feat: added update.nix

update.nix

@@ -0,0 +1,61 @@
+{ writeShellApplication
+, jq
+, curl
+, lib
+, release ? "25.05"
+, channels ? [
+    { name = "nixos-${release}"; input = "nixpkgs"; }
+    { name = "nixos-unstable"; input = "nixos-unstable"; }
+  ]
+, flakeFile ? "flake.nix"
+, lockFile ? "flake.lock"
+}:
+
+writeShellApplication {
+  name = "nixos-updater";
+  runtimeInputs = [ jq curl ];
+  text = ''
+    FLAKE_FILE="${flakeFile}"
+    LOCK_FILE="${lockFile}"
+    
+    update_channel() {
+      local channel_name="$1"
+      local flake_input_name="$2"
+      local new old
+      
+      echo "Checking channel: $channel_name -> $flake_input_name..."
+      
+      # Get latest revision from Hydra
+      new=$(curl -sL "https://monitoring.nixos.org/prometheus/api/v1/query?query=channel_revision" |
+        jq -r ".data.result[] | select(.metric.channel==\"$channel_name\") | .metric.revision")
+      
+      if [ -z "$new" ]; then
+        echo "Failed to get revision for $channel_name"
+        return 1
+      fi
+      
+      # Get current revision from flake.lock
+      old=$(jq -r ".nodes as \$nodes |
+        .nodes.root.inputs[\"$flake_input_name\"] as \$target_input |
+        \$nodes | to_entries[] |
+        select(.key == \$target_input) |
+        .value.locked.rev" "$LOCK_FILE")
+      
+      if [ "$old" = "$new" ]; then
+        echo "No update needed for $flake_input_name"
+        return 0
+      fi
+      
+      # Update the flake.nix file
+      sed -i "s|\($flake_input_name\.url = \"github:NixOS/nixpkgs/\)[^\"]*|\1$new|" "$FLAKE_FILE"
+      echo "Updated $flake_input_name: $old -> $new"
+      
+      return 0
+    }
+    
+    # Process channels based on parameters
+    ${lib.concatMapStringsSep "\n" (channel: ''
+      update_channel "${channel.name}" "${channel.input}"
+    '') channels}
+  '';
+}