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// Copyright 2019-2024 ChainSafe Systems
// SPDX-License-Identifier: Apache-2.0, MIT

pub mod db;

use crate::db::DBStatistics;
use axum::{http::StatusCode, response::IntoResponse, routing::get, Router};
use once_cell::sync::Lazy;
use parking_lot::{RwLock, RwLockWriteGuard};
use prometheus_client::{
    encoding::EncodeLabelSet,
    metrics::{counter::Counter, family::Family, histogram::Histogram},
};
use std::sync::Arc;
use std::{path::PathBuf, time::Instant};
use tokio::net::TcpListener;
use tracing::warn;

static DEFAULT_REGISTRY: Lazy<RwLock<prometheus_client::registry::Registry>> =
    Lazy::new(Default::default);

pub fn default_registry<'a>() -> RwLockWriteGuard<'a, prometheus_client::registry::Registry> {
    DEFAULT_REGISTRY.write()
}

pub static LRU_CACHE_HIT: Lazy<Family<KindLabel, Counter>> = Lazy::new(|| {
    let metric = Family::default();
    DEFAULT_REGISTRY
        .write()
        .register("lru_cache_hit", "Stats of lru cache hit", metric.clone());
    metric
});
pub static LRU_CACHE_MISS: Lazy<Family<KindLabel, Counter>> = Lazy::new(|| {
    let metric = Family::default();
    DEFAULT_REGISTRY
        .write()
        .register("lru_cache_miss", "Stats of lru cache miss", metric.clone());
    metric
});

pub async fn init_prometheus<DB>(
    prometheus_listener: TcpListener,
    db_directory: PathBuf,
    db: Arc<DB>,
) -> anyhow::Result<()>
where
    DB: DBStatistics + Send + Sync + 'static,
{
    // Add the process collector to the registry
    if let Err(err) =
        kubert_prometheus_process::register(default_registry().sub_registry_with_prefix("process"))
    {
        warn!("Failed to register process metrics: {err}");
    }

    // Add the DBCollector to the registry
    DEFAULT_REGISTRY
        .write()
        .register_collector(Box::new(crate::metrics::db::DBCollector::new(db_directory)));

    // Create an configure HTTP server
    let app = Router::new()
        .route("/metrics", get(collect_prometheus_metrics))
        .route("/stats/db", get(collect_db_metrics::<DB>))
        .with_state(db);

    // Wait for server to exit
    Ok(axum::serve(prometheus_listener, app.into_make_service()).await?)
}

async fn collect_prometheus_metrics() -> impl IntoResponse {
    let mut metrics = String::new();
    match prometheus_client::encoding::text::encode(&mut metrics, &DEFAULT_REGISTRY.read()) {
        Ok(()) => {}
        Err(e) => warn!("{e}"),
    };

    (
        StatusCode::OK,
        [("content-type", "text/plain; charset=utf-8")],
        metrics,
    )
}

async fn collect_db_metrics<DB>(
    axum::extract::State(db): axum::extract::State<Arc<DB>>,
) -> impl IntoResponse
where
    DB: DBStatistics,
{
    let mut metrics = "# DB statistics:\n".to_owned();
    if let Some(db_stats) = db.get_statistics() {
        metrics.push_str(&db_stats);
    } else {
        metrics.push_str("Not enabled. Set enable_statistics to true in config and restart daemon");
    }
    (
        StatusCode::OK,
        [("content-type", "text/plain; charset=utf-8")],
        metrics,
    )
}

#[derive(Clone, Debug, Hash, PartialEq, Eq, EncodeLabelSet)]
pub struct KindLabel {
    kind: &'static str,
}

impl KindLabel {
    pub const fn new(kind: &'static str) -> Self {
        Self { kind }
    }
}

#[derive(Clone, Debug, Hash, PartialEq, Eq, EncodeLabelSet)]
pub struct TypeLabel {
    r#type: &'static str,
}

impl TypeLabel {
    pub const fn new(t: &'static str) -> Self {
        Self { r#type: t }
    }
}

pub mod values {
    use super::KindLabel;

    /// `TipsetCache`.
    pub const TIPSET: KindLabel = KindLabel::new("tipset");
    /// tipset cache in state manager
    pub const STATE_MANAGER_TIPSET: KindLabel = KindLabel::new("sm_tipset");
}

pub fn default_histogram() -> Histogram {
    // Default values from go client(https://github.com/prometheus/client_golang/blob/5d584e2717ef525673736d72cd1d12e304f243d7/prometheus/histogram.go#L68)
    Histogram::new(
        [
            0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0,
        ]
        .into_iter(),
    )
}

pub struct HistogramTimer<'a> {
    histogram: &'a Histogram,
    start: Instant,
}

impl<'a> Drop for HistogramTimer<'a> {
    fn drop(&mut self) {
        let duration = Instant::now() - self.start;
        self.histogram.observe(duration.as_secs_f64());
    }
}

pub trait HistogramTimerExt {
    fn start_timer(&self) -> HistogramTimer<'_>;
}

impl HistogramTimerExt for Histogram {
    fn start_timer(&self) -> HistogramTimer<'_> {
        HistogramTimer {
            histogram: self,
            start: Instant::now(),
        }
    }
}