//! Prometheus scrape endpoint. Counters are updated by the server crate as
//! messages flow; table-size gauges are refreshed at scrape time.

use axum::extract::State;
use axum::http::{StatusCode, header};
use axum::response::IntoResponse;
use bgp_server::metrics::{
    LOCAL_ROUTES, RIB_ATTRIBUTE_SETS, RIB_JOURNAL_ENTRIES, RIB_PREFIXES, RIB_ROUTES,
};
use prometheus::{Encoder, TextEncoder};

use crate::AppState;

pub async fn metricz(State(state): State<AppState>) -> impl IntoResponse {
    // A scrape that cannot read a table fails. Serving the last known
    // size would hide that the daemon is broken from the one system whose
    // job is to notice.
    let gauge = |count: usize| i64::try_from(count).unwrap_or(i64::MAX);
    match state.local_rib.len().await {
        Ok(local) => LOCAL_ROUTES.set(gauge(local)),
        Err(e) => return (StatusCode::SERVICE_UNAVAILABLE, e.to_string()).into_response(),
    }
    RIB_ROUTES.set(gauge(state.rib.len()));
    RIB_PREFIXES.set(gauge(state.rib.prefix_count()));
    RIB_ATTRIBUTE_SETS.set(gauge(state.rib.attrs().len()));
    RIB_JOURNAL_ENTRIES.set(gauge(state.rib.journal_len()));

    let mut buf = Vec::new();
    match TextEncoder::new().encode(&prometheus::gather(), &mut buf) {
        Ok(()) => (
            StatusCode::OK,
            [(header::CONTENT_TYPE, "text/plain; version=0.0.4")],
            buf,
        )
            .into_response(),
        Err(e) => (StatusCode::INTERNAL_SERVER_ERROR, e.to_string()).into_response(),
    }
}