//! # PTTH Server
//! 
//! The PTTH server is an HTTP server that can serve files from
//! behind a firewall, because it only makes outgoing HTTP connections
//! to a PTTH relay.
//! 
//! ```text
//! View from outside the PTTH tunnel:
//! 
//! * HTTP client
//! |
//! |   HTTP(S) requests
//! V
//! * ptth_relay
//! ^
//! |   HTTP(S) requests
//! |
//! * ptth_server
//! 
//! View from inside the PTTH tunnel:
//! 
//! * HTTP client
//! |
//! |   HTTP(S) requests
//! V
//! * ptth_relay
//! |
//! |   HTTP(S) requests
//! V
//! * ptth_server
//! ```

#![warn (clippy::pedantic)]

// I don't see the point in documenting the errors outside of where the
// error type is defined.
#![allow (clippy::missing_errors_doc)]

// False positive on futures::select! macro
#![allow (clippy::mut_mut)]

use std::{
	future::Future,
	path::PathBuf,
	sync::Arc,
	time::Duration,
};

use futures::FutureExt;
use reqwest::Client;
use tokio::{
	sync::{
		mpsc,
		oneshot,
	},
};
use tokio_stream::wrappers::ReceiverStream;

use ptth_core::{
	http_serde,
	prelude::*,
};

pub mod errors;

/// In-process file server module with byte range and ETag support
pub mod file_server;

/// Load and de-serialize structures from TOML, with a size limit
/// and checking permissions (On Unix)
pub mod load_toml;

use errors::ServerError;

pub struct State {
	// file_server: file_server::FileServer,
	config: Config,
	client: Client,
}

// Unwrap a request from PTTH format and pass it into file_server.
// When file_server responds, wrap it back up and stream it to the relay.

async fn handle_one_req (
	state: &State,
	req_id: String,
	response: http_serde::Response,
) -> Result <(), ServerError>
{
	let mut resp_req = state.client
	.post (&format! ("{}/http_response/{}", state.config.relay_url, req_id))
	.header (ptth_core::PTTH_MAGIC_HEADER, base64::encode (rmp_serde::to_vec (&response.parts).map_err (ServerError::MessagePackEncodeResponse)?));
	
	if let Some (length) = response.content_length {
		resp_req = resp_req.header ("Content-Length", length.to_string ());
	}
	if let Some (mut body) = response.body {
		if state.config.throttle_upload {
			// Spawn another task to throttle the chunks
			
			let (tx, rx) = mpsc::channel (1);
			
			tokio::spawn (async move {
				while let Some (chunk) = body.recv ().await {
					let len = chunk.as_ref ().map (Vec::len).ok ();
					tx.send (chunk).await?;
					
					if let Some (_len) = len {
						// debug! ("Throttling {} byte chunk", len);
					}
					
					tokio::time::sleep (Duration::from_millis (1000)).await;
				}
				
				Ok::<_, anyhow::Error> (())
			});
			
			resp_req = resp_req.body (reqwest::Body::wrap_stream (ReceiverStream::new (rx)));
		}
		else {
			resp_req = resp_req.body (reqwest::Body::wrap_stream (ReceiverStream::new (body)));
		}
	}
	
	let req = resp_req.build ().map_err (ServerError::Step5Responding)?;
	
	debug! ("{:?}", req.headers ());
	
	//println! ("Step 6");
	match state.client.execute (req).await {
		Ok (r) => {
			let status = r.status ();
			let text = r.text ().await.map_err (ServerError::Step7AfterResponse)?;
			debug! ("{:?} {:?}", status, text);
		},
		Err (e) => {
			if e.is_request () {
				warn! ("Error while POSTing response. Client probably hung up.");
			}
			
			error! ("Err: {:?}", e);
		},
	}
	
	Ok::<(), ServerError> (())
}

async fn handle_requests <F, H, SH> (
	state: &Arc <State>,
	req_resp: reqwest::Response,
	spawn_handler: &mut SH,
) -> Result <(), ServerError>
where 
F: Send + Future <Output = anyhow::Result <http_serde::Response>>,
H: Send + 'static + FnOnce (http_serde::RequestParts) -> F,
SH: Send + FnMut () -> H
{
	//println! ("Step 1");
	
	let body = req_resp.bytes ().await.map_err (ServerError::CantCollectWrappedRequests)?;
	let wrapped_reqs: Vec <http_serde::WrappedRequest> = match rmp_serde::from_read_ref (&body)
	{
		Ok (x) => x,
		Err (e) => {
			error! ("Can't parse wrapped requests: {:?}", e);
			return Err (ServerError::CantParseWrappedRequests (e));
		},
	};
	
	debug! ("Unwrapped {} requests", wrapped_reqs.len ());
	
	for wrapped_req in wrapped_reqs {
		let state = Arc::clone (&state);
		let handler = spawn_handler ();
		
		// These have to detach, so we won't be able to catch the join errors.
		
		tokio::spawn (async move {
			let (req_id, parts) = (wrapped_req.id, wrapped_req.req);
			
			debug! ("Handling request {}", req_id);
			
			let f = handler (parts);
			let response = f.await?;
			
			handle_one_req (&state, req_id, response).await
		});
	}
	
	Ok (())
}

/// Config for `ptth_server` and the file server module
/// 
/// This is a complete config. 
/// The bin frontend is allowed to load an incomplete config from
/// the TOML file, fill it out with command-line options, and put
/// the completed config in this struct.

#[derive (Clone)]
pub struct ConfigFile {
	/// A name that uniquely identifies this server on the relay.
	/// May be human-readable.
	pub name: String,
	
	/// Secret API key used to authenticate the server with the relay
	pub api_key: String,
	
	/// URL of the PTTH relay server that ptth_server should connect to
	pub relay_url: String,
	
	/// Directory that the file server module will expose to clients
	/// over the relay. If None, the current working dir is used.
	pub file_server_root: Option <PathBuf>,
	
	/// For debugging.
	pub throttle_upload: bool,
}

impl ConfigFile {
	#[must_use]
	pub fn new (name: String, api_key: String, relay_url: String) -> Self {
		Self {
			name,
			api_key,
			relay_url,
			file_server_root: None,
			throttle_upload: false,
		}
	}
	
	#[must_use]
	pub fn tripcode (&self) -> String {
		base64::encode (blake3::hash (self.api_key.as_bytes ()).as_bytes ())
	}
}

/// Config for `ptth_server` itself

#[derive (Default)]
pub struct Config {
	/// The name of our `ptth_server` instance
	pub name: String,
	
	/// URL of the PTTH relay server that ptth_server should connect to
	pub relay_url: String,
	
	/// For debugging.
	pub throttle_upload: bool,
}

pub struct Builder {
	config_file: ConfigFile,
	hidden_path: Option <PathBuf>,
	asset_root: Option <PathBuf>,
}

impl Builder {
	pub fn new (
		name: String,
		relay_url: String,
	) -> Self {
		let config_file = ConfigFile {
			name,
			api_key: ptth_core::gen_key (),
			relay_url,
			file_server_root: None,
			throttle_upload: false,
		};
		
		Self {
			config_file,
			hidden_path: None,
			asset_root: None,
		}
	}
	
	pub fn build (self) -> Result <State, ServerError>
	{
		State::new (
			self.config_file, 
			self.hidden_path, 
			self.asset_root
		)
	}
	
	pub fn api_key (mut self, key: String) -> Self {
		self.config_file.api_key = key;
		self
	}
}

/// Runs a `ptth_server` instance with the built-in file server module

pub async fn run_server (
	config_file: ConfigFile,
	shutdown_oneshot: oneshot::Receiver <()>,
	hidden_path: Option <PathBuf>,
	asset_root: Option <PathBuf>
)
-> Result <(), ServerError>
{
	let metrics_interval = Arc::new (arc_swap::ArcSwap::default ());
	let interval_writer = Arc::clone (&metrics_interval);
	tokio::spawn (async move {
		file_server::metrics::Interval::monitor (interval_writer).await;
	});
	
	let file_server = file_server::FileServer::new (
		config_file.file_server_root.clone (),
		&asset_root.clone ().unwrap_or_else (PathBuf::new),
		config_file.name.clone (),
		metrics_interval,
		hidden_path.clone (),
	)?;
	let file_server = Arc::new (file_server);
	
	let state = Arc::new (State::new (
		config_file,
		hidden_path,
		asset_root,
	)?);
	
	let file_server_2 = Arc::clone (&file_server);
	
	let mut spawn_handler = || {
		let file_server = Arc::clone (&file_server);
		
		|req: http_serde::RequestParts| async move {
			Ok (file_server.serve_all (req.method, &req.uri, &req.headers).await?)
		}
	};
	
	State::run (
		&state,
		shutdown_oneshot,
		&mut spawn_handler,
	).await
}

impl State {
	pub fn new (
		config_file: ConfigFile,
		hidden_path: Option <PathBuf>,
		asset_root: Option <PathBuf>
	)
	-> Result <Self, ServerError> 
	{
		use std::convert::TryInto;
		
		use arc_swap::ArcSwap;
		
		let asset_root = asset_root.unwrap_or_else (PathBuf::new);
		
		info! ("Server name is {}", config_file.name);
		info! ("Tripcode is {}", config_file.tripcode ());
		
		let mut headers = reqwest::header::HeaderMap::new ();
		headers.insert ("X-ApiKey", config_file.api_key.try_into ().map_err (ServerError::ApiKeyInvalid)?);
		
		let client = Client::builder ()
		.default_headers (headers)
		.connect_timeout (Duration::from_secs (30))
		.build ().map_err (ServerError::CantBuildHttpClient)?;
		
		let state = State {
			config: Config {
				name: config_file.name,
				relay_url: config_file.relay_url,
				throttle_upload: config_file.throttle_upload,
			},
			client,
		};
		
		Ok (state)
	}

	pub async fn run <F, H, SH> (
		state: &Arc <Self>,
		shutdown_oneshot: oneshot::Receiver <()>,
		spawn_handler: &mut SH,
	) -> Result <(), ServerError> 
	where 
	F: Send + Future <Output = anyhow::Result <http_serde::Response>>,
	H: Send + 'static + FnOnce (http_serde::RequestParts) -> F,
	SH: Send + FnMut () -> H
	{
		use http::status::StatusCode;
		
		let mut backoff_delay = 0;
		let mut shutdown_oneshot = shutdown_oneshot.fuse ();
		
		loop {
			// TODO: Extract loop body to function?
			
			if backoff_delay > 0 {
				let sleep = tokio::time::sleep (Duration::from_millis (backoff_delay));
				tokio::pin! (sleep);
				
				tokio::select! {
					_ = &mut sleep => {},
					_ = &mut shutdown_oneshot => {
						info! ("Received graceful shutdown");
						break;
					},
				}
			}
			
			debug! ("http_listen");
			
			let req_req = state.client.get (&format! ("{}/http_listen/{}", state.config.relay_url, state.config.name))
			.timeout (Duration::from_secs (30))
			.send ();
			
			let err_backoff_delay = std::cmp::min (30_000, backoff_delay * 2 + 500);
			
			let req_req = futures::select! {
				r = req_req.fuse () => r,
				_ = shutdown_oneshot => {
					info! ("Received graceful shutdown");
					break;
				},
			};
			
			let req_resp = match req_req {
				Err (e) => {
					if e.is_timeout () {
						error! ("Client-side timeout. Is an overly-aggressive firewall closing long-lived connections? Is the network flakey?");
					}
					else {
						error! ("Err: {:?}", e);
						if backoff_delay != err_backoff_delay {
							error! ("Non-timeout issue, increasing backoff_delay");
							backoff_delay = err_backoff_delay;
						}
					}
					continue;
				},
				Ok (x) => x,
			};
			
			if req_resp.status () == StatusCode::NO_CONTENT {
				debug! ("http_listen long poll timed out on the server, good.");
				continue;
			}
			else if req_resp.status () != StatusCode::OK {
				error! ("{}", req_resp.status ());
				let body = req_resp.bytes ().await.map_err (ServerError::Step3CollectBody)?;
				let body = String::from_utf8 (body.to_vec ()).map_err (ServerError::Step3ErrorResponseNotUtf8)?;
				error! ("{}", body);
				if backoff_delay != err_backoff_delay {
					error! ("Non-timeout issue, increasing backoff_delay");
					backoff_delay = err_backoff_delay;
				}
				continue;
			}
			
			// Unpack the requests, spawn them into new tasks, then loop back
			// around.
			
			if handle_requests (
				&state, 
				req_resp,
				spawn_handler,
			).await.is_err () {
				backoff_delay = err_backoff_delay;
				continue;
			}
			
			if backoff_delay != 0 {
				debug! ("backoff_delay = 0");
				backoff_delay = 0;
			}
		}
		
		info! ("Exiting");
		
		Ok (())
	}
}

#[cfg (test)]
mod tests {
	use super::*;
	
	#[test]
	fn tripcode_algo () {
		let config = ConfigFile::new (
			"TestName".into (),
			"PlaypenCausalPlatformCommodeImproveCatalyze".into (),
			"".into (),
		);
		
		assert_eq! (config.tripcode (), "A9rPwZyY89Ag4TJjMoyYA2NeGOm99Je6rq1s0rg8PfY=".to_string ());
	}
}