import * as Objection from 'objection';

export class TransactionManager {

    private knex = null;
    public transaction: Objection.Transaction = null;
    private nestingLevel: number = 0;
    private isRollbackOnly: boolean = false;

    constructor() {
        this.knex = Objection.Model.knex();
    }

    public async begin()
    {
        this.nestingLevel++;

        if(this.nestingLevel === 1) {
            this.transaction = await Objection.transaction.start(this.knex);
        }
    }

    public async commit()
    {
        if(this.isRollbackOnly)
            throw new Error('Cannot commit - transaction is rollback only');

        if(this.nestingLevel === 0)
            throw new Error('Cannot commit - no active transaction');

        if(this.nestingLevel === 1) {
            await this.transaction.commit();
        }

        --this.nestingLevel;
    }

    public async rollback()
    {
        if(this.nestingLevel === 0)
            throw new Error('Cannot commit - no active transaction');

        if(this.nestingLevel === 1) {
            await this.transaction.rollback();
        }
        else {
            this.isRollbackOnly = true;
        }

        --this.nestingLevel;
    }
}