//! Presence update pipeline.
//!
//! This module centralizes the write path for presence updates. It keeps the
//! aggregation and timer logic in one place so the public `Service` surface
//! remains small and the update flow is easy to review.

use std::time::Duration;

use futures::TryFutureExt;
use ruma::{DeviceId, OwnedUserId, UInt, UserId, presence::PresenceState};
use tuwunel_core::{
	Error, Result, debug, error, trace,
	result::LogErr,
	utils::{future::OptionFutureExt, option::OptionExt},
};

use super::{aggregate, Service};

impl Service {
	fn device_key(device_id: Option<&DeviceId>, is_remote: bool) -> aggregate::DeviceKey {
		if is_remote {
			return aggregate::DeviceKey::Remote;
		}

		match device_id {
			| Some(device_id) => aggregate::DeviceKey::Device(device_id.to_owned()),
			| None => aggregate::DeviceKey::UnknownLocal,
		}
	}

	fn schedule_presence_timer(
		&self,
		user_id: &UserId,
		presence_state: &PresenceState,
		count: u64,
	) -> Result {
		if !(self.timeout_remote_users || self.services.globals.user_is_local(user_id))
			|| user_id == self.services.globals.server_user
		{
			return Ok(());
		}

		let timeout = match presence_state {
			| PresenceState::Online => self.services.server.config.presence_idle_timeout_s,
			| _ => self.services.server.config.presence_offline_timeout_s,
		};

		self.timer_channel
			.0
			.send((user_id.to_owned(), Duration::from_secs(timeout), count))
			.map_err(|e| {
				error!("Failed to add presence timer: {}", e);
				Error::bad_database("Failed to add presence timer")
			})
	}

	async fn apply_device_presence_update(
		&self,
		user_id: &UserId,
		device_key: aggregate::DeviceKey,
		state: &PresenceState,
		currently_active: Option<bool>,
		last_active_ago: Option<UInt>,
		status_msg: Option<String>,
		refresh_window_ms: Option<u64>,
	) -> Result {
		let now = tuwunel_core::utils::millis_since_unix_epoch();
		debug!(
			?user_id,
			?device_key,
			?state,
			currently_active,
			last_active_ago = last_active_ago.map(u64::from),
			"Presence update received"
		);
		self.device_presence
			.update(
				user_id,
				device_key,
				state,
				currently_active,
				last_active_ago,
				status_msg,
				now,
			)
			.await;

		let aggregated = self
			.device_presence
			.aggregate(user_id, now, self.idle_timeout, self.offline_timeout)
			.await;
		debug!(
			?user_id,
			agg_state = ?aggregated.state,
			agg_currently_active = aggregated.currently_active,
			agg_last_active_ts = aggregated.last_active_ts,
			agg_device_count = aggregated.device_count,
			"Presence aggregate computed"
		);

		let last_presence = self.db.get_presence(user_id).await;
		let (last_count, last_event) = match last_presence {
			| Ok((count, event)) => (Some(count), Some(event)),
			| Err(_) => (None, None),
		};

		let state_changed = match &last_event {
			| Some(event) => event.content.presence != aggregated.state,
			| None => true,
		};

		if !state_changed {
			if let (Some(refresh_ms), Some(event), Some(count)) =
				(refresh_window_ms, &last_event, last_count)
			{
				let last_last_active_ago: u64 = event
					.content
					.last_active_ago
					.unwrap_or_default()
					.into();
				if last_last_active_ago < refresh_ms {
					self.schedule_presence_timer(user_id, &event.content.presence, count)
						.log_err()
						.ok();
					debug!(
						?user_id,
						?state,
						last_last_active_ago,
						"Skipping presence update: refresh window (timer rescheduled)"
					);
					return Ok(());
				}
			}
		}

		let fallback_status = last_event
			.and_then(|event| event.content.status_msg)
			.filter(|msg| !msg.is_empty());
		let status_msg = aggregated.status_msg.or(fallback_status);
		let last_active_ago =
			Some(UInt::new_saturating(now.saturating_sub(aggregated.last_active_ts)));

		self.set_presence(
			user_id,
			&aggregated.state,
			Some(aggregated.currently_active),
			last_active_ago,
			status_msg,
		)
		.await
	}

	/// Pings the presence of the given user, setting the specified state. When
	/// device_id is supplied.
	pub async fn maybe_ping_presence(
		&self,
		user_id: &UserId,
		device_id: Option<&DeviceId>,
		new_state: &PresenceState,
	) -> Result {
		const REFRESH_TIMEOUT: u64 = 30 * 1000;

		if !self.services.server.config.allow_local_presence || self.services.db.is_read_only() {
			debug!(
				?user_id,
				?new_state,
				allow_local_presence = self.services.server.config.allow_local_presence,
				read_only = self.services.db.is_read_only(),
				"Skipping presence ping"
			);
			return Ok(());
		}

		let update_device_seen = device_id.map_async(|device_id| {
			self.services
				.users
				.update_device_last_seen(user_id, device_id, None)
		});

		let currently_active = *new_state == PresenceState::Online;
		let set_presence = self.apply_device_presence_update(
			user_id,
			Self::device_key(device_id, false),
			new_state,
			Some(currently_active),
			UInt::new(0),
			None,
			Some(REFRESH_TIMEOUT),
		);

		debug!(
			?user_id,
			?new_state,
			currently_active,
			"Presence ping accepted"
		);

		futures::future::try_join(set_presence, update_device_seen.unwrap_or(Ok(())))
			.map_ok(|_| ())
			.await
	}

	/// Applies an explicit presence update for a local device.
	pub async fn set_presence_for_device(
		&self,
		user_id: &UserId,
		device_id: Option<&DeviceId>,
		state: &PresenceState,
		status_msg: Option<String>,
	) -> Result {
		let currently_active = *state == PresenceState::Online;
		self.apply_device_presence_update(
			user_id,
			Self::device_key(device_id, false),
			state,
			Some(currently_active),
			None,
			status_msg,
			None,
		)
		.await
	}

	/// Applies a presence update received over federation.
	pub async fn set_presence_from_federation(
		&self,
		user_id: &UserId,
		state: &PresenceState,
		currently_active: bool,
		last_active_ago: UInt,
		status_msg: Option<String>,
	) -> Result {
		self.apply_device_presence_update(
			user_id,
			Self::device_key(None, true),
			state,
			Some(currently_active),
			Some(last_active_ago),
			status_msg,
			None,
		)
		.await
	}

	/// Adds a presence event which will be saved until a new event replaces it.
	pub async fn set_presence(
		&self,
		user_id: &UserId,
		state: &PresenceState,
		currently_active: Option<bool>,
		last_active_ago: Option<UInt>,
		status_msg: Option<String>,
	) -> Result {
		let presence_state = match state.as_str() {
			| "" => &PresenceState::Offline, // default an empty string to 'offline'
			| &_ => state,
		};

		let count = self
			.db
			.set_presence(user_id, presence_state, currently_active, last_active_ago, status_msg)
			.await?;

		if let Some(count) = count {
			let is_local = self.services.globals.user_is_local(user_id);
			let is_server_user = user_id == self.services.globals.server_user;
			let allow_timeout = self.timeout_remote_users || is_local;

			if allow_timeout && !is_server_user {
				self.schedule_presence_timer(user_id, presence_state, count)?;
			}
		}

		Ok(())
	}

	pub(super) async fn process_presence_timer(
		&self,
		user_id: &OwnedUserId,
		expected_count: u64,
	) -> Result {
		let (current_count, presence) = match self.db.get_presence_raw(user_id).await {
			| Ok(presence) => presence,
			| Err(_) => return Ok(()),
		};

		if current_count != expected_count {
			trace!(
				?user_id,
				expected_count,
				current_count,
				"Skipping stale presence timer"
			);
			return Ok(());
		}

		let presence_state = presence.state().clone();
		let now = tuwunel_core::utils::millis_since_unix_epoch();
		let aggregated = self
			.device_presence
			.aggregate(user_id, now, self.idle_timeout, self.offline_timeout)
			.await;

		if aggregated.device_count == 0 {
			let last_active_ago =
				Some(UInt::new_saturating(now.saturating_sub(presence.last_active_ts())));
			let status_msg = presence.status_msg();

			let new_state = match (&presence_state, last_active_ago.map(u64::from)) {
				| (PresenceState::Online, Some(ago)) if ago >= self.idle_timeout =>
					Some(PresenceState::Unavailable),
				| (PresenceState::Unavailable, Some(ago)) if ago >= self.offline_timeout =>
					Some(PresenceState::Offline),
				| _ => None,
			};

			debug!(
				"Processed presence timer for user '{user_id}': Old state = {presence_state}, New \
				 state = {new_state:?}"
			);

			if let Some(new_state) = new_state {
				self.set_presence(
					user_id,
					&new_state,
					Some(false),
					last_active_ago,
					status_msg,
				)
				.await?;
			}

			return Ok(());
		}

		if aggregated.state == presence_state {
			self.schedule_presence_timer(user_id, &presence_state, current_count)
				.log_err()
				.ok();
			return Ok(());
		}

		let status_msg = aggregated.status_msg.or_else(|| presence.status_msg());
		let last_active_ago =
			Some(UInt::new_saturating(now.saturating_sub(aggregated.last_active_ts)));

		self.set_presence(
			user_id,
			&aggregated.state,
			Some(aggregated.currently_active),
			last_active_ago,
			status_msg,
		)
		.await?;

		Ok(())
	}
}