From 23d587c6992dfae4772bfa8c44caa90f24c07a48 Mon Sep 17 00:00:00 2001
From: Tom Alexander <tom@fizz.buzz>
Date: Mon, 24 Jul 2023 16:29:31 -0400
Subject: [PATCH] Implement parser for subscript/superscript with braces.

---
 src/parser/parser_context.rs            | 18 ++++++
 src/parser/subscript_and_superscript.rs | 83 +++++++++++++++++++++++++
 2 files changed, 101 insertions(+)

diff --git a/src/parser/parser_context.rs b/src/parser/parser_context.rs
index a4809e7..e7063e4 100644
--- a/src/parser/parser_context.rs
+++ b/src/parser/parser_context.rs
@@ -194,6 +194,18 @@ pub enum ContextElement<'r, 's> {
     /// unbalanced brackets can be detected in the middle of an
     /// object.
     InlineSourceBlockBracket(InlineSourceBlockBracket<'s>),
+
+    /// Stores the current bracket or parenthesis depth inside a
+    /// superscript or superscript.
+    ///
+    /// Inside the braces of a subscript or superscript there must be
+    /// balanced braces {}, so this stores the amount of opening
+    /// braces subtracted by the amount of closing braces within the
+    /// definition must equal zero.
+    ///
+    /// A reference to the position in the string is also included so
+    /// unbalanced braces can be detected in the middle of an object.
+    SubscriptSuperscriptBrace(SubscriptSuperscriptBrace<'s>),
 }
 
 pub struct ExitMatcherNode<'r> {
@@ -225,6 +237,12 @@ pub struct InlineSourceBlockBracket<'s> {
     pub depth: usize,
 }
 
+#[derive(Debug)]
+pub struct SubscriptSuperscriptBrace<'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");
diff --git a/src/parser/subscript_and_superscript.rs b/src/parser/subscript_and_superscript.rs
index 1af3970..5ac1df7 100644
--- a/src/parser/subscript_and_superscript.rs
+++ b/src/parser/subscript_and_superscript.rs
@@ -16,7 +16,13 @@ use super::Object;
 use crate::error::CustomError;
 use crate::error::MyError;
 use crate::error::Res;
+use crate::parser::exiting::ExitClass;
+use crate::parser::object_parser::standard_set_object;
+use crate::parser::parser_context::ContextElement;
+use crate::parser::parser_context::ExitMatcherNode;
+use crate::parser::parser_context::SubscriptSuperscriptBrace;
 use crate::parser::parser_with_context::parser_with_context;
+use crate::parser::util::exit_matcher_parser;
 use crate::parser::util::get_consumed;
 use crate::parser::util::get_one_before;
 use crate::parser::Subscript;
@@ -79,6 +85,9 @@ fn script_body<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str,
         map(parser_with_context!(script_alphanum)(context), |body| {
             ScriptBody::Braceless(body)
         }),
+        map(parser_with_context!(script_with_braces)(context), |body| {
+            ScriptBody::WithBraces(body)
+        }),
     ))(input)
 }
 
@@ -119,3 +128,77 @@ fn end_script_alphanum_character<'r, 's>(
     )))(remaining)?;
     Ok((remaining, final_char))
 }
+
+#[tracing::instrument(ret, level = "debug")]
+fn script_with_braces<'r, 's>(
+    context: Context<'r, 's>,
+    input: &'s str,
+) -> Res<&'s str, Vec<Object<'s>>> {
+    let (remaining, _) = tag("{")(input)?;
+    let parser_context = context
+        .with_additional_node(ContextElement::SubscriptSuperscriptBrace(
+            SubscriptSuperscriptBrace {
+                position: remaining,
+                depth: 0,
+            },
+        ))
+        .with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
+            class: ExitClass::Beta,
+            exit_matcher: &script_with_braces_end,
+        }));
+
+    let (remaining, (children, _exit_contents)) = many_till(
+        parser_with_context!(standard_set_object)(&parser_context),
+        parser_with_context!(exit_matcher_parser)(&parser_context),
+    )(remaining)?;
+
+    let (remaining, _) = tag("}")(remaining)?;
+    Ok((remaining, children))
+}
+
+#[tracing::instrument(ret, level = "debug")]
+fn script_with_braces_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 subscript or superscript.");
+    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 subscript or superscript brace depth.")
+            }
+            '}' if current_depth > 0 => {
+                current_depth -= 1;
+            }
+            _ => {}
+        }
+    }
+    if current_depth == 0 {
+        let close_bracket = tag::<&str, &str, CustomError<&str>>("}")(input);
+        if close_bracket.is_ok() {
+            return close_bracket;
+        }
+    }
+    return Err(nom::Err::Error(CustomError::MyError(MyError(
+        "Not a valid end for subscript or superscript.",
+    ))));
+}
+
+#[tracing::instrument(ret, level = "debug")]
+fn get_bracket_depth<'r, 's>(
+    context: Context<'r, 's>,
+) -> Option<&'r SubscriptSuperscriptBrace<'s>> {
+    for node in context.iter() {
+        match node.get_data() {
+            ContextElement::SubscriptSuperscriptBrace(depth) => return Some(depth),
+            _ => {}
+        }
+    }
+    None
+}