feat: db pg adapter: define username_exists adapter

src/identity/adapters/output/db/postgres/username_exists.rs

@@ -0,0 +1,68 @@
+// SPDX-FileCopyrightText: 2024 Aravinth Manivannan <realaravinth@batsense.net>
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+use super::DBOutPostgresAdapter;
+use crate::identity::application::port::output::db::{
+    errors::*, username_exists::UsernameExistsOutDBPort,
+};
+
+#[async_trait::async_trait]
+impl UsernameExistsOutDBPort for DBOutPostgresAdapter {
+    async fn username_exists(&self, username: &str) -> OutDBPortResult<bool> {
+        let res = sqlx::query!(
+            "SELECT EXISTS (
+                SELECT 1
+                    FROM user_query
+                WHERE
+                    username = $1
+            );",
+            username
+        )
+        .fetch_one(&self.pool)
+        .await?;
+        if let Some(x) = res.exists {
+            Ok(x)
+        } else {
+            Ok(false)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[actix_rt::test]
+    async fn test_postgres_username_exists() {
+        let username = "foo@exmaple.com";
+        let settings = crate::settings::tests::get_settings().await;
+        let db = super::DBOutPostgresAdapter::new(
+            sqlx::postgres::PgPool::connect(&settings.database.url)
+                .await
+                .unwrap(),
+        );
+
+        // state doesn't exist
+        assert!(!db.username_exists(username).await.unwrap());
+
+        sqlx::query!(
+            "INSERT INTO user_query
+                (view_id, version, username, email, hashed_password)
+            VALUES ($1, $2, $3, $4, $5);",
+            "1",
+            1,
+            username,
+            "foo",
+            "passwd"
+        )
+        .execute(&db.pool)
+        .await
+        .unwrap();
+
+        // state exists
+        assert!(db.username_exists(username).await.unwrap());
+
+        settings.drop_db().await;
+    }
+}