using System.Diagnostics;

namespace GB5Shared.Telemetry.Dapr;

/// <summary>
/// Helpers for instrumenting Dapr pub/sub and state-store operations with OpenTelemetry spans.
/// Use these factory methods to wrap <c>DaprClient.PublishEventAsync</c>,
/// <c>GetStateAsync</c>, and event-handler entry points so every event can be traced
/// end-to-end across service boundaries.
/// </summary>
/// <example>
/// Publishing:
/// <code>
/// using var publishActivity = DaprEventTracing.StartPublishActivity("order-placed", "pubsub", metadata);
/// try {
///     await DaprClient.PublishEventAsync("pubsub", "order-placed", payload, metadata, ct);
///     publishActivity?.SetStatus(ActivityStatusCode.Ok);
/// } catch (Exception ex) {
///     publishActivity?.RecordException(ex);
///     publishActivity?.SetStatus(ActivityStatusCode.Error, ex.Message);
///     throw;
/// }
/// </code>
/// Subscribing (in a controller action):
/// <code>
/// using var subActivity = DaprEventTracing.StartSubscribeActivity("order-placed", "pubsub", eventMetadata);
/// try {
///     await ProcessOrderAsync(cloudEvent.Data, ct);
///     subActivity?.SetStatus(ActivityStatusCode.Ok);
/// } catch (Exception ex) {
///     subActivity?.RecordException(ex);
///     subActivity?.SetStatus(ActivityStatusCode.Error, ex.Message);
///     throw;
/// }
/// </code>
/// </example>
public static class DaprEventTracing
{
    private const string TraceParentKey = "traceparent";
    private const string TraceStateKey  = "tracestate";

    // ── Producer (publish) ────────────────────────────────────────────────────

    /// <summary>
    /// Opens a producer span for a Dapr publish operation and injects the W3C traceparent
    /// into <paramref name="metadata"/> so downstream consumers can link the trace.
    /// </summary>
    /// <param name="topic">The Dapr pub/sub topic name.</param>
    /// <param name="pubSubName">The Dapr pub/sub component name (e.g. "pubsub").</param>
    /// <param name="metadata">
    /// Optional metadata dictionary passed to <c>DaprClient.PublishEventAsync</c>.
    /// When supplied, trace context is injected automatically.
    /// </param>
    public static Activity? StartPublishActivity(
        string topic,
        string pubSubName,
        IDictionary<string, string>? metadata = null)
    {
        var activity = GB5ActivitySources.DaprPublish.StartActivity(
            $"dapr publish {pubSubName}/{topic}",
            ActivityKind.Producer);

        if (activity is null) return null;

        activity.SetTag("messaging.system",           "dapr");
        activity.SetTag("messaging.operation",        "publish");
        activity.SetTag("messaging.destination",      topic);
        activity.SetTag("messaging.destination_kind", "topic");
        activity.SetTag("dapr.pubsub.name",           pubSubName);

        if (metadata is not null)
            InjectTraceContext(activity, metadata);

        return activity;
    }

    // ── Consumer (subscribe) ──────────────────────────────────────────────────

    /// <summary>
    /// Opens a consumer span for a Dapr subscribe event handler and extracts the remote
    /// W3C traceparent from <paramref name="metadata"/> to link back to the producer's trace.
    /// </summary>
    /// <param name="topic">The Dapr pub/sub topic name.</param>
    /// <param name="pubSubName">The Dapr pub/sub component name.</param>
    /// <param name="metadata">
    /// Metadata from the received CloudEvent.  When it contains a <c>traceparent</c> key
    /// the new span is created as a child of the producer's span automatically.
    /// </param>
    public static Activity? StartSubscribeActivity(
        string topic,
        string pubSubName,
        IDictionary<string, string>? metadata = null)
    {
        var parentContext = metadata is not null ? ExtractTraceContext(metadata) : default;
        return StartSubscribeActivityCore(topic, pubSubName, parentContext);
    }

    /// <summary>
    /// Opens a consumer span for a Dapr subscribe event handler, parenting it directly from a
    /// W3C <c>traceparent</c>/<c>tracestate</c> pair carried in the message payload itself
    /// (e.g. <c>OutboxEventMessage.TraceParent</c>/<c>TraceState</c>). Use this overload instead
    /// of the metadata-dictionary one when the caller already has a strongly-typed DTO —
    /// it sidesteps any uncertainty about whether the Dapr broker/CloudEvent envelope forwards
    /// custom metadata keys through to the subscriber.
    /// </summary>
    public static Activity? StartSubscribeActivity(
        string  topic,
        string  pubSubName,
        string? traceParent,
        string? traceState = null)
    {
        var parentContext =
            traceParent is not null && ActivityContext.TryParse(traceParent, traceState, isRemote: true, out var ctx)
                ? ctx
                : default;

        return StartSubscribeActivityCore(topic, pubSubName, parentContext);
    }

    private static Activity? StartSubscribeActivityCore(string topic, string pubSubName, ActivityContext parentContext)
    {
        var activity = parentContext != default
            ? GB5ActivitySources.DaprSubscribe.StartActivity(
                $"dapr receive {pubSubName}/{topic}",
                ActivityKind.Consumer,
                parentContext)
            : GB5ActivitySources.DaprSubscribe.StartActivity(
                $"dapr receive {pubSubName}/{topic}",
                ActivityKind.Consumer);

        if (activity is null) return null;

        activity.SetTag("messaging.system",           "dapr");
        activity.SetTag("messaging.operation",        "receive");
        activity.SetTag("messaging.destination",      topic);
        activity.SetTag("messaging.destination_kind", "topic");
        activity.SetTag("dapr.pubsub.name",           pubSubName);

        return activity;
    }

    // ── State store (cache) ───────────────────────────────────────────────────

    /// <summary>
    /// Opens a client-side span for a Dapr state-store read, write, or delete operation.
    /// </summary>
    /// <param name="operation">One of: GET, SET, DELETE.</param>
    /// <param name="stateStoreName">The Dapr state store component name (e.g. "statestore").</param>
    /// <param name="key">The state key being accessed.</param>
    public static Activity? StartCacheActivity(
        string operation,
        string stateStoreName,
        string key)
    {
        var activity = GB5ActivitySources.Cache.StartActivity(
            $"dapr statestore {operation.ToUpperInvariant()} {stateStoreName}",
            ActivityKind.Client);

        if (activity is null) return null;

        activity.SetTag("db.system",             "dapr_statestore");
        activity.SetTag("db.operation",          operation.ToUpperInvariant());
        activity.SetTag("dapr.statestore.name",  stateStoreName);
        activity.SetTag("dapr.statestore.key",   key);

        return activity;
    }

    // ── W3C trace context propagation ────────────────────────────────────────

    /// <summary>
    /// Writes the current activity's W3C <c>traceparent</c> (and optional <c>tracestate</c>)
    /// into a Dapr metadata dictionary so they survive the pub/sub message boundary.
    /// </summary>
    public static void InjectTraceContext(Activity activity, IDictionary<string, string> metadata)
    {
        if (activity.Id is not null)
            metadata[TraceParentKey] = activity.Id;

        if (!string.IsNullOrEmpty(activity.TraceStateString))
            metadata[TraceStateKey] = activity.TraceStateString;
    }

    /// <summary>
    /// Reads <c>traceparent</c> / <c>tracestate</c> from a Dapr metadata dictionary and
    /// returns the parsed <see cref="ActivityContext"/>, or <c>default</c> if not present.
    /// </summary>
    public static ActivityContext ExtractTraceContext(IDictionary<string, string> metadata)
    {
        if (!metadata.TryGetValue(TraceParentKey, out var traceParent))
            return default;

        metadata.TryGetValue(TraceStateKey, out var traceState);

        return ActivityContext.TryParse(traceParent, traceState, isRemote: true, out var ctx)
            ? ctx
            : default;
    }
}