systemless 0.27.11

High-Level Emulation for classic Macintosh applications
Documentation 
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//! Architecture-neutral TextEdit editing semantics.
//!
//! The 68K trap and PowerPC import layers translate guest ABI and memory into
//! this model, then serialize the result back into their respective `TERec`.

use std::ops::Range;

/// Mutable text and normalized selection state for one TextEdit operation.
#[derive(Clone, Debug, Eq, PartialEq)]
pub(crate) struct TextEditBuffer {
    text: Vec<u8>,
    selection: Range<usize>,
}

impl TextEditBuffer {
    /// Load guest text and clamp its possibly reversed selection.
    pub(crate) fn new(text: Vec<u8>, selection_start: usize, selection_end: usize) -> Self {
        let start = selection_start.min(text.len());
        let end = selection_end.min(text.len());
        Self {
            text,
            selection: start.min(end)..start.max(end),
        }
    }

    pub(crate) fn text(&self) -> &[u8] {
        &self.text
    }

    pub(crate) fn selection(&self) -> Range<usize> {
        self.selection.clone()
    }

    pub(crate) fn selected_text(&self) -> &[u8] {
        &self.text[self.selection.clone()]
    }

    /// Replace the selected range and collapse the selection after the insert.
    ///
    /// Inside Macintosh: Text (1993), pp. 2-81 and 2-92--2-93.
    pub(crate) fn replace_selection(&mut self, inserted: &[u8]) {
        let insertion_start = self.selection.start;
        self.text
            .splice(self.selection.clone(), inserted.iter().copied());
        let insertion_end = insertion_start
            .saturating_add(inserted.len())
            .min(self.text.len());
        self.selection = insertion_end..insertion_end;
    }

    /// Delete a nonempty selection, leaving an insertion point at its start.
    ///
    /// Inside Macintosh: Text (1993), pp. 2-91--2-92.
    pub(crate) fn delete_selection(&mut self) -> bool {
        if self.selection.is_empty() {
            return false;
        }
        self.replace_selection(&[]);
        true
    }

    /// Apply the byte accepted by `TEKey`.
    ///
    /// Backspace deletes the selection or the preceding character. Left and
    /// right arrows move or collapse the caret rather than becoming text.
    /// Inside Macintosh: Text (1993), pp. 2-36--2-37 and 2-81--2-82.
    pub(crate) fn apply_key(&mut self, key: u8) {
        match key {
            0x08 | 0x7f => {
                if self.selection.is_empty() && self.selection.start > 0 {
                    self.selection.start -= 1;
                }
                self.replace_selection(&[]);
            }
            0x1c => {
                let caret = if self.selection.is_empty() {
                    self.selection.start.saturating_sub(1)
                } else {
                    self.selection.start
                };
                self.selection = caret..caret;
            }
            0x1d => {
                let caret = if self.selection.is_empty() {
                    self.selection.end.saturating_add(1).min(self.text.len())
                } else {
                    self.selection.end
                };
                self.selection = caret..caret;
            }
            _ => self.replace_selection(&[key]),
        }
    }
}

/// Horizontal origin for a TextEdit line, including its caller-selected inset.
///
/// Inside Macintosh: Text (1993), pp. 2-87--2-88.
pub(crate) fn aligned_line_left(
    left: i16,
    right: i16,
    width: i16,
    alignment: i16,
    left_inset: i16,
) -> i16 {
    match alignment {
        1 => left.saturating_add(right.saturating_sub(left).saturating_sub(width) / 2),
        -1 => right.saturating_sub(width),
        _ => left.saturating_add(left_inset),
    }
}

#[cfg(test)]
mod tests {
    use super::{aligned_line_left, TextEditBuffer};

    #[test]
    fn selection_is_clamped_and_normalized_once() {
        let buffer = TextEditBuffer::new(b"toolbox".to_vec(), 20, 3);

        assert_eq!(buffer.selection(), 3..7);
        assert_eq!(buffer.selected_text(), b"lbox");
    }

    #[test]
    fn replace_and_delete_share_selection_semantics() {
        let mut buffer = TextEditBuffer::new(b"one three".to_vec(), 4, 4);
        buffer.replace_selection(b"two ");
        assert_eq!(buffer.text(), b"one two three");
        assert_eq!(buffer.selection(), 8..8);

        let mut buffer = TextEditBuffer::new(buffer.text().to_vec(), 8, 4);
        assert!(buffer.delete_selection());
        assert_eq!(buffer.text(), b"one three");
        assert_eq!(buffer.selection(), 4..4);
        assert!(!buffer.delete_selection());
    }

    #[test]
    fn key_editing_handles_backspace_and_caret_arrows() {
        let mut buffer = TextEditBuffer::new(b"abc".to_vec(), 2, 2);
        buffer.apply_key(0x08);
        assert_eq!(buffer.text(), b"ac");
        assert_eq!(buffer.selection(), 1..1);

        buffer.apply_key(0x1c);
        assert_eq!(buffer.selection(), 0..0);
        buffer.apply_key(0x1d);
        assert_eq!(buffer.selection(), 1..1);
        assert_eq!(buffer.text(), b"ac");
    }

    #[test]
    fn alignment_is_shared_for_every_guest_adapter() {
        assert_eq!(aligned_line_left(20, 200, 80, 0, 1), 21);
        assert_eq!(aligned_line_left(20, 200, 80, -2, 1), 21);
        assert_eq!(aligned_line_left(20, 200, 80, 1, 1), 70);
        assert_eq!(aligned_line_left(20, 200, 80, -1, 1), 120);
    }
}