use crate::{
    align_view,
    clipboard::{get_clipboard_provider, ClipboardProvider},
    document::{DocumentSavedEventFuture, DocumentSavedEventResult, Mode},
    graphics::{CursorKind, Rect},
    info::Info,
    input::KeyEvent,
    theme::{self, Theme},
    tree::{self, Tree},
    view::ViewPosition,
    Align, Document, DocumentId, View, ViewId,
};
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},
        Notify, RwLock,
    },
    time::{sleep, Duration, Instant, Sleep},
};

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

pub use helix_core::diagnostic::Severity;
pub use helix_core::register::Registers;
use helix_core::Position;
use helix_core::{
    auto_pairs::AutoPairs,
    syntax::{self, AutoPairConfig},
    Change,
};
use helix_dap as dap;
use helix_lsp::lsp;

use serde::{ser::SerializeMap, Deserialize, Deserializer, Serialize, Serializer};

use arc_swap::access::{DynAccess, DynGuard};

fn deserialize_duration_millis<'de, D>(deserializer: D) -> Result<Duration, D::Error>
where
    D: serde::Deserializer<'de>,
{
    let millis = u64::deserialize(deserializer)?;
    Ok(Duration::from_millis(millis))
}

fn serialize_duration_millis<S>(duration: &Duration, serializer: S) -> Result<S::Ok, S::Error>
where
    S: Serializer,
{
    serializer.serialize_u64(
        duration
            .as_millis()
            .try_into()
            .map_err(|_| serde::ser::Error::custom("duration value overflowed u64"))?,
    )
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
pub struct GutterConfig {
    /// Gutter Layout
    pub layout: Vec<GutterType>,
    /// Options specific to the "line-numbers" gutter
    pub line_numbers: GutterLineNumbersConfig,
}

impl Default for GutterConfig {
    fn default() -> Self {
        Self {
            layout: vec![
                GutterType::Diagnostics,
                GutterType::Spacer,
                GutterType::LineNumbers,
                GutterType::Spacer,
                GutterType::Diff,
            ],
            line_numbers: GutterLineNumbersConfig::default(),
        }
    }
}

impl From<Vec<GutterType>> for GutterConfig {
    fn from(x: Vec<GutterType>) -> Self {
        GutterConfig {
            layout: x,
            ..Default::default()
        }
    }
}

fn deserialize_gutter_seq_or_struct<'de, D>(deserializer: D) -> Result<GutterConfig, D::Error>
where
    D: Deserializer<'de>,
{
    struct GutterVisitor;

    impl<'de> serde::de::Visitor<'de> for GutterVisitor {
        type Value = GutterConfig;

        fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
            write!(
                formatter,
                "an array of gutter names or a detailed gutter configuration"
            )
        }

        fn visit_seq<S>(self, mut seq: S) -> Result<Self::Value, S::Error>
        where
            S: serde::de::SeqAccess<'de>,
        {
            let mut gutters = Vec::new();
            while let Some(gutter) = seq.next_element::<String>()? {
                gutters.push(
                    gutter
                        .parse::<GutterType>()
                        .map_err(serde::de::Error::custom)?,
                )
            }

            Ok(gutters.into())
        }

        fn visit_map<M>(self, map: M) -> Result<Self::Value, M::Error>
        where
            M: serde::de::MapAccess<'de>,
        {
            let deserializer = serde::de::value::MapAccessDeserializer::new(map);
            Deserialize::deserialize(deserializer)
        }
    }

    deserializer.deserialize_any(GutterVisitor)
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
pub struct GutterLineNumbersConfig {
    /// Minimum number of characters to use for line number gutter. Defaults to 3.
    pub min_width: usize,
}

impl Default for GutterLineNumbersConfig {
    fn default() -> Self {
        Self { min_width: 3 }
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
pub struct FilePickerConfig {
    /// IgnoreOptions
    /// Enables ignoring hidden files.
    /// Whether to hide hidden files in file picker and global search results. Defaults to true.
    pub hidden: bool,
    /// Enables following symlinks.
    /// Whether to follow symbolic links in file picker and file or directory completions. Defaults to true.
    pub follow_symlinks: bool,
    /// Hides symlinks that point into the current directory. Defaults to true.
    pub deduplicate_links: bool,
    /// Enables reading ignore files from parent directories. Defaults to true.
    pub parents: bool,
    /// Enables reading `.ignore` files.
    /// Whether to hide files listed in .ignore in file picker and global search results. Defaults to true.
    pub ignore: bool,
    /// Enables reading `.gitignore` files.
    /// Whether to hide files listed in .gitignore in file picker and global search results. Defaults to true.
    pub git_ignore: bool,
    /// Enables reading global .gitignore, whose path is specified in git's config: `core.excludefile` option.
    /// Whether to hide files listed in global .gitignore in file picker and global search results. Defaults to true.
    pub git_global: bool,
    /// Enables reading `.git/info/exclude` files.
    /// Whether to hide files listed in .git/info/exclude in file picker and global search results. Defaults to true.
    pub git_exclude: bool,
    /// WalkBuilder options
    /// Maximum Depth to recurse directories in file picker and global search. Defaults to `None`.
    pub max_depth: Option<usize>,
}

impl Default for FilePickerConfig {
    fn default() -> Self {
        Self {
            hidden: true,
            follow_symlinks: true,
            deduplicate_links: true,
            parents: true,
            ignore: true,
            git_ignore: true,
            git_global: true,
            git_exclude: true,
            max_depth: None,
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
pub struct Config {
    /// Padding to keep between the edge of the screen and the cursor when scrolling. Defaults to 5.
    pub scrolloff: usize,
    /// Number of lines to scroll at once. Defaults to 3
    pub scroll_lines: isize,
    /// Mouse support. Defaults to true.
    pub mouse: bool,
    /// Shell to use for shell commands. Defaults to ["cmd", "/C"] on Windows and ["sh", "-c"] otherwise.
    pub shell: Vec<String>,
    /// Line number mode.
    pub line_number: LineNumber,
    /// Highlight the lines cursors are currently on. Defaults to false.
    pub cursorline: bool,
    /// Highlight the columns cursors are currently on. Defaults to false.
    pub cursorcolumn: bool,
    #[serde(deserialize_with = "deserialize_gutter_seq_or_struct")]
    pub gutters: GutterConfig,
    /// Middle click paste support. Defaults to true.
    pub middle_click_paste: bool,
    /// Automatic insertion of pairs to parentheses, brackets,
    /// etc. Optionally, this can be a list of 2-tuples to specify a
    /// global list of characters to pair. Defaults to true.
    pub auto_pairs: AutoPairConfig,
    /// Automatic auto-completion, automatically pop up without user trigger. Defaults to true.
    pub auto_completion: bool,
    /// Automatic formatting on save. Defaults to true.
    pub auto_format: bool,
    /// Automatic save on focus lost. Defaults to false.
    pub auto_save: bool,
    /// Time in milliseconds since last keypress before idle timers trigger.
    /// Used for autocompletion, set to 0 for instant. Defaults to 400ms.
    #[serde(
        serialize_with = "serialize_duration_millis",
        deserialize_with = "deserialize_duration_millis"
    )]
    pub idle_timeout: Duration,
    pub completion_trigger_len: u8,
    /// Whether to display infoboxes. Defaults to true.
    pub auto_info: bool,
    pub file_picker: FilePickerConfig,
    /// Configuration of the statusline elements
    pub statusline: StatusLineConfig,
    /// Shape for cursor in each mode
    pub cursor_shape: CursorShapeConfig,
    /// Set to `true` to override automatic detection of terminal truecolor support in the event of a false negative. Defaults to `false`.
    pub true_color: bool,
    /// Search configuration.
    #[serde(default)]
    pub search: SearchConfig,
    pub lsp: LspConfig,
    pub terminal: Option<TerminalConfig>,
    /// Column numbers at which to draw the rulers. Default to `[]`, meaning no rulers.
    pub rulers: Vec<u16>,
    #[serde(default)]
    pub whitespace: WhitespaceConfig,
    /// Persistently display open buffers along the top
    pub bufferline: BufferLine,
    /// Vertical indent width guides.
    pub indent_guides: IndentGuidesConfig,
    /// Whether to color modes with different colors. Defaults to `false`.
    pub color_modes: bool,
    pub soft_wrap: SoftWrap,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(default, rename_all = "kebab-case", deny_unknown_fields)]
pub struct SoftWrap {
    /// Soft wrap lines that exceed viewport width. Default to off
    pub enable: bool,
    /// Maximum space left free at the end of the line.
    /// This space is used to wrap text at word boundaries. If that is not possible within this limit
    /// the word is simply split at the end of the line.
    ///
    /// This is automatically hard-limited to a quarter of the viewport to ensure correct display on small views.
    ///
    /// Default to 20
    pub max_wrap: u16,
    /// Maximum number of indentation that can be carried over from the previous line when softwrapping.
    /// If a line is indented further then this limit it is rendered at the start of the viewport instead.
    ///
    /// This is automatically hard-limited to a quarter of the viewport to ensure correct display on small views.
    ///
    /// Default to 40
    pub max_indent_retain: u16,
    /// Indicator placed at the beginning of softwrapped lines
    ///
    /// Defaults to ↪
    pub wrap_indicator: String,
}

impl Default for SoftWrap {
    fn default() -> Self {
        SoftWrap {
            enable: false,
            max_wrap: 20,
            max_indent_retain: 40,
            wrap_indicator: "↪ ".into(),
        }
    }
}

#[derive(Debug, Default, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(default, rename_all = "kebab-case", deny_unknown_fields)]
pub struct TerminalConfig {
    pub command: String,
    #[serde(default)]
    #[serde(skip_serializing_if = "Vec::is_empty")]
    pub args: Vec<String>,
}

#[cfg(windows)]
pub fn get_terminal_provider() -> Option<TerminalConfig> {
    use crate::env::binary_exists;

    if binary_exists("wt") {
        return Some(TerminalConfig {
            command: "wt".to_string(),
            args: vec![
                "new-tab".to_string(),
                "--title".to_string(),
                "DEBUG".to_string(),
                "cmd".to_string(),
                "/C".to_string(),
            ],
        });
    }

    Some(TerminalConfig {
        command: "conhost".to_string(),
        args: vec!["cmd".to_string(), "/C".to_string()],
    })
}

#[cfg(not(any(windows, target_os = "wasm32")))]
pub fn get_terminal_provider() -> Option<TerminalConfig> {
    use crate::env::{binary_exists, env_var_is_set};

    if env_var_is_set("TMUX") && binary_exists("tmux") {
        return Some(TerminalConfig {
            command: "tmux".to_string(),
            args: vec!["split-window".to_string()],
        });
    }

    if env_var_is_set("WEZTERM_UNIX_SOCKET") && binary_exists("wezterm") {
        return Some(TerminalConfig {
            command: "wezterm".to_string(),
            args: vec!["cli".to_string(), "split-pane".to_string()],
        });
    }

    None
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(default, rename_all = "kebab-case", deny_unknown_fields)]
pub struct LspConfig {
    /// Enables LSP
    pub enable: bool,
    /// Display LSP progress messages below statusline
    pub display_messages: bool,
    /// Enable automatic pop up of signature help (parameter hints)
    pub auto_signature_help: bool,
    /// Display docs under signature help popup
    pub display_signature_help_docs: bool,
}

impl Default for LspConfig {
    fn default() -> Self {
        Self {
            enable: true,
            display_messages: false,
            auto_signature_help: true,
            display_signature_help_docs: true,
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
pub struct SearchConfig {
    /// Smart case: Case insensitive searching unless pattern contains upper case characters. Defaults to true.
    pub smart_case: bool,
    /// Whether the search should wrap after depleting the matches. Default to true.
    pub wrap_around: bool,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
pub struct StatusLineConfig {
    pub left: Vec<StatusLineElement>,
    pub center: Vec<StatusLineElement>,
    pub right: Vec<StatusLineElement>,
    pub separator: String,
    pub mode: ModeConfig,
}

impl Default for StatusLineConfig {
    fn default() -> Self {
        use StatusLineElement as E;

        Self {
            left: vec![
                E::Mode,
                E::Spinner,
                E::FileName,
                E::FileModificationIndicator,
            ],
            center: vec![],
            right: vec![E::Diagnostics, E::Selections, E::Position, E::FileEncoding],
            separator: String::from("│"),
            mode: ModeConfig::default(),
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
pub struct ModeConfig {
    pub normal: String,
    pub insert: String,
    pub select: String,
}

impl Default for ModeConfig {
    fn default() -> Self {
        Self {
            normal: String::from("NOR"),
            insert: String::from("INS"),
            select: String::from("SEL"),
        }
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case")]
pub enum StatusLineElement {
    /// The editor mode (Normal, Insert, Visual/Selection)
    Mode,

    /// The LSP activity spinner
    Spinner,

    /// The base file name, including a dirty flag if it's unsaved
    FileBaseName,

    /// The relative file path, including a dirty flag if it's unsaved
    FileName,

    // The file modification indicator
    FileModificationIndicator,

    /// The file encoding
    FileEncoding,

    /// The file line endings (CRLF or LF)
    FileLineEnding,

    /// The file type (language ID or "text")
    FileType,

    /// A summary of the number of errors and warnings
    Diagnostics,

    /// A summary of the number of errors and warnings on file and workspace
    WorkspaceDiagnostics,

    /// The number of selections (cursors)
    Selections,

    /// The number of characters currently in primary selection
    PrimarySelectionLength,

    /// The cursor position
    Position,

    /// The separator string
    Separator,

    /// The cursor position as a percent of the total file
    PositionPercentage,

    /// The total line numbers of the current file
    TotalLineNumbers,

    /// A single space
    Spacer,
}

// Cursor shape is read and used on every rendered frame and so needs
// to be fast. Therefore we avoid a hashmap and use an enum indexed array.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct CursorShapeConfig([CursorKind; 3]);

impl CursorShapeConfig {
    pub fn from_mode(&self, mode: Mode) -> CursorKind {
        self.get(mode as usize).copied().unwrap_or_default()
    }
}

impl<'de> Deserialize<'de> for CursorShapeConfig {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        let m = HashMap::<Mode, CursorKind>::deserialize(deserializer)?;
        let into_cursor = |mode: Mode| m.get(&mode).copied().unwrap_or_default();
        Ok(CursorShapeConfig([
            into_cursor(Mode::Normal),
            into_cursor(Mode::Select),
            into_cursor(Mode::Insert),
        ]))
    }
}

impl Serialize for CursorShapeConfig {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        let mut map = serializer.serialize_map(Some(self.len()))?;
        let modes = [Mode::Normal, Mode::Select, Mode::Insert];
        for mode in modes {
            map.serialize_entry(&mode, &self.from_mode(mode))?;
        }
        map.end()
    }
}

impl std::ops::Deref for CursorShapeConfig {
    type Target = [CursorKind; 3];

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl Default for CursorShapeConfig {
    fn default() -> Self {
        Self([CursorKind::Block; 3])
    }
}

/// bufferline render modes
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case")]
pub enum BufferLine {
    /// Don't render bufferline
    Never,
    /// Always render
    Always,
    /// Only if multiple buffers are open
    Multiple,
}

impl Default for BufferLine {
    fn default() -> Self {
        BufferLine::Never
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case")]
pub enum LineNumber {
    /// Show absolute line number
    Absolute,

    /// If focused and in normal/select mode, show relative line number to the primary cursor.
    /// If unfocused or in insert mode, show absolute line number.
    Relative,
}

impl std::str::FromStr for LineNumber {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s.to_lowercase().as_str() {
            "absolute" | "abs" => Ok(Self::Absolute),
            "relative" | "rel" => Ok(Self::Relative),
            _ => anyhow::bail!("Line number can only be `absolute` or `relative`."),
        }
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case")]
pub enum GutterType {
    /// Show diagnostics and other features like breakpoints
    Diagnostics,
    /// Show line numbers
    LineNumbers,
    /// Show one blank space
    Spacer,
    /// Highlight local changes
    Diff,
}

impl std::str::FromStr for GutterType {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s.to_lowercase().as_str() {
            "diagnostics" => Ok(Self::Diagnostics),
            "spacer" => Ok(Self::Spacer),
            "line-numbers" => Ok(Self::LineNumbers),
            "diff" => Ok(Self::Diff),
            _ => anyhow::bail!("Gutter type can only be `diagnostics` or `line-numbers`."),
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(default)]
pub struct WhitespaceConfig {
    pub render: WhitespaceRender,
    pub characters: WhitespaceCharacters,
}

impl Default for WhitespaceConfig {
    fn default() -> Self {
        Self {
            render: WhitespaceRender::Basic(WhitespaceRenderValue::None),
            characters: WhitespaceCharacters::default(),
        }
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(untagged, rename_all = "kebab-case")]
pub enum WhitespaceRender {
    Basic(WhitespaceRenderValue),
    Specific {
        default: Option<WhitespaceRenderValue>,
        space: Option<WhitespaceRenderValue>,
        nbsp: Option<WhitespaceRenderValue>,
        tab: Option<WhitespaceRenderValue>,
        newline: Option<WhitespaceRenderValue>,
    },
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case")]
pub enum WhitespaceRenderValue {
    None,
    // TODO
    // Selection,
    All,
}

impl WhitespaceRender {
    pub fn space(&self) -> WhitespaceRenderValue {
        match *self {
            Self::Basic(val) => val,
            Self::Specific { default, space, .. } => {
                space.or(default).unwrap_or(WhitespaceRenderValue::None)
            }
        }
    }
    pub fn nbsp(&self) -> WhitespaceRenderValue {
        match *self {
            Self::Basic(val) => val,
            Self::Specific { default, nbsp, .. } => {
                nbsp.or(default).unwrap_or(WhitespaceRenderValue::None)
            }
        }
    }
    pub fn tab(&self) -> WhitespaceRenderValue {
        match *self {
            Self::Basic(val) => val,
            Self::Specific { default, tab, .. } => {
                tab.or(default).unwrap_or(WhitespaceRenderValue::None)
            }
        }
    }
    pub fn newline(&self) -> WhitespaceRenderValue {
        match *self {
            Self::Basic(val) => val,
            Self::Specific {
                default, newline, ..
            } => newline.or(default).unwrap_or(WhitespaceRenderValue::None),
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(default)]
pub struct WhitespaceCharacters {
    pub space: char,
    pub nbsp: char,
    pub tab: char,
    pub tabpad: char,
    pub newline: char,
}

impl Default for WhitespaceCharacters {
    fn default() -> Self {
        Self {
            space: '·',    // U+00B7
            nbsp: '⍽',    // U+237D
            tab: '→',     // U+2192
            newline: '⏎', // U+23CE
            tabpad: ' ',
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(default, rename_all = "kebab-case")]
pub struct IndentGuidesConfig {
    pub render: bool,
    pub character: char,
    pub skip_levels: u8,
}

impl Default for IndentGuidesConfig {
    fn default() -> Self {
        Self {
            skip_levels: 0,
            render: false,
            character: '│',
        }
    }
}

impl Default for Config {
    fn default() -> Self {
        Self {
            scrolloff: 5,
            scroll_lines: 3,
            mouse: true,
            shell: if cfg!(windows) {
                vec!["cmd".to_owned(), "/C".to_owned()]
            } else {
                vec!["sh".to_owned(), "-c".to_owned()]
            },
            line_number: LineNumber::Absolute,
            cursorline: false,
            cursorcolumn: false,
            gutters: GutterConfig::default(),
            middle_click_paste: true,
            auto_pairs: AutoPairConfig::default(),
            auto_completion: true,
            auto_format: true,
            auto_save: false,
            idle_timeout: Duration::from_millis(400),
            completion_trigger_len: 2,
            auto_info: true,
            file_picker: FilePickerConfig::default(),
            statusline: StatusLineConfig::default(),
            cursor_shape: CursorShapeConfig::default(),
            true_color: false,
            search: SearchConfig::default(),
            lsp: LspConfig::default(),
            terminal: get_terminal_provider(),
            rulers: Vec::new(),
            whitespace: WhitespaceConfig::default(),
            bufferline: BufferLine::default(),
            indent_guides: IndentGuidesConfig::default(),
            color_modes: false,
            soft_wrap: SoftWrap::default(),
        }
    }
}

impl Default for SearchConfig {
    fn default() -> Self {
        Self {
            wrap_around: true,
            smart_case: true,
        }
    }
}

pub struct Motion(pub Box<dyn Fn(&mut Editor)>);
impl Motion {
    pub fn run(&self, e: &mut Editor) {
        (self.0)(e)
    }
}
impl std::fmt::Debug for Motion {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str("motion")
    }
}

#[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>>,
    pub diff_providers: DiffProviderRegistry,

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

    pub clipboard_provider: Box<dyn ClipboardProvider>,

    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,
    pub last_line_number: Option<usize>,
    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>>,
    pub last_motion: Option<Motion>,

    pub last_completion: Option<CompleteAction>,

    pub exit_code: i32,

    pub config_events: (UnboundedSender<ConfigEvent>, UnboundedReceiver<ConfigEvent>),
    /// Allows asynchronous tasks to control the rendering
    /// The `Notify` allows asynchronous tasks to request the editor to perform a redraw
    /// The `RwLock` blocks the editor from performing the render until an exclusive lock can be aquired
    pub redraw_handle: RedrawHandle,
    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>>>,
}

pub type RedrawHandle = (Arc<Notify>, Arc<RwLock<()>>);

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

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

enum ThemeAction {
    Set,
    Preview,
}

#[derive(Debug, Clone)]
pub struct CompleteAction {
    pub trigger_offset: usize,
    pub changes: Vec<Change>,
}

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

/// 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 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: helix_lsp::Registry::new(),
            diagnostics: BTreeMap::new(),
            diff_providers: DiffProviderRegistry::default(),
            debugger: None,
            debugger_events: SelectAll::new(),
            breakpoints: HashMap::new(),
            syn_loader,
            theme_loader,
            last_theme: None,
            last_line_number: None,
            registers: Registers::default(),
            clipboard_provider: get_clipboard_provider(),
            status_msg: None,
            autoinfo: None,
            idle_timer: Box::pin(sleep(conf.idle_timeout)),
            last_motion: None,
            last_completion: None,
            config,
            auto_pairs,
            exit_code: 0,
            config_events: unbounded_channel(),
            redraw_handle: Default::default(),
            needs_redraw: false,
            cursor_cache: Cell::new(None),
        }
    }

    /// 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();
    }

    /// Refreshes the language server for a given document
    pub fn refresh_language_server(&mut self, doc_id: DocumentId) -> Option<()> {
        self.launch_language_server(doc_id)
    }

    /// Launch a language server for a given document
    fn launch_language_server(&mut self, doc_id: DocumentId) -> Option<()> {
        if !self.config().lsp.enable {
            return None;
        }

        // if doc doesn't have a URL it's a scratch buffer, ignore it
        let (lang, path) = {
            let doc = self.document(doc_id)?;
            (doc.language.clone(), doc.path().cloned())
        };

        // try to find a language server based on the language name
        let language_server = lang.as_ref().and_then(|language| {
            self.language_servers
                .get(language, path.as_ref())
                .map_err(|e| {
                    log::error!(
                        "Failed to initialize the LSP for `{}` {{ {} }}",
                        language.scope(),
                        e
                    )
                })
                .ok()
                .flatten()
        });

        let doc = self.document_mut(doc_id)?;
        let doc_url = doc.url()?;

        if let Some(language_server) = language_server {
            // only spawn a new lang server if the servers aren't the same
            if Some(language_server.id()) != doc.language_server().map(|server| server.id()) {
                if let Some(language_server) = doc.language_server() {
                    tokio::spawn(language_server.text_document_did_close(doc.identifier()));
                }

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

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

                doc.set_language_server(Some(language_server));
            }
        }
        Some(())
    }

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

        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);
                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);
            }
        }

        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 (rope, encoding) = crate::document::from_reader(&mut stdin(), None)?;
        Ok(self.new_file_from_document(
            action,
            Document::from(rope, Some(encoding), self.config.clone()),
        ))
    }

    // ??? 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(),
            )?;

            if let Some(diff_base) = self.diff_providers.get_diff_base(&path) {
                doc.set_diff_base(diff_base, self.redraw_handle.clone());
            }

            let id = self.new_document(doc);
            let _ = self.launch_language_server(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);

        if let Some(language_server) = doc.language_server() {
            // 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);
        }

        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 future = doc.save(path, force)?;

        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);
            }
        }
    }

    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))
    }

    /// 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> {
        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)
                }

                _ = self.redraw_handle.0.notified() => {
                    if  !self.needs_redraw{
                        self.needs_redraw = true;
                        let timeout = Instant::now() + Duration::from_millis(96);
                        if timeout < self.idle_timer.deadline(){
                            self.idle_timer.as_mut().reset(timeout)
                        }
                    }
                }

                _ = &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;
        }
    }
}

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);
    }
}