subduction_cli 0.14.1

//! Prometheus metrics server for Subduction.
//!
//! Metrics are recorded by `subduction_core` when the `metrics` feature is enabled.
//! This module provides the HTTP server that exposes metrics to Prometheus.

use axum::{Router, routing::get};
use metrics_exporter_prometheus::{PrometheusBuilder, PrometheusHandle};
use std::net::SocketAddr;
use tokio::net::TcpListener;

/// Initialize the metrics recorder and return a handle for the HTTP endpoint.
///
/// This must be called once at startup before any metrics are recorded.
/// Also registers HELP/TYPE descriptions for all emitted metrics.
///
/// # Panics
///
/// Panics if the recorder cannot be installed.
#[must_use]
pub fn init_metrics() -> PrometheusHandle {
    #[allow(clippy::expect_used)]
    let handle = PrometheusBuilder::new()
        .install_recorder()
        .expect("failed to install Prometheus recorder");
    subduction_core::metrics::describe_all();
    handle
}

/// Start the metrics HTTP server on the given address.
///
/// This spawns a background task that serves the `/metrics` endpoint.
///
/// # Errors
///
/// Returns an error if the server fails to bind to the address.
pub async fn start_metrics_server(addr: SocketAddr, handle: PrometheusHandle) -> eyre::Result<()> {
    let app = Router::new().route(
        "/metrics",
        get(move || {
            let handle = handle.clone();
            async move { handle.render() }
        }),
    );

    let listener = TcpListener::bind(addr).await?;
    tracing::info!("Metrics server listening on {}", addr);

    tokio::spawn(async move {
        if let Err(e) = axum::serve(listener, app).await {
            tracing::error!("Metrics server error: {}", e);
        }
    });

    Ok(())
}