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

const UnitLesson = sequelize.define("UnitLesson", {
  unit_lesson_id: { type: DataTypes.BIGINT, primaryKey: true, autoIncrement: true },
  unit_id:        { type: DataTypes.BIGINT, allowNull: false },
  lesson_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: "unit_lessons",
  timestamps: true,
  indexes: [
    { unique: true, fields: ["unit_id", "lesson_id"], name: "uq_unit_lessons_unit_lesson" },
    { fields: ["unit_id"],     name: "idx_unit_lessons_unit_id" },
    { fields: ["lesson_id"],   name: "idx_unit_lessons_lesson_id" },
    { fields: ["order_index"], name: "idx_unit_lessons_order" },
  ],
});

module.exports = UnitLesson;