ltk/src/event_loop/text_editing/selection.rs

// SPDX-License-Identifier: LGPL-2.1-only
// Copyright (C) 2026 Liberux Labs, S. L. <info@liberux.net>

use crate::app::App;
use crate::event_loop::app_data::AppData;
use crate::event_loop::surface::SurfaceFocus;
use crate::tree::find_handlers;
use crate::types::Point;
use crate::widget::WidgetHandlers;

/// Compute the byte range of the "word" surrounding `byte_offset` in
/// `value`. A word is a maximal run of alphanumeric / underscore
/// chars; whitespace and punctuation count as separators. When
/// `byte_offset` falls *between* two non-word chars, both bounds
/// collapse to that offset (zero-width selection — the caller is
/// expected to either accept that or fall back to a click-position
/// cursor).
fn word_bounds_at( value: &str, byte_offset: usize ) -> ( usize, usize )
{
	if value.is_empty() { return ( 0, 0 ); }
	let bo = byte_offset.min( value.len() );
	let is_word = | c: char | c.is_alphanumeric() || c == '_';

	// Walk left from `bo` until we cross a non-word boundary.
	let mut start = bo;
	{
		let mut iter = value[..bo].char_indices().rev();
		while let Some( ( i, c ) ) = iter.next()
		{
			if is_word( c ) { start = i; } else { break; }
		}
	}

	// Walk right from `bo` until the same.
	let mut end = bo;
	for ( i, c ) in value[bo..].char_indices()
	{
		if is_word( c ) { end = bo + i + c.len_utf8(); } else { break; }
	}

	( start, end )
}

impl<A: App> AppData<A>
{
	/// `true` when this press should be treated as the second click
	/// of a double-click pair. Looks at the timestamp + position of
	/// the previous press and compares against a 400 ms / 6 px
	/// threshold (matching the GTK / Cocoa defaults). Always updates
	/// the snapshot so the next press can pair with this one.
	pub( crate ) fn note_press_for_double_click( &mut self, pos: Point ) -> bool
	{
		const WINDOW_MS: u128 = 400;
		const RADIUS:    f32  = 6.0;
		let now = std::time::Instant::now();
		let is_double = match ( self.last_press_time, self.last_press_pos )
		{
			( Some( t ), Some( p ) ) =>
			{
				let elapsed = now.duration_since( t ).as_millis();
				let dx      = pos.x - p.x;
				let dy      = pos.y - p.y;
				elapsed <= WINDOW_MS && dx.hypot( dy ) <= RADIUS
			}
			_ => false,
		};
		if is_double
		{
			// Consume the snapshot so a third quick click is not
			// re-paired with the same first click.
			self.last_press_time = None;
			self.last_press_pos  = None;
		} else {
			self.last_press_time = Some( now );
			self.last_press_pos  = Some( pos );
		}
		is_double
	}

	/// Select the word under the press. The "word" is the maximal
	/// run of alphanumeric / underscore chars surrounding the byte
	/// offset that `pos` falls on; everything else (whitespace,
	/// punctuation) counts as a separator. Empty value → no-op.
	pub( crate ) fn handle_text_select_word( &mut self, focus: SurfaceFocus, idx: usize, pos: Point )
	{
		// `select_on_focus` fields are short-form: the whole value is
		// already the natural selection unit, so a double-click does
		// not need to add a word-bound selection on top.
		let select_on_focus = matches!(
			find_handlers( &self.surface( focus ).frame.widget_rects, idx ),
			Some( WidgetHandlers::TextEdit { select_on_focus: true, .. } ),
		);
		if select_on_focus { return; }
		let ( rect, value, multiline, secure, align, font_size ) = match self.text_input_geometry( focus, idx )
		{
			Some( v ) => v,
			None      => return,
		};
		if value.is_empty() { return; }
		let cursor_pos = self.surface( focus ).frame.cursor_state.get( &idx ).copied().unwrap_or( 0 );
		let click_byte = {
			let ss = self.surface( focus );
			let canvas = match ss.canvas.as_ref() { Some( c ) => c, None => return };
			crate::widget::text_edit::byte_offset_at(
				canvas, rect, pos, &value, multiline, secure, cursor_pos, align, font_size,
			)
		};
		let ( start, end ) = word_bounds_at( &value, click_byte );
		let ss = self.surface_mut( focus );
		ss.frame.selection_anchor.insert( idx, start );
		ss.frame.cursor_state.insert( idx, end );
		ss.request_redraw();
	}

	/// Position the text cursor at the click and start a fresh
	/// selection (anchor = cursor). Called from the pointer / touch
	/// press handler after focus has been moved to the TextEdit.
	pub( crate ) fn handle_text_pointer_down( &mut self, focus: SurfaceFocus, idx: usize, pos: Point )
	{
		// Fields with `select_on_focus` (numeric pickers, short-form
		// inputs) keep the whole-value selection that `set_focus`
		// just installed — clicking is the *focus* gesture and the
		// next keystroke is meant to replace, not insert. Without
		// this guard the click-to-position below would collapse the
		// selection right after `set_focus` produced it.
		let select_on_focus = matches!(
			find_handlers( &self.surface( focus ).frame.widget_rects, idx ),
			Some( WidgetHandlers::TextEdit { select_on_focus: true, .. } ),
		);
		if select_on_focus { return; }
		let ( rect, value, multiline, secure, align, font_size ) = match self.text_input_geometry( focus, idx )
		{
			Some( v ) => v,
			None      => return,
		};
		let cursor_pos = self.surface( focus ).frame.cursor_state.get( &idx ).copied().unwrap_or( 0 );
		let byte_offset =
		{
			let ss = self.surface( focus );
			let canvas = match ss.canvas.as_ref() { Some( c ) => c, None => return };
			crate::widget::text_edit::byte_offset_at(
				canvas, rect, pos, &value, multiline, secure, cursor_pos, align, font_size,
			)
		};
		let ss = self.surface_mut( focus );
		ss.frame.cursor_state.insert( idx, byte_offset );
		ss.frame.selection_anchor.insert( idx, byte_offset );
		ss.request_redraw();
	}

	/// Extend the selection by moving the cursor to the new pointer
	/// position. Called from the pointer / touch motion handler while
	/// a press is active and the original press landed on a TextEdit.
	/// The selection anchor (set on press) stays put.
	pub( crate ) fn handle_text_pointer_drag( &mut self, focus: SurfaceFocus, idx: usize, pos: Point )
	{
		// Same `select_on_focus` guard as the press-down path: the
		// short-form field stays whole-selected even if the user
		// drags the pointer over the digits.
		let select_on_focus = matches!(
			find_handlers( &self.surface( focus ).frame.widget_rects, idx ),
			Some( WidgetHandlers::TextEdit { select_on_focus: true, .. } ),
		);
		if select_on_focus { return; }
		let ( rect, value, multiline, secure, align, font_size ) = match self.text_input_geometry( focus, idx )
		{
			Some( v ) => v,
			None      => return,
		};
		let cursor_pos = self.surface( focus ).frame.cursor_state.get( &idx ).copied().unwrap_or( 0 );
		let byte_offset =
		{
			let ss = self.surface( focus );
			let canvas = match ss.canvas.as_ref() { Some( c ) => c, None => return };
			crate::widget::text_edit::byte_offset_at(
				canvas, rect, pos, &value, multiline, secure, cursor_pos, align, font_size,
			)
		};
		let ss = self.surface_mut( focus );
		ss.frame.cursor_state.insert( idx, byte_offset );
		ss.request_redraw();
	}

	/// Collapse any active selection on the focused text input to its
	/// cursor position. Returns `true` when a collapse happened so
	/// the caller (Esc handler) can short-circuit other behaviour.
	pub( crate ) fn collapse_selection_if_any( &mut self, focus: SurfaceFocus ) -> bool
	{
		let idx = match self.surface( focus ).focused_idx { Some( i ) => i, None => return false };
		let cursor = self.surface( focus ).frame.cursor_state.get( &idx ).copied();
		let anchor = self.surface( focus ).frame.selection_anchor.get( &idx ).copied();
		let ( c, a ) = match ( cursor, anchor )
		{
			( Some( c ), Some( a ) ) if c != a => ( c, a ),
			_                                   => return false,
		};
		let _ = a;
		let ss = self.surface_mut( focus );
		ss.frame.selection_anchor.insert( idx, c );
		ss.request_redraw();
		true
	}

	/// Select the entire value of the focused text input. Used by
	/// Ctrl+A.
	pub( crate ) fn handle_select_all( &mut self, focus: SurfaceFocus )
	{
		let ( idx, value ) = match self.focused_text_value( focus ) { Some( v ) => v, None => return };
		let ss = self.surface_mut( focus );
		*ss.frame.cursor_state.entry( idx ).or_insert( 0 ) = value.len();
		*ss.frame.selection_anchor.entry( idx ).or_insert( 0 ) = 0;
		ss.request_redraw();
	}

	/// Snapshot the currently-selected text for the focused widget.
	/// Returns `None` when no text input is focused or the selection
	/// is empty.
	pub( crate ) fn focused_selection_text( &self, focus: SurfaceFocus ) -> Option<String>
	{
		let ( idx, value ) = self.focused_text_value( focus )?;
		let cursor = self.surface( focus ).frame.cursor_state.get( &idx ).copied()
			.unwrap_or( value.len() ).min( value.len() );
		let anchor = self.surface( focus ).frame.selection_anchor.get( &idx ).copied()
			.unwrap_or( cursor ).min( value.len() );
		if anchor == cursor { return None; }
		let s = cursor.min( anchor );
		let e = cursor.max( anchor );
		Some( value[s..e].to_string() )
	}

	/// Delete the current selection (if non-empty), updating the
	/// pending text value and cursor / anchor. Returns the resulting
	/// string when a deletion happened so the caller can dispatch the
	/// `on_change` message; returns `None` when there was no selection
	/// to delete.
	pub( crate ) fn delete_selection( &mut self, focus: SurfaceFocus ) -> Option<String>
	{
		let ( idx, value ) = self.focused_text_value( focus )?;
		let cursor = self.surface( focus ).frame.cursor_state.get( &idx ).copied()
			.unwrap_or( value.len() ).min( value.len() );
		let anchor = self.surface( focus ).frame.selection_anchor.get( &idx ).copied()
			.unwrap_or( cursor ).min( value.len() );
		if anchor == cursor { return None; }
		let s = cursor.min( anchor );
		let e = cursor.max( anchor );
		let mut new_value = value;
		new_value.replace_range( s..e, "" );
		// `select_on_focus` fields keep the cursor at the end of the
		// post-update displayed value via the `usize::MAX` sentinel —
		// see `handle_text_insert` for the reasoning.
		let select_on_focus = matches!(
			find_handlers( &self.surface( focus ).frame.widget_rects, idx ),
			Some( WidgetHandlers::TextEdit { select_on_focus: true, .. } ),
		);
		let next_cursor = if select_on_focus { usize::MAX } else { s };
		let ss = self.surface_mut( focus );
		*ss.frame.cursor_state.entry( idx ).or_insert( 0 ) = next_cursor;
		*ss.frame.selection_anchor.entry( idx ).or_insert( 0 ) = next_cursor;
		ss.pending_text_values.insert( idx, new_value.clone() );
		ss.request_redraw();
		Some( new_value )
	}
}