use arc_swap::ArcSwap;
use cached::proc_macro::cached;
use futures_lite::future::block_on;
use futures_lite::{future::Boxed, FutureExt};
use hyper::client::HttpConnector;
use hyper::header::HeaderValue;
use hyper::{body, body::Buf, client, header, Body, Client, Method, Request, Response, Uri};
use hyper_rustls::HttpsConnector;
use libflate::gzip;
use log::{error, trace, warn};
use once_cell::sync::Lazy;
use percent_encoding::{percent_encode, CONTROLS};
use serde_json::Value;

use std::sync::atomic::Ordering;
use std::sync::atomic::{AtomicBool, AtomicU16};
use std::{io, result::Result};

use crate::dbg_msg;
use crate::oauth::{force_refresh_token, token_daemon, Oauth};
use crate::server::RequestExt;
use crate::utils::format_url;

const REDDIT_URL_BASE: &str = "https://oauth.reddit.com";
const REDDIT_URL_BASE_HOST: &str = "oauth.reddit.com";

const REDDIT_SHORT_URL_BASE: &str = "https://redd.it";
const REDDIT_SHORT_URL_BASE_HOST: &str = "redd.it";

const ALTERNATIVE_REDDIT_URL_BASE: &str = "https://www.reddit.com";
const ALTERNATIVE_REDDIT_URL_BASE_HOST: &str = "www.reddit.com";

pub static CLIENT: Lazy<Client<HttpsConnector<HttpConnector>>> = Lazy::new(|| {
	let https = hyper_rustls::HttpsConnectorBuilder::new().with_native_roots().https_only().enable_http1().build();
	client::Client::builder().build(https)
});

pub static OAUTH_CLIENT: Lazy<ArcSwap<Oauth>> = Lazy::new(|| {
	let client = block_on(Oauth::new());
	tokio::spawn(token_daemon());
	ArcSwap::new(client.into())
});

pub static OAUTH_RATELIMIT_REMAINING: AtomicU16 = AtomicU16::new(99);

pub static OAUTH_IS_ROLLING_OVER: AtomicBool = AtomicBool::new(false);

static URL_PAIRS: [(&str, &str); 2] = [
	(ALTERNATIVE_REDDIT_URL_BASE, ALTERNATIVE_REDDIT_URL_BASE_HOST),
	(REDDIT_SHORT_URL_BASE, REDDIT_SHORT_URL_BASE_HOST),
];

/// Gets the canonical path for a resource on Reddit. This is accomplished by
/// making a `HEAD` request to Reddit at the path given in `path`.
///
/// This function returns `Ok(Some(path))`, where `path`'s value is identical
/// to that of the value of the argument `path`, if Reddit responds to our
/// `HEAD` request with a 2xx-family HTTP code. It will also return an
/// `Ok(Some(String))` if Reddit responds to our `HEAD` request with a
/// `Location` header in the response, and the HTTP code is in the 3xx-family;
/// the `String` will contain the path as reported in `Location`. The return
/// value is `Ok(None)` if Reddit responded with a 3xx, but did not provide a
/// `Location` header. An `Err(String)` is returned if Reddit responds with a
/// 429, or if we were unable to decode the value in the `Location` header.
#[cached(size = 1024, time = 600, result = true)]
#[async_recursion::async_recursion]
pub async fn canonical_path(path: String, tries: i8) -> Result<Option<String>, String> {
	if tries == 0 {
		return Ok(None);
	}

	// for each URL pair, try the HEAD request
	let res = {
		// for url base and host in URL_PAIRS, try reddit_short_head(path.clone(), true, url_base, url_base_host) and if it succeeds, set res. else, res = None
		let mut res = None;
		for (url_base, url_base_host) in URL_PAIRS {
			res = reddit_short_head(path.clone(), true, url_base, url_base_host).await.ok();
			if let Some(res) = &res {
				if !res.status().is_client_error() {
					break;
				}
			}
		}
		res
	};

	let res = res.ok_or_else(|| "Unable to make HEAD request to Reddit.".to_string())?;
	let status = res.status().as_u16();
	let policy_error = res.headers().get(header::RETRY_AFTER).is_some();

	match status {
		// If Reddit responds with a 2xx, then the path is already canonical.
		200..=299 => Ok(Some(path)),

		// If Reddit responds with a 301, then the path is redirected.
		301 => match res.headers().get(header::LOCATION) {
			Some(val) => {
				let Ok(original) = val.to_str() else {
					return Err("Unable to decode Location header.".to_string());
				};

				// We need to strip the .json suffix from the original path.
				// In addition, we want to remove share parameters.
				// Cut it off here instead of letting it propagate all the way
				// to main.rs
				let stripped_uri = original.strip_suffix(".json").unwrap_or(original).split('?').next().unwrap_or_default();

				// The reason why we now have to format_url, is because the new OAuth
				// endpoints seem to return full paths, instead of relative paths.
				// So we need to strip the .json suffix from the original path, and
				// also remove all Reddit domain parts with format_url.
				// Otherwise, it will literally redirect to Reddit.com.
				let uri = format_url(stripped_uri);

				// Decrement tries and try again
				canonical_path(uri, tries - 1).await
			}
			None => Ok(None),
		},

		// If Reddit responds with anything other than 3xx (except for the 2xx and 301
		// as above), return a None.
		300..=399 => Ok(None),

		// Rate limiting
		429 => Err("Too many requests.".to_string()),

		// Special condition rate limiting - https://github.com/redlib-org/redlib/issues/229
		403 if policy_error => Err("Too many requests.".to_string()),

		_ => Ok(
			res
				.headers()
				.get(header::LOCATION)
				.map(|val| percent_encode(val.as_bytes(), CONTROLS).to_string().trim_start_matches(REDDIT_URL_BASE).to_string()),
		),
	}
}

pub async fn proxy(req: Request<Body>, format: &str) -> Result<Response<Body>, String> {
	let mut url = format!("{format}?{}", req.uri().query().unwrap_or_default());

	// For each parameter in request
	for (name, value) in &req.params() {
		// Fill the parameter value in the url
		url = url.replace(&format!("{{{name}}}"), value);
	}

	stream(&url, &req).await
}

async fn stream(url: &str, req: &Request<Body>) -> Result<Response<Body>, String> {
	// First parameter is target URL (mandatory).
	let parsed_uri = url.parse::<Uri>().map_err(|_| "Couldn't parse URL".to_string())?;

	// Build the hyper client from the HTTPS connector.
	let client: Client<_, Body> = CLIENT.clone();

	let mut builder = Request::get(parsed_uri);

	// Copy useful headers from original request
	for &key in &["Range", "If-Modified-Since", "Cache-Control"] {
		if let Some(value) = req.headers().get(key) {
			builder = builder.header(key, value);
		}
	}

	let stream_request = builder.body(Body::empty()).map_err(|_| "Couldn't build empty body in stream".to_string())?;

	client
		.request(stream_request)
		.await
		.map(|mut res| {
			let mut rm = |key: &str| res.headers_mut().remove(key);

			rm("access-control-expose-headers");
			rm("server");
			rm("vary");
			rm("etag");
			rm("x-cdn");
			rm("x-cdn-client-region");
			rm("x-cdn-name");
			rm("x-cdn-server-region");
			rm("x-reddit-cdn");
			rm("x-reddit-video-features");
			rm("Nel");
			rm("Report-To");

			res
		})
		.map_err(|e| e.to_string())
}

/// Makes a GET request to Reddit at `path`. By default, this will honor HTTP
/// 3xx codes Reddit returns and will automatically redirect.
fn reddit_get(path: String, quarantine: bool) -> Boxed<Result<Response<Body>, String>> {
	request(&Method::GET, path, true, quarantine, REDDIT_URL_BASE, REDDIT_URL_BASE_HOST)
}

/// Makes a HEAD request to Reddit at `path, using the short URL base. This will not follow redirects.
fn reddit_short_head(path: String, quarantine: bool, base_path: &'static str, host: &'static str) -> Boxed<Result<Response<Body>, String>> {
	request(&Method::HEAD, path, false, quarantine, base_path, host)
}

// /// Makes a HEAD request to Reddit at `path`. This will not follow redirects.
// fn reddit_head(path: String, quarantine: bool) -> Boxed<Result<Response<Body>, String>> {
// 	request(&Method::HEAD, path, false, quarantine, false)
// }
// Unused - reddit_head is only ever called in the context of a short URL

/// Makes a request to Reddit. If `redirect` is `true`, `request_with_redirect`
/// will recurse on the URL that Reddit provides in the Location HTTP header
/// in its response.
fn request(method: &'static Method, path: String, redirect: bool, quarantine: bool, base_path: &'static str, host: &'static str) -> Boxed<Result<Response<Body>, String>> {
	// Build Reddit URL from path.
	let url = format!("{base_path}{path}");

	// Construct the hyper client from the HTTPS connector.
	let client: Client<_, Body> = CLIENT.clone();

	let (token, vendor_id, device_id, user_agent, loid) = {
		let client = OAUTH_CLIENT.load_full();
		(
			client.token.clone(),
			client.headers_map.get("Client-Vendor-Id").cloned().unwrap_or_default(),
			client.headers_map.get("X-Reddit-Device-Id").cloned().unwrap_or_default(),
			client.headers_map.get("User-Agent").cloned().unwrap_or_default(),
			client.headers_map.get("x-reddit-loid").cloned().unwrap_or_default(),
		)
	};

	// Build request to Reddit. When making a GET, request gzip compression.
	// (Reddit doesn't do brotli yet.)
	let builder = Request::builder()
		.method(method)
		.uri(&url)
		.header("User-Agent", user_agent)
		.header("Client-Vendor-Id", vendor_id)
		.header("X-Reddit-Device-Id", device_id)
		.header("x-reddit-loid", loid)
		.header("Host", host)
		.header("Authorization", &format!("Bearer {token}"))
		.header("Accept-Encoding", if method == Method::GET { "gzip" } else { "identity" })
		.header("Accept-Language", "en-US,en;q=0.5")
		.header("Connection", "keep-alive")
		.header(
			"Cookie",
			if quarantine {
				"_options=%7B%22pref_quarantine_optin%22%3A%20true%2C%20%22pref_gated_sr_optin%22%3A%20true%7D"
			} else {
				""
			},
		)
		.body(Body::empty());

	async move {
		match builder {
			Ok(req) => match client.request(req).await {
				Ok(mut response) => {
					// Reddit may respond with a 3xx. Decide whether or not to
					// redirect based on caller params.
					if response.status().is_redirection() {
						if !redirect {
							return Ok(response);
						};
						let location_header = response.headers().get(header::LOCATION);
						if location_header == Some(&HeaderValue::from_static("https://www.reddit.com/")) {
							return Err("Reddit response was invalid".to_string());
						}
						return request(
							method,
							location_header
								.map(|val| {
									// We need to make adjustments to the URI
									// we get back from Reddit. Namely, we
									// must:
									//
									//     1. Remove the authority (e.g.
									//     https://www.reddit.com) that may be
									//     present, so that we recurse on the
									//     path (and query parameters) as
									//     required.
									//
									//     2. Percent-encode the path.
									let new_path = percent_encode(val.as_bytes(), CONTROLS)
										.to_string()
										.trim_start_matches(REDDIT_URL_BASE)
										.trim_start_matches(ALTERNATIVE_REDDIT_URL_BASE)
										.to_string();
									format!("{new_path}{}raw_json=1", if new_path.contains('?') { "&" } else { "?" })
								})
								.unwrap_or_default()
								.to_string(),
							true,
							quarantine,
							base_path,
							host,
						)
						.await;
					};

					match response.headers().get(header::CONTENT_ENCODING) {
						// Content not compressed.
						None => Ok(response),

						// Content encoded (hopefully with gzip).
						Some(hdr) => {
							match hdr.to_str() {
								Ok(val) => match val {
									"gzip" => {}
									"identity" => return Ok(response),
									_ => return Err("Reddit response was encoded with an unsupported compressor".to_string()),
								},
								Err(_) => return Err("Reddit response was invalid".to_string()),
							}

							// We get here if the body is gzip-compressed.

							// The body must be something that implements
							// std::io::Read, hence the conversion to
							// bytes::buf::Buf and then transformation into a
							// Reader.
							let mut decompressed: Vec<u8>;
							{
								let mut aggregated_body = match body::aggregate(response.body_mut()).await {
									Ok(b) => b.reader(),
									Err(e) => return Err(e.to_string()),
								};

								let mut decoder = match gzip::Decoder::new(&mut aggregated_body) {
									Ok(decoder) => decoder,
									Err(e) => return Err(e.to_string()),
								};

								decompressed = Vec::<u8>::new();
								if let Err(e) = io::copy(&mut decoder, &mut decompressed) {
									return Err(e.to_string());
								};
							}

							response.headers_mut().remove(header::CONTENT_ENCODING);
							response.headers_mut().insert(header::CONTENT_LENGTH, decompressed.len().into());
							*(response.body_mut()) = Body::from(decompressed);

							Ok(response)
						}
					}
				}
				Err(e) => {
					dbg_msg!("{method} {REDDIT_URL_BASE}{path}: {}", e);

					Err(e.to_string())
				}
			},
			Err(_) => Err("Post url contains non-ASCII characters".to_string()),
		}
	}
	.boxed()
}

// Make a request to a Reddit API and parse the JSON response
#[cached(size = 100, time = 30, result = true)]
pub async fn json(path: String, quarantine: bool) -> Result<Value, String> {
	// Closure to quickly build errors
	let err = |msg: &str, e: String, path: String| -> Result<Value, String> {
		// eprintln!("{} - {}: {}", url, msg, e);
		Err(format!("{msg}: {e} | {path}"))
	};

	// First, handle rolling over the OAUTH_CLIENT if need be.
	let current_rate_limit = OAUTH_RATELIMIT_REMAINING.load(Ordering::SeqCst);
	let is_rolling_over = OAUTH_IS_ROLLING_OVER.load(Ordering::SeqCst);
	if current_rate_limit < 10 && !is_rolling_over {
		warn!("Rate limit {current_rate_limit} is low. Spawning force_refresh_token()");
		tokio::spawn(force_refresh_token());
	}
	OAUTH_RATELIMIT_REMAINING.fetch_sub(1, Ordering::SeqCst);

	// Fetch the url...
	match reddit_get(path.clone(), quarantine).await {
		Ok(response) => {
			let status = response.status();

			let reset: Option<String> = if let (Some(remaining), Some(reset), Some(used)) = (
				response.headers().get("x-ratelimit-remaining").and_then(|val| val.to_str().ok().map(|s| s.to_string())),
				response.headers().get("x-ratelimit-reset").and_then(|val| val.to_str().ok().map(|s| s.to_string())),
				response.headers().get("x-ratelimit-used").and_then(|val| val.to_str().ok().map(|s| s.to_string())),
			) {
				trace!(
					"Ratelimit remaining: Header says {remaining}, we have {current_rate_limit}. Resets in {reset}. Rollover: {}. Ratelimit used: {used}",
					if is_rolling_over { "yes" } else { "no" },
				);
				Some(reset)
			} else {
				None
			};

			// asynchronously aggregate the chunks of the body
			match hyper::body::aggregate(response).await {
				Ok(body) => {
					let has_remaining = body.has_remaining();

					if !has_remaining {
						// Rate limited, so spawn a force_refresh_token()
						tokio::spawn(force_refresh_token());
						return match reset {
							Some(val) => Err(format!(
								"Reddit rate limit exceeded. Try refreshing in a few seconds.\
								 Rate limit will reset in: {val}"
							)),
							None => Err("Reddit rate limit exceeded".to_string()),
						};
					}

					// Parse the response from Reddit as JSON
					match serde_json::from_reader(body.reader()) {
						Ok(value) => {
							let json: Value = value;

							// If user is suspended
							if let Some(data) = json.get("data") {
								if let Some(is_suspended) = data.get("is_suspended").and_then(Value::as_bool) {
									if is_suspended {
										return Err("suspended".into());
									}
								}
							}

							// If Reddit returned an error
							if json["error"].is_i64() {
								// OAuth token has expired; http status 401
								if json["message"] == "Unauthorized" {
									error!("Forcing a token refresh");
									let () = force_refresh_token().await;
									return Err("OAuth token has expired. Please refresh the page!".to_string());
								}

								// Handle quarantined
								if json["reason"] == "quarantined" {
									return Err("quarantined".into());
								}
								// Handle gated
								if json["reason"] == "gated" {
									return Err("gated".into());
								}
								// Handle private subs
								if json["reason"] == "private" {
									return Err("private".into());
								}
								// Handle banned subs
								if json["reason"] == "banned" {
									return Err("banned".into());
								}

								Err(format!("Reddit error {} \"{}\": {} | {path}", json["error"], json["reason"], json["message"]))
							} else {
								Ok(json)
							}
						}
						Err(e) => {
							error!("Got an invalid response from reddit {e}. Status code: {status}");
							if status.is_server_error() {
								Err("Reddit is having issues, check if there's an outage".to_string())
							} else {
								err("Failed to parse page JSON data", e.to_string(), path)
							}
						}
					}
				}
				Err(e) => err("Failed receiving body from Reddit", e.to_string(), path),
			}
		}
		Err(e) => err("Couldn't send request to Reddit", e, path),
	}
}

#[cfg(test)]
static POPULAR_URL: &str = "/r/popular/hot.json?&raw_json=1&geo_filter=GLOBAL";

#[tokio::test(flavor = "multi_thread")]
async fn test_localization_popular() {
	let val = json(POPULAR_URL.to_string(), false).await.unwrap();
	assert_eq!("GLOBAL", val["data"]["geo_filter"].as_str().unwrap());
}

#[tokio::test(flavor = "multi_thread")]
async fn test_obfuscated_share_link() {
	let share_link = "/r/rust/s/kPgq8WNHRK".into();
	// Correct link without share parameters
	let canonical_link = "/r/rust/comments/18t5968/why_use_tuple_struct_over_standard_struct/kfbqlbc/".into();
	assert_eq!(canonical_path(share_link, 3).await, Ok(Some(canonical_link)));
}

#[tokio::test(flavor = "multi_thread")]
async fn test_share_link_strip_json() {
	let link = "/17krzvz".into();
	let canonical_link = "/comments/17krzvz".into();
	assert_eq!(canonical_path(link, 3).await, Ok(Some(canonical_link)));
}
#[tokio::test(flavor = "multi_thread")]
async fn test_private_sub() {
	let link = json("/r/suicide/about.json?raw_json=1".into(), true).await;
	assert!(link.is_err());
	assert_eq!(link, Err("private".into()));
}

#[tokio::test(flavor = "multi_thread")]
async fn test_banned_sub() {
	let link = json("/r/aaa/about.json?raw_json=1".into(), true).await;
	assert!(link.is_err());
	assert_eq!(link, Err("banned".into()));
}

#[tokio::test(flavor = "multi_thread")]
async fn test_gated_sub() {
	// quarantine to false to specifically catch when we _don't_ catch it
	let link = json("/r/drugs/about.json?raw_json=1".into(), false).await;
	assert!(link.is_err());
	assert_eq!(link, Err("gated".into()));
}