/***********************************************************************************************************************************************************************
 * File Name: course_units.mdl.js
 * Type of Program: Model (junction)
 * Description: Attaches a standalone Unit to a Course. A Unit can live in many
 *              Courses; per-course ordering lives here (order_index), not on the
 *              Unit itself. Detaching removes the row — the Unit survives.
 *
 * Author: Kenneth Obsequio (@lash0000)
 * Date Created: Jul. 7, 2026
 ***********************************************************************************************************************************************************************/
const { DataTypes } = require("sequelize");
const sequelize = require("../../config/db.config");

const CourseUnit = sequelize.define("CourseUnit", {
  course_unit_id: { type: DataTypes.BIGINT, primaryKey: true, autoIncrement: true },
  course_id:      { type: DataTypes.BIGINT, allowNull: false },
  unit_id:        { type: DataTypes.BIGINT, allowNull: false },
  order_index:    { type: DataTypes.INTEGER, allowNull: false, defaultValue: 0 },
  createdBy:      { type: DataTypes.BIGINT, allowNull: true },
  updatedBy:      { type: DataTypes.BIGINT, allowNull: true },
}, {
  tableName: "course_units",
  timestamps: true,
  indexes: [
    { unique: true, fields: ["course_id", "unit_id"], name: "uq_course_units_course_unit" },
    { fields: ["course_id"],   name: "idx_course_units_course_id" },
    { fields: ["unit_id"],     name: "idx_course_units_unit_id" },
    { fields: ["order_index"], name: "idx_course_units_order" },
  ],
});

module.exports = CourseUnit;