Infra refactor

README.md

@@ -15,6 +15,7 @@ A modern, self-hosted note-taking application built with performance, security,
 - **Responsive**: Mobile-friendly UI built with Tailwind CSS.
 - **Architecture**:
     - **Backend**: Hexagonal Architecture (Domain, Infra, API layers) in Rust.
+    - **Infrastructure**: Configurable database backends (SQLite, Postgres).
     - **Frontend**: Modern React with TypeScript and Vite.
 - **Deployment**: Full Docker support with `compose.yml`.
 
@@ -23,7 +24,7 @@ A modern, self-hosted note-taking application built with performance, security,
 ### Backend
 - **Language**: Rust
 - **Framework**: Axum
-- **Database**: SQLite (SQLx)
+- **Database**: SQLite (Default) or Postgres (Supported via feature flag)
 - **Dependency Injection**: Manual wiring for clear boundaries
 
 ### Frontend
@@ -59,6 +60,16 @@ The frontend is automatically configured to talk to the backend.
 cargo run -p notes-api
 ```
 
+By default, this uses the **SQLite** backend.
+
+**Running with Postgres:**
+
+To use PostgreSQL, build with the `postgres` feature:
+```bash
+cargo run -p notes-api --no-default-features --features notes-infra/postgres
+```
+*Note: Ensure your `DATABASE_URL` is set to a valid Postgres connection string.*
+
 #### Frontend
 
 1.  Navigate to `k-notes-frontend`.
@@ -74,7 +85,32 @@ bun install
 bun dev
 ```
 
-## 🏗️ Project Structure
+## Database Architecture
+
+The backend follows a Hexagonal Architecture (Ports and Adapters). The `notes-domain` crate defines the repository capabilities (Ports), and `notes-infra` implements them (Adapters).
+
+### Supported Databases
+- **SQLite**: Fully implemented (default). Ideal for single-instance, self-hosted deployments.
+- **Postgres**: Structure is in place (via feature flag), ready for implementation.
+
+### Extending Database Support
+
+To add a new database (e.g., MySQL), follow these steps:
+
+1.  **Dependencies**: Add the driver to `notes-infra/Cargo.toml` (e.g., `sqlx` with `mysql` feature) and create a feature flag.
+2.  **Configuration**: Update `DatabaseConfig` in `notes-infra/src/db.rs` to handle the new connection URL scheme and connection logic in `create_pool`.
+3.  **Repository Implementation**:
+    - Implement `NoteRepository`, `TagRepository`, and `UserRepository` traits for the new database in `notes-infra`.
+4.  **Factory Integration**:
+    - Update `notes-infra/src/factory.rs` to include a builder for the new repositories.
+    - Update `build_database_pool` and repository `build_*` functions to support the new database type match arm.
+5.  **Migrations**:
+    - Add migration files in `migrations/<db_type>`.
+    - Update `run_migrations` in `db.rs` to execute them.
+
+This design ensures the `notes-api` layer remains completely agnostic to the underlying database technology.
+
+## Project Structure
 
 ```
 ├── notes-api       # API Interface (Axum, HTTP routes)