use crate::discord::api::Error::Failed;
use crate::discord::dto::{GatewayBot, RateLimitNotice};
use crate::discord::ws::{connect_discord_ws, DiscordReceiver, DiscordSocket};
use log::debug;
use reqwest::header::{HeaderMap, HeaderName, HeaderValue};
use reqwest::{Client, ClientBuilder, IntoUrl, Request, RequestBuilder, Url};
use serde::de::DeserializeOwned;
use std::borrow::BorrowMut;
use std::cmp::max;
use std::collections::HashMap;
use std::future::Future;
use std::ops::{Add, DerefMut, Sub};
use std::pin::Pin;
use std::sync::{Arc, RwLock};
use std::task::{Context, Poll};
use std::time::Instant;
use tokio::time::{delay_for, delay_until, Delay, Duration};

#[derive(Clone, Debug)]
pub struct DiscordAPI {
    rate_limit: Arc<RwLock<RateLimit>>,
    base_url: Url,
    client: Client,
    token: String,
}

#[derive(Clone, Debug)]
struct RateLimit {
    global: Instant,
    per_url: HashMap<Url, Instant>,
}

impl RateLimit {
    fn new() -> RateLimit {
        RateLimit {
            global: Instant::now().sub(Duration::from_secs(5)),
            per_url: HashMap::new(),
        }
    }

    fn wait(&self, url: Url) -> OptionalDelay {
        let now = Instant::now();
        let mut delay_till = None;
        if now < self.global {
            delay_till = Some(self.global);
        }

        if let Some(per_url) = self.per_url.get(&url) {
            if now < *per_url {
                if let Some(other) = delay_till {
                    if other < *per_url {
                        delay_till = Some(*per_url);
                    }
                } else {
                    delay_till = Some(*per_url)
                }
            }
        }

        delay_till.map(Into::into).map(delay_until).into()
    }

    fn update(&mut self, url: Url, notice: RateLimitNotice) -> OptionalDelay {
        let after = Instant::now().add(Duration::from_millis(notice.retry_after));

        if notice.global {
            self.global = max(self.global, after);
        }

        self.per_url
            .entry(url.clone())
            .and_modify(|&mut mut x| {
                let old = x.clone();
                std::mem::replace(&mut x, max(old, after));
            })
            .or_insert(after);

        self.wait(url)
    }
}

#[derive(Debug)]
pub enum Error {
    RequestError(reqwest::Error),
    Failed(u16),
}

impl From<reqwest::Error> for Error {
    fn from(x: reqwest::Error) -> Self {
        Error::RequestError(x)
    }
}

struct OptionalDelay(Option<Delay>);

impl Into<OptionalDelay> for Option<Delay> {
    fn into(self) -> OptionalDelay {
        OptionalDelay(self)
    }
}

impl Future for OptionalDelay {
    type Output = ();

    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        if self.0.is_none() {
            Poll::Ready(())
        } else {
            let pin = unsafe { Pin::new_unchecked(self.get_mut().0.as_mut().unwrap()) };

            pin.poll(cx)
        }
    }
}

impl DiscordAPI {
    pub fn url(&self, path: &str) -> Url {
        self.base_url.join(path).unwrap()
    }

    pub fn create(token: &str) -> reqwest::Result<DiscordAPI> {
        let mut headers = HeaderMap::new();

        headers.insert(
            "Authorization",
            HeaderValue::from_str(&format!("Bot {}", token)).unwrap(),
        );

        let client = ClientBuilder::new()
            .connection_verbose(true)
            .default_headers(headers)
            .build()?;
        let base_url = Url::parse("https://discordapp.com/api/").unwrap();
        let rate_limit = RateLimit::new();

        Ok(DiscordAPI {
            rate_limit: Arc::new(RwLock::new(rate_limit)),
            base_url,
            client,
            token: token.to_string(),
        })
    }

    async fn send<T: DeserializeOwned>(
        &self,
        url: Url,
        request: RequestBuilder,
    ) -> Result<T, Error> {
        loop {
            let delay = { self.rate_limit.try_read().unwrap().wait(url.clone()) };
            delay.await;

            let clone = request.try_clone().expect("Can't clone body");
            debug!("Requesting: {:?}", url);
            let response = clone.send().await?;

            let status_code = response.status().as_u16();
            if status_code == 429 {
                let rate_limit: RateLimitNotice = response.json().await?;
                let delay = {
                    self.rate_limit
                        .try_write()
                        .unwrap()
                        .update(url.clone(), rate_limit)
                };

                delay.await;
                continue;
            }

            if status_code != 200 {
                return Err(Failed(status_code));
            }

            return Ok(response.json::<T>().await?);
        }
    }

    pub async fn get_gateway_bot(&self) -> Result<GatewayBot, Error> {
        let url = self.url("gateway/bot");
        self.send(url.clone(), self.client.get(url)).await
    }

    pub async fn connect_websocket_bot(&self) -> Result<(DiscordSocket, DiscordReceiver), Error> {
        let gateway = self.get_gateway_bot().await?;
        Ok(connect_discord_ws(gateway.url.clone(), self.token.clone()).await?)
    }
}