fix and update package

flake.nix

@@ -18,36 +18,69 @@
       };
     in
     {
-      devShells.${system}.default =
-        pkgs.mkShell {
-          packages = with pkgs; [
-            stdenv.cc
+      devShells.${system}.default = pkgs.mkShell {
+        nativeBuildInputs = [
+          pkgs.pkgsBuildBuild.pkg-config
+        ];
 
-            pkg-config
+        buildInputs = with pkgs; [
+          libcamera
+          libGL
+          libglvnd
+          mesa
+        ];
 
-            libcamera
+        shellHook = ''
+          export CC=${pkgs.stdenv.cc.targetPrefix}gcc
+          export CXX=${pkgs.stdenv.cc.targetPrefix}g++
 
-            libGL
-            libglvnd
+          export PKG_CONFIG_ALLOW_CROSS=1
 
-            mesa
+          echo "Cross shell ready"
+        '';
+      };
 
-            # useful tools
-            gdb
-          ];
+      packages.${system}.default = pkgs.stdenv.mkDerivation {
+        pname = "rpi-zero-libcamera-app";
+        version = "0.1.0";
 
-          shellHook = ''
-            echo "ARM cross shell for Raspberry Pi Zero"
-            echo
+        src = ./.;
 
-            export CC=arm-linux-gnueabihf-gcc
-            export CXX=arm-linux-gnueabihf-g++
+        nativeBuildInputs = [
+          pkgs.pkgsBuildBuild.pkg-config
+        ];
 
-            export PKG_CONFIG_ALLOW_CROSS=1
+        buildInputs = with pkgs; [
+          libcamera
+          libGL
+          libglvnd
+          mesa
+        ];
 
-            echo "Compiler:"
-            $CXX --version
-          '';
-        };
+        buildPhase = ''
+          runHook preBuild
+
+          export PKG_CONFIG_ALLOW_CROSS=1
+
+          mkdir -p build
+
+          ${pkgs.stdenv.cc.targetPrefix}g++ \
+            main.cpp \
+            -o build/app \
+            $(pkg-config --cflags --libs libcamera)
+
+          runHook postBuild
+        '';
+
+        installPhase = ''
+          mkdir -p $out/bin
+          cp build/app $out/bin/app
+        '';
+      };
+
+      apps.${system}.default = {
+        type = "app";
+        program = "${self.packages.${system}.default}/bin/app";
+      };
     };
 }