using System.Diagnostics;
using OpenTelemetry;

namespace GB5Shared.Telemetry;

/// <summary>
/// Tags every span with <c>gb5.call.origin</c> so Zipkin/Jaeger can filter human-triggered
/// requests separately from system-triggered work — independent of which Host process or
/// business module produced the span (see <see cref="GB5ActivitySources"/> and the
/// <c>gb5.module</c> tag set in <c>BaseEndpoint</c> for the module-filtering half of this).
/// <list type="bullet">
///   <item><b>Interactive</b> — a real API caller (FastEndpoints request) started the trace.</item>
///   <item><b>Automated</b> — a Quartz job, hosted background service, Dapr pub/sub
///   subscription, outbox dispatch, action handler, or workflow-engine action started the
///   trace, with no user waiting on it. Automated spans additionally get
///   <c>gb5.automation.type</c> naming the exact mechanism (see <see cref="AutomationTypeBySource"/>)
///   so "Automated" traces can be filtered down to one specific trigger.</item>
/// </list>
/// Runs once per span in <see cref="OnStart"/> — zero changes needed in any BLL, DAL, or
/// endpoint file, the same zero-touch approach as <see cref="Logging.SpanEventLoggerProvider"/>.
/// Child spans inherit their root's classification so an entire trace stays one colour; spans
/// with no live in-process parent (e.g. a Dapr-subscribed handler picking up a message
/// published by a different Host) fall back to their own <see cref="ActivitySource"/> identity,
/// which is exactly the boundary where cross-process inheritance would have broken anyway.
/// </summary>
public sealed class GB5CallOriginProcessor : BaseProcessor<Activity>
{
    public const string OriginTag = "gb5.call.origin";
    public const string Interactive = "Interactive";
    public const string Automated = "Automated";

    /// <summary>Set only on Automated spans — names the exact trigger mechanism.</summary>
    public const string AutomationTypeTag = "gb5.automation.type";

    private static readonly Dictionary<string, string> AutomationTypeBySource = new(StringComparer.Ordinal)
    {
        [GB5ActivitySources.Scheduler.Name]       = "ScheduledJob",
        [GB5ActivitySources.Background.Name]      = "BackgroundService",
        [GB5ActivitySources.DaprSubscribe.Name]   = "EventSubscription",
        [GB5ActivitySources.Outbox.Name]          = "OutboxDispatch",
        [GB5ActivitySources.ActionProcessor.Name] = "ActionHandler",
        [GB5ActivitySources.WorkflowAction.Name]  = "WorkflowEngine",
    };

    public override void OnStart(Activity activity)
    {
        // Inherit from the live parent so an entire trace stays one classification.
        if (activity.Parent?.GetTagItem(OriginTag) is string inheritedOrigin)
        {
            activity.SetTag(OriginTag, inheritedOrigin);
            if (activity.Parent?.GetTagItem(AutomationTypeTag) is string inheritedType)
                activity.SetTag(AutomationTypeTag, inheritedType);
            return;
        }

        if (AutomationTypeBySource.TryGetValue(activity.Source.Name, out var automationType))
        {
            activity.SetTag(OriginTag, Automated);
            activity.SetTag(AutomationTypeTag, automationType);
        }
        else
        {
            activity.SetTag(OriginTag, Interactive);
        }
    }
}