// This file is part of Substrate.

// Copyright (C) 2021 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

use crate::{initialize_transport, TelemetryWorker};
use futures::channel::mpsc;
use libp2p::wasm_ext::ExtTransport;
use parking_lot::Mutex;
use std::convert::TryInto;
use std::io;
use tracing::{Event, Id, Subscriber};
use tracing_subscriber::{layer::Context, registry::LookupSpan, Layer};

/// Span name used to report the telemetry.
pub const TELEMETRY_LOG_SPAN: &str = "telemetry-logger";

/// `Layer` that handles the logs for telemetries.
#[derive(Debug)]
pub struct TelemetryLayer(Mutex<mpsc::Sender<(Id, u8, String)>>);

impl TelemetryLayer {
	/// Create a new [`TelemetryLayer`] and [`TelemetryWorker`].
	///
	/// The `buffer_size` defaults to 16.
	///
	/// The [`ExtTransport`] is used in WASM contexts where we need some binding between the
	/// networking provided by the operating system or environment and libp2p.
	///
	/// > **Important**: Each individual call to `write` corresponds to one message. There is no
	/// >                internal buffering going on. In the context of WebSockets, each `write`
	/// >                must be one individual WebSockets frame.
	pub fn new(
		buffer_size: Option<usize>,
		telemetry_external_transport: Option<ExtTransport>,
	) -> io::Result<(Self, TelemetryWorker)> {
		let transport = initialize_transport(telemetry_external_transport)?;
		let worker = TelemetryWorker::new(buffer_size.unwrap_or(16), transport);
		let sender = worker.message_sender();
		Ok((Self(Mutex::new(sender)), worker))
	}
}

impl<S> Layer<S> for TelemetryLayer
where
	S: Subscriber + for<'a> LookupSpan<'a>,
{
	fn on_event(&self, event: &Event<'_>, ctx: Context<S>) {
		if event.metadata().target() != TELEMETRY_LOG_SPAN {
			return;
		}

		if let Some(span) = ctx.lookup_current() {
			let parents = span.parents();

			if let Some(span) = std::iter::once(span)
				.chain(parents)
				.find(|x| x.name() == TELEMETRY_LOG_SPAN)
			{
				let id = span.id();
				let mut attrs = TelemetryAttrs::new(id.clone());
				let mut vis = TelemetryAttrsVisitor(&mut attrs);
				event.record(&mut vis);

				if let TelemetryAttrs {
					verbosity: Some(verbosity),
					json: Some(json),
					..
				} = attrs
				{
					match self.0.lock().try_send((
						id,
						verbosity
							.try_into()
							.expect("telemetry log message verbosity are u8; qed"),
						json,
					)) {
						Err(err) if err.is_full() => eprintln!("Telemetry buffer overflowed!"),
						_ => {}
					}
				} else {
					// NOTE: logging in this function doesn't work
					eprintln!(
						"missing fields in telemetry log: {:?}. This can happen if \
						`tracing::info_span!` is (mis-)used with the telemetry target \
						directly; you should use the `telemetry!` macro.",
						event,
					);
				}
			}
		}
	}
}

#[derive(Debug)]
struct TelemetryAttrs {
	verbosity: Option<u64>,
	json: Option<String>,
	id: Id,
}

impl TelemetryAttrs {
	fn new(id: Id) -> Self {
		Self {
			verbosity: None,
			json: None,
			id,
		}
	}
}

#[derive(Debug)]
struct TelemetryAttrsVisitor<'a>(&'a mut TelemetryAttrs);

impl<'a> tracing::field::Visit for TelemetryAttrsVisitor<'a> {
	fn record_debug(&mut self, _field: &tracing::field::Field, _value: &dyn std::fmt::Debug) {
		// noop
	}

	fn record_u64(&mut self, field: &tracing::field::Field, value: u64) {
		if field.name() == "verbosity" {
			(*self.0).verbosity = Some(value);
		}
	}

	fn record_str(&mut self, field: &tracing::field::Field, value: &str) {
		if field.name() == "json" {
			(*self.0).json = Some(format!(
				r#"{{"id":{},"ts":{:?},"payload":{}}}"#,
				self.0.id.into_u64(),
				chrono::Local::now().to_rfc3339().to_string(),
				value,
			));
		}
	}
}