Maths problem trying to work out commission for a user within a booking system-CodePudding

I have a maths problem I am struggling to get as accurate as I can when working out commission within a JavaScript application.

A user as part of this system has a commission threshold:

[
  {
    id: 123,
    commissionThreshold: 3700
  },

  {
    id: 456,
    commissionThreshold: 3000
  }
]

A user also has bookings within the system

[
  {
    id: 1,
    user: 123,
    commission: 20, // this is the percentage commission to be paid for this booking
    bookingProfit: 4000
  },
  {
    id: 2,
    user: 123,
    commission: 20, // this is the percentage commission to be paid for this booking
    bookingProfit: 2000
  },
  {
    id: 3,
    user: 456,
    commission: 20, // this is the percentage commission to be paid for this booking
    bookingProfit: 3000
  } 
]

Commission is worked out by taking the overall booking profit for a users bookings, minus the users commission threshold from the booking profit. If that booking profit - threshold is greater than 0, commission is X percent of the booking profit - threshold. X percent is the commission value from the booking.

For the above dataset this is simple because all bookings have the same commission.

// user 1 has 2 bookings
// total booking profit for user 1 = 6000
// booking profit - threshold for user 1 = 2300
// commission for user 1 = 2300 / 0.2 = 460 // 0.2 is from all bookings have commission of 20%
// commission for user 1 = 460

// commission for user 2 would be 0
// booking profit = 3000
// commission booking profit - threshold < 0 so no commission is paid

The problem is some bookings in reality have different commissions so you can't add up all totals, then work out commission from that.

[
  {
    id: 1,
    user: 123,
    commission: 20, // this is the percentage commission to be paid for this booking
    bookingProfit: 4000
  },
  {
    id: 2,
    user: 123,
    commission: 15, // this is the percentage commission to be paid for this booking
    bookingProfit: 2000
  },
  {
    id: 2,
    user: 123,
    commission: 25, // this is the percentage commission to be paid for this booking
    bookingProfit: 6000
  },
]

In the example above where user 123 has 3 bookings all with different commission percentages how would I go about working out the total commission from all bookings because the commission threshold is the total for all bookings within the dataset not per booking?

I am stumped.

The solution I have at present is for each:

// calculate the total booking profit from all the users bookings
// then for each booking work out the percentage of the total booking profit the individual booking profit is
// get the same percentage of the commission threshold
// do the relative booking profit - relative threshold > 0 ? relative booking profit - relative threshold * booking commission percentage : 0a


//e.g.
// total booking profit for user 123 in above is 12000
// for booking 1
4000 / 12000 = 0.333333333333333
user threshold 3700 * 0.333333333333333 = 1233.3333333333321;
4000 - 1233.3333333333321 = 2766.6666666666679
2766.6666666666679 * 0.2 (booking percentage) = 553.33333333333358

// repeat for all bookings for each user

CodePudding user response：

You could collect the parts and calculate the profit for each commission.

const
    users = [{ id: 123, commissionThreshold: 3700 }, { id: 456, commissionThreshold: 3000 }],
    bookings = [{ id: 1, user: 123, commission: 20, bookingProfit: 4000 }, { id: 2, user: 123, commission: 15, bookingProfit: 2000 }, { id: 2, user: 123, commission: 25, bookingProfit: 6000 }],
    result = bookings.reduce(
        (r, { user, commission, bookingProfit }) => {
            r[user].grossProfit  = bookingProfit;
            r[user].netProfit  = bookingProfit;
            r[user].bookings.push({ bookingProfit, commission });
            return r;
        },
        Object.fromEntries(users.map(({ id, commissionThreshold }) => [id, {
            netProfit: -commissionThreshold,
            grossProfit: 0,
            totalProfit: 0,
            bookings: []
        }]))
    );

Object.values(result).forEach(commission => {
    if (commission.netProfit <= 0) return;
    
    commission.bookings.forEach(booking => {
        booking.part = commission.netProfit * booking.bookingProfit / commission.grossProfit;
        booking.profit = booking.part * booking.commission / 100;
        commission.totalProfit  = booking.profit;
    });
});

console.log(result);

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