const cds = require("@sap/cds");
const moment = require("moment");

const LEVERAGE_DURATION = 1; // in hours. should be the same in the frontend
const CANCEL_STATUS = -1;
const UTC_DATE_TIME_FORMAT = "YYYY-MM-DDThh:mm:ss";

// the same function there is in the frontend
const isLeverageTimeExpired = (utcNowTimestamp, invoiceDate) => {
  const duration = moment.duration(
    moment(utcNowTimestamp).diff(moment(invoiceDate).valueOf())
  );
  return duration.asHours() > LEVERAGE_DURATION;
};

module.exports = async function () {
  const db = await cds.connect.to("db"); // connect to database service
  const { Invoices, InvoiceItems } = db.entities;

  this.on("READ", "Invoices", async (req) => {
    return await db.run(req.query.where({ customer_ID: req.user.attr.ID }));
  });

  this.on("invoice", async (req) => {
    const { tracks } = req.data;
    const customerId = req.user.attr.ID;
    const total = tracks.reduce(
      (acc, { unitPrice }) => acc + Number(unitPrice),
      0
    );
    const utcNowDateTime = moment().utc().format(UTC_DATE_TIME_FORMAT);

    const transaction = await db.tx(req);
    const {
      results: [{ lastID: invoiceID }],
    } = await transaction.run(
      INSERT.into(Invoices)
        .columns("customer_ID", "total", "invoiceDate")
        .values(customerId, total, utcNowDateTime)
    );
    await transaction.run(
      INSERT.into(InvoiceItems)
        .columns("invoice_ID", "track_ID", "unitPrice")
        .rows(
          tracks.map(({ ID: trackID, unitPrice }) => [
            invoiceID,
            trackID,
            unitPrice,
          ])
        )
    );
    await transaction.commit();
  });

  this.on("cancelInvoice", async (req) => {
    const { ID } = req.data;

    const currentInvoice = await db.run(
      SELECT.one(Invoices)
        .where({
          ID,
          customer_ID: req.user.attr.ID,
        })
        .columns("ID", "invoiceDate", "customer_ID")
    );
    if (!currentInvoice) {
      req.reject(
        404,
        "Seems like you are not owning this invoice or it is not exists"
      );
    }

    const utcNowTimestamp = moment(
      moment().utc().format(UTC_DATE_TIME_FORMAT)
    ).valueOf();
    if (isLeverageTimeExpired(utcNowTimestamp, currentInvoice.invoiceDate)) {
      req.reject(400, "Leverage time was expired");
    }

    return await db.run(
      UPDATE(Invoices).set({ status: CANCEL_STATUS }).where({ ID })
    );
  });
};