//! OpenTelemetry distributed tracing — OTLP exporter + tracing-opentelemetry bridge.

use opentelemetry::trace::TracerProvider as _;
use opentelemetry_otlp::{Protocol, SpanExporter, WithExportConfig};
use opentelemetry_sdk::propagation::TraceContextPropagator;
use opentelemetry_sdk::trace::{SdkTracerProvider, Tracer};
use opentelemetry_sdk::Resource;
use tracing_opentelemetry::OpenTelemetryLayer;
use tracing_subscriber::Registry;

use super::config::{OtlpProtocol, TelemetryConfig};
use crate::ImksResult;

/// Build an OTLP SpanExporter based on the configured protocol.
fn build_span_exporter(config: &TelemetryConfig) -> ImksResult<SpanExporter> {
    match config.otlp_protocol {
        OtlpProtocol::Grpc => SpanExporter::builder()
            .with_tonic()
            .with_endpoint(&config.otlp_endpoint)
            .build()
            .map_err(|e| crate::ImksError::Internal(format!("OTLP gRPC span exporter: {e}"))),
        OtlpProtocol::HttpProtobuf => SpanExporter::builder()
            .with_http()
            .with_protocol(Protocol::HttpBinary)
            .with_endpoint(&config.otlp_endpoint)
            .build()
            .map_err(|e| {
                crate::ImksError::Internal(format!("OTLP HTTP span exporter: {e}"))
            }),
    }
}

/// Initialize the tracing pipeline: OTel tracer provider + tracing-opentelemetry layer.
///
/// Returns (SdkTracerProvider, OpenTelemetryLayer).
pub fn init_tracing(
    config: &TelemetryConfig,
    resource: &Resource,
) -> ImksResult<(SdkTracerProvider, OpenTelemetryLayer<Registry, Tracer>)> {
    // Set global propagator for W3C TraceContext extraction/injection
    opentelemetry::global::set_text_map_propagator(TraceContextPropagator::new());

    let exporter = build_span_exporter(config)?;

    let provider = SdkTracerProvider::builder()
        .with_resource(resource.clone())
        .with_batch_exporter(exporter)
        .build();

    let tracer = provider.tracer("imks");

    let otel_layer = tracing_opentelemetry::layer().with_tracer(tracer);

    Ok((provider, otel_layer))
}