don't hash the slug with the visit key

this makes it easy to see if a single visitor visited multiple pages

migrations/20240317182405_hits.up.sql

@@ -1,8 +1,9 @@
 create table if not exists hits (
   id integer primary key,
   page text not null, -- the slug from the page
-  hit_key text not null unique,
+  visit_key text not null unique,
-  viewed timestamp not null default CURRENT_TIMESTAMP
+  viewed timestamp not null default CURRENT_TIMESTAMP,
+  unique(page, visit_key)
 );
 
 create index if not exists hits_page_dex on hits(page);

src/main.rs

@@ -103,13 +103,17 @@ async fn register_hit(
     // we can't just enumerate all the possible hashes based on IP, page, and
     // time alone.
     let salt = *SESSION_SALT;
-    let key = format!("{now}{host}{slug}{salt}").into_bytes();
+    let key = format!("{now}{host}{salt}").into_bytes();
     let key = hex::encode(shasum(&key));
 
     let tx = db.begin().await;
 
     if let Ok(mut tx) = tx {
-        match sqlx::query!("insert into hits (page, hit_key) values (?, ?)", slug, key,)
+        match sqlx::query!(
+            "insert into hits (page, visit_key) values (?, ?)",
+            slug,
+            key,
+        )
         .execute(&mut *tx)
         .await
         {