/***********************************************************************************************************************************************************************
 * File Name: course_reading_progress.service.js
 * Type of Program: Service
 * Description: UPSERT-based progress tracking for user reading activity across the course hierarchy.
 *
 *   upsertLessonRead — main entry point, called when a user reads a lesson.
 *                      UPSERTs the lesson row, then derives and UPSERTs the parent unit and course rows.
 *                      All three writes run in a single transaction.
 *
 * UPSERT key: (user_id, type, reference_id)
 *
 * Derivation rules:
 *   unit   → completed when ALL its non-deleted lessons have a completed row for this user
 *   course → completed when ALL its non-deleted units have a completed row for this user
 *
 * Author: Kenneth Obsequio (@lash0000)
 * Date Created: Jun. 21, 2026
 ***********************************************************************************************************************************************************************/
'use strict';

const sequelize             = require('../config/db.config');
const CourseReadingProgress = require('../models/courses/course_reading_progress.mdl');
const Lesson                = require('../models/courses/lessons.mdl');
const Unit                  = require('../models/courses/units.mdl');

// ─── Core UPSERT ─────────────────────────────────────────────────────────────

async function upsertProgress({ userId, courseId, type, referenceId, status }, t) {
    const now = new Date();
    const [record] = await CourseReadingProgress.upsert(
        {
            user_id:          userId,
            course_id:        courseId,
            reference_id:     referenceId,
            type,
            status,
            completed_at:     status === 'completed' ? now : null,
            last_accessed_at: now,
            createdBy:        userId,
            updatedBy:        userId,
        },
        {
            conflictFields: ['user_id', 'type', 'reference_id'],
            returning:      true,
            transaction:    t,
        }
    );
    return record;
}

// ─── Derivation helpers ───────────────────────────────────────────────────────

// Unit is completed when every non-deleted lesson under it has a completed row for this user.
async function deriveUnitStatus(userId, courseId, unitId, t) {
    const lessons = await Lesson.findAll({
        where:       { unit_id: unitId },
        attributes:  ['uuid'],
        transaction: t,
    });
    if (!lessons.length) return 'in_progress';

    const lessonUuids    = lessons.map(l => l.uuid);
    const completedCount = await CourseReadingProgress.count({
        where: {
            user_id:      userId,
            course_id:    courseId,
            type:         'lesson',
            reference_id: lessonUuids,
            status:       'completed',
        },
        transaction: t,
    });

    return completedCount === lessons.length ? 'completed' : 'in_progress';
}

// Course is completed when every non-deleted unit under it has a completed row for this user.
async function deriveCourseStatus(userId, courseId, t) {
    const units = await Unit.findAll({
        where:       { course_id: courseId },
        attributes:  ['uuid'],
        transaction: t,
    });
    if (!units.length) return 'in_progress';

    const unitUuids      = units.map(u => u.uuid);
    const completedCount = await CourseReadingProgress.count({
        where: {
            user_id:      userId,
            course_id:    courseId,
            type:         'unit',
            reference_id: unitUuids,
            status:       'completed',
        },
        transaction: t,
    });

    return completedCount === units.length ? 'completed' : 'in_progress';
}

// ─── Main entry point ─────────────────────────────────────────────────────────

/**
 * Called when a user reads (or finishes reading) a lesson.
 * Writes three rows in one transaction: lesson → unit → course.
 *
 * @param {number} userId
 * @param {Object} payload
 * @param {number} payload.courseId    — course BIGINT PK (FK on course_reading_progress)
 * @param {string} payload.courseUuid  — course UUID (reference_id for the course row)
 * @param {number} payload.unitId      — unit BIGINT PK (used to query sibling lessons)
 * @param {string} payload.unitUuid    — unit UUID (reference_id for the unit row)
 * @param {string} payload.lessonUuid  — lesson UUID (reference_id for the lesson row)
 * @param {string} payload.lessonStatus — 'in_progress' | 'completed'
 * @returns {{ lesson, unit, course }} — status snapshot for each level
 */
async function upsertLessonRead(userId, { courseId, courseUuid, unitId, unitUuid, lessonUuid, lessonStatus = 'in_progress' }) {
    const t = await sequelize.transaction();
    try {
        // 1. Lesson
        await upsertProgress({
            userId,
            courseId,
            type:        'lesson',
            referenceId: lessonUuid,
            status:      lessonStatus,
        }, t);

        // 2. Unit — derived from all sibling lessons
        const unitStatus = await deriveUnitStatus(userId, courseId, unitId, t);
        await upsertProgress({
            userId,
            courseId,
            type:        'unit',
            referenceId: unitUuid,
            status:      unitStatus,
        }, t);

        // 3. Course — derived from all units
        const courseStatus = await deriveCourseStatus(userId, courseId, t);
        await upsertProgress({
            userId,
            courseId,
            type:        'course',
            referenceId: courseUuid,
            status:      courseStatus,
        }, t);

        await t.commit();

        return {
            lesson: { reference_id: lessonUuid,  status: lessonStatus  },
            unit:   { reference_id: unitUuid,    status: unitStatus    },
            course: { reference_id: courseUuid,  status: courseStatus  },
        };
    } catch (err) {
        await t.rollback();
        throw err;
    }
}

// ─── Exports ──────────────────────────────────────────────────────────────────

module.exports = {
    upsertLessonRead,
    upsertProgress,
    deriveUnitStatus,
    deriveCourseStatus,
};