use crate::{
    align_view,
    document::{DocumentSavedEventFuture, DocumentSavedEventResult, Mode, SavePoint},
    graphics::{CursorKind, Rect},
    info::Info,
    input::KeyEvent,
    register::Registers,
    theme::{self, Theme},
    tree::{self, Tree},
    view::ViewPosition,
    Align, Document, DocumentId, View, ViewId,
};
use dap::StackFrame;
use helix_vcs::DiffProviderRegistry;

use futures_util::stream::select_all::SelectAll;
use futures_util::{future, StreamExt};
use helix_lsp::Call;
use tokio_stream::wrappers::UnboundedReceiverStream;

use std::{
    borrow::Cow,
    cell::Cell,
    collections::{BTreeMap, HashMap},
    io::stdin,
    num::NonZeroUsize,
    path::{Path, PathBuf},
    pin::Pin,
    sync::Arc,
};

use tokio::{
    sync::{
        mpsc::{unbounded_channel, UnboundedReceiver, UnboundedSender},
        oneshot,
    },
    time::{sleep, Duration, Instant, Sleep},
};

use anyhow::{anyhow, bail, Error};

pub use helix_core::diagnostic::Severity;
use helix_core::{
    syntax::{self, LanguageServerFeature},
    Change, Position, Selection,
};
use helix_dap as dap;
use helix_lsp::lsp;

use arc_swap::access::DynGuard;

#[derive(Debug, Clone, Default)]
pub struct Breakpoint {
    pub id: Option<usize>,
    pub verified: bool,
    pub message: Option<String>,

    pub line: usize,
    pub column: Option<usize>,
    pub condition: Option<String>,
    pub hit_condition: Option<String>,
    pub log_message: Option<String>,
}

use futures_util::stream::{Flatten, Once};

pub struct Editor {
    /// Current editing mode.
    pub mode: Mode,
    pub tree: Tree,
    pub next_document_id: DocumentId,
    pub documents: BTreeMap<DocumentId, Document>,

    // We Flatten<> to resolve the inner DocumentSavedEventFuture. For that we need a stream of streams, hence the Once<>.
    // https://stackoverflow.com/a/66875668
    pub saves: HashMap<DocumentId, UnboundedSender<Once<DocumentSavedEventFuture>>>,
    pub save_queue: SelectAll<Flatten<UnboundedReceiverStream<Once<DocumentSavedEventFuture>>>>,
    pub write_count: usize,

    pub count: Option<std::num::NonZeroUsize>,
    pub selected_register: Option<char>,
    pub registers: Registers,
    pub macro_recording: Option<(char, Vec<KeyEvent>)>,
    pub macro_replaying: Vec<char>,
    pub language_servers: helix_lsp::Registry,
    pub diagnostics: BTreeMap<lsp::Url, Vec<(lsp::Diagnostic, usize)>>,
    pub diff_providers: DiffProviderRegistry,

    pub debugger: Option<dap::Client>,
    pub debugger_events: SelectAll<UnboundedReceiverStream<dap::Payload>>,
    pub breakpoints: HashMap<PathBuf, Vec<Breakpoint>>,

    pub syn_loader: Arc<syntax::Loader>,
    pub theme_loader: Arc<theme::Loader>,
    /// last_theme is used for theme previews. We store the current theme here,
    /// and if previewing is cancelled, we can return to it.
    pub last_theme: Option<Theme>,
    /// The currently applied editor theme. While previewing a theme, the previewed theme
    /// is set here.
    pub theme: Theme,

    /// The primary Selection prior to starting a goto_line_number preview. This is
    /// restored when the preview is aborted, or added to the jumplist when it is
    /// confirmed.
    pub last_selection: Option<Selection>,

    pub status_msg: Option<(Cow<'static, str>, Severity)>,
    pub autoinfo: Option<Info>,

    pub config: Arc<dyn DynAccess<Config>>,
    pub auto_pairs: Option<AutoPairs>,

    pub idle_timer: Pin<Box<Sleep>>,
    redraw_timer: Pin<Box<Sleep>>,
    last_motion: Option<Motion>,
    pub last_completion: Option<CompleteAction>,

    pub exit_code: i32,

    pub config_events: (UnboundedSender<ConfigEvent>, UnboundedReceiver<ConfigEvent>),
    pub needs_redraw: bool,
    /// Cached position of the cursor calculated during rendering.
    /// The content of `cursor_cache` is returned by `Editor::cursor` if
    /// set to `Some(_)`. The value will be cleared after it's used.
    /// If `cursor_cache` is `None` then the `Editor::cursor` function will
    /// calculate the cursor position.
    ///
    /// `Some(None)` represents a cursor position outside of the visible area.
    /// This will just cause `Editor::cursor` to return `None`.
    ///
    /// This cache is only a performance optimization to
    /// avoid calculating the cursor position multiple
    /// times during rendering and should not be set by other functions.
    pub cursor_cache: Cell<Option<Option<Position>>>,
    /// When a new completion request is sent to the server old
    /// unfinished request must be dropped. Each completion
    /// request is associated with a channel that cancels
    /// when the channel is dropped. That channel is stored
    /// here. When a new completion request is sent this
    /// field is set and any old requests are automatically
    /// canceled as a result
    pub completion_request_handle: Option<oneshot::Sender<()>>,
}

pub type Motion = Box<dyn Fn(&mut Editor)>;

#[derive(Debug)]
pub enum EditorEvent {
    DocumentSaved(DocumentSavedEventResult),
    ConfigEvent(ConfigEvent),
    LanguageServerMessage((usize, Call)),
    DebuggerEvent(dap::Payload),
    IdleTimer,
    Redraw,
}

#[derive(Debug, Clone)]
pub enum ConfigEvent {
    Refresh,
    Update(Box<Config>),
}

enum ThemeAction {
    Set,
    Preview,
}

#[derive(Debug, Clone)]
pub enum CompleteAction {
    Applied {
        trigger_offset: usize,
        changes: Vec<Change>,
    },
    /// A savepoint of the currently selected completion. The savepoint
    /// MUST be restored before sending any event to the LSP
    Selected { savepoint: Arc<SavePoint> },
}

#[derive(Debug, Copy, Clone)]
pub enum Action {
    Load,
    Replace,
    HorizontalSplit,
    VerticalSplit,
}

impl Action {
    /// Whether to align the view to the cursor after executing this action
    pub fn align_view(&self, view: &View, new_doc: DocumentId) -> bool {
        !matches!((self, view.doc == new_doc), (Action::Load, false))
    }
}

/// Error thrown on failed document closed
pub enum CloseError {
    /// Document doesn't exist
    DoesNotExist,
    /// Buffer is modified
    BufferModified(String),
    /// Document failed to save
    SaveError(anyhow::Error),
}

impl Editor {
    pub fn new(
        mut area: Rect,
        theme_loader: Arc<theme::Loader>,
        syn_loader: Arc<syntax::Loader>,
        config: Arc<dyn DynAccess<Config>>,
    ) -> Self {
        let language_servers = helix_lsp::Registry::new(syn_loader.clone());
        let conf = config.load();
        let auto_pairs = (&conf.auto_pairs).into();

        // HAXX: offset the render area height by 1 to account for prompt/commandline
        area.height -= 1;

        Self {
            mode: Mode::Normal,
            tree: Tree::new(area),
            next_document_id: DocumentId::default(),
            documents: BTreeMap::new(),
            saves: HashMap::new(),
            save_queue: SelectAll::new(),
            write_count: 0,
            count: None,
            selected_register: None,
            macro_recording: None,
            macro_replaying: Vec::new(),
            theme: theme_loader.default(),
            language_servers,
            diagnostics: BTreeMap::new(),
            diff_providers: DiffProviderRegistry::default(),
            debugger: None,
            debugger_events: SelectAll::new(),
            breakpoints: HashMap::new(),
            syn_loader,
            theme_loader,
            last_theme: None,
            last_selection: None,
            registers: Registers::default(),
            status_msg: None,
            autoinfo: None,
            idle_timer: Box::pin(sleep(conf.idle_timeout)),
            redraw_timer: Box::pin(sleep(Duration::MAX)),
            last_motion: None,
            last_completion: None,
            config,
            auto_pairs,
            exit_code: 0,
            config_events: unbounded_channel(),
            needs_redraw: false,
            cursor_cache: Cell::new(None),
            completion_request_handle: None,
        }
    }

    pub fn popup_border(&self) -> bool {
        self.config().popup_border == PopupBorderConfig::All
            || self.config().popup_border == PopupBorderConfig::Popup
    }

    pub fn menu_border(&self) -> bool {
        self.config().popup_border == PopupBorderConfig::All
            || self.config().popup_border == PopupBorderConfig::Menu
    }

    pub fn apply_motion<F: Fn(&mut Self) + 'static>(&mut self, motion: F) {
        motion(self);
        self.last_motion = Some(Box::new(motion));
    }

    pub fn repeat_last_motion(&mut self, count: usize) {
        if let Some(motion) = self.last_motion.take() {
            for _ in 0..count {
                motion(self);
            }
            self.last_motion = Some(motion);
        }
    }
    /// Current editing mode for the [`Editor`].
    pub fn mode(&self) -> Mode {
        self.mode
    }

    pub fn config(&self) -> DynGuard<Config> {
        self.config.load()
    }

    /// Call if the config has changed to let the editor update all
    /// relevant members.
    pub fn refresh_config(&mut self) {
        let config = self.config();
        self.auto_pairs = (&config.auto_pairs).into();
        self.reset_idle_timer();
        self._refresh();
    }

    pub fn clear_idle_timer(&mut self) {
        // equivalent to internal Instant::far_future() (30 years)
        self.idle_timer
            .as_mut()
            .reset(Instant::now() + Duration::from_secs(86400 * 365 * 30));
    }

    pub fn reset_idle_timer(&mut self) {
        let config = self.config();
        self.idle_timer
            .as_mut()
            .reset(Instant::now() + config.idle_timeout);
    }

    pub fn clear_status(&mut self) {
        self.status_msg = None;
    }

    #[inline]
    pub fn set_status<T: Into<Cow<'static, str>>>(&mut self, status: T) {
        let status = status.into();
        log::debug!("editor status: {}", status);
        self.status_msg = Some((status, Severity::Info));
    }

    #[inline]
    pub fn set_error<T: Into<Cow<'static, str>>>(&mut self, error: T) {
        let error = error.into();
        log::error!("editor error: {}", error);
        self.status_msg = Some((error, Severity::Error));
    }

    #[inline]
    pub fn get_status(&self) -> Option<(&Cow<'static, str>, &Severity)> {
        self.status_msg.as_ref().map(|(status, sev)| (status, sev))
    }

    /// Returns true if the current status is an error
    #[inline]
    pub fn is_err(&self) -> bool {
        self.status_msg
            .as_ref()
            .map(|(_, sev)| *sev == Severity::Error)
            .unwrap_or(false)
    }

    pub fn unset_theme_preview(&mut self) {
        if let Some(last_theme) = self.last_theme.take() {
            self.set_theme(last_theme);
        }
        // None likely occurs when the user types ":theme" and then exits before previewing
    }

    pub fn set_theme_preview(&mut self, theme: Theme) {
        self.set_theme_impl(theme, ThemeAction::Preview);
    }

    pub fn set_theme(&mut self, theme: Theme) {
        self.set_theme_impl(theme, ThemeAction::Set);
    }

    fn set_theme_impl(&mut self, theme: Theme, preview: ThemeAction) {
        // `ui.selection` is the only scope required to be able to render a theme.
        if theme.find_scope_index_exact("ui.selection").is_none() {
            self.set_error("Invalid theme: `ui.selection` required");
            return;
        }

        let scopes = theme.scopes();
        self.syn_loader.set_scopes(scopes.to_vec());

        match preview {
            ThemeAction::Preview => {
                let last_theme = std::mem::replace(&mut self.theme, theme);
                // only insert on first preview: this will be the last theme the user has saved
                self.last_theme.get_or_insert(last_theme);
            }
            ThemeAction::Set => {
                self.last_theme = None;
                self.theme = theme;
            }
        }

        self._refresh();
    }

    #[inline]
    pub fn language_server_by_id(&self, language_server_id: usize) -> Option<&helix_lsp::Client> {
        self.language_servers.get_by_id(language_server_id)
    }

    /// Refreshes the language server for a given document
    pub fn refresh_language_servers(&mut self, doc_id: DocumentId) {
        self.launch_language_servers(doc_id)
    }

    /// Launch a language server for a given document
    fn launch_language_servers(&mut self, doc_id: DocumentId) {
        if !self.config().lsp.enable {
            return;
        }
        // if doc doesn't have a URL it's a scratch buffer, ignore it
        let Some(doc) = self.documents.get_mut(&doc_id) else {
            return;
        };
        let Some(doc_url) = doc.url() else {
            return;
        };
        let (lang, path) = (doc.language.clone(), doc.path().cloned());
        let config = doc.config.load();
        let root_dirs = &config.workspace_lsp_roots;

        // store only successfully started language servers
        let language_servers = lang.as_ref().map_or_else(HashMap::default, |language| {
            self.language_servers
                .get(language, path.as_ref(), root_dirs, config.lsp.snippets)
                .filter_map(|(lang, client)| match client {
                    Ok(client) => Some((lang, client)),
                    Err(err) => {
                        log::error!(
                            "Failed to initialize the language servers for  `{}` {{ {} }}",
                            lang,
                            err
                        );
                        None
                    }
                })
                .collect::<HashMap<_, _>>()
        });

        if language_servers.is_empty() {
            return;
        }

        let language_id = doc.language_id().map(ToOwned::to_owned).unwrap_or_default();

        // only spawn new language servers if the servers aren't the same
        let doc_language_servers_not_in_registry =
            doc.language_servers.iter().filter(|(name, doc_ls)| {
                language_servers
                    .get(*name)
                    .map_or(true, |ls| ls.id() != doc_ls.id())
            });

        for (_, language_server) in doc_language_servers_not_in_registry {
            tokio::spawn(language_server.text_document_did_close(doc.identifier()));
        }

        let language_servers_not_in_doc = language_servers.iter().filter(|(name, ls)| {
            doc.language_servers
                .get(*name)
                .map_or(true, |doc_ls| ls.id() != doc_ls.id())
        });

        for (_, language_server) in language_servers_not_in_doc {
            // TODO: this now races with on_init code if the init happens too quickly
            tokio::spawn(language_server.text_document_did_open(
                doc_url.clone(),
                doc.version(),
                doc.text(),
                language_id.clone(),
            ));
        }

        doc.language_servers = language_servers;
    }

    fn _refresh(&mut self) {
        let config = self.config();

        // Reset the inlay hints annotations *before* updating the views, that way we ensure they
        // will disappear during the `.sync_change(doc)` call below.
        //
        // We can't simply check this config when rendering because inlay hints are only parts of
        // the possible annotations, and others could still be active, so we need to selectively
        // drop the inlay hints.
        if !config.lsp.display_inlay_hints {
            for doc in self.documents_mut() {
                doc.reset_all_inlay_hints();
            }
        }

        for (view, _) in self.tree.views_mut() {
            let doc = doc_mut!(self, &view.doc);
            view.sync_changes(doc);
            view.gutters = config.gutters.clone();
            view.ensure_cursor_in_view(doc, config.scrolloff)
        }
    }

    fn replace_document_in_view(&mut self, current_view: ViewId, doc_id: DocumentId) {
        let view = self.tree.get_mut(current_view);
        view.doc = doc_id;
        view.offset = ViewPosition::default();

        let doc = doc_mut!(self, &doc_id);
        doc.ensure_view_init(view.id);
        view.sync_changes(doc);
        doc.mark_as_focused();

        align_view(doc, view, Align::Center);
    }

    pub fn switch(&mut self, id: DocumentId, action: Action) {
        use crate::tree::Layout;

        if !self.documents.contains_key(&id) {
            log::error!("cannot switch to document that does not exist (anymore)");
            return;
        }

        self.enter_normal_mode();

        match action {
            Action::Replace => {
                let (view, doc) = current_ref!(self);
                // If the current view is an empty scratch buffer and is not displayed in any other views, delete it.
                // Boolean value is determined before the call to `view_mut` because the operation requires a borrow
                // of `self.tree`, which is mutably borrowed when `view_mut` is called.
                let remove_empty_scratch = !doc.is_modified()
                    // If the buffer has no path and is not modified, it is an empty scratch buffer.
                    && doc.path().is_none()
                    // If the buffer we are changing to is not this buffer
                    && id != doc.id
                    // Ensure the buffer is not displayed in any other splits.
                    && !self
                        .tree
                        .traverse()
                        .any(|(_, v)| v.doc == doc.id && v.id != view.id);

                let (view, doc) = current!(self);
                let view_id = view.id;

                // Append any outstanding changes to history in the old document.
                doc.append_changes_to_history(view);

                if remove_empty_scratch {
                    // Copy `doc.id` into a variable before calling `self.documents.remove`, which requires a mutable
                    // borrow, invalidating direct access to `doc.id`.
                    let id = doc.id;
                    self.documents.remove(&id);

                    // Remove the scratch buffer from any jumplists
                    for (view, _) in self.tree.views_mut() {
                        view.remove_document(&id);
                    }
                } else {
                    let jump = (view.doc, doc.selection(view.id).clone());
                    view.jumps.push(jump);
                    // Set last accessed doc if it is a different document
                    if doc.id != id {
                        view.add_to_history(view.doc);
                        // Set last modified doc if modified and last modified doc is different
                        if std::mem::take(&mut doc.modified_since_accessed)
                            && view.last_modified_docs[0] != Some(view.doc)
                        {
                            view.last_modified_docs = [Some(view.doc), view.last_modified_docs[0]];
                        }
                    }
                }

                self.replace_document_in_view(view_id, id);

                return;
            }
            Action::Load => {
                let view_id = view!(self).id;
                let doc = doc_mut!(self, &id);
                doc.ensure_view_init(view_id);
                doc.mark_as_focused();
                return;
            }
            Action::HorizontalSplit | Action::VerticalSplit => {
                // copy the current view, unless there is no view yet
                let view = self
                    .tree
                    .try_get(self.tree.focus)
                    .filter(|v| id == v.doc) // Different Document
                    .cloned()
                    .unwrap_or_else(|| View::new(id, self.config().gutters.clone()));
                let view_id = self.tree.split(
                    view,
                    match action {
                        Action::HorizontalSplit => Layout::Horizontal,
                        Action::VerticalSplit => Layout::Vertical,
                        _ => unreachable!(),
                    },
                );
                // initialize selection for view
                let doc = doc_mut!(self, &id);
                doc.ensure_view_init(view_id);
                doc.mark_as_focused();
            }
        }

        self._refresh();
    }

    /// Generate an id for a new document and register it.
    fn new_document(&mut self, mut doc: Document) -> DocumentId {
        let id = self.next_document_id;
        // Safety: adding 1 from 1 is fine, probably impossible to reach usize max
        self.next_document_id =
            DocumentId(unsafe { NonZeroUsize::new_unchecked(self.next_document_id.0.get() + 1) });
        doc.id = id;
        self.documents.insert(id, doc);

        let (save_sender, save_receiver) = tokio::sync::mpsc::unbounded_channel();
        self.saves.insert(id, save_sender);

        let stream = UnboundedReceiverStream::new(save_receiver).flatten();
        self.save_queue.push(stream);

        id
    }

    fn new_file_from_document(&mut self, action: Action, doc: Document) -> DocumentId {
        let id = self.new_document(doc);
        self.switch(id, action);
        id
    }

    pub fn new_file(&mut self, action: Action) -> DocumentId {
        self.new_file_from_document(action, Document::default(self.config.clone()))
    }

    pub fn new_file_from_stdin(&mut self, action: Action) -> Result<DocumentId, Error> {
        let (stdin, encoding, has_bom) = crate::document::read_to_string(&mut stdin(), None)?;
        let doc = Document::from(
            helix_core::Rope::default(),
            Some((encoding, has_bom)),
            self.config.clone(),
        );
        let doc_id = self.new_file_from_document(action, doc);
        let doc = doc_mut!(self, &doc_id);
        let view = view_mut!(self);
        doc.ensure_view_init(view.id);
        let transaction =
            helix_core::Transaction::insert(doc.text(), doc.selection(view.id), stdin.into())
                .with_selection(Selection::point(0));
        doc.apply(&transaction, view.id);
        doc.append_changes_to_history(view);
        Ok(doc_id)
    }

    // ??? possible use for integration tests
    pub fn open(&mut self, path: &Path, action: Action) -> Result<DocumentId, Error> {
        let path = helix_core::path::get_canonicalized_path(path);
        let id = self.document_by_path(&path).map(|doc| doc.id);

        let id = if let Some(id) = id {
            id
        } else {
            let mut doc = Document::open(
                &path,
                None,
                Some(self.syn_loader.clone()),
                self.config.clone(),
            )?;

            let diagnostics =
                Editor::doc_diagnostics(&self.language_servers, &self.diagnostics, &doc);
            doc.replace_diagnostics(diagnostics, &[], None);

            if let Some(diff_base) = self.diff_providers.get_diff_base(&path) {
                doc.set_diff_base(diff_base);
            }
            doc.set_version_control_head(self.diff_providers.get_current_head_name(&path));

            let id = self.new_document(doc);
            self.launch_language_servers(id);

            id
        };

        self.switch(id, action);
        Ok(id)
    }

    pub fn close(&mut self, id: ViewId) {
        // Remove selections for the closed view on all documents.
        for doc in self.documents_mut() {
            doc.remove_view(id);
        }
        self.tree.remove(id);
        self._refresh();
    }

    pub fn close_document(&mut self, doc_id: DocumentId, force: bool) -> Result<(), CloseError> {
        let doc = match self.documents.get_mut(&doc_id) {
            Some(doc) => doc,
            None => return Err(CloseError::DoesNotExist),
        };
        if !force && doc.is_modified() {
            return Err(CloseError::BufferModified(doc.display_name().into_owned()));
        }

        // This will also disallow any follow-up writes
        self.saves.remove(&doc_id);

        for language_server in doc.language_servers() {
            // TODO: track error
            tokio::spawn(language_server.text_document_did_close(doc.identifier()));
        }

        enum Action {
            Close(ViewId),
            ReplaceDoc(ViewId, DocumentId),
        }

        let actions: Vec<Action> = self
            .tree
            .views_mut()
            .filter_map(|(view, _focus)| {
                view.remove_document(&doc_id);

                if view.doc == doc_id {
                    // something was previously open in the view, switch to previous doc
                    if let Some(prev_doc) = view.docs_access_history.pop() {
                        Some(Action::ReplaceDoc(view.id, prev_doc))
                    } else {
                        // only the document that is being closed was in the view, close it
                        Some(Action::Close(view.id))
                    }
                } else {
                    None
                }
            })
            .collect();

        for action in actions {
            match action {
                Action::Close(view_id) => {
                    self.close(view_id);
                }
                Action::ReplaceDoc(view_id, doc_id) => {
                    self.replace_document_in_view(view_id, doc_id);
                }
            }
        }

        self.documents.remove(&doc_id);

        // If the document we removed was visible in all views, we will have no more views. We don't
        // want to close the editor just for a simple buffer close, so we need to create a new view
        // containing either an existing document, or a brand new document.
        if self.tree.views().next().is_none() {
            let doc_id = self
                .documents
                .iter()
                .map(|(&doc_id, _)| doc_id)
                .next()
                .unwrap_or_else(|| self.new_document(Document::default(self.config.clone())));
            let view = View::new(doc_id, self.config().gutters.clone());
            let view_id = self.tree.insert(view);
            let doc = doc_mut!(self, &doc_id);
            doc.ensure_view_init(view_id);
            doc.mark_as_focused();
        }

        self._refresh();

        Ok(())
    }

    pub fn save<P: Into<PathBuf>>(
        &mut self,
        doc_id: DocumentId,
        path: Option<P>,
        force: bool,
    ) -> anyhow::Result<()> {
        // convert a channel of futures to pipe into main queue one by one
        // via stream.then() ? then push into main future

        let path = path.map(|path| path.into());
        let doc = doc_mut!(self, &doc_id);
        let doc_save_future = doc.save(path, force)?;

        // When a file is written to, notify the file event handler.
        // Note: This can be removed once proper file watching is implemented.
        let handler = self.language_servers.file_event_handler.clone();
        let future = async move {
            let res = doc_save_future.await;
            if let Ok(event) = &res {
                handler.file_changed(event.path.clone());
            }
            res
        };

        use futures_util::stream;

        self.saves
            .get(&doc_id)
            .ok_or_else(|| anyhow::format_err!("saves are closed for this document!"))?
            .send(stream::once(Box::pin(future)))
            .map_err(|err| anyhow!("failed to send save event: {}", err))?;

        self.write_count += 1;

        Ok(())
    }

    pub fn resize(&mut self, area: Rect) {
        if self.tree.resize(area) {
            self._refresh();
        };
    }

    pub fn focus(&mut self, view_id: ViewId) {
        let prev_id = std::mem::replace(&mut self.tree.focus, view_id);

        // if leaving the view: mode should reset and the cursor should be
        // within view
        if prev_id != view_id {
            self.enter_normal_mode();
            self.ensure_cursor_in_view(view_id);

            // Update jumplist selections with new document changes.
            for (view, _focused) in self.tree.views_mut() {
                let doc = doc_mut!(self, &view.doc);
                view.sync_changes(doc);
            }
        }

        let view = view!(self, view_id);
        let doc = doc_mut!(self, &view.doc);
        doc.mark_as_focused();
    }

    pub fn focus_next(&mut self) {
        self.focus(self.tree.next());
    }

    pub fn focus_prev(&mut self) {
        self.focus(self.tree.prev());
    }

    pub fn focus_direction(&mut self, direction: tree::Direction) {
        let current_view = self.tree.focus;
        if let Some(id) = self.tree.find_split_in_direction(current_view, direction) {
            self.focus(id)
        }
    }

    pub fn swap_split_in_direction(&mut self, direction: tree::Direction) {
        self.tree.swap_split_in_direction(direction);
    }

    pub fn transpose_view(&mut self) {
        self.tree.transpose();
    }

    pub fn should_close(&self) -> bool {
        self.tree.is_empty()
    }

    pub fn ensure_cursor_in_view(&mut self, id: ViewId) {
        let config = self.config();
        let view = self.tree.get_mut(id);
        let doc = &self.documents[&view.doc];
        view.ensure_cursor_in_view(doc, config.scrolloff)
    }

    #[inline]
    pub fn document(&self, id: DocumentId) -> Option<&Document> {
        self.documents.get(&id)
    }

    #[inline]
    pub fn document_mut(&mut self, id: DocumentId) -> Option<&mut Document> {
        self.documents.get_mut(&id)
    }

    #[inline]
    pub fn documents(&self) -> impl Iterator<Item = &Document> {
        self.documents.values()
    }

    #[inline]
    pub fn documents_mut(&mut self) -> impl Iterator<Item = &mut Document> {
        self.documents.values_mut()
    }

    pub fn document_by_path<P: AsRef<Path>>(&self, path: P) -> Option<&Document> {
        self.documents()
            .find(|doc| doc.path().map(|p| p == path.as_ref()).unwrap_or(false))
    }

    pub fn document_by_path_mut<P: AsRef<Path>>(&mut self, path: P) -> Option<&mut Document> {
        self.documents_mut()
            .find(|doc| doc.path().map(|p| p == path.as_ref()).unwrap_or(false))
    }

    /// Returns all supported diagnostics for the document
    pub fn doc_diagnostics<'a>(
        language_servers: &'a helix_lsp::Registry,
        diagnostics: &'a BTreeMap<lsp::Url, Vec<(lsp::Diagnostic, usize)>>,
        document: &Document,
    ) -> impl Iterator<Item = helix_core::Diagnostic> + 'a {
        Editor::doc_diagnostics_with_filter(language_servers, diagnostics, document, |_, _| true)
    }

    /// Returns all supported diagnostics for the document
    /// filtered by `filter` which is invocated with the raw `lsp::Diagnostic` and the language server id it came from
    pub fn doc_diagnostics_with_filter<'a>(
        language_servers: &'a helix_lsp::Registry,
        diagnostics: &'a BTreeMap<lsp::Url, Vec<(lsp::Diagnostic, usize)>>,

        document: &Document,
        filter: impl Fn(&lsp::Diagnostic, usize) -> bool + 'a,
    ) -> impl Iterator<Item = helix_core::Diagnostic> + 'a {
        let text = document.text().clone();
        let language_config = document.language.clone();
        document
            .path()
            .and_then(|path| url::Url::from_file_path(path).ok()) // TODO log error?
            .and_then(|uri| diagnostics.get(&uri))
            .map(|diags| {
                diags.iter().filter_map(move |(diagnostic, lsp_id)| {
                    let ls = language_servers.get_by_id(*lsp_id)?;
                    language_config
                        .as_ref()
                        .and_then(|c| {
                            c.language_servers.iter().find(|features| {
                                features.name == ls.name()
                                    && features.has_feature(LanguageServerFeature::Diagnostics)
                            })
                        })
                        .and_then(|_| {
                            if filter(diagnostic, *lsp_id) {
                                Document::lsp_diagnostic_to_diagnostic(
                                    &text,
                                    language_config.as_deref(),
                                    diagnostic,
                                    *lsp_id,
                                    ls.offset_encoding(),
                                )
                            } else {
                                None
                            }
                        })
                })
            })
            .into_iter()
            .flatten()
    }

    /// Gets the primary cursor position in screen coordinates,
    /// or `None` if the primary cursor is not visible on screen.
    pub fn cursor(&self) -> (Option<Position>, CursorKind) {
        let config = self.config();
        let (view, doc) = current_ref!(self);
        let cursor = doc
            .selection(view.id)
            .primary()
            .cursor(doc.text().slice(..));
        let pos = self
            .cursor_cache
            .get()
            .unwrap_or_else(|| view.screen_coords_at_pos(doc, doc.text().slice(..), cursor));
        if let Some(mut pos) = pos {
            let inner = view.inner_area(doc);
            pos.col += inner.x as usize;
            pos.row += inner.y as usize;
            let cursorkind = config.cursor_shape.from_mode(self.mode);
            (Some(pos), cursorkind)
        } else {
            (None, CursorKind::default())
        }
    }

    /// Closes language servers with timeout. The default timeout is 10000 ms, use
    /// `timeout` parameter to override this.
    pub async fn close_language_servers(
        &self,
        timeout: Option<u64>,
    ) -> Result<(), tokio::time::error::Elapsed> {
        // Remove all language servers from the file event handler.
        // Note: this is non-blocking.
        for client in self.language_servers.iter_clients() {
            self.language_servers
                .file_event_handler
                .remove_client(client.id());
        }

        tokio::time::timeout(
            Duration::from_millis(timeout.unwrap_or(3000)),
            future::join_all(
                self.language_servers
                    .iter_clients()
                    .map(|client| client.force_shutdown()),
            ),
        )
        .await
        .map(|_| ())
    }

    pub async fn wait_event(&mut self) -> EditorEvent {
        // the loop only runs once or twice and would be better implemented with a recursion + const generic
        // however due to limitations with async functions that can not be implemented right now
        loop {
            tokio::select! {
                biased;

                Some(event) = self.save_queue.next() => {
                    self.write_count -= 1;
                    return EditorEvent::DocumentSaved(event)
                }
                Some(config_event) = self.config_events.1.recv() => {
                    return EditorEvent::ConfigEvent(config_event)
                }
                Some(message) = self.language_servers.incoming.next() => {
                    return EditorEvent::LanguageServerMessage(message)
                }
                Some(event) = self.debugger_events.next() => {
                    return EditorEvent::DebuggerEvent(event)
                }

                _ = helix_event::redraw_requested() => {
                    if  !self.needs_redraw{
                        self.needs_redraw = true;
                        let timeout = Instant::now() + Duration::from_millis(33);
                        if timeout < self.idle_timer.deadline() && timeout < self.redraw_timer.deadline(){
                            self.redraw_timer.as_mut().reset(timeout)
                        }
                    }
                }

                _ = &mut self.redraw_timer  => {
                    self.redraw_timer.as_mut().reset(Instant::now() + Duration::from_secs(86400 * 365 * 30));
                    return EditorEvent::Redraw
                }
                _ = &mut self.idle_timer  => {
                    return EditorEvent::IdleTimer
                }
            }
        }
    }

    pub async fn flush_writes(&mut self) -> anyhow::Result<()> {
        while self.write_count > 0 {
            if let Some(save_event) = self.save_queue.next().await {
                self.write_count -= 1;

                let save_event = match save_event {
                    Ok(event) => event,
                    Err(err) => {
                        self.set_error(err.to_string());
                        bail!(err);
                    }
                };

                let doc = doc_mut!(self, &save_event.doc_id);
                doc.set_last_saved_revision(save_event.revision);
            }
        }

        Ok(())
    }

    /// Switches the editor into normal mode.
    pub fn enter_normal_mode(&mut self) {
        use helix_core::{graphemes, Range};

        if self.mode == Mode::Normal {
            return;
        }

        self.mode = Mode::Normal;
        let (view, doc) = current!(self);

        try_restore_indent(doc, view);

        // if leaving append mode, move cursor back by 1
        if doc.restore_cursor {
            let text = doc.text().slice(..);
            let selection = doc.selection(view.id).clone().transform(|range| {
                Range::new(
                    range.from(),
                    graphemes::prev_grapheme_boundary(text, range.to()),
                )
            });

            doc.set_selection(view.id, selection);
            doc.restore_cursor = false;
        }
    }

    pub fn current_stack_frame(&self) -> Option<&StackFrame> {
        self.debugger
            .as_ref()
            .and_then(|debugger| debugger.current_stack_frame())
    }

    /// Returns the id of a view that this doc contains a selection for,
    /// making sure it is synced with the current changes
    /// if possible or there are no selections returns current_view
    /// otherwise uses an arbitrary view
    pub fn get_synced_view_id(&mut self, id: DocumentId) -> ViewId {
        let current_view = view_mut!(self);
        let doc = self.documents.get_mut(&id).unwrap();
        if doc.selections().contains_key(&current_view.id) {
            // only need to sync current view if this is not the current doc
            if current_view.doc != id {
                current_view.sync_changes(doc);
            }
            current_view.id
        } else if let Some(view_id) = doc.selections().keys().next() {
            let view_id = *view_id;
            let view = self.tree.get_mut(view_id);
            view.sync_changes(doc);
            view_id
        } else {
            doc.ensure_view_init(current_view.id);
            current_view.id
        }
    }
}

fn try_restore_indent(doc: &mut Document, view: &mut View) {
    use helix_core::{
        chars::char_is_whitespace, line_ending::line_end_char_index, Operation, Transaction,
    };

    fn inserted_a_new_blank_line(changes: &[Operation], pos: usize, line_end_pos: usize) -> bool {
        if let [Operation::Retain(move_pos), Operation::Insert(ref inserted_str), Operation::Retain(_)] =
            changes
        {
            move_pos + inserted_str.len() == pos
                && inserted_str.starts_with('\n')
                && inserted_str.chars().skip(1).all(char_is_whitespace)
                && pos == line_end_pos // ensure no characters exists after current position
        } else {
            false
        }
    }

    let doc_changes = doc.changes().changes();
    let text = doc.text().slice(..);
    let range = doc.selection(view.id).primary();
    let pos = range.cursor(text);
    let line_end_pos = line_end_char_index(&text, range.cursor_line(text));

    if inserted_a_new_blank_line(doc_changes, pos, line_end_pos) {
        // Removes tailing whitespaces.
        let transaction =
            Transaction::change_by_selection(doc.text(), doc.selection(view.id), |range| {
                let line_start_pos = text.line_to_char(range.cursor_line(text));
                (line_start_pos, pos, None)
            });
        doc.apply(&transaction, view.id);
    }
}