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// Copyright 2020 The Druid Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! Types and functions for cross-platform text input.
//!
//! Text input is a notoriously difficult problem. Unlike many other aspects of
//! user interfaces, text input can not be correctly modeled using discrete
//! events passed from the platform to the application. For example, many mobile
//! phones implement autocorrect: when the user presses the spacebar, the
//! platform peeks at the word directly behind the caret, and potentially
//! replaces it if it's mispelled. This means the platform needs to know the
//! contents of a text field. On other devices, the platform may need to draw an
//! emoji window under the caret, or look up the on-screen locations of letters
//! for crossing out with a stylus, both of which require fetching on-screen
//! coordinates from the application.
//!
//! This is all to say: text editing is a bidirectional conversation between the
//! application and the platform. The application, when the platform asks for
//! it, serves up text field coordinates and content. The platform looks at
//! this information and combines it with input from keyboards (physical or
//! onscreen), voice, styluses, the user's language settings, and then sends
//! edit commands to the application.
//!
//! Many platforms have an additional complication: this input fusion often
//! happens in a different process from your application. If we don't
//! specifically account for this fact, we might get race conditions! In the
//! autocorrect example, if I sloppily type "meoow" and press space, the
//! platform might issue edits to "delete backwords one word and insert meow".
//! However, if I concurrently click somewhere else in the document to move the
//! caret, this will replace some *other* word with "meow", and leave the
//! "meoow" disappointingly present. To mitigate this problem, we use locks,
//! represented by the `InputHandler` trait.
//!
//! ## Lifecycle of a Text Input
//!
//! 1. The user clicks a link or switches tabs, and the window content now
//! contains a new text field. The application registers this new field by
//! calling `WindowHandle::add_text_field`, and gets a `TextFieldToken` that
//! represents this new field.
//! 2. The user clicks on that text field, focusing it. The application lets the
//! platform know by calling `WindowHandle::set_focused_text_field` with that
//! field's `TextFieldToken`.
//! 3. The user presses a key on the keyboard. The platform first calls
//! `WinHandler::key_down`. If this method returns `true`, the application
//! has indicated the keypress was captured, and we skip the remaining steps.
//! 4. If `key_down` returned `false`, druid-shell forwards the key event to the
//! platform's text input system
//! 5. The platform, in response to either this key event or some other user
//! action, determines it's time for some text input. It calls
//! `WinHandler::text_input` to acquire a lock on the text field's state.
//! The application returns an `InputHandler` object corresponding to the
//! requested text field. To prevent race conditions, your application may
//! not make any changes
//! to the text field's state until the platform drops the `InputHandler`.
//! 6. The platform calls various `InputHandler` methods to inspect and edit the
//! text field's state. Later, usually within a few milliseconds, the
//! platform drops the `InputHandler`, allowing the application to once again
//! make changes to the text field's state. These commands might be "insert
//! `q`" for a smartphone user tapping on their virtual keyboard, or
//! "move the caret one word left" for a user pressing the left arrow key
//! while holding control.
//! 7. Eventually, after many keypresses cause steps 3–6 to repeat, the user
//! unfocuses the text field. The application indicates this to the platform
//! by calling `set_focused_text_field`. Note that even though focus has
//! shifted away from our text field, the platform may still send edits to it
//! by calling `WinHandler::text_input`.
//! 8. At some point, the user clicks a link or switches a tab, and the text
//! field is no longer present in the window. The application calls
//! `WindowHandle::remove_text_field`, and the platform may no longer call
//! `WinHandler::text_input` to make changes to it.
//!
//! The application also has a series of steps it follows if it wants to make
//! its own changes to the text field's state:
//!
//! 1. The application determines it would like to make a change to the text
//! field; perhaps the user has scrolled and and the text field has changed
//! its visible location on screen, or perhaps the user has clicked to move
//! the caret to a new location.
//! 2. The application first checks to see if there's an outstanding
//! `InputHandler` lock for this text field; if so, it waits until the last
//! `InputHandler` is dropped before continuing.
//! 3. The application then makes the change to the text input. If the change
//! would affect state visible from an `InputHandler`, the application must
//! notify the platform via `WinHandler::update_text_field`.
//!
//! ## Supported Platforms
//!
//! Currently, `druid-shell` text input is fully implemented on macOS. Our goal
//! is to have full support for all druid-shell targets, but for now,
//! `InputHandler` calls are simulated from keypresses on other platforms, which
//! doesn't allow for IME input, dead keys, etc.
use crate::keyboard::{KbKey, KeyEvent};
use crate::kurbo::{Point, Rect};
use crate::piet::HitTestPoint;
use crate::window::{TextFieldToken, WinHandler};
use std::borrow::Cow;
use std::ops::Range;
/// An event representing an application-initiated change in [`InputHandler`]
/// state.
///
/// When we change state that may have previously been retreived from an
/// [`InputHandler`], we notify the platform so that it can invalidate any
/// data if necessary.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
#[non_exhaustive]
pub enum Event {
/// Indicates the value returned by `InputHandler::selection` may have changed.
SelectionChanged,
/// Indicates the values returned by one or more of these methods may have changed:
/// - `InputHandler::hit_test_point`
/// - `InputHandler::line_range`
/// - `InputHandler::bounding_box`
/// - `InputHandler::slice_bounding_box`
LayoutChanged,
/// Indicates any value returned from any `InputHandler` method may have changed.
Reset,
}
/// A range of selected text, or a caret.
///
/// A caret is the blinking vertical bar where text is to be inserted. We
/// represent it as a selection with zero length, where `anchor == active`.
/// Indices are always expressed in UTF-8 bytes, and must be between 0 and the
/// document length, inclusive.
///
/// As an example, if the input caret is at the start of the document `hello
/// world`, we would expect both `anchor` and `active` to be `0`. If the user
/// holds shift and presses the right arrow key five times, we would expect the
/// word `hello` to be selected, the `anchor` to still be `0`, and the `active`
/// to now be `5`.
#[derive(Clone, Copy, Debug, Default, PartialEq)]
#[non_exhaustive]
pub struct Selection {
/// The 'anchor' end of the selection.
///
/// This is the end of the selection that stays unchanged while holding
/// shift and pressing the arrow keys.
pub anchor: usize,
/// The 'active' end of the selection.
///
/// This is the end of the selection that moves while holding shift and
/// pressing the arrow keys.
pub active: usize,
/// The saved horizontal position, during vertical movement.
///
/// This should not be set by the IME; it will be tracked and handled by
/// the text field.
pub h_pos: Option<f64>,
}
#[allow(clippy::len_without_is_empty)]
impl Selection {
/// Create a new `Selection` with the provided `anchor` and `active` positions.
///
/// Both positions refer to UTF-8 byte indices in some text.
///
/// If your selection is a caret, you can use [`Selection::caret`] instead.
pub fn new(anchor: usize, active: usize) -> Selection {
Selection {
anchor,
active,
h_pos: None,
}
}
/// Create a new caret (zero-length selection) at the provided UTF-8 byte index.
///
/// `index` must be a grapheme cluster boundary.
pub fn caret(index: usize) -> Selection {
Selection {
anchor: index,
active: index,
h_pos: None,
}
}
/// Construct a new selection from this selection, with the provided h_pos.
///
/// # Note
///
/// `h_pos` is used to track the *pixel* location of the cursor when moving
/// vertically; lines may have available cursor positions at different
/// positions, and arrowing down and then back up should always result
/// in a cursor at the original starting location; doing this correctly
/// requires tracking this state.
///
/// You *probably* don't need to use this, unless you are implementing a new
/// text field, or otherwise implementing vertical cursor motion, in which
/// case you will want to set this during vertical motion if it is not
/// already set.
pub fn with_h_pos(mut self, h_pos: Option<f64>) -> Self {
self.h_pos = h_pos;
self
}
/// Create a new selection that is guaranteed to be valid for the provided
/// text.
#[must_use = "constrained constructs a new Selection"]
pub fn constrained(mut self, s: &str) -> Self {
let s_len = s.len();
self.anchor = self.anchor.min(s_len);
self.active = self.active.min(s_len);
while !s.is_char_boundary(self.anchor) {
self.anchor += 1;
}
while !s.is_char_boundary(self.active) {
self.active += 1;
}
self
}
/// Return the position of the upstream end of the selection.
///
/// This is end with the lesser byte index.
///
/// Because of bidirectional text, this is not necessarily "left".
pub fn min(&self) -> usize {
usize::min(self.anchor, self.active)
}
/// Return the position of the downstream end of the selection.
///
/// This is the end with the greater byte index.
///
/// Because of bidirectional text, this is not necessarily "right".
pub fn max(&self) -> usize {
usize::max(self.anchor, self.active)
}
/// The sequential range of the document represented by this selection.
///
/// This is the range that would be replaced if text were inserted at this
/// selection.
pub fn range(&self) -> Range<usize> {
self.min()..self.max()
}
/// The length, in bytes of the selected region.
///
/// If the selection is a caret, this is `0`.
pub fn len(&self) -> usize {
if self.anchor > self.active {
self.anchor - self.active
} else {
self.active - self.anchor
}
}
/// Returns `true` if the selection's length is `0`.
pub fn is_caret(&self) -> bool {
self.len() == 0
}
}
/// A lock on a text field that allows the platform to retrieve state and make
/// edits.
///
/// This trait is implemented by the application or UI framework. The platform
/// acquires this lock temporarily to apply edits corresponding to some user
/// input. So long as the `InputHandler` has not been dropped, the only changes
/// to the document state must come from calls to `InputHandler`.
///
/// Some methods require a mutable lock, as indicated when acquiring the lock
/// with `WinHandler::text_input`. If a mutable method is called on a immutable
/// lock, `InputHandler` may panic.
///
/// All ranges, lengths, and indices are specified in UTF-8 code units, unless
/// specified otherwise.
pub trait InputHandler {
/// The document's current [`Selection`].
///
/// If the selection is a vertical caret bar, then `range.start == range.end`.
/// Both `selection.anchor` and `selection.active` must be less than or
/// equal to the value returned from `InputHandler::len()`, and must land on
/// a extended grapheme cluster boundary in the document.
fn selection(&self) -> Selection;
/// Set the document's selection.
///
/// If the selection is a vertical caret bar, then `range.start == range.end`.
/// Both `selection.anchor` and `selection.active` must be less
/// than or equal to the value returned from `InputHandler::len()`.
///
/// Properties of the `Selection` *other* than `anchor` and `active` may
/// be ignored by the handler.
///
/// The `set_selection` implementation should round up (downstream) both
/// `selection.anchor` and `selection.active` to the nearest extended
/// grapheme cluster boundary.
///
/// Requries a mutable lock.
fn set_selection(&mut self, selection: Selection);
/// The current composition region.
///
/// This should be `Some` only if the IME is currently active, in which
/// case it represents the range of text that may be modified by the IME.
///
/// Both `range.start` and `range.end` must be less than or equal
/// to the value returned from `InputHandler::len()`, and must land on a
/// extended grapheme cluster boundary in the document.
fn composition_range(&self) -> Option<Range<usize>>;
/// Set the composition region.
///
/// If this is `Some` it means that the IME is currently active for this
/// region of the document. If it is `None` it means that hte IME is not
/// currently active.
///
/// Both `range.start` and `range.end` must be less than or equal to the
/// value returned from `InputHandler::len()`.
///
/// The `set_selection` implementation should round up (downstream) both
/// `range.start` and `range.end` to the nearest extended grapheme cluster
/// boundary.
///
/// Requries a mutable lock.
fn set_composition_range(&mut self, range: Option<Range<usize>>);
/// Check if the provided index is the first byte of a UTF-8 code point
/// sequence, or is the end of the document.
///
/// Equivalent in functionality to [`str::is_char_boundary`].
fn is_char_boundary(&self, i: usize) -> bool;
/// The length of the document in UTF-8 code units.
fn len(&self) -> usize;
/// Returns `true` if the length of the document is `0`.
fn is_empty(&self) -> bool {
self.len() == 0
}
/// Returns the subslice of the document represented by `range`.
///
/// # Panics
///
/// Panics if the start or end of the range do not fall on a code point
/// boundary.
fn slice(&self, range: Range<usize>) -> Cow<str>;
/// Returns the number of UTF-16 code units in the provided UTF-8 range.
///
/// Converts the document into UTF-8, looks up the range specified by
/// `utf8_range` (in UTF-8 code units), reencodes that substring into
/// UTF-16, and then returns the number of UTF-16 code units in that
/// substring.
///
/// This is automatically implemented, but you can override this if you have
/// some faster system to determine string length.
///
/// # Panics
///
/// Panics if the start or end of the range do not fall on a code point
/// boundary.
fn utf8_to_utf16(&self, utf8_range: Range<usize>) -> usize {
self.slice(utf8_range).encode_utf16().count()
}
/// Returns the number of UTF-8 code units in the provided UTF-16 range.
///
/// Converts the document into UTF-16, looks up the range specified by
/// `utf16_range` (in UTF-16 code units), reencodes that substring into
/// UTF-8, and then returns the number of UTF-8 code units in that
/// substring.
///
/// This is automatically implemented, but you can override this if you have
/// some faster system to determine string length.
fn utf16_to_utf8(&self, utf16_range: Range<usize>) -> usize {
if utf16_range.is_empty() {
return 0;
}
let doc_range = 0..self.len();
let text = self.slice(doc_range);
//FIXME: we can do this without allocating; there's an impl in piet
let utf16: Vec<u16> = text
.encode_utf16()
.skip(utf16_range.start)
.take(utf16_range.end)
.collect();
String::from_utf16_lossy(&utf16).len()
}
/// Replaces a range of the text document with `text`.
///
/// This method also sets the composition range to `None`, and updates the
/// selection:
///
/// - If both the selection's anchor and active are `< range.start`, then
/// nothing is updated. - If both the selection's anchor and active are `>
/// range.end`, then subtract `range.len()` from both, and add `text.len()`.
/// - If neither of the previous two conditions are true, then set both
/// anchor and active to `range.start + text.len()`.
///
/// After the above update, if we increase each end of the selection if
/// necessary to put it on a grapheme cluster boundary.
///
/// Requries a mutable lock.
///
/// # Panics
///
/// Panics if either end of the range does not fall on a code point
/// boundary.
fn replace_range(&mut self, range: Range<usize>, text: &str);
/// Given a `Point`, determine the corresponding text position.
fn hit_test_point(&self, point: Point) -> HitTestPoint;
/// Returns the range, in UTF-8 code units, of the line (soft- or hard-wrapped)
/// containing the byte specified by `index`.
fn line_range(&self, index: usize, affinity: Affinity) -> Range<usize>;
/// Returns the bounding box, in window coordinates, of the visible text
/// document.
///
/// For instance, a text box's bounding box would be the rectangle
/// of the border surrounding it, even if the text box is empty. If the
/// text document is completely offscreen, return `None`.
fn bounding_box(&self) -> Option<Rect>;
/// Returns the bounding box, in window coordinates, of the range of text specified by `range`.
///
/// Ranges will always be equal to or a subrange of some line range returned
/// by `InputHandler::line_range`. If a range spans multiple lines,
/// `slice_bounding_box` may panic.
fn slice_bounding_box(&self, range: Range<usize>) -> Option<Rect>;
/// Applies an [`Action`] to the text field.
///
/// Requries a mutable lock.
fn handle_action(&mut self, action: Action);
}
#[allow(dead_code)]
/// Simulates `InputHandler` calls on `handler` for a given keypress `event`.
///
/// This circumvents the platform, and so can't work with important features
/// like input method editors! However, it's necessary while we build up our
/// input support on various platforms, which takes a lot of time. We want
/// applications to start building on the new `InputHandler` interface
/// immediately, with a hopefully seamless upgrade process as we implement IME
/// input on more platforms.
pub fn simulate_input<H: WinHandler + ?Sized>(
handler: &mut H,
token: Option<TextFieldToken>,
event: KeyEvent,
) -> bool {
if handler.key_down(event.clone()) {
return true;
}
let token = match token {
Some(v) => v,
None => return false,
};
let mut input_handler = handler.acquire_input_lock(token, true);
match event.key {
KbKey::Character(c) if !event.mods.ctrl() && !event.mods.meta() && !event.mods.alt() => {
let selection = input_handler.selection();
input_handler.replace_range(selection.range(), &c);
let new_caret_index = selection.min() + c.len();
input_handler.set_selection(Selection::caret(new_caret_index));
}
KbKey::ArrowLeft => {
let movement = if event.mods.ctrl() {
Movement::Word(Direction::Left)
} else {
Movement::Grapheme(Direction::Left)
};
if event.mods.shift() {
input_handler.handle_action(Action::MoveSelecting(movement));
} else {
input_handler.handle_action(Action::Move(movement));
}
}
KbKey::ArrowRight => {
let movement = if event.mods.ctrl() {
Movement::Word(Direction::Right)
} else {
Movement::Grapheme(Direction::Right)
};
if event.mods.shift() {
input_handler.handle_action(Action::MoveSelecting(movement));
} else {
input_handler.handle_action(Action::Move(movement));
}
}
KbKey::ArrowUp => {
let movement = Movement::Vertical(VerticalMovement::LineUp);
if event.mods.shift() {
input_handler.handle_action(Action::MoveSelecting(movement));
} else {
input_handler.handle_action(Action::Move(movement));
}
}
KbKey::ArrowDown => {
let movement = Movement::Vertical(VerticalMovement::LineDown);
if event.mods.shift() {
input_handler.handle_action(Action::MoveSelecting(movement));
} else {
input_handler.handle_action(Action::Move(movement));
}
}
KbKey::Backspace => {
let movement = if event.mods.ctrl() {
Movement::Word(Direction::Upstream)
} else {
Movement::Grapheme(Direction::Upstream)
};
input_handler.handle_action(Action::Delete(movement));
}
KbKey::Delete => {
let movement = if event.mods.ctrl() {
Movement::Word(Direction::Downstream)
} else {
Movement::Grapheme(Direction::Downstream)
};
input_handler.handle_action(Action::Delete(movement));
}
KbKey::Enter => {
// I'm sorry windows, you'll get IME soon.
input_handler.handle_action(Action::InsertNewLine {
ignore_hotkey: false,
newline_type: '\n',
});
}
KbKey::Tab => {
let action = if event.mods.shift() {
Action::InsertBacktab
} else {
Action::InsertTab {
ignore_hotkey: false,
}
};
input_handler.handle_action(action);
}
KbKey::Home => {
let movement = if event.mods.ctrl() {
Movement::Vertical(VerticalMovement::DocumentStart)
} else {
Movement::Line(Direction::Upstream)
};
if event.mods.shift() {
input_handler.handle_action(Action::MoveSelecting(movement));
} else {
input_handler.handle_action(Action::Move(movement));
}
}
KbKey::End => {
let movement = if event.mods.ctrl() {
Movement::Vertical(VerticalMovement::DocumentEnd)
} else {
Movement::Line(Direction::Downstream)
};
if event.mods.shift() {
input_handler.handle_action(Action::MoveSelecting(movement));
} else {
input_handler.handle_action(Action::Move(movement));
}
}
KbKey::PageUp => {
let movement = Movement::Vertical(VerticalMovement::PageUp);
if event.mods.shift() {
input_handler.handle_action(Action::MoveSelecting(movement));
} else {
input_handler.handle_action(Action::Move(movement));
}
}
KbKey::PageDown => {
let movement = Movement::Vertical(VerticalMovement::PageDown);
if event.mods.shift() {
input_handler.handle_action(Action::MoveSelecting(movement));
} else {
input_handler.handle_action(Action::Move(movement));
}
}
_ => {
handler.release_input_lock(token);
return false;
}
};
handler.release_input_lock(token);
true
}
/// Indicates a movement that transforms a particular text position in a
/// document.
///
/// These movements transform only single indices — not selections.
///
/// You'll note that a lot of these operations are idempotent, but you can get
/// around this by first sending a `Grapheme` movement. If for instance, you
/// want a `ParagraphStart` that is not idempotent, you can first send
/// `Movement::Grapheme(Direction::Upstream)`, and then follow it with
/// `ParagraphStart`.
#[non_exhaustive]
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum Movement {
/// A movement that stops when it reaches an extended grapheme cluster boundary.
///
/// This movement is achieved on most systems by pressing the left and right
/// arrow keys. For more information on grapheme clusters, see
/// [Unicode Text Segmentation](https://unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries).
Grapheme(Direction),
/// A movement that stops when it reaches a word boundary.
///
/// This movement is achieved on most systems by pressing the left and right
/// arrow keys while holding control. For more information on words, see
/// [Unicode Text Segmentation](https://unicode.org/reports/tr29/#Word_Boundaries).
Word(Direction),
/// A movement that stops when it reaches a soft line break.
///
/// This movement is achieved on macOS by pressing the left and right arrow
/// keys while holding command. `Line` should be idempotent: if the
/// position is already at the end of a soft-wrapped line, this movement
/// should never push it onto another soft-wrapped line.
///
/// In order to implement this properly, your text positions should remember
/// their affinity.
Line(Direction),
/// An upstream movement that stops when it reaches a hard line break.
///
/// `ParagraphStart` should be idempotent: if the position is already at the
/// start of a hard-wrapped line, this movement should never push it onto
/// the previous line.
ParagraphStart,
/// A downstream movement that stops when it reaches a hard line break.
///
/// `ParagraphEnd` should be idempotent: if the position is already at the
/// end of a hard-wrapped line, this movement should never push it onto the
/// next line.
ParagraphEnd,
/// A vertical movement, see `VerticalMovement` for more details.
Vertical(VerticalMovement),
}
/// Indicates a horizontal direction in the text.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum Direction {
/// The direction visually to the left.
///
/// This may be byte-wise forwards or backwards in the document, depending
/// on the text direction around the position being moved.
Left,
/// The direction visually to the right.
///
/// This may be byte-wise forwards or backwards in the document, depending
/// on the text direction around the position being moved.
Right,
/// Byte-wise backwards in the document.
///
/// In a left-to-right context, this value is the same as `Left`.
Upstream,
/// Byte-wise forwards in the document.
///
/// In a left-to-right context, this value is the same as `Right`.
Downstream,
}
impl Direction {
/// Returns `true` if this direction is byte-wise backwards for
/// the provided [`WritingDirection`].
///
/// The provided direction *must not be* `WritingDirection::Natural`.
pub fn is_upstream_for_direction(self, direction: WritingDirection) -> bool {
assert!(
!matches!(direction, WritingDirection::Natural),
"writing direction must be resolved"
);
match self {
Direction::Upstream => true,
Direction::Downstream => false,
Direction::Left => matches!(direction, WritingDirection::LeftToRight),
Direction::Right => matches!(direction, WritingDirection::RightToLeft),
}
}
}
/// Distinguishes between two visually distinct locations with the same byte
/// index.
///
/// Sometimes, a byte location in a document has two visual locations. For
/// example, the end of a soft-wrapped line and the start of the subsequent line
/// have different visual locations (and we want to be able to place an input
/// caret in either place!) but the same byte-wise location. This also shows up
/// in bidirectional text contexts. Affinity allows us to disambiguate between
/// these two visual locations.
pub enum Affinity {
Upstream,
Downstream,
}
/// Indicates a horizontal direction for writing text.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum WritingDirection {
LeftToRight,
RightToLeft,
/// Indicates writing direction should be automatically detected based on
/// the text contents.
Natural,
}
/// Indicates a vertical movement in a text document.
#[non_exhaustive]
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum VerticalMovement {
LineUp,
LineDown,
PageUp,
PageDown,
DocumentStart,
DocumentEnd,
}
/// A special text editing command sent from the platform to the application.
#[non_exhaustive]
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum Action {
/// Moves the selection.
///
/// Before moving, if the active and the anchor of the selection are not at
/// the same position (it's a non-caret selection), then:
///
/// 1. First set both active and anchor to the same position: the
/// selection's upstream index if `Movement` is an upstream movement, or
/// the downstream index if `Movement` is a downstream movement.
///
/// 2. If `Movement` is `Grapheme`, then stop. Otherwise, apply the
/// `Movement` as per the usual rules.
Move(Movement),
/// Moves just the selection's active edge.
///
/// Equivalent to holding shift while performing movements or clicks on most
/// operating systems.
MoveSelecting(Movement),
/// Select the entire document.
SelectAll,
/// Expands the selection to the entire soft-wrapped line.
///
/// If multiple lines are already selected, expands the selection to
/// encompass all soft-wrapped lines that intersected with the prior
/// selection. If the selection is a caret is on a soft line break, uses
/// the affinity of the caret to determine which of the two lines to select.
/// `SelectLine` should be idempotent: it should never expand onto adjacent
/// lines.
SelectLine,
/// Expands the selection to the entire hard-wrapped line.
///
/// If multiple lines are already selected, expands the selection to
/// encompass all hard-wrapped lines that intersected with the prior
/// selection. `SelectParagraph` should be idempotent: it should never
/// expand onto adjacent lines.
SelectParagraph,
/// Expands the selection to the entire word.
///
/// If multiple words are already selected, expands the selection to
/// encompass all words that intersected with the prior selection. If the
/// selection is a caret is on a word boundary, selects the word downstream
/// of the caret. `SelectWord` should be idempotent: it should never expand
/// onto adjacent words.
///
/// For more information on what these so-called "words" are, see
/// [Unicode Text Segmentation](https://unicode.org/reports/tr29/#Word_Boundaries).
SelectWord,
/// Deletes some text.
///
/// If some text is already selected, `Movement` is ignored, and the
/// selection is deleted. If the selection's anchor is the same as the
/// active, then first apply `MoveSelecting(Movement)` and then delete the
/// resulting selection.
Delete(Movement),
/// Delete backwards, potentially breaking graphemes.
///
/// A special kind of backspace that, instead of deleting the entire
/// grapheme upstream of the caret, may in some cases and character sets
/// delete a subset of that grapheme's code points.
DecomposingBackspace,
/// Maps the characters in the selection to uppercase.
///
/// For more information on case mapping, see the
/// [Unicode Case Mapping FAQ](https://unicode.org/faq/casemap_charprop.html#7)
UppercaseSelection,
/// Maps the characters in the selection to lowercase.
///
/// For more information on case mapping, see the
/// [Unicode Case Mapping FAQ](https://unicode.org/faq/casemap_charprop.html#7)
LowercaseSelection,
/// Maps the characters in the selection to titlecase.
///
/// When calculating whether a character is at the beginning of a word, you
/// may have to peek outside the selection to other characters in the document.
///
/// For more information on case mapping, see the
/// [Unicode Case Mapping FAQ](https://unicode.org/faq/casemap_charprop.html#7)
TitlecaseSelection,
/// Inserts a newline character into the document.
InsertNewLine {
/// If `true`, then always insert a newline, even if normally you
/// would run a keyboard shortcut attached to the return key, like
/// sending a message or activating autocomplete.
///
/// On macOS, this is triggered by pressing option-return.
ignore_hotkey: bool,
/// Either `U+000A`, `U+2029`, or `U+2028`. For instance, on macOS, control-enter inserts `U+2028`.
//FIXME: what about windows?
newline_type: char,
},
/// Inserts a tab character into the document.
InsertTab {
/// If `true`, then always insert a tab, even if normally you would run
/// a keyboard shortcut attached to the return key, like indenting a
/// line or activating autocomplete.
///
/// On macOS, this is triggered by pressing option-tab.
ignore_hotkey: bool,
},
/// Indicates the reverse of inserting tab; corresponds to shift-tab on most
/// operating systems.
InsertBacktab,
InsertSingleQuoteIgnoringSmartQuotes,
InsertDoubleQuoteIgnoringSmartQuotes,
/// Scrolls the text field without modifying the selection.
Scroll(VerticalMovement),
/// Centers the selection vertically in the text field.
///
/// The average of the anchor's y and the active's y should be exactly
/// halfway down the field. If the selection is taller than the text
/// field's visible height, then instead scrolls the minimum distance such
/// that the text field is completely vertically filled by the selection.
ScrollToSelection,
/// Sets the writing direction of the selected text or caret.
SetSelectionWritingDirection(WritingDirection),
/// Sets the writing direction of all paragraphs that partially or fully
/// intersect with the selection or caret.
SetParagraphWritingDirection(WritingDirection),
/// Cancels the current window or operation.
///
/// Triggered on most operating systems with escape.
Cancel,
}