Beginning to hand out footnote ids.

default_environment/templates/html/footnote_reference.dust

@@ -1 +1 @@
-!!!!!!!! footnote_reference
+<sup><a id="{.reference_id}" href="{.definition_link}">{.label}</a></sup>

org_test_documents/footnote_definitions.org

@@ -0,0 +1,25 @@
+# Test proves that:
+#
+# - Anonymous references with identical content get unique IDs.
+# - Unreferenced footnote definitions are dropped.
+# - Footnote definitions that come before their first reference are dropped.
+
+foo[fn:2:something]
+
+bar[fn::something]
+
+baz[fn::something]
+
+cat[fn::something]
+
+dog[fn:3]
+
+[fn:3] ipsum
+
+[fn:4] lorem
+
+[fn:3] dolar
+
+[fn:5] not referenced
+
+stuff[fn:4] and things

src/intermediate/footnote_reference.rs

@@ -3,13 +3,16 @@ use crate::error::CustomError;
 use super::registry::Registry;
 
 #[derive(Debug)]
-pub(crate) struct IFootnoteReference {}
+pub(crate) struct IFootnoteReference {
+    footnote_id: usize,
+}
 
 impl IFootnoteReference {
     pub(crate) async fn new<'parse>(
         registry: &mut Registry<'parse>,
         original: &organic::types::FootnoteReference<'parse>,
     ) -> Result<IFootnoteReference, CustomError> {
-        Ok(IFootnoteReference {})
+        let footnote_id = registry.get_footnote_reference_id(original.label, &original.definition);
+        Ok(IFootnoteReference { footnote_id })
     }
 }

src/intermediate/registry.rs

@@ -1,10 +1,13 @@
 use std::collections::HashMap;
 
+use organic::types::Object;
+
 type IdCounter = u16;
 
-pub(crate) struct Registry<'parse> {
+pub(crate) struct Registry<'intermediate, 'parse> {
     id_counter: IdCounter,
     targets: HashMap<&'parse str, String>,
+    footnote_ids: Vec<(Option<&'parse str>, &Vec<Object<'parse>>)>,
 }
 
 impl<'parse> Registry<'parse> {
@@ -12,6 +15,7 @@ impl<'parse> Registry<'parse> {
         Registry {
             id_counter: 0,
             targets: HashMap::new(),
+            footnote_ids: Vec::new(),
         }
     }
 
@@ -21,4 +25,37 @@ impl<'parse> Registry<'parse> {
             format!("target_{}", self.id_counter)
         })
     }
+
+    /// Get a 0-indexed ID for a footnote.
+    ///
+    /// This needs to be incremented to be 1-indexed for render.
+    pub(crate) fn get_footnote_reference_id<'b>(
+        &'b mut self,
+        label: Option<&'parse str>,
+        definition: &'parse Vec<Object<'parse>>,
+    ) -> usize {
+        if let None = label {
+            // If it has no label then it must always get a new ID.
+            self.footnote_ids.push((None, definition));
+            return self.footnote_ids.len();
+        }
+
+        if let Some(existing_id) = self
+            .footnote_ids
+            .iter()
+            .position(|(id, _definition)| *id == label)
+        {
+            if !definition.is_empty() {
+                let entry = self
+                    .footnote_ids
+                    .get_mut(existing_id)
+                    .expect("If-statement proves this to be Some.");
+                entry.1 = definition;
+            }
+            existing_id
+        } else {
+            self.footnote_ids.push((label, definition));
+            self.footnote_ids.len()
+        }
+    }
 }