introduce BidiParagraphs iterator

src/bidi_para.rs

@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+use unicode_bidi::{bidi_class, BidiClass, BidiInfo, ParagraphInfo};
+
+/// An iterator over the paragraphs in the input text.
+/// It is equivalent to [`core::str::Lines`] but follows `unicode-bidi` behaviour.
+pub struct BidiParagraphs<'text> {
+    text: &'text str,
+    info: std::vec::IntoIter<ParagraphInfo>,
+}
+
+impl<'text> BidiParagraphs<'text> {
+    /// Create an iterator to split the input text into paragraphs
+    /// in accordance with `unicode-bidi` behaviour.
+    pub fn new(text: &'text str) -> Self {
+        let info = BidiInfo::new(text, None);
+        let info = info.paragraphs.into_iter();
+        Self { text, info }
+    }
+}
+
+impl<'text> Iterator for BidiParagraphs<'text> {
+    type Item = &'text str;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let para = self.info.next()?;
+        let paragraph = &self.text[para.range];
+        // `para.range` includes the newline that splits the line, so remove it if present
+        let mut char_indices = paragraph.char_indices();
+        if let Some(i) = char_indices.next_back().and_then(|(i, c)| {
+            // `BidiClass::B` is a Paragraph_Separator (various newline characters)
+            (bidi_class(c) == BidiClass::B).then_some(i)
+        }) {
+            Some(&paragraph[0..i])
+        } else {
+            Some(paragraph)
+        }
+    }
+}

src/lib.rs

@@ -95,6 +95,9 @@ extern crate alloc;
 pub use self::attrs::*;
 mod attrs;
 
+pub use self::bidi_para::*;
+mod bidi_para;
+
 pub use self::buffer::*;
 mod buffer;