import { Test, TestingModule } from '@nestjs/testing';
import { getDataSourceToken } from '@nestjs/typeorm';
import { DatabaseMigrationsService } from './database-migrations.service';

function createRunner(tableExists: boolean, columns: string[] = []) {
  return {
    connect: jest.fn(),
    release: jest.fn(),
    getTables: jest.fn().mockResolvedValue(tableExists ? [{ name: 'class_student' }] : []),
    getTable: jest.fn().mockResolvedValue({
      name: 'class_student',
      columns: columns.map((name) => ({ name })),
    }),
    dropColumn: jest.fn().mockResolvedValue(undefined),
  };
}

async function createService(runner: ReturnType<typeof createRunner>) {
  const module: TestingModule = await Test.createTestingModule({
    providers: [
      DatabaseMigrationsService,
      {
        provide: getDataSourceToken(),
        useValue: {
          options: { type: 'better-sqlite3' },
          createQueryRunner: jest.fn().mockReturnValue(runner),
        },
      },
    ],
  }).compile();
  return module.get(DatabaseMigrationsService) as DatabaseMigrationsService & {
    removeUnusedClassStudentColumns(): Promise<void>;
  };
}

describe('DatabaseMigrationsService — class student cleanup', () => {
  it('drops the unused enrollment_id column', async () => {
    const runner = createRunner(true, ['id', 'enrollment_id']);
    const service = await createService(runner);

    await service.removeUnusedClassStudentColumns();

    expect(runner.dropColumn).toHaveBeenCalledWith('class_student', 'enrollment_id');
    expect(runner.release).toHaveBeenCalled();
  });

  it('does nothing when the table is absent', async () => {
    const runner = createRunner(false);
    const service = await createService(runner);

    await service.removeUnusedClassStudentColumns();

    expect(runner.dropColumn).not.toHaveBeenCalled();
    expect(runner.release).toHaveBeenCalled();
  });
});