'use strict';

/**
 * Junction revamp — Units and Lessons run independently.
 *
 *   courses ⇄ course_units ⇄ units ⇄ unit_lessons ⇄ lessons
 *
 * 1. Create course_units + unit_lessons (ordering lives on the junction rows)
 * 2. Backfill from the old direct FKs (units.course_id / lessons.unit_id),
 *    preserving each row's order_index
 * 3. Progress tables accept NULL course/unit context (standalone reads)
 * 4. Drop the old FK + order columns from units / lessons
 */
module.exports = {
  async up(queryInterface, Sequelize) {
    // ── 1. Junction tables ────────────────────────────────────────────────────
    await queryInterface.createTable('course_units', {
      course_unit_id: { type: Sequelize.BIGINT, primaryKey: true, autoIncrement: true },
      course_id:      { type: Sequelize.BIGINT, allowNull: false, references: { model: 'courses', key: 'course_id' }, onDelete: 'CASCADE' },
      unit_id:        { type: Sequelize.BIGINT, allowNull: false, references: { model: 'units',   key: 'unit_id'   }, onDelete: 'CASCADE' },
      order_index:    { type: Sequelize.INTEGER, allowNull: false, defaultValue: 0 },
      createdBy:      { type: Sequelize.BIGINT, allowNull: true },
      updatedBy:      { type: Sequelize.BIGINT, allowNull: true },
      createdAt:      { type: Sequelize.DATE, allowNull: false, defaultValue: Sequelize.literal('CURRENT_TIMESTAMP') },
      updatedAt:      { type: Sequelize.DATE, allowNull: false, defaultValue: Sequelize.literal('CURRENT_TIMESTAMP') },
    });
    await queryInterface.addIndex('course_units', { fields: ['course_id', 'unit_id'], unique: true, name: 'uq_course_units_course_unit' });
    await queryInterface.addIndex('course_units', { fields: ['course_id'],   name: 'idx_course_units_course_id' });
    await queryInterface.addIndex('course_units', { fields: ['unit_id'],     name: 'idx_course_units_unit_id' });
    await queryInterface.addIndex('course_units', { fields: ['order_index'], name: 'idx_course_units_order' });

    await queryInterface.createTable('unit_lessons', {
      unit_lesson_id: { type: Sequelize.BIGINT, primaryKey: true, autoIncrement: true },
      unit_id:        { type: Sequelize.BIGINT, allowNull: false, references: { model: 'units',   key: 'unit_id'   }, onDelete: 'CASCADE' },
      lesson_id:      { type: Sequelize.BIGINT, allowNull: false, references: { model: 'lessons', key: 'lesson_id' }, onDelete: 'CASCADE' },
      order_index:    { type: Sequelize.INTEGER, allowNull: false, defaultValue: 0 },
      createdBy:      { type: Sequelize.BIGINT, allowNull: true },
      updatedBy:      { type: Sequelize.BIGINT, allowNull: true },
      createdAt:      { type: Sequelize.DATE, allowNull: false, defaultValue: Sequelize.literal('CURRENT_TIMESTAMP') },
      updatedAt:      { type: Sequelize.DATE, allowNull: false, defaultValue: Sequelize.literal('CURRENT_TIMESTAMP') },
    });
    await queryInterface.addIndex('unit_lessons', { fields: ['unit_id', 'lesson_id'], unique: true, name: 'uq_unit_lessons_unit_lesson' });
    await queryInterface.addIndex('unit_lessons', { fields: ['unit_id'],     name: 'idx_unit_lessons_unit_id' });
    await queryInterface.addIndex('unit_lessons', { fields: ['lesson_id'],   name: 'idx_unit_lessons_lesson_id' });
    await queryInterface.addIndex('unit_lessons', { fields: ['order_index'], name: 'idx_unit_lessons_order' });

    // ── 2. Backfill from the old direct FKs ───────────────────────────────────
    await queryInterface.sequelize.query(`
      INSERT INTO course_units (course_id, unit_id, order_index, "createdBy", "createdAt", "updatedAt")
      SELECT u.course_id, u.unit_id, COALESCE(u.order_index, 0), u."createdBy", CURRENT_TIMESTAMP, CURRENT_TIMESTAMP
      FROM units u
      WHERE u.course_id IS NOT NULL
    `);
    await queryInterface.sequelize.query(`
      INSERT INTO unit_lessons (unit_id, lesson_id, order_index, "createdBy", "createdAt", "updatedAt")
      SELECT l.unit_id, l.lesson_id, COALESCE(l.order_index, 0), l."createdBy", CURRENT_TIMESTAMP, CURRENT_TIMESTAMP
      FROM lessons l
      WHERE l.unit_id IS NOT NULL
    `);

    // ── 3. Progress tables — allow standalone (course-less / unit-less) reads ──
    await queryInterface.changeColumn('unit_reading_progress',   'course_id', { type: Sequelize.BIGINT, allowNull: true });
    await queryInterface.changeColumn('lesson_reading_progress', 'course_id', { type: Sequelize.BIGINT, allowNull: true });
    await queryInterface.changeColumn('lesson_reading_progress', 'unit_id',   { type: Sequelize.BIGINT, allowNull: true });

    // ── 4. Drop the old FK + order columns ────────────────────────────────────
    await queryInterface.removeColumn('units',   'course_id');
    await queryInterface.removeColumn('units',   'order_index');
    await queryInterface.removeColumn('lessons', 'unit_id');
    await queryInterface.removeColumn('lessons', 'order_index');
  },

  async down(queryInterface, Sequelize) {
    // Recreate the direct FK columns and restore one parent per child
    await queryInterface.addColumn('units',   'course_id',   { type: Sequelize.BIGINT, allowNull: true });
    await queryInterface.addColumn('units',   'order_index', { type: Sequelize.INTEGER, allowNull: false, defaultValue: 0 });
    await queryInterface.addColumn('lessons', 'unit_id',     { type: Sequelize.BIGINT, allowNull: true });
    await queryInterface.addColumn('lessons', 'order_index', { type: Sequelize.INTEGER, allowNull: false, defaultValue: 0 });

    // Keep the FIRST attachment per child (multi-parent data collapses)
    await queryInterface.sequelize.query(`
      UPDATE units u SET course_id = cu.course_id, order_index = cu.order_index
      FROM (SELECT DISTINCT ON (unit_id) unit_id, course_id, order_index
              FROM course_units ORDER BY unit_id, course_unit_id) cu
      WHERE u.unit_id = cu.unit_id
    `);
    await queryInterface.sequelize.query(`
      UPDATE lessons l SET unit_id = ul.unit_id, order_index = ul.order_index
      FROM (SELECT DISTINCT ON (lesson_id) lesson_id, unit_id, order_index
              FROM unit_lessons ORDER BY lesson_id, unit_lesson_id) ul
      WHERE l.lesson_id = ul.lesson_id
    `);

    await queryInterface.changeColumn('unit_reading_progress',   'course_id', { type: Sequelize.BIGINT, allowNull: false });
    await queryInterface.changeColumn('lesson_reading_progress', 'course_id', { type: Sequelize.BIGINT, allowNull: false });
    await queryInterface.changeColumn('lesson_reading_progress', 'unit_id',   { type: Sequelize.BIGINT, allowNull: false });

    await queryInterface.dropTable('unit_lessons');
    await queryInterface.dropTable('course_units');
  },
};