Move parsers for specific objects/elements to their own files.

The parsers are the most complicated part, so I want them in their own files. I am uncertain if I want to move their corresponding structs or just the parsers.

src/parser/plain_text.rs

@@ -0,0 +1,68 @@
+use nom::combinator::not;
+
+use crate::parser::error::CustomError;
+use crate::parser::error::MyError;
+
+use super::error::Res;
+use super::object::PlainText;
+use super::Context;
+
+pub fn plain_text<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, PlainText<'s>> {
+    if input.len() == 0 {
+        return Err(nom::Err::Error(CustomError::MyError(MyError(
+            "Zero input length to plain_text.",
+        ))));
+    }
+    // not(|i| context.check_exit_matcher(i))(input)?;
+    let mut current_input = input.char_indices();
+    loop {
+        match current_input.next() {
+            Some((offset, _char)) => {
+                let remaining = &input[offset..];
+                let exit_matcher_status = not(|i| context.check_exit_matcher(i))(remaining);
+                if exit_matcher_status.is_err() {
+                    if offset == 0 {
+                        // If we're at the start of the input, then nothing is plain text, so fire an error for zero-length match.
+                        exit_matcher_status?;
+                    } else {
+                        return Ok((
+                            &input[offset..],
+                            PlainText {
+                                source: &input[..offset],
+                            },
+                        ));
+                    }
+                }
+            }
+            None => {
+                // We hit the end of the file, so all input must be plain text
+                return Ok((&input[input.len()..], PlainText { source: input }));
+            }
+        };
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use nom::combinator::map;
+
+    use crate::parser::object::Object;
+    use crate::parser::parser_context::ContextElement;
+    use crate::parser::parser_context::ContextTree;
+    use crate::parser::parser_with_context::parser_with_context;
+    use crate::parser::source::Source;
+
+    use super::*;
+
+    #[test]
+    fn plain_text_simple() {
+        let input = "foobarbaz";
+        let initial_context: ContextTree<'_, '_> = ContextTree::new();
+        let document_context =
+            initial_context.with_additional_node(ContextElement::DocumentRoot(input));
+        let plain_text_matcher = parser_with_context!(plain_text)(&document_context);
+        let (remaining, result) = map(plain_text_matcher, Object::PlainText)(input).unwrap();
+        assert_eq!(remaining, "");
+        assert_eq!(result.get_source(), input);
+    }
+}