use std::time::Duration;

use feed_rs::parser::parse;
use reqwest::{Response, StatusCode};
use server::ServerState;
use sqlx::{
    SqlitePool,
    sqlite::{SqliteConnectOptions, SqliteJournalMode, SqlitePoolOptions},
    types::chrono::{DateTime, Utc},
};
use tokio::{sync::mpsc::UnboundedSender, task::JoinSet};
use tokio_util::{bytes::Buf, sync::CancellationToken};
use unicode_segmentation::UnicodeSegmentation;

pub mod server;

const MAX_CONNS: u32 = 200;
const MIN_CONNS: u32 = 5;
const TIMEOUT: u64 = 2000; // in milliseconds

const ZULIP_INTERVAL: Duration = Duration::from_millis(250);
const ZULIP_MESSAGE_CUTOFF: usize = 700;

const LAST_FETCHED: DateTime<Utc> = DateTime::from_timestamp_nanos(0);

const STALE_FETCH_THRESHOLD: Duration = Duration::from_hours(24);

pub struct BlogdorTheAggregator {
    db: SqlitePool,
    client: reqwest::Client,
    cancel: CancellationToken,
    endpoint: String,
    channel_id: u32,
    blogdor_to_zulip_email: String,
    zulip_to_blogdor_email: String,
    zulip_token: String,   // sent *to zulip* in POSTs *from us*
    blogdor_token: String, // sent *from zulip* in POSTs *to us*
}

#[derive(Debug, Default, Clone, PartialEq, Eq)]
pub struct FeedEntry {
    post_url: String,
    feed_url: String,
    feed_id: i64,
    title: String,
    published: DateTime<Utc>,
    received: DateTime<Utc>,
    feed_description: Option<String>,
    body: Option<String>,
}

#[derive(Debug, Default, Clone, PartialEq, Eq)]
pub struct FeedResult {
    pub entries: Option<Vec<FeedEntry>>,
    pub url: String,
    pub feed_id: i64,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct NewFeed {
    feed: String,
    user: String,
}

#[derive(Debug, Default, Clone, PartialEq, Eq, serde::Serialize)]
struct ZulipMessage<'s> {
    to: u32,
    #[serde(rename = "type")]
    typ: MessageType,
    content: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    topic: Option<&'s str>,
}

#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, serde::Serialize)]
#[serde(rename_all = "lowercase")]
enum MessageType {
    #[default]
    Stream,
    Direct,
}

impl BlogdorTheAggregator {
    pub async fn new() -> Self {
        let db = get_db_pool().await;
        let client = reqwest::Client::new(); // TODO: retries?
        let cancel = CancellationToken::new();
        let endpoint = std::env::var("ZULIP_URL").expect("ZULIP_URL must be set");
        let channel_id: u32 = std::env::var("ZULIP_CHANNEL")
            .expect("ZULIP_CHANNEL must be set")
            .parse()
            .expect("ZULIP_CHANNEL must be an integer");
        let password = std::env::var("ZULIP_TOKEN").expect("ZULIP_TOKEN must be set");
        let b2z_email =
            std::env::var("BLOGDOR_TO_ZULIP_EMAIL").expect("BLOGDOR_TO_ZULIP_EMAIL must be set");
        let z2b_email =
            std::env::var("ZULIP_TO_BLOGDOR_EMAIL").expect("ZULIP_TO_BLOGDOR_EMAIL must be set");
        let token = std::env::var("BLOGDOR_TOKEN").expect("BLOGDOR_TOKEN must be set");

        Self {
            db,
            client,
            cancel,
            endpoint,
            channel_id,
            blogdor_to_zulip_email: b2z_email,
            zulip_to_blogdor_email: z2b_email,
            zulip_token: password,
            blogdor_token: token,
        }
    }

    pub async fn cancelled(&self) {
        self.cancel.cancelled().await
    }

    pub async fn spawn_http(&self, announce_tx: UnboundedSender<NewFeed>) {
        let state = ServerState::new(
            self.db.clone(),
            &self.zulip_to_blogdor_email,
            &self.blogdor_token,
            announce_tx,
        );
        server::spawn_server(state, self.cancel.clone()).await;
    }

    pub async fn check_feeds(&self) -> Result<Vec<Result<FeedResult, String>>, String> {
        tracing::debug!("checking feeds");
        let feeds = sqlx::query!("select id, url from feeds where active = true")
            .fetch_all(&self.db)
            .await
            .map_err(|e| format!("{e}"))?;

        let mut handles = JoinSet::new();
        for feed in feeds {
            handles.spawn(check_feed(
                self.db.clone(),
                feed.id,
                self.client.clone(),
                feed.url,
            ));
        }

        let mut feed_results = Vec::new();
        while let Some(feed_result) = handles.join_next().await {
            let Ok(feed_result) = feed_result else {
                let e = feed_result.unwrap_err();
                tracing::error!("got join error: {e}");
                continue;
            };
            feed_results.push(feed_result);
        }

        Ok(feed_results)
    }

    pub async fn check_stale(&self) {
        let feeds = match sqlx::query!("select id, url, added_by, created_at from feeds")
            .fetch_all(&self.db)
            .await
        {
            Err(e) => {
                tracing::error!("could not fetch feeds: {e}");
                return;
            }
            Ok(f) => f,
        };

        let now = Utc::now();

        for feed in feeds.into_iter() {
            let id = feed.id;
            let url = &feed.url;
            let user = feed.added_by;
            let fetched = match sqlx::query!(
                "select fetched from fetches where feed = ? order by id desc limit 1",
                id
            )
            .fetch_optional(&self.db)
            .await
            {
                Err(e) => {
                    tracing::error!("could not get last fetched for {url} from db: {e}");
                    continue;
                }
                Ok(f) => f,
            };
            let dur = if let Some(fetched) = fetched {
                now - fetched.fetched.and_utc()
            } else {
                now - feed.created_at.and_utc()
            };

            if dur.num_seconds() > STALE_FETCH_THRESHOLD.as_secs() as i64 {
                let hours = dur.num_hours() % 24;
                let days = dur.num_days();
                let content = format!(
                    "It has been {days} days and {hours} hours since Blogdor was able to check your feed at {url}. If you'd like to remove it, you can DM @blogdor's manager with 'remove {url}'."
                );
                let msg = ZulipMessage {
                    to: user as u32,
                    typ: MessageType::Direct,
                    content,
                    topic: None,
                };
                if let Err(e) = self.send_zulip_message(&msg).await {
                    tracing::error!("error sending zulip message to user {user}: {e}");
                }
            }
        }
    }

    pub async fn announce_feed(&self, announce: &NewFeed) {
        let content = format!("{} added a new feed: {}", announce.user, announce.feed);
        let msg = ZulipMessage {
            to: self.channel_id,
            typ: MessageType::Stream,
            content,
            topic: Some("New feeds"),
        };
        match self.send_zulip_message(&msg).await {
            Err(e) => {
                tracing::error!("got error sending to zulip: {e}");
            }
            Ok(r) => {
                if r.status() != StatusCode::OK {
                    tracing::warn!("did not successfully post to zulip: status {}", r.status());
                }
            }
        }
    }

    // will also update the successful_runs table if it posts to zulip
    pub async fn post_entries(&self, posts: &[FeedEntry]) {
        let FeedEntry {
            feed_id, received, ..
        } = posts.last().unwrap();
        let mut success = true;
        let Ok(user) = sqlx::query!("select added_by from feeds where id = ?", feed_id)
            .fetch_one(&self.db)
            .await
        else {
            tracing::error!("could not get user from db");
            return;
        };
        let user = user.added_by;
        for post in posts.iter() {
            let body = post.body.as_deref().unwrap_or("");

            let tail = if body.len() < ZULIP_MESSAGE_CUTOFF {
                ""
            } else {
                "..."
            };

            let url = post.post_url.as_str();
            let title = post.title.as_str();

            let header = format!("New post in a feed added by @**|{user}**: {title}");

            let content = format!(
                "{header}\n---\n{body}{tail}\n\n---\noriginally posted to {url}, on {}",
                post.published.format("%B %e, %Y"),
            );

            let msg = ZulipMessage {
                to: self.channel_id,
                typ: MessageType::Stream,
                content,
                topic: Some(title),
            };

            match self.send_zulip_message(&msg).await {
                Err(e) => {
                    tracing::error!("got error sending to zulip: {e}");
                    success = false;
                }
                Ok(r) => {
                    if r.status() == StatusCode::OK {
                        success &= true;
                    } else {
                        tracing::warn!("did not successfully post to zulip: status {}", r.status());
                        success = false;
                    }
                }
            }
            tokio::time::sleep(ZULIP_INTERVAL).await;
        }
        if success
            && let Err(e) = sqlx::query!(
                "insert into successful_runs (feed, date_time) values (?, ?)",
                feed_id,
                received
            )
            .execute(&self.db)
            .await
        {
            tracing::error!("could not insert run for {feed_id}, got {e}");
        }
    }

    pub async fn close_db(&self) {
        self.db.close().await;
    }

    async fn send_zulip_message<'s>(&'s self, msg: &ZulipMessage<'s>) -> Result<Response, String> {
        let msg = serde_urlencoded::to_string(msg).expect("serialize msg");
        self.client
            .post(&self.endpoint)
            .basic_auth(&self.blogdor_to_zulip_email, Some(&self.zulip_token))
            .body(msg)
            .header("Content-Type", "application/x-www-form-urlencoded")
            .send()
            .await
            .map_err(|e| format!("{e}"))
    }
}

trait Posted {
    fn posted(&self) -> Option<DateTime<Utc>>;
}

impl Posted for feed_rs::model::Entry {
    fn posted(&self) -> Option<DateTime<Utc>> {
        self.published.or(self.updated)
    }
}

// takes args by value because it's meant to be called from inside a spawned
// tokio task scope
async fn check_feed(
    db: SqlitePool,
    feed_id: i64,
    client: reqwest::Client,
    url: String,
) -> Result<FeedResult, String> {
    let rec = sqlx::query!(
        "select date_time from successful_runs where feed = ? order by id desc limit 1",
        feed_id
    )
    .fetch_optional(&db)
    .await
    .map_err(|e| format!("Could not fetch runs for {url} from DB, got {e}"))?;

    tracing::debug!("checking {url}");
    let last_fetched = rec.map(|d| d.date_time.and_utc()).unwrap_or(LAST_FETCHED);
    let now = Utc::now();
    let mut entries = None;
    let feed = client
        .get(&url)
        .send()
        .await
        .map_err(|e| format!("could not get feed from {url}, got {e}"))?
        .bytes()
        .await
        .map_err(|e| format!("could not get bytes from response from {url}, got {e}"))?;
    let mut feed =
        parse(feed.reader()).map_err(|e| format!("could not parse feed from {url}, got {e}"))?;

    if let Err(e) = sqlx::query!("insert into fetches (feed) values (?)", feed_id)
        .execute(&db)
        .await
    {
        tracing::error!("got error inserting {feed_id} into fetches: {e}");
    }

    feed.entries.sort_by_key(|e| std::cmp::Reverse(e.posted()));
    for post in feed.entries.into_iter().take(5) {
        if post.posted().unwrap_or(LAST_FETCHED) > last_fetched {
            let entry = FeedEntry {
                post_url: post
                    .links
                    .first()
                    .cloned()
                    .map(|l| l.href)
                    .unwrap_or("<url not found>".to_string()),
                feed_id,
                feed_url: url.clone(),
                title: post
                    .title
                    .clone()
                    .map(|t| t.content)
                    .unwrap_or("<no title found>".to_string()),
                published: post.posted().unwrap_or(now),
                received: now,
                feed_description: feed.description.to_owned().map(|d| d.content),
                body: post.content.and_then(|c| {
                    c.body.map(|f| {
                        let s = html2md::parse_html(&f)
                            .graphemes(false)
                            .take(ZULIP_MESSAGE_CUTOFF)
                            .collect::<String>();
                        s.to_string()
                    })
                }),
            };
            entries.get_or_insert(Vec::new()).push(entry);
        }
    }

    Ok(FeedResult {
        entries,
        url,
        feed_id,
    })
}

async fn get_db_pool() -> SqlitePool {
    let db_filename = {
        std::env::var("DATABASE_FILE").unwrap_or_else(|_| {
            #[cfg(not(test))]
            {
                tracing::info!("connecting to default db file");
                "blogdor.db".to_string()
            }
            #[cfg(test)]
            {
                use rand::RngCore;
                let mut rng = rand::rng();
                let id = rng.next_u64();
                // see https://www.sqlite.org/inmemorydb.html for meaning of the string;
                // it allows each separate test to have its own dedicated memory-backed db that
                // will live as long as the whole process
                format!("file:testdb-{id}?mode=memory&cache=shared")
            }
        })
    };

    tracing::info!("Connecting to DB at {db_filename}");

    let conn_opts = SqliteConnectOptions::new()
        .foreign_keys(true)
        .journal_mode(SqliteJournalMode::Wal)
        .synchronous(sqlx::sqlite::SqliteSynchronous::Normal)
        .filename(&db_filename)
        .busy_timeout(Duration::from_secs(TIMEOUT))
        .pragma("temp_store", "memory")
        .create_if_missing(true)
        .optimize_on_close(true, None)
        .pragma("mmap_size", "3000000000");

    let pool = SqlitePoolOptions::new()
        .max_connections(MAX_CONNS)
        .min_connections(MIN_CONNS)
        .idle_timeout(Some(Duration::from_secs(3)))
        .max_lifetime(Some(Duration::from_secs(3600)))
        .connect_with(conn_opts)
        .await
        .expect("could not get sqlite pool");

    sqlx::migrate!()
        .run(&pool)
        .await
        .expect("could not run migrations");
    tracing::info!("Ran migrations");

    pool
}

//-************************************************************************
// Tests for `db` module.
//-************************************************************************
#[cfg(test)]
mod tests {

    #[tokio::test]
    async fn it_migrates_the_db() {
        let db = super::get_db_pool().await;

        let r = sqlx::query!("select count(*) as count from feeds")
            .fetch_one(&db)
            .await;

        assert!(r.is_ok());
    }
}