Start writing the parser for headings.

src/main.rs

@@ -1,3 +1,4 @@
+#![feature(round_char_boundary)]
 // use crate::parser::document;
 use tracing::Level;
 use tracing_subscriber::fmt::format::FmtSpan;

src/parser/document.rs

@@ -1,9 +1,22 @@
+use nom::branch::alt;
+use nom::bytes::complete::tag;
+use nom::combinator::eof;
+use nom::combinator::recognize;
+use nom::multi::many1_count;
+use nom::sequence::tuple;
+
+use crate::parser::error::CustomError;
+use crate::parser::error::MyError;
+use crate::parser::parser_context::ChainBehavior;
 use crate::parser::parser_context::ContextElement;
 use crate::parser::parser_context::ContextTree;
+use crate::parser::parser_context::ExitMatcherNode;
 
 use super::element::Element;
 use super::error::Res;
+use super::parser_with_context::parser_with_context;
 use super::source::Source;
+use super::Context;
 
 #[derive(Debug)]
 pub struct Document<'s> {
@@ -52,3 +65,76 @@ pub fn document(input: &str) -> Res<&str, Document> {
 
     todo!()
 }
+
+fn section<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Section<'s>> {
+    // TODO: The zeroth section is specialized so it probably needs its own parser
+    let parser_context = context
+        .with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
+            exit_matcher: ChainBehavior::AndParent(Some(&section_end)),
+        }))
+        .with_additional_node(ContextElement::Context("section"));
+    todo!()
+}
+
+fn section_end<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, &'s str> {
+    let heading_matcher = parser_with_context!(heading)(context);
+    alt((recognize(heading_matcher), eof))(input)
+}
+
+fn heading<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Heading<'s>> {
+    let document_root = context.get_document_root().unwrap();
+    let preceding_character = get_one_before(document_root, input)
+        .map(|slice| slice.chars().next())
+        .flatten();
+    match preceding_character {
+        Some('\n') => {}
+        Some(_) =>  {
+            // Not at start of line, cannot be a heading
+            return Err(nom::Err::Error(CustomError::MyError(MyError(
+                "Heading not at start of line",
+            ))));
+        }
+        // If None, we are at the start of the file which allows for headings
+        None => {}
+    };
+
+    tuple((
+        many1_count(tag("*")),
+        // standard set of objects
+    ))(input)?;
+
+    todo!()
+}
+
+fn get_one_before<'s>(document: &'s str, current_position: &'s str) -> Option<&'s str> {
+    assert!(is_slice_of(document, current_position));
+    if document.as_ptr() as usize == current_position.as_ptr() as usize {
+        return None;
+    }
+    let offset = current_position.as_ptr() as usize - document.as_ptr() as usize;
+    let previous_character_offset = document.floor_char_boundary(offset - 1);
+    Some(&document[previous_character_offset..offset])
+}
+
+fn is_slice_of(parent: &str, child: &str) -> bool {
+    let parent_start = parent.as_ptr() as usize;
+    let parent_end = parent_start + parent.len();
+    let child_start = child.as_ptr() as usize;
+    let child_end = child_start + child.len();
+    child_start >= parent_start && child_end <= parent_end
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn get_one_before_unicode() {
+        let input = "🧡💛💚💙💜";
+        let (green_heart_index, _) = input.char_indices().skip(2).next().unwrap();
+        let starting_with_green_heart = &input[green_heart_index..];
+        let yellow_heart = get_one_before(input, starting_with_green_heart).unwrap();
+        assert!(is_slice_of(input, yellow_heart));
+        assert_eq!(yellow_heart, "💛");
+    }
+}

src/parser/mod.rs

@@ -14,6 +14,6 @@ mod parser_with_context;
 // mod plain_list;
 mod source;
 // mod text;
-mod token;
+// mod token;
 mod util;
 type Context<'r, 's> = &'r parser_context::ContextTree<'r, 's>;

src/parser/parser_context.rs

@@ -7,7 +7,6 @@ use super::error::MyError;
 use super::error::Res;
 use super::list::List;
 use super::list::Node;
-use super::token::Token;
 use super::Context;
 
 type Matcher = dyn for<'r, 's> Fn(Context<'r, 's>, &'s str) -> Res<&'s str, &'s str>;
@@ -90,13 +89,25 @@ impl<'r, 's> ContextTree<'r, 's> {
         // TODO: Make this a specific error instead of just a generic MyError
         return Err(nom::Err::Error(CustomError::MyError(MyError("NoExit"))));
     }
+
+    pub fn get_document_root(&self) -> Option<&'s str> {
+        for current_node in self.iter() {
+            let context_element = current_node.get_data();
+            match context_element {
+                ContextElement::DocumentRoot(body) => {
+                    return Some(body);
+                }
+                _ => {}
+            }
+        }
+        None
+    }
 }
 
 #[derive(Debug)]
 pub enum ContextElement<'r, 's> {
     DocumentRoot(&'s str),
     ExitMatcherNode(ExitMatcherNode<'r>),
-    PreviousElementNode(PreviousElementNode<'s>),
     Context(&'r str),
     ListItem(usize),
     StartOfParagraph,
@@ -107,11 +118,6 @@ pub struct ExitMatcherNode<'r> {
     pub exit_matcher: ChainBehavior<'r>,
 }
 
-#[derive(Debug)]
-pub struct PreviousElementNode<'r> {
-    pub element: Token<'r>,
-}
-
 #[derive(Clone)]
 pub enum ChainBehavior<'r> {
     AndParent(Option<&'r Matcher>),