From d582c8603a4ed534dcd5eb5b2bd73be60dfedb95 Mon Sep 17 00:00:00 2001
From: Tom Alexander <tom@fizz.buzz>
Date: Sat, 25 Mar 2023 11:22:59 -0400
Subject: [PATCH] Implement a basic paragraph parser.

---
 src/parser/document.rs       |  4 +--
 src/parser/element.rs        | 47 +++++++++++++++++++++++++++++++++++-
 src/parser/lesser_element.rs |  3 +++
 3 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/src/parser/document.rs b/src/parser/document.rs
index a256f5ac..52fa5f38 100644
--- a/src/parser/document.rs
+++ b/src/parser/document.rs
@@ -155,7 +155,7 @@ fn headline<'r, 's>(
 }
 
 fn headline_end<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, &'s str> {
-    line_ending(input)
+    alt((line_ending, eof))(input)
 }
 
 /// Check that we are at the start of a line
@@ -199,7 +199,7 @@ fn is_slice_of(parent: &str, child: &str) -> bool {
 }
 
 /// Get a slice of the string that was consumed in a parser using the original input to the parser and the remaining input after the parser.
-fn get_consumed<'s>(input: &'s str, remaining: &'s str) -> &'s str {
+pub fn get_consumed<'s>(input: &'s str, remaining: &'s str) -> &'s str {
     assert!(is_slice_of(input, remaining));
     let source = {
         let offset = remaining.as_ptr() as usize - input.as_ptr() as usize;
diff --git a/src/parser/element.rs b/src/parser/element.rs
index ecfa993e..aa42936e 100644
--- a/src/parser/element.rs
+++ b/src/parser/element.rs
@@ -1,4 +1,19 @@
+use nom::branch::alt;
+use nom::character::complete::line_ending;
+use nom::character::complete::space0;
+use nom::combinator::eof;
+use nom::combinator::map;
 use nom::combinator::not;
+use nom::combinator::recognize;
+use nom::multi::many1;
+use nom::sequence::tuple;
+
+use crate::parser::document::get_consumed;
+use crate::parser::object::standard_set_object;
+use crate::parser::parser_context::ChainBehavior;
+use crate::parser::parser_context::ContextElement;
+use crate::parser::parser_context::ExitMatcherNode;
+use crate::parser::parser_with_context::parser_with_context;
 
 use super::error::Res;
 use super::greater_element::PlainList;
@@ -23,5 +38,35 @@ impl<'s> Source<'s> for Element<'s> {
 
 pub fn element<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Element<'s>> {
     not(|i| context.check_exit_matcher(i))(input)?;
-    todo!()
+
+    let paragraph_matcher = parser_with_context!(paragraph)(context);
+
+    map(paragraph_matcher, Element::Paragraph)(input)
+}
+
+fn paragraph<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Paragraph<'s>> {
+    let parser_context =
+        context.with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
+            exit_matcher: ChainBehavior::AndParent(Some(&paragraph_end)),
+        }));
+    let standard_set_object_matcher = parser_with_context!(standard_set_object)(&parser_context);
+
+    let (remaining, children) = many1(standard_set_object_matcher)(input)?;
+
+    let source = get_consumed(input, remaining);
+
+    Ok((remaining, Paragraph { source, children }))
+}
+
+fn paragraph_end<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, &'s str> {
+    // TODO: Other elements should also end paragraphs
+    alt((recognize(tuple((line_ending, many1(blank_line)))), eof))(input)
+}
+
+/// A line containing only whitespace and then a line break
+///
+/// It is up to the caller to ensure this is called at the start of a line.
+fn blank_line(input: &str) -> Res<&str, &str> {
+    not(eof)(input)?;
+    recognize(tuple((space0, alt((line_ending, eof)))))(input)
 }
diff --git a/src/parser/lesser_element.rs b/src/parser/lesser_element.rs
index 83fd38b0..5abc4b38 100644
--- a/src/parser/lesser_element.rs
+++ b/src/parser/lesser_element.rs
@@ -1,4 +1,7 @@
+use super::object::Object;
+
 #[derive(Debug)]
 pub struct Paragraph<'s> {
     pub source: &'s str,
+    pub children: Vec<Object<'s>>,
 }