//! Accounts sync on open, on demand and on a timer.

use std::{
    collections::HashMap,
    time::{Duration, SystemTime, UNIX_EPOCH},
};

use ely_mail_engine::{AccountId, LocalFolder, MailboxId, Protocol, Synced, sync};
use gpui::Context;
use tokio::task::AbortHandle;

use crate::mail::Mail;

/// How often every account syncs while the window is open.
pub const EVERY: Duration = Duration::from_secs(10 * 60);

/// One account's sync as the window shows it.
#[derive(Default)]
pub struct Syncing {
    pub task: Option<AbortHandle>,
    /// Which sync `task` is; older completions are stale.
    pub run: u64,
    /// A folder changed mid-sync: sync once more.
    pub again: bool,
    pub synced: Option<Synced>,
    pub failed: Option<String>,
    pub folders: Vec<LocalFolder>,
}

pub type Syncs = HashMap<AccountId, Syncing>;

impl Mail {
    pub fn sync(&mut self, id: AccountId, cx: &mut Context<Self>) {
        if self.paused {
            return log::info!("mail: account {} not synced: paused", id.0);
        }
        let Some((_, account)) = self.accounts().iter().find(|(each, _)| *each == id) else {
            return log::info!("mail: sync asked of a gone account");
        };
        if self.syncs.get(&id).is_some_and(|each| each.task.is_some()) {
            return log::info!("mail: account {} is already syncing", id.0);
        }
        let Ok(store) = self.store.clone() else {
            return log::error!("mail: no store to sync with");
        };
        let tls = match self.tls.clone() {
            Ok(tls) => tls,
            Err(error) => {
                log::warn!("mail: account {} cannot sync without TLS", id.0);
                self.syncs.entry(id).or_default().failed = Some(error);
                return self.read_synced(id, cx);
            }
        };
        let (account, vault) = (account.clone(), self.vault.clone());
        self.runs += 1;
        let run = self.runs;
        self.syncs.entry(id).or_default().run = run;
        let work = async move {
            let now = SystemTime::now()
                .duration_since(UNIX_EPOCH)
                .map_err(|err| ely_mail_engine::Error::Store(format!("the clock: {err}")))?
                .as_secs() as i64;
            let secret = sync::secret(&account, &vault).await?;
            match account.protocol {
                Protocol::Imap => sync::imap(&account, id, secret, &tls, &store, now).await,
                Protocol::Pop { .. } => sync::pop(&account, id, secret, &tls, &store, now).await,
            }
        };
        let task = self.on_runtime(cx, work, move |mail, done, cx| {
            let failed = match done {
                Ok(Ok(_)) => None,
                Ok(Err(error)) => Some(error.to_string()),
                Err(error) => Some(error),
            };
            if failed.is_some() {
                log::warn!("mail: account {} did not sync", id.0);
            }
            let Some(syncing) = mail.syncs.get_mut(&id) else {
                return log::info!("mail: a sync ended for a removed account");
            };
            if syncing.run != run {
                return log::info!("mail: account {} sync {run} ended after a newer one", id.0);
            }
            syncing.task = None;
            syncing.failed = failed;
            let again = std::mem::take(&mut syncing.again);
            mail.read_synced(id, cx);
            if again {
                log::info!("mail: account {} syncs again for a changed folder", id.0);
                mail.sync(id, cx);
            }
        });
        self.syncs.entry(id).or_default().task = Some(task);
        self.read_synced(id, cx);
    }

    pub fn sync_all(&mut self, cx: &mut Context<Self>) {
        if self.paused {
            return log::info!("mail: sync is paused");
        }
        let ids: Vec<_> = self.accounts().iter().map(|(id, _)| *id).collect();
        for id in ids {
            self.sync(id, cx);
        }
    }

    /// Pausing stops running syncs; resuming syncs every account.
    pub fn set_paused(&mut self, paused: bool, cx: &mut Context<Self>) {
        log::info!("mail: sync paused: {paused}");
        self.paused = paused;
        if paused {
            for syncing in self.syncs.values_mut() {
                syncing.again = false;
                if let Some(task) = syncing.task.take() {
                    task.abort();
                }
            }
        } else {
            self.sync_all(cx);
        }
        self.notify(cx);
    }

    /// Syncs every account each `EVERY` until the window goes.
    pub fn sync_on_a_timer(cx: &mut Context<Self>) {
        cx.spawn(async move |this, cx| {
            loop {
                cx.background_executor().timer(EVERY).await;
                if this.update(cx, |mail, cx| mail.sync_all(cx)).is_err() {
                    break;
                }
            }
        })
        .detach();
    }

    /// Takes the folder's mail whole, then syncs to fetch it.
    pub fn set_offline(
        &mut self,
        id: AccountId,
        mailbox: MailboxId,
        offline: bool,
        cx: &mut Context<Self>,
    ) {
        self.with_store(
            cx,
            move |store| store.set_offline(mailbox, offline),
            move |mail, done, cx| match done {
                Ok(()) => {
                    mail.read_synced(id, cx);
                    match mail.syncs.get_mut(&id) {
                        Some(syncing) if offline && syncing.task.is_some() => {
                            log::info!("mail: account {} syncs again after this one", id.0);
                            syncing.again = true;
                        }
                        _ if offline => mail.sync(id, cx),
                        _ => {}
                    }
                }
                Err(error) => mail.failed("mail.sync.offline_failed", &error, cx),
            },
        );
    }

    /// Stops the account's sync and forgets it.
    pub fn stop_sync(&mut self, id: AccountId) {
        if let Some(task) = self.syncs.remove(&id).and_then(|each| each.task) {
            task.abort();
        }
    }

    fn read_synced(&mut self, id: AccountId, cx: &mut Context<Self>) {
        self.with_store(
            cx,
            move |store| Ok((store.synced(id)?, store.folders(id)?)),
            move |mail, read, cx| match (read, mail.syncs.get_mut(&id)) {
                (Ok((synced, folders)), Some(syncing)) => {
                    syncing.synced = Some(synced);
                    syncing.folders = folders;
                    mail.read_mail(cx);
                }
                (Err(error), Some(_)) => mail.failed("mail.sync.unread", &error, cx),
                (_, None) => {}
            },
        );
    }
}