Adding an add-on to an item and receiving an updated quote (Java)

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

Client calls the BAP server to trigger select:

    @PostMapping("/local_retail/add_addon")
    public ResponseEntity addAddon(
            @RequestHeader HttpHeaders headers,
            @RequestBody ClientSelectRequest request) {
        var response = bapApplicationService.generateSelectRequest(request, headers);
        return ResponseEntity.ok(response);
    }

BAP server generates the protocol request body

/*
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"
                }
            ]
        }
    }
}
*/

    public Response generateSelectRequest(ClientSelectRequest request, HttpHeaders headers) {

        // Generate message id
        var messageId = UUID.randomUUID().toString();

        // Check if transaction id exists in the request.
        // Generate if not exists
        var txnId = StringUtils.hasText(request.getTransactionId())
                ? request.getTransactionId()
                : UUID.randomUUID().toString();

        // Construct the Context based on the request parameters
        var context = Context.builder().domain(request.getDomain())
                .action(Context.ActionEnum.select)
                .messageId(messageId)
                .transactionId(txnId)
                .transactionId(UUID.randomUUID().toString())
                .timestamp(new Date().toString())
                .build();

        // Construct the protocol specific object to be passed to the BPP/BG
        // Add the selected item(s) from the catalog to get a draft quote
        var selectRequest = SelectRequest.builder()
                .context(context)
                .message(Message.builder().order(Order.builder()
                        .items(ClientAssembler.of(request.getItems()))
                        .build()).build())
                .build();

        return invokeSelect(selectRequest, headers);
    }
}

BAP server calls protocol select to the network

    public Response invokeSelect(SelectRequest request, HttpHeaders headers) {

        // Call to look up function which returns the the public key and BPP Endpoint to be called
        var url = lookUp(headers);

        // Call BPP Select api from the returned endpoint.
        // Construct request headers with the public key
        var selectResponse = apiClient.post(url[0] + Context.ActionEnum.select,
                constructRequestHeaders(),
                request,
                Response.class);

        // Validate the received response
        if (responseEntity.getBody() == null || responseEntity.getBody().getError() != null ||
                "NACK".equals(responseEntity.getBody().getMessage().getAck().getStatus())) {
            // Return custom error to the client
            return null;
        }
        return selectResponse.getBody();
    }

BAP receives protocol on_select

/*
Example Response 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"
            }
        }
    }
}
*/
    @PostMapping("/bap/on_select")
    public ResponseEntity onSelect(
            @RequestHeader HttpHeaders headers,
            @RequestBody OnSelectRequest request) {
        var response = bapCallbackApplicationService.onSelect(request, headers);
        return ResponseEntity.ok(response);
    }

    public Response onSelect(OnSelectRequest request, HttpHeaders headers) {
        // Validate the headers received
        var isHeadersValid = validateHeaders(headers);
        // Construct and return error if the received headers are invalid
        if (!isHeadersValid) return null;

        // Store the data received based on message id for the client to poll
        saveToDB(request);

        return Response.of("ACK", null);
    }

Client polls BAP to get the on_select results

    // Endpoint for the client to poll the select data based on the message id
    @GetMapping("/local_retail/on_select")
    public ResponseEntity selectByMessageId(
            @PathVariable(ClientRoutes.PARAM_MESSAGE_ID) String messageId,
            @RequestHeader HttpHeaders headers) {
        var data = bapApplicationService.get(messageId);
        return ResponseEntity.ok(data);
    }