PRICE.md

Calculate Price

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On the POST request to http://localhost:5000/api/calculate-price, calculatePrice controller code is called for calculating the total cost of food delivery.

calculatePrice module

1. First and foremost, we will be validating the passed parameters in request body (req.body).
2. validateReqBody utility function is used for this validation purpose.
   1. The first step is to create an array of missing fields (missingFields). We are checking if the zone, organization_id, total_distance and item_type are there in the request body or not.
   2. If any of these above 4 parameters are not passed, we will be pushing the name of those parameters to the missingFields array.
   3. If the missingFields has any data, then we will return the function with success: false and error with missing field(s). Now as we have these 4 parameters in request body, we will now use 4 different hooks namely validateZone, validateOrganizationId, validateTotalDistance and validateItemType to validate them.
      1. validateZone utility function:
         • It takes zone as parameter and checks if its value is string or not. If zone is not string, then we will return error.
         • Then we check that the zone is in allowedZones array or not. If it is not in the array, then return error.
         • Now if the zone is in the allowed zones, then we will replace hyphen (-) with underscore (_). Its because we can't add hyphen symbol as data in our PostgreSQL table.
         • Then after passing all checks, we will return formatted zone as data from this utility function.
      2. validateOrganizationId utility function:
         • It takes organization_id as parameter and checks if its value is string or not. If organization_id is not string, then we will return error.
         • Then we will check if the organization_id is empty or not. If it is empty, then we will return error.
         • Now, we will be adding leading zeros to organization_id to make it at least 3 characters long.
         • Then we will return formatted organization ID as data from this utility function.
      3. validateTotalDistance utility function:
         • It takes total_distance as parameter and checks if its value is number or not. If total_distance is not number, then we will return error.
         • Now we check if this total_distance is negative. If it is negative, the we return error.
         • After passing these above checks, we will return total_distance as data from this utility function.
      4. validateItemType utility function:
         • It takes item_type as parameter and checks if its value is string or not. If item_type is not string, then we will return error.
         • Then we check that the item_type is in allowedTypes array or not. If it is not in the array, then return error.
         • Now if the item_type is in the allowed types, then we will replace hyphen (-) with underscore (_).
         • Then we will return formatted item type as data from this utility function.
   4. Using these above 4 validation hooks, we will store their returned value to validationResults array. Then we will check if in this array, there is any error which might be returned from any of these hooks and store it in in hasErrors constant.
   5. If there is any error (hasErrors is true), then we will filter the validationResults which has truthy result.error and store it in errorMessages. Then we will return success: false and error messages in error from this validateReqBody function.
   6. If there wasn't any error (hasErrors is false), then return success: true and validatedZone, validatedOrganizationId, validatedTotalDistance and validatedItemType in data from this validateReqBody function.
3. Now in calculatePrice controller, we will be using validateReqBody utility function to get success (true or false), error (if there was any error returned - when success: false) or data (valiadted parametrs passed in request body - when success: true) and store it in validationResult.
4. Then if validationResult object has success: false, then we return response from this POST request with error. Here's the response object:

{
    success: false,
    error: appropiate error message in the form of string
}

5. If the validationResult object has success: true, then we destructure the validationResult.data to get validatedZone, validatedOrganizationId, validatedTotalDistance and validatedItemType.
6. Now we query the Pricing table and find if there exists any row for

{ organizationId: validatedOrganizationId },
{ item: { type: validatedItemType } },
{ zone: validatedZone }

and if there is no such data with matching parameters, then return

{
    success: false,
    error: "No Item found"
}

7. If we do get any row with the matching data, then we calculate the totalCost with the logic
   • If validated total distance is greater than 5 km, then

     totalCost = fixPrice + ((validatedTotalDistance - baseDistanceInKm) * kmPrice);
     

   • Else when validated total distance is less than or equal to 5 km, then

     totalCost = fixPrice
     

The data available:

fixPrice = 1000 cents
validatedTotalDistance = validated total_distance
baseDistanceInKm = 5 km
kmPrice = decided based upon if type is "perishable" (150 cents) or "non_perishable" (100 cents)

8. Our cost in the Pricing table is in cents. So we divide the totalCost with 100 to get the cost in the Euro (€) and return the response

{ 
    success: true, 
    total_price: (totalCost / 100) 
}