gistfile1.txt

/*
Given Brief
# Find a total ordered quantity of a product for every weekday

You are asked to improve the analytics of an e-commerce platform: calculating a total quantity of a given product ordered should be added.

# Task

Implement `OrdersAnalyzer.totalQuantity(orders, productId)` method which

1. For given order collections, it calculates **total quantity of a given product ordered, grouped by days of weeks**.

2. The result is an object which includes names of all days of the week as a keys, and a sum of ordered quantity for a given product id as a value.

3. The method should always return an object. If there are no orders for passed `productId` for some weekday, there might be no entry in the resulting object or there might be an entry with a `0` value. 

## Example

### Example data

The _orders_ collection is available in `data.json`:

```
[
    {
        orderId: 554,
        creationDate: "2017-03-25T10:35:20", // Saturday
        orderLines: [
            {productId: 9872, name: 'Pencil', quantity: 3, unitPrice: 3.00}
        ]
    },
    {
        orderId: 555,
        creationDate: "2017-03-25T11:24:20", // Saturday
        orderLines: [
            {productId: 9872, name: 'Pencil', quantity: 1, unitPrice: 3.00},
            {productId: 1746, name: 'Eraser', quantity: 1, unitPrice: 1.00}
        ]
    },
    {
        orderId: 453,
        creationDate: "2017-03-27T14:53:12", // Monday
        orderLines: [
            {productId: 5723, name: 'Pen', quantity: 4, unitPrice: 4.22},
            {productId: 9872, name: 'Pencil', quantity: 3, unitPrice: 3.12},
            {productId: 3433, name: 'Erasers Set', quantity: 1, unitPrice: 6.15}
        ]
    },
    {
        orderId: 431,
        creationDate: "2017-03-20T12:15:02", // Monday
        orderLines: [
            {productId: 5723, name: 'Pen', quantity: 7, unitPrice: 4.22},
            {productId: 3433, name: 'Erasers Set', quantity: 2, unitPrice: 6.15}
        ]
    },
    {
        orderId: 690,
        creationDate: "2017-03-26T11:14:00", // Sunday
        orderLines: [
            {productId: 9872, name: 'Pencil', quantity: 4, unitPrice: 3.12},
            {productId: 4098, name: 'Marker', quantity: 5, unitPrice: 4.50}
        ]
    }
];
```

### Example usage

```js
const analyzer = new OrdersAnalyzer();
analyzer.analyzer.totalQuantity(orders, 9872);
```

## Example output

Your implementation should return following output for **product id=9872** for example data:

```json
{
  "MONDAY" : 3, 
  "TUESDAY" : 0, 
  "WEDNESDAY" : 0, 
  "THURSDAY" : 0, 
  "FRIDAY " : 0, 
  "SATURDAY" : 4,
  "SUNDAY" : 4 
}
```

In the example above, there are:
- two orders placed on **Saturday**
  - first with quantity equal to `3` (id:`554`) and second with quantity equal to `1` (id:`555`), so the sum of quantities is `4`.
- one order placed on **Sunday**
  - so the total quantity is `4`.
- two orders placed on **Monday**
  - and only one of them (id:`453`) includes this product with quantity equal to `3`. So total quantity is also `3`.

### Testcases

Testcases are defined in `testcases.json`. They include all days of week, like the following:

```json
{
  "1746": {
    "SUNDAY": 0,
    "MONDAY": 0,
    "TUESDAY": 0,
    "WEDNESDAY": 0,
    "THURSDAY": 0,
    "FRIDAY": 0,
    "SATURDAY": 1
  },
  "3433": {
    "SUNDAY": 0,
    "MONDAY": 3,
    "TUESDAY": 0,
    "WEDNESDAY": 0,
    "THURSDAY": 0,
    "FRIDAY": 0,
    "SATURDAY": 0
  },
  ...
}
```

This means that for a given dataset, there would be tests for each day-of-week AND product combination:
- test scenario 1: product id:1746, all days of week
- test scenario 2: product id:3433, all days of week
*/

export default class OrdersAnalyzer {
  constructor() {
    this.weekdays = [
      "SUNDAY",
      "MONDAY",
      "TUESDAY",
      "WEDNESDAY",
      "THURSDAY",
      "FRIDAY",
      "SATURDAY",
    ];
  }

  totalQuantity(orders, productId) {
    let weeklyQuantities = Array(7).fill(0);

    orders.forEach((order) => {
      const orderDate = new Date(order.creationDate);
      let dayOfWeek = orderDate.getDay();
      order.orderLines?.forEach((orderLine) => {
        if (productId === orderLine.productId)
          weeklyQuantities[dayOfWeek] += orderLine.quantity;
      });
    });

    return {
      SUNDAY: weeklyQuantities[0],
      MONDAY: weeklyQuantities[1],
      TUESDAY: weeklyQuantities[2],
      WEDNESDAY: weeklyQuantities[3],
      THURSDAY: weeklyQuantities[4],
      FRIDAY: weeklyQuantities[5],
      SATURDAY: weeklyQuantities[6],
    };
  }
}