use std::cmp;

use futures_util::StreamExt;
use gtk::{gio, glib, glib::clone, prelude::*, subclass::prelude::*};
use indexmap::{IndexMap, IndexSet};
use matrix_sdk::Client;
use ruma::OwnedUserId;
use tokio::task::AbortHandle;
use tracing::error;

mod user_session;

pub use self::user_session::UserSession;
use self::user_session::UserSessionData;
use super::Session;
use crate::{spawn, spawn_tokio, utils::LoadingState};

mod imp {
    use std::{
        cell::{Cell, OnceCell, RefCell},
        marker::PhantomData,
    };

    use super::*;

    #[derive(Debug, glib::Properties)]
    #[properties(wrapper_type = super::UserSessionsList)]
    pub struct UserSessionsList {
        /// The current session.
        #[property(get)]
        pub session: glib::WeakRef<Session>,
        /// The ID of the user the sessions belong to.
        pub user_id: OnceCell<OwnedUserId>,
        /// The other user sessions.
        #[property(get)]
        pub other_sessions: gio::ListStore,
        /// The current user session.
        #[property(get)]
        current_session: RefCell<Option<UserSession>>,
        /// The loading state of the list.
        #[property(get, builder(LoadingState::default()))]
        pub loading_state: Cell<LoadingState>,
        /// Whether the list is empty.
        #[property(get = Self::is_empty)]
        pub is_empty: PhantomData<bool>,
        pub sessions_watch_abort_handle: RefCell<Option<AbortHandle>>,
    }

    impl Default for UserSessionsList {
        fn default() -> Self {
            Self {
                session: Default::default(),
                user_id: Default::default(),
                other_sessions: gio::ListStore::new::<UserSession>(),
                current_session: Default::default(),
                loading_state: Default::default(),
                is_empty: Default::default(),
                sessions_watch_abort_handle: Default::default(),
            }
        }
    }

    #[glib::object_subclass]
    impl ObjectSubclass for UserSessionsList {
        const NAME: &'static str = "UserSessionsList";
        type Type = super::UserSessionsList;
    }

    #[glib::derived_properties]
    impl ObjectImpl for UserSessionsList {
        fn dispose(&self) {
            if let Some(abort_handle) = self.sessions_watch_abort_handle.take() {
                abort_handle.abort();
            }
        }
    }

    impl UserSessionsList {
        /// Set the current user session.
        pub(super) fn set_current_session(&self, user_session: Option<UserSession>) {
            if *self.current_session.borrow() == user_session {
                return;
            }

            let was_empty = self.is_empty();

            self.current_session.replace(user_session);

            let obj = self.obj();
            obj.notify_current_session();

            if self.is_empty() != was_empty {
                obj.notify_is_empty();
            }
        }

        /// Set the loading state of the list.
        pub(super) fn set_loading_state(&self, loading_state: LoadingState) {
            if self.loading_state.get() == loading_state {
                return;
            }

            self.loading_state.set(loading_state);
            self.obj().notify_loading_state();
        }

        /// Whether the list is empty.
        pub(super) fn is_empty(&self) -> bool {
            self.current_session.borrow().is_none() && self.other_sessions.n_items() == 0
        }
    }
}

glib::wrapper! {
    /// List of active user sessions for a user.
    pub struct UserSessionsList(ObjectSubclass<imp::UserSessionsList>);
}

impl UserSessionsList {
    pub fn new() -> Self {
        glib::Object::new()
    }

    /// Initialize this list with the given session and user ID.
    pub fn init(&self, session: &Session, user_id: OwnedUserId) {
        let imp = self.imp();
        imp.session.set(Some(session));
        imp.user_id.set(user_id).unwrap();

        spawn!(clone!(@weak self as obj => async move {
            obj.load().await;
        }));
        spawn!(clone!(@weak self as obj, @weak session => async move {
            obj.init_sessions_watch(session.client()).await;
        }));
    }

    /// Start listening to changes in the user sessions.
    async fn init_sessions_watch(&self, client: Client) {
        let stream = match client.encryption().devices_stream().await {
            Ok(stream) => stream,
            Err(error) => {
                error!("Could not access the user sessions stream: {error}");
                return;
            }
        };

        let obj_weak = glib::SendWeakRef::from(self.downgrade());
        let user_id = self.user_id().clone();
        let fut = stream.for_each(move |updates| {
            let user_id = user_id.clone();
            let obj_weak = obj_weak.clone();

            async move {
                if !updates.new.contains_key(&user_id) && !updates.changed.contains_key(&user_id) {
                    return;
                }

                let ctx = glib::MainContext::default();
                ctx.spawn(async move {
                    spawn!(async move {
                        if let Some(obj) = obj_weak.upgrade() {
                            obj.load().await;
                        }
                    });
                });
            }
        });

        let abort_handle = spawn_tokio!(fut).abort_handle();
        self.imp()
            .sessions_watch_abort_handle
            .replace(Some(abort_handle));
    }

    /// The ID of the user the sessions belong to.
    pub fn user_id(&self) -> &OwnedUserId {
        self.imp().user_id.get().unwrap()
    }

    /// Load the list of user sessions.
    pub async fn load(&self) {
        if self.loading_state() == LoadingState::Loading {
            // Don't load the list twice at the same time.
            return;
        }

        let Some(session) = self.session() else {
            return;
        };
        let imp = self.imp();

        imp.set_loading_state(LoadingState::Loading);

        let user_id = self.user_id().clone();
        let client = session.client();
        let handle = spawn_tokio!(async move {
            let crypto_sessions = match client.encryption().get_user_devices(&user_id).await {
                Ok(crypto_sessions) => Some(crypto_sessions),
                Err(error) => {
                    error!("Could not get crypto sessions for user {user_id}: {error}");
                    None
                }
            };

            let is_own_user = client.user_id().unwrap() == user_id;

            let mut api_sessions = None;
            if is_own_user {
                match client.devices().await {
                    Ok(response) => {
                        api_sessions = Some(response.devices);
                    }
                    Err(error) => {
                        error!("Could not get sessions list for user {user_id}: {error}");
                    }
                }
            }

            (api_sessions, crypto_sessions)
        });

        let (api_sessions, crypto_sessions) = handle.await.unwrap();

        if api_sessions.is_none() && crypto_sessions.is_none() {
            imp.set_loading_state(LoadingState::Error);
            return;
        };

        // Convert API sessions to a map.
        let mut api_sessions = api_sessions
            .into_iter()
            .flatten()
            .map(|d| (d.device_id.clone(), d))
            .collect::<IndexMap<_, _>>();

        // Sort the API sessions, last seen first, then sort by device ID.
        api_sessions.sort_by(|_key_a, val_a, _key_b, val_b| {
            match val_b.last_seen_ts.cmp(&val_a.last_seen_ts) {
                cmp::Ordering::Equal => val_a.device_id.cmp(&val_b.device_id),
                cmp => cmp,
            }
        });

        // Build the full list of IDs while preserving the sorting order.
        let ids = api_sessions
            .keys()
            .cloned()
            .chain(
                crypto_sessions
                    .iter()
                    .flat_map(|s| s.keys())
                    .map(ToOwned::to_owned),
            )
            .collect::<IndexSet<_>>();

        let (current, others) = ids
            .into_iter()
            .filter_map(|id| {
                let data = match (
                    api_sessions.shift_remove(&id),
                    crypto_sessions.as_ref().and_then(|s| s.get(&id)),
                ) {
                    (Some(api), Some(crypto)) => UserSessionData::Both { api, crypto },
                    (Some(api), None) => UserSessionData::DevicesApi(api),
                    (None, Some(crypto)) => UserSessionData::Crypto(crypto),
                    _ => return None,
                };

                Some(UserSession::new(&session, data))
            })
            .partition::<Vec<_>, _>(|s| s.is_current());

        if let Some(current) = current.into_iter().next() {
            imp.set_current_session(Some(current));
        }

        let was_empty = imp.is_empty();

        let removed = imp.other_sessions.n_items();
        imp.other_sessions.splice(0, removed, &others);

        if imp.is_empty() != was_empty {
            self.notify_is_empty();
        }

        imp.set_loading_state(LoadingState::Ready);
    }
}

impl Default for UserSessionsList {
    fn default() -> Self {
        Self::new()
    }
}
