Purview Telemetry Source Generator

using Purview.Telemetry;

// Multi-target interface: generates Activities, Logging, AND Metrics from combined methods
[ActivitySource]
[Logger]
[Meter]
interface IEntityStoreTelemetry
{
    // MULTI-TARGET: Creates Activity + Logs Info + Increments Counter - all from one method!
    [Activity]
    [Info]
    [AutoCounter]
    Activity? GettingEntityFromStore(int entityId, [Baggage]string serviceUrl);

    // MULTI-TARGET: Adds ActivityEvent + Logs the duration as Trace.
    [Event]
    [Trace]
    void GetDuration(Activity? activity, int durationInMS);

    // Single-target examples (when you only need one telemetry type):
    
    // Activity-only: Adds Baggage to the Activity
    [Context]
    void RetrievedEntity(Activity? activity, float totalValue, int lastUpdatedByUserId);

    // Log-only: Structured log message
    [Warning]
    void EntityNotFound(int entityId);

    // Metric-only: Histogram for tracking values
    [Histogram]
    void RecordEntitySize(int sizeInBytes);
}

// Generated extension method
services.AddEntityStoreTelemetry();

public class EntityService(IEntityStoreTelemetry telemetry)
{
    public async Task<Entity> GetEntityAsync(int id, string serviceUrl, CancellationToken cancellationToken)
    {
        // Single call creates Activity AND logs AND increments counter
        using var activity = telemetry.GettingEntityFromStore(id, serviceUrl);
        
        var entity = await _repository.GetAsync(id, cancellationToken);
                        
        // Adds event to activity AND logs duration
        telemetry.GetDuration(activity, stopwatch.ElapsedMilliseconds);

        if (entity == null)
        {
            // Logs warning if entity not found
            telemetry.EntityNotFound(id);
            return null;
        }

        // Activity context addition
        telemetry.RetrievedEntity(activity, entity.TotalValue, entity.LastUpdatedByUserId);
        
        // Histogram only records size
        telemetry.RecordEntitySize(entity.SizeInBytes);

        return entity;
    }
}

using Purview.Telemetry.Activities;
using Purview.Telemetry.Logging;
using Purview.Telemetry.Metrics;

using Purview.Telemetry;

// Generated code:
new ActivitySource("myapp")           // lowercase
activity.SetTag("entityid", ...)      // smashed compound
var meter = meterFactory.Create("MyApp.Products");
meter.CreateCounter<int>("recordcount")  // smashed compound, no meter prefix

// Generated code:
new ActivitySource("MyApp")           // preserves casing
activity.SetTag("entity_id", ...)     // snake_case
var meter = meterFactory.Create("MyApp.Products");
meter.CreateCounter<int>("myapp.products.record.count")  // hierarchical: meter + instrument

using Purview.Telemetry;

// Revert ALL telemetry to v3 naming (assembly-level)
[assembly: TelemetryGeneration(NamingConvention = NamingConvention.Legacy)]

// Legacy naming for this interface only
[TelemetryGeneration(NamingConvention = NamingConvention.Legacy)]
interface IMyTelemetry { }

public enum NamingConvention
{
    Legacy = 0,          // v3 behaviour: lowercase, smashed compounds
    OpenTelemetry = 1    // v4 default: OTel conventions (dot.separated, snake_case)
}