use crate::Context;
use beacon_chain::BeaconChainTypes;
use lighthouse_metrics::{Encoder, TextEncoder};
use malloc_utils::scrape_allocator_metrics;

pub use lighthouse_metrics::*;

pub fn gather_prometheus_metrics<T: BeaconChainTypes>(
    ctx: &Context<T>,
) -> std::result::Result<String, String> {
    let mut buffer = vec![];
    let encoder = TextEncoder::new();

    // There are two categories of metrics:
    //
    // - Dynamically updated: things like histograms and event counters that are updated on the
    // fly.
    // - Statically updated: things which are only updated at the time of the scrape (used where we
    // can avoid cluttering up code with metrics calls).
    //
    // The `lighthouse_metrics` crate has a `DEFAULT_REGISTRY` global singleton (via `lazy_static`)
    // which keeps the state of all the metrics. Dynamically updated things will already be
    // up-to-date in the registry (because they update themselves) however statically updated
    // things need to be "scraped".
    //
    // We proceed by, first updating all the static metrics using `scrape_for_metrics(..)`. Then,
    // using `lighthouse_metrics::gather(..)` to collect the global `DEFAULT_REGISTRY` metrics into
    // a string that can be returned via HTTP.

    if let Some(beacon_chain) = ctx.chain.as_ref() {
        slot_clock::scrape_for_metrics::<T::EthSpec, T::SlotClock>(&beacon_chain.slot_clock);
        beacon_chain::scrape_for_metrics(beacon_chain);
    }

    if let (Some(db_path), Some(freezer_db_path)) =
        (ctx.db_path.as_ref(), ctx.freezer_db_path.as_ref())
    {
        store::scrape_for_metrics(db_path, freezer_db_path);
    }

    eth2_libp2p::scrape_discovery_metrics();

    warp_utils::metrics::scrape_health_metrics();

    // It's important to ensure these metrics are explicitly enabled in the case that users aren't
    // using glibc and this function causes panics.
    if ctx.config.allocator_metrics_enabled {
        scrape_allocator_metrics();
    }

    encoder
        .encode(&lighthouse_metrics::gather(), &mut buffer)
        .unwrap();

    String::from_utf8(buffer).map_err(|e| format!("Failed to encode prometheus info: {:?}", e))
}