Set up a local MariaDB instance from the Nix flake

flake.nix

@@ -6,19 +6,108 @@
     flake-utils.url = "github:numtide/flake-utils";
   };
 
-  outputs = { self, nixpkgs, flake-utils }:
+  outputs = { nixpkgs, flake-utils, ... }:
     flake-utils.lib.eachDefaultSystem (system:
       let
         pkgs = nixpkgs.legacyPackages.${system};
+
+        # Project-local MariaDB instance. Data lives in $MARIADB_HOME (.mariadb/ in the repo root).
+        # Database name, user and password are read from backend/.env, falling back to backend/.env.example.
+        db-start = pkgs.writeShellApplication {
+          name = "db-start";
+          runtimeInputs = [ pkgs.mariadb pkgs.util-linux ];
+          text = ''
+            env_file="$PROJECT_ROOT/backend/.env"
+            [ -f "$env_file" ] || env_file="$PROJECT_ROOT/backend/.env.example"
+            set -a
+            # shellcheck source=/dev/null
+            . "$env_file"
+            set +a
+            : "''${DB_NAME:?DB_NAME missing in $env_file}"
+            : "''${DB_USER:?DB_USER missing in $env_file}"
+            DB_PORT="''${DB_PORT:-3306}"
+            DB_PASSWORD="''${DB_PASSWORD:-}"
+
+            mkdir -p "$MARIADB_HOME"
+            if [ ! -d "$MARIADB_HOME/data/mysql" ]; then
+              echo "Initializing MariaDB data directory..."
+              mariadb-install-db \
+                --datadir="$MARIADB_HOME/data" \
+                --auth-root-authentication-method=socket \
+                > "$MARIADB_HOME/install.log" 2>&1
+            fi
+
+            if ! mariadb-admin ping >/dev/null 2>&1; then
+              setsid mariadbd \
+                --no-defaults \
+                --datadir="$MARIADB_HOME/data" \
+                --socket="$MYSQL_UNIX_PORT" \
+                --pid-file="$MARIADB_HOME/mariadb.pid" \
+                --log-error="$MARIADB_HOME/mariadb.log" \
+                --bind-address=127.0.0.1 \
+                --port="$DB_PORT" \
+                < /dev/null > /dev/null 2>&1 &
+
+              for _ in $(seq 1 30); do
+                mariadb-admin ping >/dev/null 2>&1 && break
+                sleep 0.5
+              done
+              if ! mariadb-admin ping >/dev/null 2>&1; then
+                echo "MariaDB failed to start, see $MARIADB_HOME/mariadb.log" >&2
+                exit 1
+              fi
+            fi
+
+            # Escape for use inside SQL identifiers/literals.
+            name="''${DB_NAME//\`/\`\`}"
+            user="''${DB_USER//\'/\\\'}"
+            pass="''${DB_PASSWORD//\'/\\\'}"
+
+            mariadb <<SQL
+            CREATE DATABASE IF NOT EXISTS \`$name\`;
+            CREATE USER IF NOT EXISTS '$user'@'localhost' IDENTIFIED BY '$pass';
+            CREATE USER IF NOT EXISTS '$user'@'127.0.0.1' IDENTIFIED BY '$pass';
+            ALTER USER '$user'@'localhost' IDENTIFIED BY '$pass';
+            ALTER USER '$user'@'127.0.0.1' IDENTIFIED BY '$pass';
+            GRANT ALL PRIVILEGES ON \`$name\`.* TO '$user'@'localhost';
+            GRANT ALL PRIVILEGES ON \`$name\`.* TO '$user'@'127.0.0.1';
+            SQL
+
+            echo "MariaDB running on 127.0.0.1:$DB_PORT with database '$DB_NAME' and user '$DB_USER' (from $env_file)."
+          '';
+        };
+
+        db-stop = pkgs.writeShellApplication {
+          name = "db-stop";
+          runtimeInputs = [ pkgs.mariadb ];
+          text = ''
+            if mariadb-admin shutdown 2>/dev/null; then
+              echo "MariaDB stopped."
+            else
+              echo "MariaDB is not running."
+            fi
+          '';
+        };
       in
       {
         devShells.default = pkgs.mkShell {
-          packages = with pkgs; [
-            nodejs_24
+          packages = [
+            pkgs.nodejs_24
+            pkgs.mariadb
+            db-start
+            db-stop
           ];
 
           shellHook = ''
+            export PROJECT_ROOT="$(git rev-parse --show-toplevel 2>/dev/null || pwd)"
+            export MARIADB_HOME="$PROJECT_ROOT/.mariadb"
+
+            # Picked up by the mariadb client tools, so they connect to the local instance by default.
+            export MYSQL_UNIX_PORT="$MARIADB_HOME/mysqld.sock"
+
             echo "Node $(node -v) & npm $(npm -v) ready."
+            db-start || echo "Could not start MariaDB, see $MARIADB_HOME/mariadb.log"
+            echo "MariaDB keeps running after you leave the shell; run 'db-stop' to stop it."
           '';
         };
       });