rebuild script use specified host from env with warnings

rebuild-nix-system.sh

@@ -1,10 +1,37 @@
 #!/bin/bash
 
+# Source .env file
+if [ -f ".env" ]; then
+    source .env
+else
+    echo "Error: No .env file found. Copy example.env to .env and set your NIXOS_HOST"
+    exit 1
+fi
+
+if [ -z "$NIXOS_HOST" ]; then
+    echo "Error: NIXOS_HOST not set in .env file"
+    exit 1
+fi
+
+# Validate that the host configuration exists
+AVAILABLE_HOSTS=$(nix flake show --json 2>/dev/null | jq -r '.nixosConfigurations | keys[]' 2>/dev/null)
+if [ $? -ne 0 ] || [ -z "$AVAILABLE_HOSTS" ]; then
+    echo "Warning: Could not validate host configuration. Proceeding anyway..."
+else
+    if ! echo "$AVAILABLE_HOSTS" | grep -q "^$NIXOS_HOST$"; then
+        echo "Error: Host '$NIXOS_HOST' not found in flake.nix"
+        echo "Available hosts: $(echo $AVAILABLE_HOSTS | tr '\n' ' ')"
+        exit 1
+    fi
+fi
+
+echo "Building configuration for host: $NIXOS_HOST"
+
 # First, run a check to see if the flake is valid
 nix flake check
 
 # Rebuild the system
-sudo nixos-rebuild switch --flake ./#default
+sudo nixos-rebuild switch --flake ./#$NIXOS_HOST
 
 # Clean up old generations older than 180 days
 sudo nix-collect-garbage --delete-older-than 180d