Add support for getting `char`s from bytes

1 files changed, 22 insertions, 0 deletions

diff --git a/src/util/slice.rs b/src/util/slice.rs
index 0734d78..d02a526 100644
--- a/src/util/slice.rs
+++ b/src/util/slice.rs
@@ -5,6 +5,28 @@ use crate::util::constant::TAB_SIZE;
 use alloc::string::String;
 use core::str;
 
+/// Get a [`char`][] right before `index` in bytes (`&[u8]`).
+///
+/// In most cases, markdown operates on ASCII bytes.
+/// In a few cases, it is unicode aware, so we need to find an actual char.
+pub fn char_before_index(bytes: &[u8], index: usize) -> Option<char> {
+    let start = if index < 4 { 0 } else { index - 4 };
+    String::from_utf8_lossy(&bytes[start..index]).chars().last()
+}
+
+/// Get a [`char`][] right at `index` in bytes (`&[u8]`).
+///
+/// In most cases, markdown operates on ASCII bytes.
+/// In a few cases, it is unicode aware, so we need to find an actual char.
+pub fn char_after_index(bytes: &[u8], index: usize) -> Option<char> {
+    let end = if index + 4 > bytes.len() {
+        bytes.len()
+    } else {
+        index + 4
+    };
+    String::from_utf8_lossy(&bytes[index..end]).chars().next()
+}
+
 /// A range between two points.
 #[derive(Debug)]
 pub struct Position<'a> {