Canadian cities labeler over Bluesky DMs

Users DM @cities.pds.cosocial.ca their city and get a signed account label.
Serves com.atproto.label.queryLabels and subscribeLabels, built on jacquard.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/labeler.rs

@@ -0,0 +1,61 @@
+use std::sync::Arc;
+
+use anyhow::Result;
+use jacquard::types::string::Did;
+use k256::ecdsa::SigningKey;
+use tokio::sync::broadcast;
+
+use crate::db::{Db, SeqLabel};
+use crate::labels::sign_label;
+
+pub struct Labeler {
+    pub db: Arc<Db>,
+    pub did: Did,
+    key: SigningKey,
+    published: broadcast::Sender<SeqLabel>,
+}
+
+impl Labeler {
+    pub fn new(db: Arc<Db>, did: Did, key: SigningKey) -> Self {
+        let (published, _) = broadcast::channel(1024);
+        Self {
+            db,
+            did,
+            key,
+            published,
+        }
+    }
+
+    /// Live labels for `subscribeLabels`.
+    pub fn subscribe(&self) -> broadcast::Receiver<SeqLabel> {
+        self.published.subscribe()
+    }
+
+    pub fn current_city(&self, subject: &Did<&str>) -> Result<Option<String>> {
+        Ok(self.db.active_vals(subject.as_str())?.into_iter().next())
+    }
+
+    /// Make `city` the account's only city label; `None` removes it.
+    pub fn set_city(&self, subject: &Did<&str>, city: Option<&str>) -> Result<()> {
+        let active = self.db.active_vals(subject.as_str())?;
+        for val in active.iter().filter(|v| Some(v.as_str()) != city) {
+            self.emit(subject, val, true)?;
+        }
+        if let Some(city) = city.filter(|c| !active.iter().any(|v| v == c)) {
+            self.emit(subject, city, false)?;
+        }
+        Ok(())
+    }
+
+    fn emit(&self, subject: &Did<&str>, val: &str, neg: bool) -> Result<()> {
+        let label = sign_label(&self.key, &self.did, subject, val, neg)?;
+        let seq = self.db.insert_label(&label)?;
+        // no receivers just means no one is subscribed right now
+        let _ = self.published.send(SeqLabel { seq, label });
+        println!(
+            "{} {val} on {subject} (seq {seq})",
+            if neg { "negated" } else { "applied" }
+        );
+        Ok(())
+    }
+}