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//! Word wrapping.
//!
//! Port of upstream `rich/_wrap.py`. [`divide_line`] returns the offsets (in
//! **char** indices, matching upstream) at which a string should be split to fit
//! within a cell width. [`Text`](crate::text::Text) uses it to wrap.
use crate::cells::{cell_len, chop_cells};
/// Yield each word as `(start_char, end_char, word)` where a "word" is any
/// leading whitespace + a non-whitespace run + its trailing whitespace.
/// Port of `_wrap.words` (regex `\s*\S+\s*`).
fn words(text: &str) -> Vec<(usize, usize, String)> {
let chars: Vec<char> = text.chars().collect();
let n = chars.len();
let mut result = Vec::new();
let mut pos = 0;
while pos < n {
let start = pos;
while pos < n && chars[pos].is_whitespace() {
pos += 1;
}
if pos >= n {
// Only whitespace remained: the `\S+` part can't match, so no word.
break;
}
while pos < n && !chars[pos].is_whitespace() {
pos += 1;
}
while pos < n && chars[pos].is_whitespace() {
pos += 1;
}
let word: String = chars[start..pos].iter().collect();
result.push((start, pos, word));
}
result
}
/// Return the char offsets at which `text` should break to fit `width` cells.
///
/// Direct port of `_wrap.divide_line`. With `fold`, words longer than `width`
/// are folded across lines; otherwise such a word is simply moved to its own
/// line (and later cropped by the caller).
pub fn divide_line(text: &str, width: usize, fold: bool) -> Vec<usize> {
let mut break_positions: Vec<usize> = Vec::new();
let mut cell_offset = 0usize;
for (start, _end, word) in words(text) {
let word_length = cell_len(word.trim_end());
// Signed, because upstream's `width - cell_offset` goes NEGATIVE once a
// line has overshot (an unfoldable word wider than the whole width bumps
// `cell_offset` past `width`). Clamping that to zero made a following
// zero-cell word — a word joiner, a lone variation selector — "fit" in
// the nothing that was left, so its break was never emitted and the rest
// of the line vanished from the output.
let remaining_space = width as isize - cell_offset as isize;
let word_fits_remaining_space = remaining_space >= word_length as isize;
if word_fits_remaining_space {
cell_offset += cell_len(&word);
} else if word_length > width {
// The word doesn't fit on any line.
if fold {
let folded_word = chop_cells(&word, width);
let last_index = folded_word.len().saturating_sub(1);
let mut start = start;
for (index, line) in folded_word.iter().enumerate() {
if start != 0 {
break_positions.push(start);
}
if index == last_index {
cell_offset = cell_len(line);
} else {
start += line.chars().count();
}
}
} else {
if start != 0 {
break_positions.push(start);
}
cell_offset = cell_len(&word);
}
} else if cell_offset != 0 && start != 0 {
// Fits on the next (empty) line.
break_positions.push(start);
cell_offset = cell_len(&word);
}
}
break_positions
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn no_break_when_it_fits() {
assert_eq!(divide_line("hello world", 20, true), Vec::<usize>::new());
}
#[test]
fn breaks_between_words() {
// "hello " is 6 cells; "world" doesn't fit in width 8 → break at char 6.
assert_eq!(divide_line("hello world", 8, true), vec![6]);
}
#[test]
fn folds_overlong_word() {
// A 10-char word folded at width 4 → breaks every 4 chars.
assert_eq!(divide_line("abcdefghij", 4, true), vec![4, 8]);
}
/// An unfoldable word wider than the line pushes `cell_offset` **past** the
/// width, so upstream's `width - cell_offset` is negative and nothing fits
/// on that line any more. Computing it with `saturating_sub` clamped it to
/// zero, and a following word measuring zero cells — a word joiner, a lone
/// variation selector — then "fit" in the nothing that was left, so its
/// break was never emitted and the rest of the text disappeared.
///
/// Real rich 15.0.0: `divide_line("aaaaaaaa ", 2, fold=False) == [9]`.
#[test]
fn a_zero_cell_word_after_an_overflowing_line_still_breaks() {
assert_eq!(divide_line("aaaaaaaa \u{2060}", 2, false), vec![9]);
}
/// The grapheme-aware fold, seen from `divide_line`: at width 4 a run of
/// 2-cell VS16 hearts breaks every two hearts (four code points), not every
/// four. Real rich 15.0.0: `divide_line("❤️" * 6, 4) == [4, 8]`.
#[test]
fn folds_an_emoji_run_by_cell_width() {
assert_eq!(
divide_line(&"\u{2764}\u{fe0f}".repeat(6), 4, true),
vec![4, 8]
);
}
}