editable_text.rs

// This software is licensed under Apache License 2.0 and distributed on an
// "as-is" basis without warranties of any kind. See the LICENSE file for
// details.

//! Traits for text editing and a basic String implementation.

use std::borrow::Cow;
use std::ops::{Deref, Range};
use std::sync::Arc;

use unicode_segmentation::{GraphemeCursor, UnicodeSegmentation};

/// An EditableText trait.
pub trait EditableText: Sized {
    // TODO: would be nice to have something like
    // type Cursor: EditableTextCursor<Self>;

    /// Create a cursor with a reference to the text and a offset position.
    ///
    /// Returns None if the position isn't a codepoint boundary.
    fn cursor(&self, position: usize) -> Option<StringCursor>;

    /// Replace range with new text.
    /// Can panic if supplied an invalid range.
    // TODO: make this generic over Self
    fn edit(&mut self, range: Range<usize>, new: impl Into<String>);

    /// Get slice of text at range.
    fn slice(&self, range: Range<usize>) -> Option<Cow<str>>;

    /// Get length of text (in bytes).
    fn len(&self) -> usize;

    /// Get the previous word offset from the given offset, if it exists.
    fn prev_word_offset(&self, offset: usize) -> Option<usize>;

    /// Get the next word offset from the given offset, if it exists.
    fn next_word_offset(&self, offset: usize) -> Option<usize>;

    /// Get the next grapheme offset from the given offset, if it exists.
    fn prev_grapheme_offset(&self, offset: usize) -> Option<usize>;

    /// Get the next grapheme offset from the given offset, if it exists.
    fn next_grapheme_offset(&self, offset: usize) -> Option<usize>;

    /// Get the previous codepoint offset from the given offset, if it exists.
    fn prev_codepoint_offset(&self, offset: usize) -> Option<usize>;

    /// Get the next codepoint offset from the given offset, if it exists.
    fn next_codepoint_offset(&self, offset: usize) -> Option<usize>;

    /// Get the preceding line break offset from the given offset
    fn preceding_line_break(&self, offset: usize) -> usize;

    /// Get the next line break offset from the given offset
    fn next_line_break(&self, offset: usize) -> usize;

    /// Returns `true` if this text has 0 length.
    fn is_empty(&self) -> bool;

    /// Construct an instance of this type from a `&str`.
    fn from_str(s: &str) -> Self;
}

impl EditableText for String {
    fn cursor<'a>(&self, position: usize) -> Option<StringCursor> {
        let new_cursor = StringCursor {
            text: self,
            position,
        };

        if new_cursor.is_boundary() {
            Some(new_cursor)
        } else {
            None
        }
    }

    fn edit(&mut self, range: Range<usize>, new: impl Into<String>) {
        self.replace_range(range, &new.into());
    }

    fn slice(&self, range: Range<usize>) -> Option<Cow<str>> {
        self.get(range).map(Cow::from)
    }

    fn len(&self) -> usize {
        self.len()
    }

    fn prev_grapheme_offset(&self, from: usize) -> Option<usize> {
        let mut c = GraphemeCursor::new(from, self.len(), true);
        c.prev_boundary(self, 0).unwrap()
    }

    fn next_grapheme_offset(&self, from: usize) -> Option<usize> {
        let mut c = GraphemeCursor::new(from, self.len(), true);
        c.next_boundary(self, 0).unwrap()
    }

    fn prev_codepoint_offset(&self, from: usize) -> Option<usize> {
        let mut c = self.cursor(from).unwrap();
        c.prev()
    }

    fn next_codepoint_offset(&self, from: usize) -> Option<usize> {
        let mut c = self.cursor(from).unwrap();
        if c.next().is_some() {
            Some(c.pos())
        } else {
            None
        }
    }

    fn prev_word_offset(&self, from: usize) -> Option<usize> {
        let mut offset = from;
        let mut passed_alphanumeric = false;
        for prev_grapheme in self.get(0..from)?.graphemes(true).rev() {
            let is_alphanumeric = prev_grapheme.chars().next()?.is_alphanumeric();
            if is_alphanumeric {
                passed_alphanumeric = true;
            } else if passed_alphanumeric {
                return Some(offset);
            }
            offset -= prev_grapheme.len();
        }
        None
    }

    fn next_word_offset(&self, from: usize) -> Option<usize> {
        let mut offset = from;
        let mut passed_alphanumeric = false;
        for next_grapheme in self.get(from..)?.graphemes(true) {
            let is_alphanumeric = next_grapheme.chars().next()?.is_alphanumeric();
            if is_alphanumeric {
                passed_alphanumeric = true;
            } else if passed_alphanumeric {
                return Some(offset);
            }
            offset += next_grapheme.len();
        }
        Some(self.len())
    }

    fn is_empty(&self) -> bool {
        self.is_empty()
    }

    fn from_str(s: &str) -> Self {
        s.to_string()
    }

    fn preceding_line_break(&self, from: usize) -> usize {
        let mut offset = from;

        for byte in self.get(0..from).unwrap_or("").bytes().rev() {
            if byte == 0x0a {
                return offset;
            }
            offset -= 1;
        }

        0
    }

    fn next_line_break(&self, from: usize) -> usize {
        let mut offset = from;

        for char in self.get(from..).unwrap_or("").bytes() {
            if char == 0x0a {
                return offset;
            }
            offset += 1;
        }

        self.len()
    }
}

impl EditableText for Arc<String> {
    fn cursor(&self, position: usize) -> Option<StringCursor> {
        <String as EditableText>::cursor(self, position)
    }
    fn edit(&mut self, range: Range<usize>, new: impl Into<String>) {
        let new = new.into();
        if !range.is_empty() || !new.is_empty() {
            Arc::make_mut(self).edit(range, new)
        }
    }
    fn slice(&self, range: Range<usize>) -> Option<Cow<str>> {
        Some(Cow::Borrowed(&self[range]))
    }
    fn len(&self) -> usize {
        self.deref().len()
    }
    fn prev_word_offset(&self, offset: usize) -> Option<usize> {
        self.deref().prev_word_offset(offset)
    }
    fn next_word_offset(&self, offset: usize) -> Option<usize> {
        self.deref().next_word_offset(offset)
    }
    fn prev_grapheme_offset(&self, offset: usize) -> Option<usize> {
        self.deref().prev_grapheme_offset(offset)
    }
    fn next_grapheme_offset(&self, offset: usize) -> Option<usize> {
        self.deref().next_grapheme_offset(offset)
    }
    fn prev_codepoint_offset(&self, offset: usize) -> Option<usize> {
        self.deref().prev_codepoint_offset(offset)
    }
    fn next_codepoint_offset(&self, offset: usize) -> Option<usize> {
        self.deref().next_codepoint_offset(offset)
    }
    fn preceding_line_break(&self, offset: usize) -> usize {
        self.deref().preceding_line_break(offset)
    }
    fn next_line_break(&self, offset: usize) -> usize {
        self.deref().next_line_break(offset)
    }
    fn is_empty(&self) -> bool {
        self.deref().is_empty()
    }
    fn from_str(s: &str) -> Self {
        Arc::new(s.to_owned())
    }
}

/// A cursor with convenience functions for moving through EditableText.
pub trait EditableTextCursor<EditableText> {
    /// Set cursor position.
    fn set(&mut self, position: usize);

    /// Get cursor position.
    fn pos(&self) -> usize;

    /// Check if cursor position is at a codepoint boundary.
    fn is_boundary(&self) -> bool;

    /// Move cursor to previous codepoint boundary, if it exists.
    /// Returns previous codepoint as usize offset.
    fn prev(&mut self) -> Option<usize>;

    /// Move cursor to next codepoint boundary, if it exists.
    /// Returns current codepoint as usize offset.
    fn next(&mut self) -> Option<usize>;

    /// Get the next codepoint after the cursor position, without advancing
    /// the cursor.
    fn peek_next_codepoint(&self) -> Option<char>;

    /// Return codepoint preceding cursor offset and move cursor backward.
    fn prev_codepoint(&mut self) -> Option<char>;

    /// Return codepoint at cursor offset and move cursor forward.
    fn next_codepoint(&mut self) -> Option<char>;

    /// Return current offset if it's a boundary, else next.
    fn at_or_next(&mut self) -> Option<usize>;

    /// Return current offset if it's a boundary, else previous.
    fn at_or_prev(&mut self) -> Option<usize>;
}

/// A cursor type that implements EditableTextCursor for String
#[derive(Debug)]
pub struct StringCursor<'a> {
    text: &'a str,
    position: usize,
}

impl<'a> EditableTextCursor<&'a String> for StringCursor<'a> {
    fn set(&mut self, position: usize) {
        self.position = position;
    }

    fn pos(&self) -> usize {
        self.position
    }

    fn is_boundary(&self) -> bool {
        self.text.is_char_boundary(self.position)
    }

    fn prev(&mut self) -> Option<usize> {
        let current_pos = self.pos();

        if current_pos == 0 {
            None
        } else {
            let mut len = 1;
            while !self.text.is_char_boundary(current_pos - len) {
                len += 1;
            }
            self.set(self.pos() - len);
            Some(self.pos())
        }
    }

    fn next(&mut self) -> Option<usize> {
        let current_pos = self.pos();

        if current_pos == self.text.len() {
            None
        } else {
            let b = self.text.as_bytes()[current_pos];
            self.set(current_pos + len_utf8_from_first_byte(b));
            Some(current_pos)
        }
    }

    fn peek_next_codepoint(&self) -> Option<char> {
        self.text[self.pos()..].chars().next()
    }

    fn prev_codepoint(&mut self) -> Option<char> {
        if let Some(prev) = self.prev() {
            self.text[prev..].chars().next()
        } else {
            None
        }
    }

    fn next_codepoint(&mut self) -> Option<char> {
        let current_index = self.pos();
        if self.next().is_some() {
            self.text[current_index..].chars().next()
        } else {
            None
        }
    }

    fn at_or_next(&mut self) -> Option<usize> {
        if self.is_boundary() {
            Some(self.pos())
        } else {
            self.next()
        }
    }

    fn at_or_prev(&mut self) -> Option<usize> {
        if self.is_boundary() {
            Some(self.pos())
        } else {
            self.prev()
        }
    }
}

pub fn len_utf8_from_first_byte(b: u8) -> usize {
    match b {
        b if b < 0x80 => 1,
        b if b < 0xe0 => 2,
        b if b < 0xf0 => 3,
        _ => 4,
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn replace() {
        let mut a = String::from("hello world");
        a.edit(1..9, "era");
        assert_eq!("herald", a);
    }

    #[test]
    fn prev_codepoint_offset() {
        let a = String::from("a\u{00A1}\u{4E00}\u{1F4A9}");
        assert_eq!(Some(6), a.prev_codepoint_offset(10));
        assert_eq!(Some(3), a.prev_codepoint_offset(6));
        assert_eq!(Some(1), a.prev_codepoint_offset(3));
        assert_eq!(Some(0), a.prev_codepoint_offset(1));
        assert_eq!(None, a.prev_codepoint_offset(0));
        let b = a.slice(1..10).unwrap().to_string();
        assert_eq!(Some(5), b.prev_codepoint_offset(9));
        assert_eq!(Some(2), b.prev_codepoint_offset(5));
        assert_eq!(Some(0), b.prev_codepoint_offset(2));
        assert_eq!(None, b.prev_codepoint_offset(0));
    }

    #[test]
    fn next_codepoint_offset() {
        let a = String::from("a\u{00A1}\u{4E00}\u{1F4A9}");
        assert_eq!(Some(10), a.next_codepoint_offset(6));
        assert_eq!(Some(6), a.next_codepoint_offset(3));
        assert_eq!(Some(3), a.next_codepoint_offset(1));
        assert_eq!(Some(1), a.next_codepoint_offset(0));
        assert_eq!(None, a.next_codepoint_offset(10));
        let b = a.slice(1..10).unwrap().to_string();
        assert_eq!(Some(9), b.next_codepoint_offset(5));
        assert_eq!(Some(5), b.next_codepoint_offset(2));
        assert_eq!(Some(2), b.next_codepoint_offset(0));
        assert_eq!(None, b.next_codepoint_offset(9));
    }

    #[test]
    fn prev_next() {
        let input = String::from("abc");
        let mut cursor = input.cursor(0).unwrap();
        assert_eq!(cursor.next(), Some(0));
        assert_eq!(cursor.next(), Some(1));
        assert_eq!(cursor.prev(), Some(1));
        assert_eq!(cursor.next(), Some(1));
        assert_eq!(cursor.next(), Some(2));
    }

    #[test]
    fn peek_next_codepoint() {
        let inp = String::from("$¢€£💶");
        let mut cursor = inp.cursor(0).unwrap();
        assert_eq!(cursor.peek_next_codepoint(), Some('$'));
        assert_eq!(cursor.peek_next_codepoint(), Some('$'));
        assert_eq!(cursor.next_codepoint(), Some('$'));
        assert_eq!(cursor.peek_next_codepoint(), Some('¢'));
        assert_eq!(cursor.prev_codepoint(), Some('$'));
        assert_eq!(cursor.peek_next_codepoint(), Some('$'));
        assert_eq!(cursor.next_codepoint(), Some('$'));
        assert_eq!(cursor.next_codepoint(), Some('¢'));
        assert_eq!(cursor.peek_next_codepoint(), Some('€'));
        assert_eq!(cursor.next_codepoint(), Some('€'));
        assert_eq!(cursor.peek_next_codepoint(), Some('£'));
        assert_eq!(cursor.next_codepoint(), Some('£'));
        assert_eq!(cursor.peek_next_codepoint(), Some('💶'));
        assert_eq!(cursor.next_codepoint(), Some('💶'));
        assert_eq!(cursor.peek_next_codepoint(), None);
        assert_eq!(cursor.next_codepoint(), None);
        assert_eq!(cursor.peek_next_codepoint(), None);
    }

    #[test]
    fn prev_grapheme_offset() {
        // A with ring, hangul, regional indicator "US"
        let a = String::from("A\u{030a}\u{110b}\u{1161}\u{1f1fa}\u{1f1f8}");
        assert_eq!(Some(9), a.prev_grapheme_offset(17));
        assert_eq!(Some(3), a.prev_grapheme_offset(9));
        assert_eq!(Some(0), a.prev_grapheme_offset(3));
        assert_eq!(None, a.prev_grapheme_offset(0));
    }

    #[test]
    fn next_grapheme_offset() {
        // A with ring, hangul, regional indicator "US"
        let a = String::from("A\u{030a}\u{110b}\u{1161}\u{1f1fa}\u{1f1f8}");
        assert_eq!(Some(3), a.next_grapheme_offset(0));
        assert_eq!(Some(9), a.next_grapheme_offset(3));
        assert_eq!(Some(17), a.next_grapheme_offset(9));
        assert_eq!(None, a.next_grapheme_offset(17));
    }

    #[test]
    fn prev_word_offset() {
        let a = String::from("Technically a word: ৬藏A\u{030a}\u{110b}\u{1161}");
        assert_eq!(Some(20), a.prev_word_offset(35));
        assert_eq!(Some(20), a.prev_word_offset(27));
        assert_eq!(Some(20), a.prev_word_offset(23));
        assert_eq!(Some(14), a.prev_word_offset(20));
        assert_eq!(Some(14), a.prev_word_offset(19));
        assert_eq!(Some(12), a.prev_word_offset(13));
        assert_eq!(None, a.prev_word_offset(12));
        assert_eq!(None, a.prev_word_offset(11));
        assert_eq!(None, a.prev_word_offset(0));
    }

    #[test]
    fn next_word_offset() {
        let a = String::from("Technically a word: ৬藏A\u{030a}\u{110b}\u{1161}");
        assert_eq!(Some(11), a.next_word_offset(0));
        assert_eq!(Some(11), a.next_word_offset(7));
        assert_eq!(Some(13), a.next_word_offset(11));
        assert_eq!(Some(18), a.next_word_offset(14));
        assert_eq!(Some(35), a.next_word_offset(18));
        assert_eq!(Some(35), a.next_word_offset(19));
        assert_eq!(Some(35), a.next_word_offset(20));
        assert_eq!(Some(35), a.next_word_offset(26));
        assert_eq!(Some(35), a.next_word_offset(35));
    }

    #[test]
    fn preceding_line_break() {
        let a = String::from("Technically\na word:\n ৬藏A\u{030a}\n\u{110b}\u{1161}");
        assert_eq!(0, a.preceding_line_break(0));
        assert_eq!(0, a.preceding_line_break(11));
        assert_eq!(12, a.preceding_line_break(12));
        assert_eq!(12, a.preceding_line_break(13));
        assert_eq!(20, a.preceding_line_break(21));
        assert_eq!(31, a.preceding_line_break(31));
        assert_eq!(31, a.preceding_line_break(34));

        let b = String::from("Technically a word: ৬藏A\u{030a}\u{110b}\u{1161}");
        assert_eq!(0, b.preceding_line_break(0));
        assert_eq!(0, b.preceding_line_break(11));
        assert_eq!(0, b.preceding_line_break(13));
        assert_eq!(0, b.preceding_line_break(21));
    }

    #[test]
    fn next_line_break() {
        let a = String::from("Technically\na word:\n ৬藏A\u{030a}\n\u{110b}\u{1161}");
        assert_eq!(11, a.next_line_break(0));
        assert_eq!(11, a.next_line_break(11));
        assert_eq!(19, a.next_line_break(13));
        assert_eq!(30, a.next_line_break(21));
        assert_eq!(a.len(), a.next_line_break(31));

        let b = String::from("Technically a word: ৬藏A\u{030a}\u{110b}\u{1161}");
        assert_eq!(b.len(), b.next_line_break(0));
        assert_eq!(b.len(), b.next_line_break(11));
        assert_eq!(b.len(), b.next_line_break(13));
        assert_eq!(b.len(), b.next_line_break(19));
    }

    #[test]
    fn arcstring_empty_edit() {
        let a = Arc::new("hello".to_owned());
        let mut b = a.clone();
        b.edit(5..5, "");
        assert!(Arc::ptr_eq(&a, &b));
    }
}