nix: fix order of iOS shell components

Possible fix for errors like:
```
bundler: failed to load command: fastlane (/Users/jenkins/.bundle/ruby/2.7.0/bin/fastlane)
/Users/jenkins/.bundle/ruby/2.7.0/gems/fastlane-2.205.2/fastlane_core/lib/fastlane_core/ui/interface.rb:153:in `shell_error!': [!] Shell command exited with exit status 51 instead of 0. (FastlaneCore::Interface::FastlaneShellError)
```

Signed-off-by: Jakub Sokołowski <jakub@status.im>

nix/mobile/ios/default.nix

@@ -1,14 +1,15 @@
-{ callPackage, lib, mkShell, deps, pkgs
+{ callPackage, lib, mkShell, pkgs
 , status-go, fastlane }:
 
 let
   inherit (lib) catAttrs unique;
 
-  pod-shell = callPackage ./pod-shell.nix { };
-  status-go-shell = callPackage ./status-go-shell.nix { inherit status-go; };
+  nodejs-sh = callPackage ./shells/nodejs.nix { };
+  cocoapods-sh = callPackage ./shells/pod.nix { };
+  status-go-sh = callPackage ./shells/status-go.nix { inherit status-go; };
 
 in {
-  inherit pod-shell status-go-shell;
+  inherit nodejs-sh cocoapods-sh status-go-sh;
 
   shell = mkShell {
     buildInputs = with pkgs; [
@@ -19,14 +20,9 @@ in {
     # WARNING: Executes shellHook in reverse order.
     inputsFrom = [
       fastlane.shell
-      pod-shell
-      status-go-shell # Needs to run before pod-install
+      cocoapods-sh
+      nodejs-sh # before 'pod install'
+      status-go-sh # before 'pod install'
     ];
-
-    shellHook = ''
-      # check if node modules changed and if so install them
-      ./nix/scripts/node_modules.sh "${deps.nodejs-patched}"
-    '';
   };
-
 }

nix/mobile/ios/shells/nodejs.nix

@@ -0,0 +1,9 @@
+{ mkShell, deps }:
+
+mkShell {
+  # check if node modules changed and if so install them
+  shellHook = ''
+    export STATUS_MOBILE_HOME=$(git rev-parse --show-toplevel)
+    "$STATUS_MOBILE_HOME/nix/scripts/node_modules.sh" ${deps.nodejs-patched}
+  '';
+}

nix/mobile/ios/shells/pod.nix

@@ -0,0 +1,24 @@
+{ mkShell, cocoapods }:
+
+let
+  # source of what pod should install
+  podfileLock = "ios/Podfile.lock";
+  # current state of pods installed by pod
+  manifestLock = "ios/Pods/Manifest.lock";
+in mkShell {
+  buildInputs = [ cocoapods ];
+  shellHook = ''
+    pushd "$STATUS_MOBILE_HOME" > /dev/null
+    {
+      echo "Checking for modifications in ios/Pods..."
+      if diff -q ${podfileLock} ${manifestLock}; then
+        echo "No modifications detected."
+      else
+        # CocoaPods are trash and can't handle other pod instances running
+        ./scripts/wait-for.sh 240 'pod install'
+        (cd ios && pod install)
+      fi
+    }
+    popd > /dev/null
+  '';
+}

nix/shells.nix

@@ -13,23 +13,18 @@ let
   default = callPackage ./shell.nix { };
 
   # Combines with many other shells
-  node-sh = mkShell {
-    shellHook = ''
-      export STATUS_MOBILE_HOME=$(git rev-parse --show-toplevel)
-      "$STATUS_MOBILE_HOME/nix/scripts/node_modules.sh" ${pkgs.deps.nodejs-patched}
-    '';
-  };
+  nodejs-sh = targets.mobile.ios.nodejs-sh;
 
   # An attrset for easier merging with default shell
   shells = {
     inherit default;
 
-    nodejs = node-sh;
+    nodejs = nodejs-sh;
 
     # for calling clojure targets in CI or Makefile
     clojure = mkShell {
       buildInputs = with pkgs; [ clojure flock maven openjdk ];
-      inputsFrom = [ node-sh ];
+      inputsFrom = [ nodejs-sh ];
       # CLASSPATH from clojure deps with 'src' appended to find local sources.
       shellHook = with pkgs; ''
         export CLASS_PATH="$(find ${deps.clojure} -iname '*.jar' | tr '\n' ':')src"
@@ -47,7 +42,7 @@ let
     # for running gradle by hand
     gradle = mkShell {
       buildInputs = with pkgs; [ gradle maven goMavenResolver ];
-      inputsFrom = [ node-sh ];
+      inputsFrom = [ nodejs-sh ];
       shellHook = ''
         export STATUS_GO_ANDROID_LIBDIR="DUMMY"
         export STATUS_NIX_MAVEN_REPO="${pkgs.deps.gradle}"