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// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use hyper::{
	http::StatusCode,
	server::Server,
	service::{make_service_fn, service_fn},
	Body, Request, Response,
};
pub use prometheus::{
	self,
	core::{
		AtomicF64 as F64, AtomicI64 as I64, AtomicU64 as U64, GenericCounter as Counter,
		GenericCounterVec as CounterVec, GenericGauge as Gauge, GenericGaugeVec as GaugeVec,
	},
	exponential_buckets, Error as PrometheusError, Histogram, HistogramOpts, HistogramVec, Opts,
	Registry,
};
use prometheus::{core::Collector, Encoder, TextEncoder};
use std::net::SocketAddr;

mod sourced;

pub use sourced::{MetricSource, SourcedCounter, SourcedGauge, SourcedMetric};

pub fn register<T: Clone + Collector + 'static>(
	metric: T,
	registry: &Registry,
) -> Result<T, PrometheusError> {
	registry.register(Box::new(metric.clone()))?;
	Ok(metric)
}

#[derive(Debug, thiserror::Error)]
pub enum Error {
	/// Hyper internal error.
	#[error(transparent)]
	Hyper(#[from] hyper::Error),

	/// Http request error.
	#[error(transparent)]
	Http(#[from] hyper::http::Error),

	/// i/o error.
	#[error(transparent)]
	Io(#[from] std::io::Error),

	#[error("Prometheus port {0} already in use.")]
	PortInUse(SocketAddr),
}

async fn request_metrics(req: Request<Body>, registry: Registry) -> Result<Response<Body>, Error> {
	if req.uri().path() == "/metrics" {
		let metric_families = registry.gather();
		let mut buffer = vec![];
		let encoder = TextEncoder::new();
		encoder.encode(&metric_families, &mut buffer).unwrap();

		Response::builder()
			.status(StatusCode::OK)
			.header("Content-Type", encoder.format_type())
			.body(Body::from(buffer))
			.map_err(Error::Http)
	} else {
		Response::builder()
			.status(StatusCode::NOT_FOUND)
			.body(Body::from("Not found."))
			.map_err(Error::Http)
	}
}

/// Initializes the metrics context, and starts an HTTP server
/// to serve metrics.
pub async fn init_prometheus(prometheus_addr: SocketAddr, registry: Registry) -> Result<(), Error> {
	let listener = tokio::net::TcpListener::bind(&prometheus_addr)
		.await
		.map_err(|_| Error::PortInUse(prometheus_addr))?;

	init_prometheus_with_listener(listener, registry).await
}

/// Init prometheus using the given listener.
async fn init_prometheus_with_listener(
	listener: tokio::net::TcpListener,
	registry: Registry,
) -> Result<(), Error> {
	let listener = hyper::server::conn::AddrIncoming::from_listener(listener)?;
	log::info!("〽️ Prometheus exporter started at {}", listener.local_addr());

	let service = make_service_fn(move |_| {
		let registry = registry.clone();

		async move {
			Ok::<_, hyper::Error>(service_fn(move |req: Request<Body>| {
				request_metrics(req, registry.clone())
			}))
		}
	});

	let (signal, on_exit) = tokio::sync::oneshot::channel::<()>();
	let server = Server::builder(listener).serve(service).with_graceful_shutdown(async {
		let _ = on_exit.await;
	});

	let result = server.await.map_err(Into::into);

	// Gracefully shutdown server, otherwise the server does not stop if it has open connections
	let _ = signal.send(());

	result
}

#[cfg(test)]
mod tests {
	use super::*;
	use hyper::{Client, Uri};

	#[test]
	fn prometheus_works() {
		const METRIC_NAME: &str = "test_test_metric_name_test_test";

		let runtime = tokio::runtime::Runtime::new().expect("Creates the runtime");

		let listener = runtime
			.block_on(tokio::net::TcpListener::bind("127.0.0.1:0"))
			.expect("Creates listener");

		let local_addr = listener.local_addr().expect("Returns the local addr");

		let registry = Registry::default();
		register(
			prometheus::Counter::new(METRIC_NAME, "yeah").expect("Creates test counter"),
			&registry,
		)
		.expect("Registers the test metric");

		runtime.spawn(init_prometheus_with_listener(listener, registry));

		runtime.block_on(async {
			let client = Client::new();

			let res = client
				.get(Uri::try_from(&format!("http://{}/metrics", local_addr)).expect("Parses URI"))
				.await
				.expect("Requests metrics");

			let buf = hyper::body::to_bytes(res).await.expect("Converts body to bytes");

			let body = String::from_utf8(buf.to_vec()).expect("Converts body to String");
			assert!(body.contains(&format!("{} 0", METRIC_NAME)));
		});
	}
}