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title: “Badge Function (GetScanCount)” layout: default permalink: /docs/badge-function/ —

Azure Function: GetScanCount (NFC Scan Badge)

This Azure Function powers the “Total NFC Scans” badge shown in the README:

It queries Application Insights using the App Insights REST API (read-only) and returns shields.io compatible JSON.

Why a separate function?

• Keeps badge logic isolated from the mobile app and proxy services.
• Allows independent deployment/scaling of the public badge endpoint (anonymous).
• The count is derived from customEvents telemetry emitted by the MAUI app during NFC scans, provisioning, and inventory operations (see DeviceService.ScanPhoneAsync + TelemetryClient.TrackEvent).

Required App Settings

Name	Required	Description
APP_INSIGHTS_APP_ID	Yes	Application Insights application ID (from the resource used by the mobile app).
APP_INSIGHTS_API_KEY	Yes	API key with read permissions for the App Insights resource (create via Azure Portal > API Access).

Optional App Settings

Name	Default	Description
APP_INSIGHTS_KQL_QUERY	customEvents \| count	Full KQL query that must return a single numeric value in the first cell of the first row. You can embed constants (baselines), filters, time ranges, etc. directly in the query. Example: print 1234 + toscalar(customEvents \| count).

Error / Configuration States

The endpoint always returns HTTP 200 + valid shields.io JSON so the badge renders reliably in GitHub READMEs.

Visible message values in the badge:

• Normal count (e.g. 1247)
• unconfigured (light grey) — missing APP_INSIGHTS_APP_ID / APP_INSIGHTS_API_KEY
• error (red) — query failure, bad API key, malformed result shape, parse error, etc.

Logs in the Function App will contain details for troubleshooting.

Deployment Notes

• The Function App is a .NET 9 isolated Azure Functions app (src/DeviceFX.Function).
• It has no dependency on the main mobile app build (excluded from azure-pipelines.yml).
• Deploy via:
  • Azure Functions Core Tools (func azure functionapp publish ...)
  • Azure Portal / GitHub Actions / Azure DevOps (separate pipeline recommended)
  • VS Code Azure Functions extension
• Requires the two App Insights read settings above (plus standard AzureWebJobsStorage and FUNCTIONS_WORKER_RUNTIME).

Local Development

1. Copy src/DeviceFX.Function/local.settings.json and fill real values (or keep placeholders to test the “unconfigured” path).
2. Run the function project (F5 in VS Code or func start from the src/DeviceFX.Function dir after dotnet build).
3. Hit http://localhost:PORT/api/GetScanCount (port shown in launch profile or output).

Updating the Badge Query Without Code Changes

Update the APP_INSIGHTS_KQL_QUERY Application Setting. The query itself can include any baseline or calculation (e.g. print 1234 + toscalar(customEvents | count)). No code change or mobile app rebuild is required.

References

• Source: src/DeviceFX.Function/GetScanCount.cs
• Telemetry source: src/DeviceFX.NfcApp/Services/DeviceService.cs (TrackEvent calls)
• Badge URL in README: https://img.shields.io/endpoint?url=.../api/GetScanCount
• Issue: #14 — Extend scan badge to preserve lifetime total beyond App Insights retention.