//! Metrics Server
//!
//! This server serves metrics over /metrics in OpenMetrics format.

use {
    crate::{config::RunOptions, state::metrics::Metrics},
    anyhow::Result,
    axum::{extract::State, http::header, response::IntoResponse, routing::get, Router},
    std::sync::Arc,
};

#[tracing::instrument(skip(opts, state))]
pub async fn run<S>(opts: RunOptions, state: Arc<S>) -> Result<()>
where
    S: Metrics,
    S: Send + Sync + 'static,
{
    tracing::info!(endpoint = %opts.metrics.server_listen_addr, "Starting Metrics Server.");

    let app = Router::new();
    let app = app
        .route("/metrics", get(metrics))
        .with_state(state.clone());

    // Binds the axum's server to the configured address and port. This is a blocking call and will
    // not return until the server is shutdown.
    axum::Server::try_bind(&opts.metrics.server_listen_addr)?
        .serve(app.into_make_service())
        .with_graceful_shutdown(async {
            let _ = crate::EXIT.subscribe().changed().await;
            tracing::info!("Shutting down metrics server...");
        })
        .await?;

    Ok(())
}

pub async fn metrics<S>(State(state): State<Arc<S>>) -> impl IntoResponse
where
    S: Metrics,
{
    let buffer = Metrics::encode(&*state).await;
    (
        [(
            header::CONTENT_TYPE,
            "application/openmetrics-text; version=1.0.0; charset=utf-8",
        )],
        buffer,
    )
}