use std::collections::HashSet;
use std::future::Future;
use std::sync::Arc;
use std::time::{Duration, Instant};
use cave::{
    feed::{Feed, EncodablePost},
    store::Store,
};
use futures::{StreamExt, future};
use crate::posts_cache::PostsCache;
use crate::scheduler::Host;

#[derive(Clone)]
pub struct RobotsTxt {
    robot: Arc<Option<texting_robots::Robot>>,
}

impl RobotsTxt {
    pub async fn fetch(
        client: &reqwest::Client,
        host: &Host,
    ) -> Self {
        let url = format!("https://{}/robots.txt", host);
        metrics::increment_gauge!("hunter_requests", 1.0, "type" => "robotstxt");
        let robot = async {
            let body = client.get(url)
                .send().await
                .ok()?
                .text().await
                .ok()?;
            texting_robots::Robot::new(
                env!("CARGO_PKG_NAME"),
                body.as_bytes(),
            ).ok()
        }.await;
        metrics::decrement_gauge!("hunter_requests", 1.0, "type" => "robotstxt");
        RobotsTxt {
            robot: Arc::new(robot),
        }
    }

    pub fn allowed(&self, url: &str) -> bool {
        if let Some(ref robot) = self.robot.as_ref() {
            robot.allowed(url)
        } else {
            true
        }
    }

    pub fn delay(&self) -> Option<Duration> {
        if let Some(ref robot) = self.robot.as_ref() {
            robot.delay.map(|delay| Duration::from_secs(delay as u64))
        } else {
            None
        }
    }
}

#[derive(Debug)]
pub enum Message {
    WorkerDone,
    Fetched {
        host: Host,
        new_post_ratio: Option<f64>,
        mean_interval: Option<Duration>,
    },
    IntroduceHosts { hosts: Vec<String> },
}

pub async fn run(
    message_tx: tokio::sync::mpsc::UnboundedSender<Message>,
    store: Store,
    posts_cache: PostsCache,
    client: reqwest::Client,
    host: Host,
) {
    // Fetch /robots.txt
    let robots_txt = RobotsTxt::fetch(&client, &host).await;
    let robots_delay = robots_txt.delay();
    // Fetch posts and open stream
    let ((mut new_post_ratio, mut mean_interval), stream_result) = future::join(
        fetch_timeline(
            message_tx.clone(), store.clone(),
            &posts_cache,
            &client, robots_txt.clone(), &host
        ),
        open_stream(
            message_tx.clone(), store.clone(),
            &posts_cache,
            &client, robots_txt, host.clone()
        ),
    ).await;

    // Next worker can start
    message_tx.send(Message::WorkerDone).unwrap();

    // Process stream
    if let Ok(stream) = stream_result {
        tracing::info!("Processing stream for {}", host);
        metrics::increment_gauge!("hunter_requests", 1.0, "type" => "stream");

        let start_time = Instant::now();
        let post_count = stream.await;
        let end_time = Instant::now();
        metrics::decrement_gauge!("hunter_requests", 1.0, "type" => "stream");
        tracing::warn!("Ended stream for {}. {} posts in {:?}", host, post_count, end_time - start_time);

        if post_count > 0 {
            if let Some(ref mut new_post_ratio) = new_post_ratio {
                *new_post_ratio += post_count as f64 / 100.;
            }
            let stream_avg_interval = Duration::from_secs_f64(
                (end_time - start_time).as_secs_f64() / (post_count as f64)
            );
            if mean_interval.map_or(true, |mean_interval| stream_avg_interval < mean_interval) {
                mean_interval = Some(stream_avg_interval);
            }
        }
    }

    // Ready for reenqueue
    if let Some(mean_interval) = &mut mean_interval {
        if let Some(robots_delay) = robots_delay {
            *mean_interval = (*mean_interval).max(robots_delay);
        }
    }
    message_tx.send(Message::Fetched {
        host: host,
        new_post_ratio,
        mean_interval,
    }).unwrap();
}

async fn fetch_timeline(
    message_tx: tokio::sync::mpsc::UnboundedSender<Message>,
    mut store: Store,
    posts_cache: &PostsCache,
    client: &reqwest::Client,
    robots_txt: RobotsTxt,
    host: &Host,
) -> (Option<f64>, Option<Duration>) {
    let url = format!("https://{}/api/v1/timelines/public?limit=40", host);
    if ! robots_txt.allowed(&url) {
        tracing::warn!("Timeline of {} forbidden by robots.txt", host);
        return (None, None);
    }
    // free as early as possible
    drop(robots_txt);

    metrics::increment_gauge!("hunter_requests", 1.0, "type" => "timeline");
    let t1 = Instant::now();
    let result = Feed::fetch(&client, &url).await;
    let t2 = Instant::now();
    metrics::decrement_gauge!("hunter_requests", 1.0, "type" => "timeline");
    metrics::histogram!("hunter_fetch_seconds", t2 - t1, "result" => if result.is_ok() { "ok" } else { "error" });

    match result {
        Ok(feed) => {
            let mean_interval = feed.mean_post_interval();

            let (new_post_ratio, introduce_hosts) = process_posts(&mut store, posts_cache, &host, feed.posts.into_iter()).await;
            let _ = message_tx.send(Message::IntroduceHosts {
                hosts: introduce_hosts.into_iter().collect(),
            });

            // successfully fetched, save for future run
            store.save_host(&host).await.unwrap();

            (new_post_ratio, mean_interval)
        }
        Err(e) => {
            tracing::error!("Failed fetching {}: {}", host, e);
            (None, None)
        }
    }
}

async fn process_posts(
    store: &mut Store,
    posts_cache: &PostsCache,
    host: &Host,
    posts: impl Iterator<Item = EncodablePost>,
) -> (Option<f64>, HashSet<String>) {
    // introduce new hosts, validate posts
    let mut introduce_hosts = HashSet::new();
    let mut new_posts = 0;
    let mut posts_len = 0;
    for post in posts {
        posts_len += 1;

        // potentially save a round-trip to redis with an in-process cache
        if ! posts_cache.insert(post.uri.clone()) {
            let t1 = Instant::now();

            // introduce instances from reblog authors
            if let Some(reblog_account_host) = post.reblog.as_ref().and_then(|reblog| reblog.account.host()) {
                introduce_hosts.insert(reblog_account_host);
            }
            // introduce instances from mentions
            for mention in &post.mentions {
                if let Some(user_host) = mention.user_host() {
                    introduce_hosts.insert(user_host);
                }
            }

            // check if it's an actual post
            if let Some(account_host) = post.account.host() {
                // send away to redis
                if store.save_post(post).await == Ok(true) {
                    new_posts += 1;
                }
                // introduce instances from accounts
                introduce_hosts.insert(account_host);
            } else {
                tracing::warn!("drop repost ({:?} on {})", post.account.host(), host);
            }

            let t2 = Instant::now();
            metrics::histogram!("hunter_post_process_seconds", t2 - t1)
        }
    }
    tracing::trace!("{}: {}/{} new posts", host, new_posts, posts_len);
    metrics::counter!("hunter_posts", new_posts, "type" => "new");
    metrics::counter!("hunter_posts", posts_len, "type" => "total");
    let new_post_ratio = if posts_len > 0 {
        let ratio = (new_posts as f64) / (posts_len as f64);
        metrics::histogram!("hunter_new_post_ratio", ratio);
        Some(ratio)
    } else {
        None
    };

    (new_post_ratio, introduce_hosts)
}

async fn open_stream(
    message_tx: tokio::sync::mpsc::UnboundedSender<Message>,
    store: Store,
    posts_cache: &PostsCache,
    client: &reqwest::Client,
    robots_txt: RobotsTxt,
    host: Host,
) -> Result<impl Future<Output = usize>, ()> {
    let url = format!("https://{}/api/v1/streaming/public", host);
    if ! robots_txt.allowed(&url) {
        tracing::warn!("Streaming of {} forbidden by robots.txt", host);
        return Err(());
    }
    // free as early as possible
    drop(robots_txt);
    let posts_cache = posts_cache.clone();

    metrics::increment_gauge!("hunter_requests", 1.0, "type" => "stream_open");
    let stream = Feed::stream(client, &url).await;
    metrics::decrement_gauge!("hunter_requests", 1.0, "type" => "stream_open");
    let stream = stream.map_err(|e| {
        tracing::error!("Stream error for {}: {}", host, e);
    })?;

    Ok(stream.fold(0, move |post_count, post| {
        let message_tx = message_tx.clone();
        let mut store = store.clone();
        let posts_cache = posts_cache.clone();
        let host = host.clone();
        async move {
            let (_, introduce_hosts) =
                process_posts(&mut store, &posts_cache, &host, [post].into_iter()).await;
            let _ = message_tx.send(Message::IntroduceHosts {
                hosts: introduce_hosts.into_iter().collect(),
            });
            post_count + 1
        }
    }))
}