From 5fb66a586d81215518eec95298d5664e87340431 Mon Sep 17 00:00:00 2001
From: Tom Alexander <tom@fizz.buzz>
Date: Wed, 19 Jul 2023 20:52:09 -0400
Subject: [PATCH] Implement a function to detect the end of a footnote
 reference definition with balanced brackets.

---
 src/parser/footnote_definition.rs |  2 +-
 src/parser/footnote_reference.rs  | 68 ++++++++++++++++++++++++++++++-
 src/parser/parser_context.rs      | 18 ++++++++
 3 files changed, 86 insertions(+), 2 deletions(-)

diff --git a/src/parser/footnote_definition.rs b/src/parser/footnote_definition.rs
index 833360e..61318dc 100644
--- a/src/parser/footnote_definition.rs
+++ b/src/parser/footnote_definition.rs
@@ -67,7 +67,7 @@ pub fn footnote_definition<'r, 's>(
 }
 
 #[tracing::instrument(ret, level = "debug")]
-fn label<'s>(input: &'s str) -> Res<&'s str, &'s str> {
+pub fn label<'s>(input: &'s str) -> Res<&'s str, &'s str> {
     alt((
         digit1,
         take_while(|c| WORD_CONSTITUENT_CHARACTERS.contains(c) || "-_".contains(c)),
diff --git a/src/parser/footnote_reference.rs b/src/parser/footnote_reference.rs
index c43253b..6d88df0 100644
--- a/src/parser/footnote_reference.rs
+++ b/src/parser/footnote_reference.rs
@@ -1,13 +1,79 @@
+use nom::branch::alt;
+use nom::bytes::complete::tag;
+use nom::bytes::complete::tag_no_case;
+
+use super::parser_context::ContextElement;
 use super::Context;
+use crate::error::CustomError;
+use crate::error::MyError;
 use crate::error::Res;
-use crate::parser::FootnoteReference;
+use crate::parser::parser_context::FootnoteReferenceDefinition;
+use crate::parser::parser_with_context::parser_with_context;
+use crate::parser::util::get_consumed;
 use crate::parser::util::not_yet_implemented;
+use crate::parser::FootnoteReference;
+use crate::parser::Object;
 
 #[tracing::instrument(ret, level = "debug")]
 pub fn footnote_reference<'r, 's>(
     context: Context<'r, 's>,
     input: &'s str,
 ) -> Res<&'s str, FootnoteReference<'s>> {
+    alt((parser_with_context!(anonymous_footnote)(context),))(input)
+}
+
+#[tracing::instrument(ret, level = "debug")]
+pub fn anonymous_footnote<'r, 's>(
+    context: Context<'r, 's>,
+    input: &'s str,
+) -> Res<&'s str, FootnoteReference<'s>> {
+    let (remaining, _) = tag_no_case("[fn::")(input)?;
+
     not_yet_implemented()?;
     todo!()
 }
+
+#[tracing::instrument(ret, level = "debug")]
+fn definition<'s>(input: &'s str) -> Res<&'s str, Vec<Object<'s>>> {
+    Ok((input, vec![]))
+}
+
+#[tracing::instrument(ret, level = "debug")]
+fn footnote_definition_end<'r, 's>(
+    context: Context<'r, 's>,
+    input: &'s str,
+) -> Res<&'s str, &'s str> {
+    let context_depth = get_bracket_depth(context).expect("This function should only be called from inside a footnote definition.");
+    let text_since_context_entry = get_consumed(context_depth.position, input);
+    let mut current_depth = context_depth.depth;
+    for c in text_since_context_entry.chars() {
+        match c {
+            '[' => {current_depth += 1;},
+            ']' if current_depth == 0 => {
+                panic!("Exceeded footnote reference definition bracket depth.")
+            },
+            ']' if current_depth > 0 => {
+                current_depth -= 1;
+            },
+            _ => {}
+        }
+    }
+    if current_depth > 0 {
+        // Its impossible for the next character to end the footnote reference definition if we're any amount of brackets deep
+        return Err(nom::Err::Error(CustomError::MyError(MyError("NoFootnoteReferenceDefinitionEnd"))));
+    }
+    tag("]")(input)
+}
+
+#[tracing::instrument(ret, level = "debug")]
+fn get_bracket_depth<'r, 's>(
+    context: Context<'r, 's>,
+) -> Option<&'r FootnoteReferenceDefinition<'s>> {
+    for node in context.iter() {
+        match node.get_data() {
+            ContextElement::FootnoteReferenceDefinition(depth) => return Some(depth),
+            _ => {}
+        }
+    }
+    None
+}
diff --git a/src/parser/parser_context.rs b/src/parser/parser_context.rs
index c49e099..d2c105e 100644
--- a/src/parser/parser_context.rs
+++ b/src/parser/parser_context.rs
@@ -141,6 +141,18 @@ pub enum ContextElement<'r, 's> {
     /// org-mode document since text needs to be re-parsed to look for
     /// radio links matching the contents of radio targets.
     RadioTarget(Vec<&'r Vec<Object<'s>>>),
+
+    /// Stores the current bracket depth inside a footnote reference's definition.
+    ///
+    /// The definition inside a footnote reference must have balanced
+    /// brackets [] inside the definition, so this stores the amount
+    /// of opening brackets subtracted by the amount of closing
+    /// brackets within the definition.
+    ///
+    /// A reference to the position in the string is also included so
+    /// unbalanced brackets can be detected in the middle of an
+    /// object.
+    FootnoteReferenceDefinition(FootnoteReferenceDefinition<'s>),
 }
 
 pub struct ExitMatcherNode<'r> {
@@ -148,6 +160,12 @@ pub struct ExitMatcherNode<'r> {
     pub class: ExitClass,
 }
 
+#[derive(Debug)]
+pub struct FootnoteReferenceDefinition<'s> {
+    pub position: &'s str,
+    pub depth: usize,
+}
+
 impl<'r> std::fmt::Debug for ExitMatcherNode<'r> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let mut formatter = f.debug_struct("ExitMatcherNode");