interface SequelizeRequest {
    request: (t: Transaction, params: any, thenRequest: SequelizeRequest[], data?: any) => Promise<any>;
    thenRequest?: SequelizeRequest[];
    catchCallback?: (err: Error) => Promise<any> | never;
}

export abstract class AbstractModel {

    private readonly sequelize: Sequelize;

    constructor(sequelize: Sequelize) {
        this.sequelize = sequelize;
    }

    start(params: any): Promise<any> {
        const requestRoot: SequelizeRequest = this.getAllSequelizeRequests();

        return this.sequelize.transaction((t: Transaction) => requestRoot
            .request(t, params, requestRoot.thenRequest || [])
            .catch(requestRoot.catchCallback || ((err: Error) => {
                throw new Error(); //ROOLBACK
            }))
        );
    }

    protected abstract getAllSequelizeRequests(): SequelizeRequest;

}

export class InscriptionModel extends AbstractModel {

    protected getAllSequelizeRequests(): SequelizeRequest {
        return {
            request: this.checkUsername,
            thenRequest: [
                {
                    request: this.checkEmail,
                    thenRequest: [
                        //etc...
                    ]
                }
            ]
        };
    }

    protected checkUsername(t: Transaction, params: any, thenRequest: SequelizeRequest[]): Promise<any> {
        return User.findOne({
            where: {username: params.username},
            transaction: t
        })
            .then((data: any) => {
                if (data) {
                    throw new Error(); //Provoque un ROLLBACK
                }

                return Promise.all(
                    thenRequest.map(r => r.request(t, params, r.thenRequest || [], data))
                );
            });
    }

    protected checkEmail(t: Transaction, params: any, thenRequest: SequelizeRequest[]): Promise<any> {
        return User.findOne({
            where: {email: params.email},
            transaction: t
        })
            .then((data: any) => {
                if (data) {
                    throw new Error(); //Provoque un ROLLBACK
                }

                return Promise.all(
                    thenRequest.map(r => r.request(t, params, r.thenRequest || [], data))
                );
            });
    }

}