Adding an add-on to an item and sending an updated quote (Node.js)

In this use case, the user adds an optional add-on to a particular product in the cart. This is generally useful in the case of restaurants where the user is allowed additional customization on individual items like adding extra cheese to a pizza or adding sugar-free sachets to his coffee. This is rarer in the case of local retail but not unheard of.

Code snippets

BPP receives protocol select

/*
Example Request JSON:
{
    "context": {
        "domain": "local_retail",
        "country": "IND",
        "city": "std:080",
        "action": "select",
        "core_version": "0.9.2",
        "bap_id": "https://mock_bap.com/",
        "bap_uri": "https://mock_bap.com/beckn/",
        "transaction_id": "1239890342",
        "message_id": "123793824",
        "timestamp": "2021-03-23T10:00:40.065Z"
    },
    "message": {
        "order": {
            "add_ons": [
                {
                    "id": "add_on_1"
                }
            ]
        }
    }
}
*/
    // Auth middleware authenticates the digital signature of the incoming request
    router.post('/local_retail/select', auth, select);

    function select({ headers, body }, res) {
        try {
            const message = _.get(body, "message");
            const context = _.get(body, "context");
            if (!context) {
                return res.status(400).send(httpResponse("NACK", "Missing Context"));
            }
            if (!message) {
                return res.status(400).send(httpResponse("NACK", "Missing Message"));
            }
            // ... Returns the ack immediately and continue the processing after validation
            res.status(200).send(httpResponse("ACK"));
            processSelect(headers, body)
        } catch (error) {
            res.status(500).send(httpResponse("NACK", error));
        }
    };

BPP processes the search

    function processSelect(requestHeaders, selectRequestBody) {
        // Execute business logic here
        let selectResponse = {}
        generateResponse(requestHeaders, selectResponse)
    }

BPP generates response

    function generateResponse(requestHeaders, rawResponse){
/*
Example Request JSON :
{
    "context": {
        "domain": "local_retail",
        "country": "IND",
        "city": "std:080",
        "action": "on_select",
        "core_version": "0.9.2",
        "bap_id": "https://mock_bap.com/",
        "bap_uri": "https://mock_bap.com/beckn/",
        "transaction_id": "1239890342",
        "message_id": "123793824",
        "timestamp": "2021-03-23T10:00:40.065Z"
    },
    "message": {
        "order": {
            "items": [
                {
                    "id": "item_1",
                    "price" : {
                        "currency": "INR",
                        "value": "40"
                    },
                    "quantity": {
                        "selected": {
                            "count": 1
                        }
                    }
                },
                {
                    "id": "item_4",
                    "price" : {
                        "currency": "INR",
                        "value": "60"
                    },
                    "quantity": {
                        "selected": {
                            "count": 2
                        }
                    }
                }
            ],
            "add_ons": [
                {
                    "id": "add_on_1",
                    "price" : {
                        "currency": "INR",
                        "value": "10"
                    }
                }
            ],
            "quote": {
                "price": {
                    "currency": "INR",
                    "value": "170"
                },
                "breakup": [
                    {
                        "title": "Brown Bread 400 gm",
                        "price": {
                            "currency": "INR",
                            "value": "40"
                        }
                    },
                    {
                        "title": "Good Life Toned Milk 1L",
                        "price": {
                            "currency": "INR",
                            "value": "120"
                        }
                    },
                    {
                        "title": "Sachet of tea powder Add on",
                        "price": {
                            "currency": "INR",
                            "value": "10"
                        }
                    }
                ],
                "ttl": "P4D"
            }
        }
    }
}
*/
        let onSelectResponseBody = {

        }
        //call protocol on_rating
        await callOnSelect(requestHeaders, onSelectResponseBody);
    }

BPP calls protocol on_select

    async function callOnSelect(requestHeaders, onSelectResponseBody) {
        // Take the subscriber Id from the header and calls the registry to get the url. If already cached it need not to call again
        const uri = await lookup(requestHeaders);
        // Construct Header
        const headers = constructAuthHeader(); // Auth Header with digital Signature
        return axios({ url: `${uri}/local_retail/on_select`, method: "POST", headers, data: onSelectResponseBody });
    }