, "percent must be a number.", 400);
    const unitUuid = req.body.unit_uuid ?? null;
    const blockId = req.body.block_id ?? null;
    const blockType = req.body.block_type ?? null;

    const lesson = await Lesson.findOne({ where: { uuid, ...notDeleted }, attributes: ["lesson_id", "uuid"] });
    if (!lesson) return R.error(res, "Lesson not found.", 404);
    if (!await coursesCtrl.canAccessLesson(userId, lesson.lesson_id)) {
      return R.error(res, "You do not have access to this lesson.", 403);
    }

    let unitId = null;
    if (unitUuid) {
      const unit = await Unit.findOne({ where: { uuid: unitUuid, ...notDeleted }, attributes: ["unit_id"] });
      if (!unit) return R.error(res, "Unit not found.", 404);
      unitId = unit.unit_id;
    }

    const result = await recordWatchProgress(userId, {
      lessonId: lesson.lesson_id, lessonUuid: lesson.uuid,
      unitId, unitUuid,
      courseId: null, courseUuid: null,
      percent, blockId, blockType,
    });

    return R.success(res, "Watch progress updated.", result, 200);
  } catch (err) {
    console.error("[CLIENT][LESSONS][STANDALONE WATCH PROGRESS]", err);
    return R.error(res, "Could not update watch progress.", 500);
  }
};

// ─── STANDALONE MARK COMPLETE ──────────────────────────────────────────────────
// POST /client/lessons/:uuid/mark-complete   Body: { unit_uuid? }
exports.markStandaloneLessonComplete = async (req, res) => {
  try {
    const { uuid } = req.params;
    const userId = req.user.user_id;
    const unitUuid = req.body.unit_uuid ?? null;

    const lesson = await Lesson.findOne({ where: { uuid, ...notDeleted }, attributes: ["lesson_id", "uuid"] });
    if (!lesson) return R.error(res, "Lesson not found.", 404);
    if (!await coursesCtrl.canAccessLesson(userId, lesson.lesson_id)) {
      return R.error(res, "You do not have access to this lesson.", 403);
    }

    let unitId = null;
    if (unitUuid) {
      const unit = await Unit.findOne({ where: { uuid: unitUuid, ...notDeleted }, attributes: ["unit_id"] });
      if (!unit) return R.error(res, "Unit not found.", 404);
      unitId = unit.unit_id;
    }

    const result = await recordManualComplete(userId, {
      entityType: "lesson", entityId: lesson.lesson_id,
      lessonUuid: lesson.uuid,
      unitId, unitUuid,
      courseId: null, courseUuid: null,
    });

    return R.success(res, "Lesson marked complete.", result, 200);
  } catch (err) {
    console.error("[CLIENT][LESSONS][STANDALONE MARK COMPLETE]", err);
    return R.error(res, "Could not mark lesson complete.", 500);
  }
};

// ─── Shared UUID handlers re-exported for the standalone routes ───────────────

exports.getUnitByUuid       = coursesCtrl.getUnitByUuid;
exports.getLessonsByUnitUuid = coursesCtrl.getLessonsByUnitUuid;
exports.getLessonByUuid     = coursesCtrl.getLessonByUuid;