io-email 0.1.0

//! JMAP watch-mailbox coroutine: EventSource (closeafter=state) +
//! Email/changes + Email/get diffed against an in-memory shadow.
//!
//! State machine: Subscribing → FetchingChanges → FetchingEmails →
//! Emitting → back to Subscribing. Shutdown via the caller-owned
//! [`Arc<AtomicBool>`] polled at every resume.
//!
//! Bootstrap cycle (`sinceState = ""`) returns the full inventory as
//! `created`; events from that cycle populate the shadow silently.
//!
//! # Example
//!
//! ```rust,ignore
//! use io_email::envelope::jmap::watch::JmapWatchMailbox;
//!
//! let cor = JmapWatchMailbox::new(&session, &auth, "mailbox-id", shutdown)?;
//! // drive with a JMAP-aware watch loop that handles the Event yield.
//! ```

use alloc::{
    collections::{BTreeMap, BTreeSet, VecDeque},
    string::String,
    sync::Arc,
    vec::Vec,
};
use core::{
    mem,
    sync::atomic::{AtomicBool, Ordering},
};

use io_jmap::{
    coroutine::{JmapCoroutine, JmapCoroutineState, JmapYield},
    rfc8620::{
        JmapSession,
        changes::JmapChangesOutput,
        event_source::{
            JmapCloseAfter, JmapStateChange,
            subscribe::{JmapEventSource, JmapEventSourceError, JmapEventSourceYield},
        },
    },
    rfc8621::email::{
        JmapEmail, JmapEmailProperty,
        changes::{JmapEmailChanges, JmapEmailChangesError, JmapEmailChangesOptions},
        get::{JmapEmailGet, JmapEmailGetError, JmapEmailGetOptions},
    },
};
use log::trace;
use secrecy::SecretString;
use thiserror::Error;

use crate::{
    envelope::event::WatchEvent,
    flag::types::Flag,
    jmap::convert::{account_id_of, envelope_from, envelope_properties},
};

/// JMAP type tag we subscribe to and diff against.
const EMAIL_TYPE: &str = "Email";
/// Server-side ping cadence (seconds) for the SSE channel.
const PING_SECONDS: u64 = 30;

/// Errors produced by [`JmapWatchMailbox`].
#[derive(Debug, Error)]
pub enum JmapWatchMailboxError {
    #[error(transparent)]
    EventSource(#[from] JmapEventSourceError),
    #[error(transparent)]
    EmailChanges(#[from] JmapEmailChangesError),
    #[error(transparent)]
    EmailGet(#[from] JmapEmailGetError),
}

/// Yield mixing socket I/O requests and pre-diffed [`WatchEvent`]s.
#[derive(Debug)]
pub enum JmapWatchMailboxYield {
    /// Read more bytes and feed them via `bytes` on the next resume.
    WantsRead,
    /// Write these bytes; the next resume usually takes `bytes: None`.
    WantsWrite(Vec<u8>),
    /// One pre-diffed delta from the in-memory shadow.
    Event(WatchEvent),
}

/// I/O-free coroutine watching a single JMAP mailbox over one
/// HTTP/1.1 connection.
pub struct JmapWatchMailbox {
    state: State,
    mailbox_id: String,
    session: JmapSession,
    http_auth: SecretString,
    account_id: String,
    shutdown: Arc<AtomicBool>,
    /// email_id to keyword bag; mirrors the server view of the mailbox.
    shadow: BTreeMap<String, BTreeSet<String>>,
    /// Latest Email-type state; `sinceState` on the next Email/changes.
    email_state: Option<String>,
    /// FIFO of events drained one per resume between cycles.
    pending: VecDeque<WatchEvent>,
    /// True until the bootstrap cycle has populated the shadow.
    suppress_events: bool,
}

impl JmapWatchMailbox {
    pub fn new(
        session: &JmapSession,
        http_auth: &SecretString,
        mailbox: &str,
        shutdown: Arc<AtomicBool>,
    ) -> Result<Self, JmapWatchMailboxError> {
        trace!("prepare JMAP mailbox watch");
        let es = JmapEventSource::new(
            session,
            http_auth,
            &[EMAIL_TYPE],
            PING_SECONDS,
            JmapCloseAfter::State,
            shutdown.clone(),
        )?;
        Ok(Self {
            state: State::Subscribing {
                es,
                latest_change: None,
            },
            mailbox_id: mailbox.into(),
            session: session.clone(),
            http_auth: http_auth.clone(),
            account_id: account_id_of(session),
            shutdown,
            shadow: BTreeMap::new(),
            email_state: None,
            pending: VecDeque::new(),
            suppress_events: true,
        })
    }

    /// Fresh [`State::Subscribing`] for the next SSE round.
    fn fresh_subscription_state(&self) -> Result<State, JmapWatchMailboxError> {
        let es = JmapEventSource::new(
            &self.session,
            &self.http_auth,
            &[EMAIL_TYPE],
            PING_SECONDS,
            JmapCloseAfter::State,
            self.shutdown.clone(),
        )?;
        Ok(State::Subscribing {
            es,
            latest_change: None,
        })
    }

    /// Inspects the trailing [`JmapStateChange`] and picks the next
    /// State: Email/changes, KeepAlive, or fresh subscription.
    fn handle_cycle_end(
        &mut self,
        change: Option<JmapStateChange>,
    ) -> Result<State, JmapWatchMailboxError> {
        let observed_state = change
            .as_ref()
            .and_then(|c| c.changed.get(&self.account_id))
            .and_then(|ts| ts.get(EMAIL_TYPE))
            .cloned();

        let needs_diff = match (&observed_state, &self.email_state) {
            (Some(observed), Some(known)) => observed != known,
            // NOTE: bootstrap or first observation: always sync.
            (_, None) => true,
            // NOTE: no Email state for our account: nothing to do.
            (None, _) => false,
        };

        if needs_diff {
            let since = self.email_state.clone().unwrap_or_default();
            let changes = JmapEmailChanges::new(
                &self.session,
                &self.http_auth,
                since,
                JmapEmailChangesOptions::default(),
            )?;
            return Ok(State::FetchingChanges(changes));
        }

        if !self.suppress_events && change.is_some() {
            self.pending.push_back(WatchEvent::KeepAlive);
        }
        Ok(State::Emitting)
    }

    /// Email/get for the union of created+updated ids; carries the
    /// destroyed list for later diffing.
    fn dispatch_get(&self, ok: JmapChangesOutput) -> Result<State, JmapWatchMailboxError> {
        let JmapChangesOutput {
            new_state,
            has_more_changes,
            mut created,
            updated,
            destroyed,
            ..
        } = ok;

        if has_more_changes {
            trace!("JMAP Email/changes truncated; next subscription cycle will catch up");
        }

        created.extend(updated);
        let mut properties = envelope_properties();
        properties.push(JmapEmailProperty::MailboxIds);

        let opts = JmapEmailGetOptions {
            properties: Some(properties),
            ..Default::default()
        };
        let get = JmapEmailGet::new(&self.session, &self.http_auth, created, opts)?;

        Ok(State::FetchingEmails {
            get,
            destroyed,
            new_state,
        })
    }

    /// Folds emails + destroyed ids into the shadow, queueing one
    /// [`WatchEvent`] per delta unless the bootstrap cycle is running.
    fn apply_diff(&mut self, emails: Vec<JmapEmail>, destroyed: Vec<String>) {
        for email in emails {
            let Some(id) = email.id.clone() else {
                continue;
            };
            let in_mailbox = email
                .mailbox_ids
                .as_ref()
                .is_some_and(|map| map.get(&self.mailbox_id).copied().unwrap_or(false));
            let new_keywords: BTreeSet<String> = email
                .keywords
                .clone()
                .unwrap_or_default()
                .into_iter()
                .filter_map(|(k, v)| if v { Some(k) } else { None })
                .collect();
            let was_in_shadow = self.shadow.contains_key(&id);

            if in_mailbox {
                if was_in_shadow {
                    let old = self.shadow.get(&id).cloned().unwrap_or_default();
                    let added: BTreeSet<String> = new_keywords.difference(&old).cloned().collect();
                    let removed: BTreeSet<String> =
                        old.difference(&new_keywords).cloned().collect();
                    if !added.is_empty() && !self.suppress_events {
                        self.pending.push_back(WatchEvent::FlagsAdded {
                            mailbox: self.mailbox_id.clone(),
                            id: id.clone(),
                            flags: added.into_iter().map(Flag::from_raw).collect(),
                        });
                    }
                    if !removed.is_empty() && !self.suppress_events {
                        self.pending.push_back(WatchEvent::FlagsRemoved {
                            mailbox: self.mailbox_id.clone(),
                            id: id.clone(),
                            flags: removed.into_iter().map(Flag::from_raw).collect(),
                        });
                    }
                    self.shadow.insert(id, new_keywords);
                } else {
                    let envelope = envelope_from(email);
                    if !self.suppress_events {
                        self.pending.push_back(WatchEvent::EnvelopeAdded {
                            mailbox: self.mailbox_id.clone(),
                            envelope: envelope.clone(),
                        });
                    }
                    self.shadow.insert(envelope.id, new_keywords);
                }
            } else if was_in_shadow {
                if !self.suppress_events {
                    self.pending.push_back(WatchEvent::EnvelopeRemoved {
                        mailbox: self.mailbox_id.clone(),
                        id: id.clone(),
                    });
                }
                self.shadow.remove(&id);
            }
        }

        for id in destroyed {
            if self.shadow.remove(&id).is_some() && !self.suppress_events {
                self.pending.push_back(WatchEvent::EnvelopeRemoved {
                    mailbox: self.mailbox_id.clone(),
                    id,
                });
            }
        }
    }
}

impl JmapCoroutine for JmapWatchMailbox {
    type Yield = JmapWatchMailboxYield;
    type Return = Result<(), JmapWatchMailboxError>;

    fn resume(&mut self, bytes: Option<&[u8]>) -> JmapCoroutineState<Self::Yield, Self::Return> {
        if self.shutdown.load(Ordering::SeqCst) {
            self.state = State::Done;
            return JmapCoroutineState::Complete(Ok(()));
        }

        let mut bytes = bytes;
        loop {
            match mem::replace(&mut self.state, State::Done) {
                State::Subscribing {
                    mut es,
                    mut latest_change,
                } => match es.resume(bytes.take()) {
                    JmapCoroutineState::Yielded(JmapEventSourceYield::WantsRead) => {
                        self.state = State::Subscribing { es, latest_change };
                        return JmapCoroutineState::Yielded(JmapWatchMailboxYield::WantsRead);
                    }
                    JmapCoroutineState::Yielded(JmapEventSourceYield::WantsWrite(out)) => {
                        self.state = State::Subscribing { es, latest_change };
                        return JmapCoroutineState::Yielded(JmapWatchMailboxYield::WantsWrite(out));
                    }
                    JmapCoroutineState::Yielded(JmapEventSourceYield::Frame(change)) => {
                        latest_change = Some(change);
                        self.state = State::Subscribing { es, latest_change };
                    }
                    JmapCoroutineState::Complete(Ok(())) => {
                        self.state = match self.handle_cycle_end(latest_change) {
                            Ok(s) => s,
                            Err(err) => return JmapCoroutineState::Complete(Err(err)),
                        };
                    }
                    JmapCoroutineState::Complete(Err(err)) => {
                        return JmapCoroutineState::Complete(Err(err.into()));
                    }
                },
                State::FetchingChanges(mut changes) => match changes.resume(bytes.take()) {
                    JmapCoroutineState::Yielded(JmapYield::WantsRead) => {
                        self.state = State::FetchingChanges(changes);
                        return JmapCoroutineState::Yielded(JmapWatchMailboxYield::WantsRead);
                    }
                    JmapCoroutineState::Yielded(JmapYield::WantsWrite(out)) => {
                        self.state = State::FetchingChanges(changes);
                        return JmapCoroutineState::Yielded(JmapWatchMailboxYield::WantsWrite(out));
                    }
                    JmapCoroutineState::Complete(Err(err)) => {
                        return JmapCoroutineState::Complete(Err(err.into()));
                    }
                    JmapCoroutineState::Complete(Ok(ok)) => {
                        self.state = match self.dispatch_get(ok) {
                            Ok(s) => s,
                            Err(err) => return JmapCoroutineState::Complete(Err(err)),
                        };
                    }
                },
                State::FetchingEmails {
                    mut get,
                    destroyed,
                    new_state,
                } => match get.resume(bytes.take()) {
                    JmapCoroutineState::Yielded(JmapYield::WantsRead) => {
                        self.state = State::FetchingEmails {
                            get,
                            destroyed,
                            new_state,
                        };
                        return JmapCoroutineState::Yielded(JmapWatchMailboxYield::WantsRead);
                    }
                    JmapCoroutineState::Yielded(JmapYield::WantsWrite(out)) => {
                        self.state = State::FetchingEmails {
                            get,
                            destroyed,
                            new_state,
                        };
                        return JmapCoroutineState::Yielded(JmapWatchMailboxYield::WantsWrite(out));
                    }
                    JmapCoroutineState::Complete(Err(err)) => {
                        return JmapCoroutineState::Complete(Err(err.into()));
                    }
                    JmapCoroutineState::Complete(Ok(ok)) => {
                        self.apply_diff(ok.emails, destroyed);
                        self.email_state = Some(new_state);
                        self.suppress_events = false;
                        self.state = State::Emitting;
                    }
                },
                State::Emitting => {
                    if let Some(evt) = self.pending.pop_front() {
                        self.state = State::Emitting;
                        return JmapCoroutineState::Yielded(JmapWatchMailboxYield::Event(evt));
                    }
                    self.state = match self.fresh_subscription_state() {
                        Ok(s) => s,
                        Err(err) => return JmapCoroutineState::Complete(Err(err)),
                    };
                }
                State::Done => return JmapCoroutineState::Complete(Ok(())),
            }
        }
    }
}

/// Internal progression of [`JmapWatchMailbox`].
enum State {
    Subscribing {
        es: JmapEventSource,
        latest_change: Option<JmapStateChange>,
    },
    FetchingChanges(JmapEmailChanges),
    FetchingEmails {
        get: JmapEmailGet,
        destroyed: Vec<String>,
        new_state: String,
    },
    Emitting,
    Done,
}