ARCADIA-Studio/crates/oa-desktop/src/source_navigation/selection.rs

//! Effective selected-byte ranges for a committed departure from a source view.
//!
//! Iced's `Cursor` omits cosmic-text's Word/Line selection kind. Saving its raw
//! endpoints can therefore save an empty range for a visibly selected word/line.
//! Capture only after navigation admission and destination validation succeed,
//! immediately before replacing/leaving the live editor. Never use this to inspect
//! pending queries, failed/no-op navigation, or restore focus to the same editor.
use iced::advanced::{graphics, text};
use iced::widget::text_editor::{Action, Content, Cursor, Motion, Position};

/// Capture the effective range for restoration on fresh Content via `move_to`.
///
/// A nonempty selection is collapsed to its start in the departing Content; text
/// is not edited. The returned Normal range preserves selected bytes and typing
/// replacement, not Word/Line gesture-extension mode or an interior click point.
/// Unequal raw endpoint direction is preserved; coincident Word/Line endpoints
/// canonically restore with the active cursor at the effective end.
///
/// The renderer constraint is intentional: the inspected Iced graphics editor
/// collapses any selection to its effective start for `Move(Left)`, and its copied
/// selection joins editor lines with LF regardless of physical CRLF/LF endings.
/// Only the selected text is temporarily copied; retained state is one Cursor.
pub fn capture<R>(content: &mut Content<R>) -> Cursor
where
    R: text::Renderer<Editor = graphics::text::Editor>,
{
    let original = content.cursor();
    let Some(selected) = content.selection().filter(|selected| !selected.is_empty()) else {
        // Moving an unselected caret Left would be a user-visible navigation.
        return original;
    };
    let active_start = original.selection.is_some_and(|anchor| {
        (original.position.line, original.position.column) < (anchor.line, anchor.column)
    });
    content.perform(Action::Move(Motion::Left));
    let start = content.cursor().position;
    let end = match selected.rsplit_once('\n') {
        Some((prefix, suffix)) => Position {
            line: start.line + prefix.bytes().filter(|byte| *byte == b'\n').count() + 1,
            column: suffix.len(),
        },
        None => Position {
            line: start.line,
            column: start.column + selected.len(),
        },
    };
    // These sums describe an existing selection in this same allocated buffer;
    // neither can exceed its line count / existing UTF-8 line length. A checked
    // error after collapsing would leave a failed departure with lost selection.
    debug_assert!(content.cursor().selection.is_none());
    debug_assert!(start.line < content.line_count() && end.line < content.line_count());
    debug_assert!((start.line, start.column) < (end.line, end.column));
    Cursor {
        position: if active_start { start } else { end },
        selection: Some(if active_start { end } else { start }),
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use iced::widget::text_editor::Edit;
    use std::sync::Arc;

    type EditorContent = Content<iced::Renderer>;

    fn at(line: usize, column: usize) -> Position {
        Position { line, column }
    }

    fn range(start: Position, end: Position, active_start: bool) -> Cursor {
        Cursor {
            position: if active_start { start } else { end },
            selection: Some(if active_start { end } else { start }),
        }
    }

    fn caret(content: &mut EditorContent, position: Position) {
        content.move_to(Cursor {
            position,
            selection: None,
        });
    }

    fn roundtrip(
        source: &str,
        prepare: impl Fn(&mut EditorContent),
        selected: &str,
        expected: Cursor,
        lossy_raw: bool,
    ) {
        let mut departing = EditorContent::with_text(source);
        prepare(&mut departing);
        assert_eq!(departing.text(), source);
        assert_eq!(departing.selection().as_deref(), Some(selected));
        let raw = departing.cursor();

        // Independent direct-typing control retains the original semantic mode.
        let replacement = Action::Edit(Edit::Paste(Arc::new("替🚀".into())));
        let mut direct = EditorContent::with_text(source);
        prepare(&mut direct);
        direct.perform(replacement.clone());

        let captured = capture(&mut departing);
        assert_eq!(captured, expected);
        assert_eq!(
            departing.text(),
            source,
            "capture cannot edit physical source bytes"
        );
        assert!(departing.cursor().selection.is_none());
        let mut restored = EditorContent::with_text(source);
        restored.move_to(captured);
        assert_eq!(restored.selection().as_deref(), Some(selected));
        assert_eq!(restored.text(), source);
        restored.perform(replacement);
        assert_eq!(
            restored.text(),
            direct.text(),
            "restored range must replace exactly the original selected bytes"
        );
        assert_eq!(restored.cursor(), direct.cursor());
        if lossy_raw {
            let mut old = EditorContent::with_text(source);
            old.move_to(raw);
            assert_ne!(
                old.selection().as_deref(),
                Some(selected),
                "negative control must discriminate raw cursor storage"
            );
        } else {
            assert_eq!(
                captured, raw,
                "ordinary directional ranges are already canonical"
            );
        }
    }

    #[test]
    fn unicode_normal_ranges_preserve_forward_and_reverse_direction() {
        let source = "先 αβ 救助 🚀 tail\r\n";
        for active_start in [false, true] {
            let expected = range(
                at(0, "先 ".len()),
                at(0, "先 αβ 救助 🚀".len()),
                active_start,
            );
            roundtrip(
                source,
                |content| content.move_to(expected),
                "αβ 救助 🚀",
                expected,
                false,
            );
        }
    }

    #[test]
    fn repeated_unicode_words_capture_the_selected_occurrence_without_searching() {
        let source = "éclair éclair éclair\r\n";
        let start = "éclair ".len();
        roundtrip(
            source,
            |content| {
                caret(content, at(0, start + "écl".len()));
                content.perform(Action::SelectWord);
            },
            "éclair",
            range(at(0, start), at(0, start + "éclair".len()), false),
            true,
        );
    }

    #[test]
    fn line_selection_expands_past_its_interior_unicode_caret() {
        let source = "first\r\n救助 🚀 tail\r\nlast";
        roundtrip(
            source,
            |content| {
                caret(content, at(1, "救助 ".len()));
                content.perform(Action::SelectLine);
            },
            "救助 🚀 tail",
            range(at(1, 0), at(1, "救助 🚀 tail".len()), false),
            true,
        );
    }

    #[test]
    fn multiline_ranges_use_copied_lf_and_utf8_columns_for_physical_crlf_and_mixed_endings() {
        for source in ["pré α\r\n中 🚀\r\nfin Ω", "pré α\n中 🚀\r\nfin Ω"] {
            for active_start in [false, true] {
                let expected = range(at(0, "pré ".len()), at(2, "fin ".len()), active_start);
                roundtrip(
                    source,
                    |content| content.move_to(expected),
                    "α\n中 🚀\nfin ",
                    expected,
                    false,
                );
            }
        }
    }

    #[test]
    fn expanded_word_and_line_modes_capture_multiline_ranges_in_both_directions() {
        let source = "one alpha\r\ntwo beta\nthree gamma";
        for line in [false, true] {
            for reverse in [false, true] {
                let (start, end, selected) = match (line, reverse) {
                    (false, false) => (at(0, 4), at(2, 11), "alpha\ntwo beta\nthree gamma"),
                    (false, true) => (at(0, 0), at(2, 11), "one alpha\ntwo beta\nthree gamma"),
                    (true, _) => (at(0, 0), at(2, 11), "one alpha\ntwo beta\nthree gamma"),
                };
                roundtrip(
                    source,
                    |content| {
                        caret(content, if reverse { at(2, 8) } else { at(0, 6) });
                        content.perform(if line {
                            Action::SelectLine
                        } else {
                            Action::SelectWord
                        });
                        // Iced preserves existing Word/Line mode for Select motions.
                        content.perform(Action::Select(if reverse {
                            Motion::DocumentStart
                        } else {
                            Motion::DocumentEnd
                        }));
                    },
                    selected,
                    range(start, end, reverse),
                    true,
                );
            }
        }
    }

    #[test]
    fn trailing_newline_selection_restores_endpoint_on_the_empty_last_line() {
        let source = "雨\r\n🚀\r\n";
        let expected = range(at(0, 0), at(2, 0), false);
        roundtrip(
            source,
            |content| content.perform(Action::SelectAll),
            "雨\n🚀\n",
            expected,
            false,
        );
    }

    #[test]
    fn absent_and_empty_selection_do_not_move_the_departing_caret() {
        for source in ["", "\r\n", "alpha\r\n\r\ntail"] {
            for empty_selection in [false, true] {
                let mut content = EditorContent::with_text(source);
                let position = if source.starts_with("alpha") {
                    at(1, 0)
                } else {
                    at(0, 0)
                };
                caret(&mut content, position);
                if empty_selection {
                    content.perform(Action::SelectLine);
                    assert_eq!(content.selection().as_deref(), Some(""));
                } else {
                    assert!(content.selection().is_none());
                }
                let raw = content.cursor();
                let selected = content.selection();
                assert_eq!(capture(&mut content), raw);
                assert_eq!(content.cursor(), raw);
                assert_eq!(content.selection(), selected);
                assert_eq!(content.text(), source);
            }
        }
        for empty_normal in [false, true] {
            let mut content = EditorContent::with_text("éclair");
            let position = at(0, "écl".len());
            content.move_to(Cursor {
                position,
                selection: empty_normal.then_some(position),
            });
            let raw = content.cursor();
            let selected = content.selection();
            assert_eq!(capture(&mut content), raw);
            assert_eq!(
                content.cursor(),
                raw,
                "an unselected interior caret must not move left"
            );
            assert_eq!(content.selection(), selected);
        }
    }
}