Starting to parse text markup.

src/parser/text_markup.rs

@@ -1,5 +1,11 @@
+use nom::branch::alt;
+use nom::bytes::complete::tag;
+
 use super::Context;
+use crate::error::CustomError;
+use crate::error::MyError;
 use crate::error::Res;
+use crate::parser::util::get_one_before;
 use crate::parser::TextMarkup;
 
 #[tracing::instrument(ret, level = "debug")]
@@ -7,5 +13,36 @@ pub fn text_markup<'r, 's>(
     context: Context<'r, 's>,
     input: &'s str,
 ) -> Res<&'s str, TextMarkup<'s>> {
+    let (remaining, _) = pre(context, input)?;
+    let (remaining, open) = marker(remaining)?;
+    return Err(nom::Err::Error(CustomError::MyError(MyError(
+        "text markup not implemented yet.",
+    ))));
+
     todo!()
 }
+
+#[tracing::instrument(ret, level = "debug")]
+pub fn pre<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, ()> {
+    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 {
+        // If None, we are at the start of the file which is technically the beginning of a line.
+        None | Some('\r') | Some('\n') | Some(' ') | Some('\t') | Some('-') | Some('(')
+        | Some('{') | Some('\'') | Some('"') => {}
+        Some(_) => {
+            // Not at start of line, cannot be a heading
+            return Err(nom::Err::Error(CustomError::MyError(MyError(
+                "Not a valid pre character for text markup.",
+            ))));
+        }
+    };
+    Ok((input, ()))
+}
+
+#[tracing::instrument(ret, level = "debug")]
+pub fn marker(input: &str) -> Res<&str, &str> {
+    alt((tag("*"), tag("/"), tag("_"), tag("="), tag("~"), tag("+")))(input)
+}