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#[cfg(feature = "grapheme-clusters")]
use unicode_segmentation::UnicodeSegmentation;
use std::{cell::{Ref, RefCell}};
/// Pre-cached line/column lookup table for a string slice.
pub struct LineColLookup<'source> {
src: &'source str,
line_heads: RefCell<Option<Vec<usize>>>,
}
impl<'source> LineColLookup<'source> {
/// Creates a new line/col lookup table. The `src` parameter provides the input string used to calculate lines and columns.
///
/// Internally, this scans `src` and caches the starting positions of all lines. This means this is an O(n) operation.
pub fn new(src: &'source str) -> Self {
Self {
src,
line_heads: RefCell::new(None),
}
}
fn heads(&self) -> Ref<'_, Option<Vec<usize>>> {
if self.line_heads.borrow().is_none() {
let line_heads: Vec<usize> = std::iter::once(0)
.chain(self.src
.char_indices()
.filter_map(|(i, c)| Some(i + 1).filter(|_| c == '\n')))
.collect();
self.line_heads.replace(Some(line_heads));
}
self.line_heads.borrow()
}
/// Looks up the 1-based line and column numbers of the specified byte index.
///
/// Returns a tuple with the line number first, then column number.
///
/// # Example
/// ```rust
/// use line_col::*;
/// let text = "One\nTwo";
/// let lookup = LineColLookup::new(text);
/// assert_eq!(lookup.get(0), (1, 1)); // 'O' (line 1, col 1)
/// assert_eq!(lookup.get(1), (1, 2)); // 'n' (line 1, col 2)
/// assert_eq!(lookup.get(2), (1, 3)); // 'e' (line 1, col 3)
/// assert_eq!(lookup.get(4), (2, 1)); // 'T' (line 2, col 1)
/// assert_eq!(lookup.get(5), (2, 2)); // 'w' (line 2, col 2)
/// assert_eq!(lookup.get(6), (2, 3)); // 'o' (line 2, col 3)
/// assert_eq!(lookup.get(7), (2, 4)); // <end> (line 2, col 4)
/// ```
///
/// # Panics
///
/// Panics if `index` is greater than the length of the input `&str`.
///
/// # Notes
/// This function uses a binary search to locate the line on which `index` resides.
/// This means that it runs in approximately O(log n) time.
pub fn get(&self, index: usize) -> (usize, usize) {
if index > self.src.len() {
panic!("Index cannot be greater than the length of the input slice.");
}
if let Some(heads) = self.heads().as_ref() {
// Perform a binary search to locate the line on which `index` resides
let mut line_range = 0..heads.len();
while line_range.end - line_range.start > 1 {
let range_middle = line_range.start + (line_range.end - line_range.start) / 2;
let (left, right) = (line_range.start..range_middle, range_middle..line_range.end);
// Check which line window contains our character index
if (heads[left.start] .. heads[left.end]).contains(&index) {
line_range = left;
} else {
line_range = right;
}
}
let line_start_index = heads[line_range.start];
let line = line_range.start + 1;
let col = index - line_start_index + 1;
return (line, col)
}
unreachable!()
}
/// Looks up the 1-based line and column numbers of the specified byte index.
/// The column number correlates to the number of grapheme clusters up to and at the specified index.
///
/// Returns a tuple with the line number first, then column number.
///
/// # Panics
///
/// Panics if `index` is greater than the length of the input `&str`.
///
/// # Notes
/// This function uses a binary search to locate the line on which `index` resides.
/// This means that it runs in approximately O(log n) time.
#[cfg(feature = "grapheme-clusters")]
pub fn get_by_cluster(&self, index: usize) -> (usize, usize) {
if index > self.src.len() {
panic!("Index cannot be greater than the length of the input slice.");
}
if let Some(heads) = self.heads().as_ref() {
// Perform a binary search to locate the line on which `index` resides
let mut line_range = 0..heads.len();
while line_range.end - line_range.start > 1 {
let range_middle = line_range.start + (line_range.end - line_range.start) / 2;
let (left, right) = (line_range.start..range_middle, range_middle..line_range.end);
// Check which line window contains our character index
if (heads[left.start] .. heads[left.end]).contains(&index) {
line_range = left;
} else {
line_range = right;
}
}
let line_start_index = heads[line_range.start];
let line = line_range.start + 1;
let col = UnicodeSegmentation::graphemes(&self.src[line_start_index..index], true).count() + 1;
return (line, col)
}
unreachable!()
}
}
#[cfg(test)]
mod tests {
use crate::*;
#[test]
fn empty_str() {
let text = "";
let lookup = LineColLookup::new(text);
assert_eq!(lookup.get(0), (1, 1));
}
#[test]
fn line_col_iter_by_codepoints() {
let text = "a\nab\nabc";
let lookup = LineColLookup::new(text);
assert_eq!(lookup.get(0), (1, 1));
assert_eq!(lookup.get(1), (1, 2));
assert_eq!(lookup.get(2), (2, 1));
assert_eq!(lookup.get(3), (2, 2));
assert_eq!(lookup.get(4), (2, 3));
assert_eq!(lookup.get(5), (3, 1));
assert_eq!(lookup.get(6), (3, 2));
assert_eq!(lookup.get(7), (3, 3));
assert_eq!(lookup.get(8), (3, 4));
}
#[test]
#[cfg(feature = "grapheme-clusters")]
fn emoji_text_by_grapheme_clusters() {
let text = "The 👨👩👦 emoji is made of 5 code points and 18 bytes in UTF-8.";
let lookup = LineColLookup::new(text);
assert_eq!(lookup.get_by_cluster(4), (1, 5));
assert_eq!(lookup.get_by_cluster(22), (1, 6));
}
#[test]
fn emoji_text_by_codepoints() {
let text = "The 👨👩👦 emoji is made of 5 code points and 18 bytes in UTF-8.";
let lookup = LineColLookup::new(text);
assert_eq!(lookup.get(4), (1, 5));
assert_eq!(lookup.get(22), (1, 23));
}
}