Add support for a target variable in regular links.

This will initially be used for supporting "post://" links.

src/intermediate/regular_link.rs

@@ -9,6 +9,7 @@ use crate::error::CustomError;
 pub(crate) struct IRegularLink {
     pub(crate) raw_link: String,
     pub(crate) children: Vec<IObject>,
+    pub(crate) target: LinkTarget,
     pub(crate) post_blank: organic::types::PostBlank,
 }
 
@@ -25,10 +26,32 @@ intermediate!(
             }
             ret
         };
+        let raw_link = original.get_raw_link();
+        let target = LinkTarget::from_string(&raw_link)?;
         Ok(IRegularLink {
-            raw_link: original.get_raw_link().into_owned(),
+            raw_link: raw_link.into_owned(),
             children,
+            target,
             post_blank: original.get_post_blank(),
         })
     }
 );
+
+#[derive(Debug, Clone)]
+pub(crate) enum LinkTarget {
+    Raw(String),
+    Post { post_id: String },
+}
+
+impl LinkTarget {
+    pub(crate) fn from_string<S: AsRef<str>>(input: S) -> Result<LinkTarget, CustomError> {
+        fn impl_from_string(input: &str) -> Result<LinkTarget, CustomError> {
+            Ok(LinkTarget::Raw(input.to_owned()))
+        }
+        impl_from_string(input.as_ref())
+    }
+
+    pub(crate) fn generate_final_target(&self) -> Result<Option<String>, CustomError> {
+        todo!()
+    }
+}