From e54218c0d77cb1918dc49ca87857898b4ac6b351 Mon Sep 17 00:00:00 2001
From: Tom Alexander <tom@fizz.buzz>
Date: Sat, 22 Jul 2023 01:36:00 -0400
Subject: [PATCH] Implement the target parser.

---
 src/parser/target.rs | 60 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 src/parser/target.rs

diff --git a/src/parser/target.rs b/src/parser/target.rs
new file mode 100644
index 00000000..8b9e029c
--- /dev/null
+++ b/src/parser/target.rs
@@ -0,0 +1,60 @@
+use nom::bytes::complete::tag;
+use nom::character::complete::anychar;
+use nom::character::complete::one_of;
+use nom::character::complete::space0;
+use nom::combinator::peek;
+use nom::combinator::recognize;
+use nom::combinator::verify;
+use nom::multi::many_till;
+
+use super::Context;
+use crate::error::CustomError;
+use crate::error::MyError;
+use crate::error::Res;
+use crate::parser::exiting::ExitClass;
+use crate::parser::parser_context::ContextElement;
+use crate::parser::parser_context::ExitMatcherNode;
+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::Target;
+
+#[tracing::instrument(ret, level = "debug")]
+pub fn target<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Target<'s>> {
+    let (remaining, _) = tag("<<")(input)?;
+    let (remaining, _) = peek(verify(anychar, |c| {
+        !c.is_whitespace() && !"<>\n".contains(*c)
+    }))(remaining)?;
+
+    let parser_context =
+        context.with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
+            class: ExitClass::Beta,
+            exit_matcher: &target_end,
+        }));
+    let (remaining, body) = recognize(many_till(
+        anychar,
+        parser_with_context!(exit_matcher_parser)(&parser_context),
+    ))(remaining)?;
+
+    let document_root = context.get_document_root().unwrap();
+    let preceding_character = get_one_before(document_root, remaining)
+        .map(|slice| slice.chars().next())
+        .flatten()
+        .expect("We cannot be at the start of the file because we are inside a target.");
+    if preceding_character.is_whitespace() {
+        return Err(nom::Err::Error(CustomError::MyError(MyError(
+            "Targets cannot end with whitespace.",
+        ))));
+    }
+    let (remaining, _) = tag(">>")(remaining)?;
+    let (remaining, _) = space0(remaining)?;
+    let source = get_consumed(input, remaining);
+
+    Ok((remaining, Target { source }))
+}
+
+#[tracing::instrument(ret, level = "debug")]
+fn target_end<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, &'s str> {
+    recognize(one_of("<>\n"))(input)
+}