gpui-base 0.6.0

use futures::Stream as _;
use std::{
    ops::RangeInclusive,
    pin::Pin,
    sync::{Arc, Mutex},
    task::Poll,
};

use gpui::{
    App, AppContext as _, Bounds, Context, FocusHandle, IntoElement, KeyBinding, ListState,
    ParentElement as _, Pixels, Point, Render, SharedString, Styled as _, Task, Window,
    prelude::FluentBuilder as _, px,
};

use crate::{
    AutoScroll, ElementExt, TextSelection,
    async_util::{Receiver, Sender, unbounded},
    input::{self, SelectAll},
    text::{
        CodeBlockActionsFn, CodeBlockHighlighterFn, LinkClickHandlerFn, MarkdownExtensions,
        TableActionsFn, TextViewStyle,
        document::ParsedDocument,
        format,
        node::{self, NodeContext},
        selection_adapter::TextViewSelectionAdapter,
    },
    v_flex,
};

const CONTEXT: &'static str = "TextView";
// Keep coalescing bounded so sustained streams still render intermediate updates.
const MAX_COALESCED_UPDATES_PER_PARSE: usize = 64;
// Preserve exact first-layout height for small documents while bounding the
// amount of source parsed synchronously on the UI thread.
const MAX_SYNC_FULL_REPLACE_BYTES: usize = 4 * 1024;

pub(crate) fn init(cx: &mut App) {
    cx.bind_keys(vec![
        #[cfg(target_os = "macos")]
        KeyBinding::new("cmd-c", input::Copy, Some(CONTEXT)),
        #[cfg(not(target_os = "macos"))]
        KeyBinding::new("ctrl-c", input::Copy, Some(CONTEXT)),
        #[cfg(target_os = "macos")]
        KeyBinding::new("cmd-a", input::SelectAll, Some(CONTEXT)),
        #[cfg(not(target_os = "macos"))]
        KeyBinding::new("ctrl-a", input::SelectAll, Some(CONTEXT)),
    ]);
}

/// The content format of the text view.
#[derive(Clone, Copy, PartialEq, Eq)]
pub(super) enum TextViewFormat {
    /// Markdown view
    Markdown,
    /// HTML view
    Html,
}

/// The format of the text returned by
/// [`TextViewState::selected_text`], which is also what copy writes to the
/// clipboard.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub enum SelectionFormat {
    /// The rendered text, without any markup.
    #[default]
    Plain,
    /// The source of the selection.
    ///
    /// Select-all returns the original source verbatim, a partial selection is
    /// reconstructed as Markdown from the parsed nodes (e.g. selecting inside
    /// a `**bold**` run yields `**bold**`).
    Source,
}

/// One text element's laid-out vertical extent, reported by `Inline` during
/// prepaint so `TextView` can snap its `max_lines` clip to a whole-line
/// boundary.
#[derive(Clone, Copy)]
pub(super) struct LineSpan {
    pub(super) top: Pixels,
    pub(super) bottom: Pixels,
    pub(super) line_height: Pixels,
}

/// The state of a TextView.
pub struct TextViewState {
    pub(super) focus_handle: FocusHandle,
    pub(super) list_state: ListState,

    /// The bounds of the text view
    bounds: Bounds<Pixels>,

    pub(super) selectable: bool,
    pub(super) selection_format: SelectionFormat,
    pub(super) scrollable: bool,
    pub(super) max_lines: Option<usize>,
    /// Line spans reported by `Inline` during prepaint (collected only while
    /// [`Self::max_lines`] is set); cleared by `TextView` at each frame start.
    pub(super) line_spans: Arc<Mutex<Vec<LineSpan>>>,
    /// Whether the last painted frame clipped content due to `max_lines`.
    pub(super) clamped: bool,
    pub(super) text_view_style: TextViewStyle,
    pub(super) code_block_actions: Option<std::sync::Arc<CodeBlockActionsFn>>,
    pub(super) code_block_highlighter: Option<std::sync::Arc<CodeBlockHighlighterFn>>,
    pub(super) table_actions: Option<std::sync::Arc<TableActionsFn>>,
    pub(super) link_click_handler: Option<std::sync::Arc<LinkClickHandlerFn>>,
    pub(super) markdown_extensions: Arc<MarkdownExtensions>,

    pub(super) is_selecting: bool,
    multi_click_selection: Option<TextViewMultiClickSelection>,
    selected_text_override: Option<String>,
    select_all: bool,
    pub(super) auto_scroll: AutoScroll,
    pub(super) selection_adapter: TextViewSelectionAdapter,

    pub(super) parsed_content: ParsedContent,
    /// Content format (markdown / html), used for bounded synchronous parsing
    /// of small full-replace updates.
    format: TextViewFormat,
    text: String,
    revision: usize,
    pub(super) selection_revision: usize,
    compatible_layout_update: bool,
    parsed_error: Option<SharedString>,
    tx: Sender<UpdateOptions>,
    _parse_task: Task<()>,
    _receive_task: Task<()>,
}

impl TextViewState {
    /// Create a Markdown TextViewState.
    pub fn markdown(text: &str, cx: &mut Context<Self>) -> Self {
        Self::new(TextViewFormat::Markdown, text, cx)
    }

    /// Create a HTML TextViewState.
    pub fn html(text: &str, cx: &mut Context<Self>) -> Self {
        Self::new(TextViewFormat::Html, text, cx)
    }

    /// Create a new TextViewState.
    fn new(format: TextViewFormat, text: &str, cx: &mut Context<Self>) -> Self {
        let focus_handle = cx.focus_handle();
        let selection_adapter = TextViewSelectionAdapter::new(cx.entity().downgrade(), cx);

        let (tx, rx) = unbounded::<UpdateOptions>();
        let (tx_result, rx_result) = unbounded::<ParsedUpdate>();
        let _receive_task = cx.spawn({
            async move |weak_self, cx| {
                while let Ok(parsed_update) = rx_result.recv().await {
                    _ = weak_self.update(cx, |state, cx| {
                        if parsed_update.revision != state.revision {
                            return;
                        }
                        if parsed_update.baseline_ack {
                            debug_assert!(parsed_update.full_parse);
                            return;
                        }

                        match parsed_update.result {
                            Ok(content) => {
                                state.parsed_content = content;
                                state.parsed_error = None;
                                state.compatible_layout_update = parsed_update.selection_compatible;
                            }
                            Err(err) => {
                                state.parsed_error = Some(err);
                            }
                        }
                        // Don't interrupt an active drag-selection; the stored
                        // positions remain valid for append-only updates and will
                        // self-correct on the next mouse-move event.
                        if !parsed_update.selection_compatible && !state.is_selecting {
                            state.reset_selection_and_adapter(cx);
                        }
                        cx.notify();
                    });
                }
            }
        });

        let _parse_task = cx.background_spawn(UpdateFuture::new(format, rx, tx_result));

        let mut this = Self {
            focus_handle,
            bounds: Bounds::default(),
            multi_click_selection: None,
            selected_text_override: None,
            select_all: false,
            selectable: false,
            selection_format: SelectionFormat::default(),
            scrollable: false,
            max_lines: None,
            line_spans: Arc::default(),
            clamped: false,
            // Measure all blocks (not just visible ones) so the scrollbar
            // thumb size stays stable. Without this, off-screen blocks count
            // as zero height until scrolled into view, which makes the
            // scrollbar jitter as more blocks get measured during scrolling.
            list_state: ListState::new(0, gpui::ListAlignment::Top, px(1000.)).measure_all(),
            text_view_style: TextViewStyle::default(),
            code_block_actions: None,
            code_block_highlighter: None,
            table_actions: None,
            link_click_handler: None,
            markdown_extensions: Arc::default(),
            is_selecting: false,
            auto_scroll: AutoScroll::default(),
            selection_adapter,
            parsed_content: Default::default(),
            format,
            parsed_error: None,
            text: text.to_string(),
            revision: 0,
            selection_revision: 0,
            compatible_layout_update: false,
            tx,
            _parse_task,
            _receive_task,
        };
        this.increment_update(&text, false, cx);
        this
    }

    /// Get the text content.
    pub(crate) fn source(&self) -> SharedString {
        self.parsed_content.document.source.clone()
    }

    /// Set whether the text is selectable, default false.
    pub fn selectable(mut self, selectable: bool) -> Self {
        self.selectable = selectable;
        self
    }

    /// Set whether the text is selectable, default false.
    pub fn set_selectable(&mut self, selectable: bool, cx: &mut Context<Self>) {
        self.selectable = selectable;
        cx.notify();
    }

    /// Set the [`SelectionFormat`], default is [`SelectionFormat::Plain`].
    pub fn selection_format(mut self, selection_format: SelectionFormat) -> Self {
        self.selection_format = selection_format;
        self
    }

    /// Set the [`SelectionFormat`], default is [`SelectionFormat::Plain`].
    pub fn set_selection_format(
        &mut self,
        selection_format: SelectionFormat,
        cx: &mut Context<Self>,
    ) {
        self.selection_format = selection_format;
        cx.notify();
    }

    /// Set whether the text view scrolls internally, default false.
    pub fn scrollable(mut self, scrollable: bool) -> Self {
        self.scrollable = scrollable;
        self
    }

    /// Set whether the text view scrolls internally, default false.
    pub fn set_scrollable(&mut self, scrollable: bool, cx: &mut Context<Self>) {
        if !scrollable {
            self.reset_selection_and_adapter(cx);
        }
        self.scrollable = scrollable;
        cx.notify();
    }

    /// Whether the last painted frame clipped content because of
    /// [`TextView::max_lines`](crate::text::TextView::max_lines).
    pub fn is_clamped(&self) -> bool {
        self.clamped
    }

    /// Set the text content.
    pub fn set_text(&mut self, text: &str, cx: &mut Context<Self>) {
        if self.text.as_str() == text {
            return;
        }

        self.text.clear();
        self.text.push_str(text);
        self.parsed_error = None;
        self.increment_update(text, false, cx);
    }

    /// Append partial text content to the existing text.
    pub fn push_str(&mut self, new_text: &str, cx: &mut Context<Self>) {
        if new_text.is_empty() {
            return;
        }
        self.text.push_str(new_text);
        self.increment_update(new_text, true, cx);
    }

    pub(crate) fn set_markdown_extensions(
        &mut self,
        markdown_extensions: Arc<MarkdownExtensions>,
        cx: &mut Context<Self>,
    ) {
        if self.markdown_extensions.revision() == markdown_extensions.revision() {
            return;
        }

        let parser_configuration_changed = !self
            .markdown_extensions
            .has_same_parser_configuration(&markdown_extensions);
        self.markdown_extensions = markdown_extensions;
        if parser_configuration_changed && self.format == TextViewFormat::Markdown {
            let text = self.text.clone();
            self.increment_update(&text, false, cx);
        }
    }

    /// Return the selected text, in the view's [`SelectionFormat`].
    pub fn selected_text(&self) -> String {
        self.selected_text_in(None)
    }

    /// The format to copy in, which is [`SelectionFormat::Plain`] whenever the
    /// requested one cannot be produced.
    ///
    /// Only a Markdown view can return source. Reconstructing HTML would mean
    /// spelling every attribute back out — a mark's color, an image's
    /// dimensions, a cell's alignment — with a new way to lose one at each
    /// step, and html5ever records no source offsets to fall back on (it
    /// reports only line numbers), so there is no original text to copy from
    /// either.
    fn effective_format(&self) -> SelectionFormat {
        match self.format {
            TextViewFormat::Markdown => self.selection_format,
            TextViewFormat::Html => SelectionFormat::Plain,
        }
    }

    /// Return the selected text, with `blocks` bounding which top-level blocks
    /// the selection covers.
    ///
    /// The range comes from the selection endpoints, which know their block
    /// even after it scrolls out of view; see
    /// [`ParsedDocument::selected_text`](crate::text::document::ParsedDocument).
    pub(super) fn selected_text_in(&self, blocks: Option<RangeInclusive<usize>>) -> String {
        let format = self.effective_format();

        if self.select_all {
            if format == SelectionFormat::Source {
                return self.source().to_string();
            }

            return self.parsed_content.document.text();
        }

        // A multi-click stores the plain text it selected, which is a shortcut
        // past the block walk. Source mode cannot take it: the word it stored
        // has lost its markup. The click also set the inline selection it came
        // from, so the walk reconstructs the same range with the markup intact.
        if format != SelectionFormat::Source
            && let Some(text) = &self.selected_text_override
        {
            return text.clone();
        }

        self.parsed_content.document.selected_text(format, blocks)
    }

    fn increment_update(&mut self, text: &str, append: bool, cx: &mut Context<Self>) {
        self.revision += 1;
        if !append {
            self.selection_revision = self.selection_revision.wrapping_add(1);
        }
        let parse_synchronously = !append && text.len() <= MAX_SYNC_FULL_REPLACE_BYTES;
        let update_options = UpdateOptions {
            revision: self.revision,
            append,
            mode: if append {
                ParseMode::Compatible
            } else if parse_synchronously {
                ParseMode::BaselineAck
            } else {
                ParseMode::Replace
            },
            pending_text: text.to_string(),
            markdown_extensions: self.markdown_extensions.clone(),
        };

        // Keep small full replacements synchronous so their first layout has
        // the exact content height. Larger replacements use the existing
        // background parser, bounding synchronous parser input on the UI thread.
        if parse_synchronously {
            match parse_content(self.format, ParsedContent::default(), &update_options) {
                Ok(content) => {
                    self.parsed_content = content;
                    self.parsed_error = None;
                    if !self.is_selecting {
                        self.reset_selection_and_adapter(cx);
                    }
                }
                Err(err) => {
                    self.parsed_error = Some(err);
                }
            }
            // Keep the background parser's accumulated document in sync so a
            // later append extends this baseline instead of parsing the delta
            // as a standalone document.
            _ = self.tx.try_send(update_options);
            cx.notify();
            return;
        }

        _ = self.tx.try_send(update_options);
    }

    /// Save bounds and unselect if bounds changed.
    pub(super) fn update_bounds(&mut self, bounds: Bounds<Pixels>, _cx: &mut App) {
        self.bounds = bounds;
    }

    /// The index of the top-level block at `content_y`, in this view's content
    /// coordinates (the same space the base selection endpoint stores its point in).
    ///
    /// Only laid-out blocks can be located, which is enough for a selection
    /// endpoint: the user can only put one where they can see it. Returns
    /// `None` for a view that is not virtualized, where every block paints and
    /// the range is not needed.
    pub(super) fn block_ix_at(&self, content_y: Pixels) -> Option<usize> {
        if !self.scrollable {
            return None;
        }

        let origin = self.bounds.origin.y + self.scroll_offset().y;
        let count = self.list_state.item_count();
        let mut ix = self.list_state.logical_scroll_top().item_ix;
        while ix < count {
            let bounds = self.list_state.bounds_for_item(ix)?;
            if content_y < bounds.bottom() - origin {
                return Some(ix);
            }
            ix += 1;
        }

        count.checked_sub(1)
    }

    #[doc(hidden)]
    pub fn bounds(&self) -> Bounds<Pixels> {
        self.bounds
    }

    #[doc(hidden)]
    pub fn list_state(&self) -> &ListState {
        &self.list_state
    }

    #[doc(hidden)]
    pub fn is_selecting(&self) -> bool {
        self.is_selecting
    }

    #[doc(hidden)]
    pub fn focus_handle(&self) -> &FocusHandle {
        &self.focus_handle
    }

    /// Whether this view has a view-local selection (select-all, multi-click, or override),
    /// independent of the window-level selection.
    pub(super) fn has_view_selection(&self) -> bool {
        self.select_all
            || self.multi_click_selection.is_some()
            || self.selected_text_override.is_some()
    }

    pub(super) fn stop_auto_scroll(&mut self) {
        self.auto_scroll.stop();
    }

    pub(super) fn reset_selection(&mut self) {
        self.multi_click_selection = None;
        self.selected_text_override = None;
        self.select_all = false;
        self.is_selecting = false;
        self.auto_scroll.stop();
        // Clear the inline selection state synchronously, so offscreen
        // (virtualized) views that won't repaint don't leak stale selection
        // text into a new cross-view copy.
        self.parsed_content.document.clear_selection();
    }

    fn reset_selection_and_adapter(&mut self, cx: &mut App) {
        self.reset_selection();
        self.selection_adapter.set_local_selection(false, cx);
    }

    /// Clear the current text selection.
    pub fn clear_selection(&mut self, cx: &mut Context<Self>) {
        self.reset_selection_and_adapter(cx);
        cx.notify();
    }

    pub(super) fn scroll_offset(&self) -> Point<Pixels> {
        if self.scrollable {
            self.list_state.scroll_px_offset_for_scrollbar()
        } else {
            Point::default()
        }
    }

    /// Select all rendered text in this view.
    pub fn select_all(&mut self, cx: &mut Context<Self>) {
        self.multi_click_selection = None;
        self.selected_text_override = None;
        self.select_all = true;
        self.is_selecting = false;
        self.auto_scroll.stop();
        self.selection_adapter.set_local_selection(true, cx);
        cx.notify();
    }

    pub(crate) fn set_multi_click_selection(
        &mut self,
        pos: Point<Pixels>,
        kind: TextViewMultiClickKind,
        selected_text: String,
        cx: &mut App,
    ) {
        let scroll_offset = self.scroll_offset();
        let pos = pos - self.bounds.origin - scroll_offset;
        self.multi_click_selection = Some(TextViewMultiClickSelection { pos, kind });
        self.selected_text_override = Some(selected_text);
        self.select_all = false;
        self.is_selecting = false;
        self.auto_scroll.stop();
        self.selection_adapter.set_local_selection(true, cx);
    }

    pub(super) fn set_auto_scroll(&mut self, delta: Option<Pixels>, cx: &mut Context<Self>) {
        self.auto_scroll.set(delta, cx, |delta, state, cx| {
            state.list_state.scroll_by(delta);
            cx.notify();
        });
    }

    /// Return the window selection (anchor, cursor) in window coordinates if
    /// this view participates in it.
    ///
    /// Single-view fast path: when both endpoints are anchored inside one
    /// TextView, only that view participates (identical to the previous
    /// per-view behavior).
    pub(crate) fn selection_points(&self, cx: &App) -> Option<(Point<Pixels>, Point<Pixels>)> {
        if !self.selectable {
            return None;
        }
        self.selection_adapter.selection_points(cx)
    }

    pub(crate) fn has_selection(&self, cx: &App) -> bool {
        self.has_view_selection() || self.selection_points(cx).is_some()
    }

    pub(super) fn on_action_select_all(
        &mut self,
        _: &SelectAll,
        _: &mut Window,
        cx: &mut Context<Self>,
    ) {
        if !self.selectable {
            cx.propagate();
            return;
        }

        self.select_all(cx);
    }

    pub(crate) fn is_selectable(&self) -> bool {
        self.selectable
    }

    pub(crate) fn is_all_selected(&self) -> bool {
        self.select_all
    }

    pub(crate) fn multi_click_selection(&self) -> Option<TextViewMultiClickSelection> {
        let scroll_offset = self.scroll_offset();
        self.multi_click_selection.map(|selection| {
            let pos = selection.pos + scroll_offset + self.bounds.origin;
            TextViewMultiClickSelection { pos, ..selection }
        })
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub(crate) struct TextViewMultiClickSelection {
    pub(crate) pos: Point<Pixels>,
    pub(crate) kind: TextViewMultiClickKind,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub(crate) enum TextViewMultiClickKind {
    Word,
    Paragraph,
}

impl Render for TextViewState {
    fn render(&mut self, window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
        let state = cx.entity();
        let document = self.parsed_content.document.clone();
        let mut node_cx = self.parsed_content.node_cx.clone();

        node_cx.code_block_actions = self.code_block_actions.clone();
        node_cx.code_block_highlighter = self.code_block_highlighter.clone();
        node_cx.table_actions = self.table_actions.clone();
        node_cx.link_click_handler = self.link_click_handler.clone();
        node_cx.markdown_extensions = self.markdown_extensions.clone();
        node_cx.style = self.text_view_style.clone();

        v_flex()
            .w_full()
            // Clamped content must keep its natural height: stretching it to
            // the capped box would hide the overflow the clamp has to measure.
            .when(self.max_lines.is_none(), |this| this.h_full())
            .map(|this| match &mut self.parsed_error {
                None => this.child(document.render_root(
                    if self.scrollable {
                        Some(self.list_state.clone())
                    } else {
                        None
                    },
                    &node_cx,
                    window,
                    cx,
                )),
                Some(err) => this.child(
                    v_flex()
                        .gap_1()
                        .child("Failed to parse content")
                        .child(err.to_string()),
                ),
            })
            .on_prepaint(move |bounds, window, cx| {
                let (
                    size_changed,
                    selection_involves_view,
                    has_selection_snapshot,
                    is_selecting,
                    compatible_layout_update,
                ) = {
                    let state = state.read(cx);
                    (
                        state.bounds().size != bounds.size,
                        state.selection_adapter.is_part_of_window_selection(cx),
                        state.selection_adapter.has_selection_snapshot(cx),
                        state.is_selecting,
                        state.compatible_layout_update,
                    )
                };
                let mut revision_changed = false;
                state.update(cx, |state, cx| {
                    revision_changed = state
                        .selection_adapter
                        .update_layout_revision(state.selection_revision, state.is_selecting);
                    state.update_bounds(bounds, cx);
                    state.compatible_layout_update = false;
                });
                if !is_selecting
                    && ((size_changed && selection_involves_view && !compatible_layout_update)
                        || (revision_changed && has_selection_snapshot))
                {
                    TextSelection::clear(window, cx);
                }
            })
    }
}

#[derive(Clone, PartialEq, Default)]
pub(crate) struct ParsedContent {
    pub(crate) document: ParsedDocument,
    pub(crate) node_cx: node::NodeContext,
}

struct UpdateFuture {
    format: TextViewFormat,
    content: ParsedContent,
    rx: Pin<Box<Receiver<UpdateOptions>>>,
    tx_result: Sender<ParsedUpdate>,
}

impl UpdateFuture {
    fn new(
        format: TextViewFormat,
        rx: Receiver<UpdateOptions>,
        tx_result: Sender<ParsedUpdate>,
    ) -> Self {
        Self {
            format,
            content: Default::default(),
            rx: Box::pin(rx),
            tx_result,
        }
    }
}

impl Future for UpdateFuture {
    type Output = ();

    fn poll(mut self: Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> Poll<Self::Output> {
        loop {
            match self.rx.as_mut().poll_next(cx) {
                Poll::Ready(Some(mut options)) => {
                    let hit_coalesce_budget =
                        merge_pending_options(&mut options, self.rx.as_ref().get_ref());

                    let res = parse_content(self.format, self.content.clone(), &options);
                    if let Ok(content) = &res {
                        self.content = content.clone();
                    }
                    _ = self.tx_result.try_send(ParsedUpdate {
                        revision: options.revision,
                        full_parse: !options.append,
                        selection_compatible: options.mode == ParseMode::Compatible,
                        baseline_ack: options.mode == ParseMode::BaselineAck,
                        result: res,
                    });
                    if hit_coalesce_budget {
                        cx.waker().wake_by_ref();
                        return Poll::Pending;
                    }
                    continue;
                }
                Poll::Ready(None) => return Poll::Ready(()),
                Poll::Pending => return Poll::Pending,
            }
        }
    }
}

#[derive(Clone)]
struct UpdateOptions {
    revision: usize,
    pending_text: String,
    append: bool,
    mode: ParseMode,
    markdown_extensions: Arc<MarkdownExtensions>,
}

impl UpdateOptions {
    fn merge(&mut self, next: UpdateOptions) {
        if next.append {
            self.pending_text.push_str(&next.pending_text);
            self.revision = next.revision;
            if self.mode != ParseMode::Replace {
                self.mode = ParseMode::Compatible;
            }
        } else {
            *self = next;
        }
    }
}

struct ParsedUpdate {
    revision: usize,
    full_parse: bool,
    selection_compatible: bool,
    baseline_ack: bool,
    result: Result<ParsedContent, SharedString>,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
enum ParseMode {
    BaselineAck,
    Replace,
    Compatible,
}

fn merge_pending_options(options: &mut UpdateOptions, rx: &Receiver<UpdateOptions>) -> bool {
    let mut update_count = 1;

    while update_count < MAX_COALESCED_UPDATES_PER_PARSE {
        match rx.try_recv() {
            Ok(next_options) => {
                options.merge(next_options);
                update_count += 1;
            }
            Err(_) => return false,
        }
    }

    true
}

fn parse_content(
    format: TextViewFormat,
    mut content: ParsedContent,
    options: &UpdateOptions,
) -> Result<ParsedContent, SharedString> {
    let mut node_cx = NodeContext {
        markdown_extensions: options.markdown_extensions.clone(),
        ..NodeContext::default()
    };

    // Re-parse the last block together with the appended text, so a block the
    // new text continues (an unclosed list, a fenced code block) is not split
    // in two. A block without a span cannot be located in `source` — the HTML
    // parser never records spans — so it is left in place and only the
    // appended text is parsed, positioned at the end of the current source.
    let last_span = options
        .append
        .then(|| {
            content
                .document
                .blocks
                .last()
                .and_then(|block| block.span())
        })
        .flatten();

    let mut source = String::new();
    if let Some(span) = last_span {
        Arc::make_mut(&mut content.document.blocks).pop();
        node_cx.offset = span.start;
        source.push_str(&content.document.source[span.start..]);
        source.push_str(&options.pending_text);
    } else {
        if options.append {
            node_cx.offset = content.document.source.len();
        }
        source.push_str(&options.pending_text);
    }

    let new_document = match format {
        TextViewFormat::Markdown => format::markdown::parse(&source, &mut node_cx),
        TextViewFormat::Html => format::html::parse(&source, &mut node_cx),
    }?;

    if options.append {
        content.document.source =
            format!("{}{}", content.document.source, options.pending_text).into();
        Arc::make_mut(&mut content.document.blocks)
            .extend(Arc::unwrap_or_clone(new_document.blocks));
    } else {
        content.document = new_document;
    }

    Ok(content)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::text::MarkdownNode;
    use gpui::TestAppContext;

    #[gpui::test]
    fn small_full_replace_parses_before_background_executor_runs(cx: &mut TestAppContext) {
        cx.update(crate::init);
        let markdown = "# ready";
        let state = cx.update(|cx| cx.new(|cx| TextViewState::markdown(markdown, cx)));

        state.read_with(cx, |state, _| {
            assert_eq!(state.source().as_str(), markdown);
            assert_eq!(state.parsed_content.document.blocks.len(), 1);
        });
    }

    #[gpui::test]
    fn large_markdown_and_html_full_replacements_wait_for_background_executor(
        cx: &mut TestAppContext,
    ) {
        cx.update(crate::init);
        let markdown = "# x\n\n".repeat(MAX_SYNC_FULL_REPLACE_BYTES / 5 + 1);
        let html = format!("<p>{}</p>", "x".repeat(MAX_SYNC_FULL_REPLACE_BYTES + 1));
        assert!(markdown.len() > MAX_SYNC_FULL_REPLACE_BYTES);
        assert!(html.len() > MAX_SYNC_FULL_REPLACE_BYTES);

        let (markdown_state, html_state) = cx.update(|cx| {
            (
                cx.new(|cx| TextViewState::markdown(&markdown, cx)),
                cx.new(|cx| TextViewState::html(&html, cx)),
            )
        });

        markdown_state.read_with(cx, |state, _| {
            assert_eq!(state.text.as_str(), markdown.as_str());
            assert!(state.source().as_str().is_empty());
            assert!(state.parsed_content.document.blocks.is_empty());
        });
        html_state.read_with(cx, |state, _| {
            assert_eq!(state.text.as_str(), html.as_str());
            assert!(state.source().as_str().is_empty());
            assert!(state.parsed_content.document.blocks.is_empty());
        });

        cx.run_until_parked();

        markdown_state.read_with(cx, |state, _| {
            assert_eq!(state.source().as_str(), markdown.as_str());
            assert!(!state.parsed_content.document.blocks.is_empty());
        });
        html_state.read_with(cx, |state, _| {
            assert_eq!(state.source().as_str(), html.as_str());
            assert!(!state.parsed_content.document.blocks.is_empty());
        });
    }

    #[gpui::test]
    fn async_full_replace_then_push_str_preserves_complete_source(cx: &mut TestAppContext) {
        cx.update(crate::init);
        let state = cx.update(|cx| cx.new(|cx| TextViewState::markdown("old", cx)));
        cx.run_until_parked();

        let replacement = "x".repeat(MAX_SYNC_FULL_REPLACE_BYTES + 1);
        let expected = format!("{replacement} tail");
        state.update(cx, |state, cx| {
            state.set_text(&replacement, cx);
            state.push_str(" tail", cx);
        });
        cx.run_until_parked();

        state.read_with(cx, |state, _| {
            assert_eq!(state.text.as_str(), expected.as_str());
            assert_eq!(state.source().as_str(), expected.as_str());
        });
    }

    #[gpui::test]
    fn html_push_str_keeps_earlier_blocks(cx: &mut TestAppContext) {
        cx.update(crate::init);
        let state = cx.update(|cx| cx.new(|cx| TextViewState::html("<p>first</p>", cx)));
        cx.run_until_parked();

        state.update(cx, |state, cx| {
            state.push_str("<p>second</p>", cx);
        });
        cx.run_until_parked();

        state.read_with(cx, |state, _| {
            assert_eq!(state.source().as_str(), "<p>first</p><p>second</p>");
            let text = state
                .parsed_content
                .document
                .blocks
                .iter()
                .map(|block| block.text())
                .collect::<String>();
            assert!(text.contains("first"), "lost the first block: {text:?}");
            assert!(text.contains("second"), "lost the appended block: {text:?}");
        });
    }

    #[gpui::test]
    fn set_text_then_push_str_appends_to_replaced_content(cx: &mut TestAppContext) {
        cx.update(crate::init);
        let state = cx.update(|cx| cx.new(|cx| TextViewState::markdown("old", cx)));
        cx.run_until_parked();

        state.update(cx, |state, cx| {
            state.set_text("", cx);
            state.push_str("new", cx);
            state.push_str(" text", cx);
        });
        cx.run_until_parked();

        state.read_with(cx, |state, _| {
            assert_eq!(state.text.as_str(), "new text");
            assert_eq!(state.source().as_str(), "new text");
        });

        state.update(cx, |state, cx| {
            state.set_text("", cx);
        });
        cx.run_until_parked();

        state.read_with(cx, |state, _| {
            assert_eq!(state.text.as_str(), "");
            assert_eq!(state.source().as_str(), "");
        });
    }

    #[gpui::test]
    fn full_parse_coalesced_with_append_preserves_new_select_all(cx: &mut TestAppContext) {
        cx.update(crate::init);
        let state = cx.update(|cx| cx.new(|cx| TextViewState::markdown("old", cx)));
        cx.run_until_parked();

        state.update(cx, |state, cx| {
            state.set_text("new", cx);
            state.push_str(" text", cx);
            state.select_all(cx);
        });
        cx.run_until_parked();

        state.read_with(cx, |state, _| {
            assert!(state.select_all);
            assert_eq!(state.selected_text().trim(), "new text");
        });
    }

    #[test]
    fn update_options_merge_keeps_latest_full_text() {
        let mut options = UpdateOptions {
            revision: 1,
            pending_text: "old".to_string(),
            append: true,
            mode: ParseMode::Compatible,
            markdown_extensions: Arc::default(),
        };

        options.merge(UpdateOptions {
            revision: 2,
            pending_text: "new".to_string(),
            append: false,
            mode: ParseMode::BaselineAck,
            markdown_extensions: Arc::default(),
        });
        options.merge(UpdateOptions {
            revision: 3,
            pending_text: " text".to_string(),
            append: true,
            mode: ParseMode::Compatible,
            markdown_extensions: Arc::default(),
        });

        assert_eq!(options.revision, 3);
        assert_eq!(options.pending_text, "new text");
        assert!(!options.append);
    }

    #[test]
    fn append_merged_into_async_replace_remains_a_replacement() {
        let mut options = UpdateOptions {
            revision: 1,
            pending_text: "new".to_string(),
            append: false,
            mode: ParseMode::Replace,
            markdown_extensions: Arc::default(),
        };

        options.merge(UpdateOptions {
            revision: 2,
            pending_text: " text".to_string(),
            append: true,
            mode: ParseMode::Compatible,
            markdown_extensions: Arc::default(),
        });

        assert_eq!(options.revision, 2);
        assert_eq!(options.pending_text, "new text");
        assert!(!options.append);
        assert_eq!(options.mode, ParseMode::Replace);
    }

    #[test]
    fn update_future_yields_before_coalescing_all_queued_updates() {
        let (tx, rx) = unbounded::<UpdateOptions>();
        let (tx_result, rx_result) = unbounded::<ParsedUpdate>();
        let total_updates = 128;

        for revision in 1..=total_updates {
            tx.try_send(UpdateOptions {
                revision,
                pending_text: format!("{revision}\n"),
                append: revision != 1,
                mode: if revision == 1 {
                    ParseMode::BaselineAck
                } else {
                    ParseMode::Compatible
                },
                markdown_extensions: Arc::default(),
            })
            .unwrap();
        }

        let mut future = Box::pin(UpdateFuture::new(TextViewFormat::Markdown, rx, tx_result));
        let waker = futures::task::noop_waker();
        let mut task_cx = std::task::Context::from_waker(&waker);

        assert!(matches!(
            std::future::Future::poll(future.as_mut(), &mut task_cx),
            Poll::Pending
        ));
        let parsed_update = rx_result.try_recv().expect("parse result");

        assert!(
            parsed_update.revision < total_updates,
            "single poll coalesced every queued update through revision {}",
            parsed_update.revision
        );

        assert!(matches!(
            std::future::Future::poll(future.as_mut(), &mut task_cx),
            Poll::Pending
        ));
        let parsed_update = rx_result.try_recv().expect("next parse result");
        assert_eq!(parsed_update.revision, total_updates);
    }

    #[gpui::test]
    fn select_all_returns_rendered_text(cx: &mut TestAppContext) {
        cx.update(crate::init);
        let state = cx.update(|cx| cx.new(|cx| TextViewState::markdown("**quick** value", cx)));
        cx.run_until_parked();

        state.update(cx, |state, cx| {
            state.select_all(cx);
        });

        state.read_with(cx, |state, _| {
            assert!(state.has_view_selection());
            assert_eq!(state.selected_text().trim(), "quick value");
        });

        state.update(cx, |state, cx| {
            state.clear_selection(cx);
        });

        state.read_with(cx, |state, _| {
            assert!(!state.has_view_selection());
            assert_eq!(state.selected_text(), "");
        });
    }

    #[gpui::test]
    fn select_all_in_source_format_returns_source(cx: &mut TestAppContext) {
        cx.update(crate::init);
        let markdown = "**quick** value";
        let state = cx.update(|cx| cx.new(|cx| TextViewState::markdown(markdown, cx)));
        cx.run_until_parked();

        state.update(cx, |state, cx| state.select_all(cx));

        // The default (plain) mode strips the markup.
        state.read_with(cx, |state, _| {
            assert_eq!(state.selected_text().trim(), "quick value");
        });

        state.update(cx, |state, cx| {
            state.set_selection_format(SelectionFormat::Source, cx)
        });

        // Source mode yields the whole source verbatim.
        state.read_with(cx, |state, _| {
            assert_eq!(state.selected_text().trim(), markdown);
        });
    }

    #[gpui::test]
    fn set_markdown_extensions_reparses_existing_text(cx: &mut TestAppContext) {
        cx.update(crate::init);
        let state = cx.update(|cx| cx.new(|cx| TextViewState::markdown("$TSLA.US", cx)));
        cx.run_until_parked();

        let extensions = MarkdownExtensions::default().block_parser(|node, cx| {
            let markdown::mdast::Node::Paragraph(paragraph) = node else {
                return None;
            };
            let [markdown::mdast::Node::Text(text)] = paragraph.children.as_slice() else {
                return None;
            };
            let symbol = text.value.strip_prefix('$')?.to_string();
            let node_text = format!("${symbol}");

            Some(
                MarkdownNode::new("ticker", symbol)
                    .text(node_text)
                    .markdown(cx.node_source(node).unwrap_or_default()),
            )
        });

        state.update(cx, |state, cx| {
            state.set_markdown_extensions(Arc::new(extensions), cx);
        });
        cx.run_until_parked();

        state.read_with(cx, |state, _| {
            let node::BlockNode::Custom(node) = &state.parsed_content.document.blocks[0] else {
                panic!("expected custom markdown node");
            };
            assert_eq!(node.name(), "ticker");
            assert_eq!(node.data::<String>().map(String::as_str), Some("TSLA.US"));
        });
    }
}