//! Notifications (hub spec §10): who to tell about an event, the inbox
//! row, and email when the account asked for it and SMTP is configured.

use crate::db::{self, accounts::Account, notify as ndb};
use crate::Shared;
use std::collections::BTreeSet;

/// An event worth telling people about.
pub struct Event<'a> {
    pub kind: &'a str,
    pub title: String,
    pub url: String,
    pub actor: &'a Account,
    pub repo_id: i64,
    /// `issue` or `proposal` and its id, for thread subscribers.
    pub thread: Option<(&'a str, i64)>,
    /// Bodies to scan for `@mentions`.
    pub mention_text: &'a str,
    /// Accounts to tell whatever their subscriptions (author, assignees).
    pub direct: Vec<i64>,
}

/// `@username` tokens in a text, unique.
pub fn mentions(text: &str) -> Vec<String> {
    let re = regex::Regex::new(r"(?:^|[^\w/])@([A-Za-z0-9][A-Za-z0-9._-]{0,63})").unwrap();
    let mut out = BTreeSet::new();
    for c in re.captures_iter(text) {
        out.insert(c[1].trim_end_matches('.').to_string());
    }
    out.into_iter().collect()
}

/// Deliver an event: subscribers of the thread, watchers of the
/// repository, mentioned accounts and direct targets, never the actor.
pub async fn deliver(app: &Shared, ev: Event<'_>) {
    let pool = &app.db;
    // Participants: the thread's subscribers, the mentioned, direct targets.
    // Watchers of the repository who are none of those are only watching.
    let mut participants: BTreeSet<i64> = BTreeSet::new();
    if let Some((kind, id)) = ev.thread {
        if let Ok(subs) = ndb::subscribers(pool, kind, id).await {
            participants.extend(subs);
        }
        // Acting on a thread subscribes the actor to it.
        ndb::subscribe(pool, ev.actor.id, kind, id).await.ok();
    }
    for name in mentions(ev.mention_text) {
        if let Ok(Some(a)) = db::accounts::account_by_name(pool, &name).await {
            participants.insert(a.id);
        }
    }
    participants.extend(ev.direct.iter().copied());
    let mut targets: Vec<(i64, ndb::Reason)> = participants.iter().map(|id| (*id, ndb::Reason::Participating)).collect();
    if let Ok(w) = ndb::watchers(pool, ev.repo_id).await {
        targets.extend(w.into_iter().filter(|id| !participants.contains(id)).map(|id| (id, ndb::Reason::Watching)));
    }
    targets.retain(|(id, _)| *id != ev.actor.id);
    let repo_id = (ev.repo_id > 0).then_some(ev.repo_id);
    for (id, reason) in targets {
        ndb::add(
            pool,
            ndb::New { account_id: id, repo_id, reason, kind: ev.kind, title: &ev.title, url: &ev.url, actor: &ev.actor.username },
        )
        .await
        .ok();
        if let Ok(Some(a)) = db::accounts::account_by_id(pool, id).await {
            // Only to addresses the account has proven it reads (hub spec §5.1.1).
            if a.email_notifications && a.email_verified && !a.email.is_empty() && crate::mail::enabled(app) {
                email(app, &a, &ev.title, &ev.url, &ev.actor.username).await;
            }
        }
    }
}

async fn email(app: &Shared, to: &Account, title: &str, url: &str, actor: &str) {
    let unsubscribe = format!("{}/settings/notifications?unsubscribe={}", app.config.base_url(), to.unsubscribe_key);
    let body = format!("{actor}: {title}\n\n{}{url}\n\nStop these emails: {unsubscribe}\n", app.config.base_url());
    if let Err(e) = crate::mail::send(app, to.name(), &to.email, title, &body).await {
        tracing::warn!("email to {}: {e}", to.email);
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn finds_mentions() {
        assert_eq!(mentions("cc @andy and @bob. not an email x@y.z, nor /@path"), vec!["andy", "bob"]);
        assert!(mentions("nothing here").is_empty());
    }
}