nix: Add macOS script to flash the device

flake.nix

@@ -16,9 +16,16 @@
         inherit (self.legacyPackages.${system}) buildSplitKeyboard;
       };
 
-      flash = pkgs.callPackage ./nix/flash.nix {
-        inherit firmware;
-      };
+      flash =
+        if pkgs.lib.strings.hasSuffix "linux" system
+        then
+          pkgs.callPackage ./nix/flash-linux.nix {
+            inherit firmware;
+          }
+        else
+          pkgs.callPackage ./nix/flash-darwin.nix {
+            inherit firmware;
+          };
 
       update = pkgs.callPackage ./nix/update.nix {};
     });

nix/flash-darwin.nix

@@ -0,0 +1,84 @@
+{ lib
+, writeShellApplication
+, firmware
+, script-name ? "zmk-uf2-flash"
+}:
+
+writeShellApplication {
+  name = script-name;
+
+  runtimeInputs = [
+  ];
+
+  text = ''
+    available() {
+      if system_profiler SPUSBDataType 2>/dev/null | grep -Fsq 'nRF UF2'; then
+        for device in $(diskutil list | rg -oNI '/dev/[^ ]*'); do
+          if diskutil info "$device" | grep -Fsq 'nRF UF2'; then
+            diskutil info "$device" | grep -F 'Mount Point:' | cut -d':' -f2 | tr -d '[:space:]'
+          fi
+        done
+      fi
+    }
+
+    mounted() {
+      findmnt "$device" -no target
+    }
+
+    flash=("$@")
+    parts=(${toString firmware.parts or ""})
+
+    if [ "''${#flash[@]}" -eq 0 ]; then
+      if [ "''${#parts[@]}" -eq 0 ]; then
+        flash=("")
+      else
+        flash=("''${parts[@]}")
+      fi
+    else
+      for part in "''${flash[@]}"; do
+        if ! printf '%s\0' "''${parts[@]}" | grep -Fxqz -- "$part"; then
+          echo "The '$part' part does not exist in the firmware '"'${firmware.name}'"'"
+          exit 1
+        fi
+      done
+    fi
+
+    for part in "''${flash[@]}"; do
+      echo -n "Double tap reset and plug in$([ -n "$part" ] && echo " the '$part' part of") the keyboard via USB or press ^C to cancel."
+      mountpoint="$(available)"
+      while [[ -z "$mountpoint" ]]; do
+        echo -n .
+        sleep 1
+        mountpoint="$(available)"
+      done
+      echo
+
+      echo -n "Copying firmware to$([ -n "$part" ] && echo " the '$part' part of") the device..."
+      # On macOS, the ZMK firmware finishes its "flashing" process before the
+      # `cp` command finishes its execution. This is normal, and expected
+      # behavior. For us, though, means that this piece of the script will
+      # signalize a failure to Nix, since `cp` will exit with code != than `0`.
+      # The way we prevent a "command failure", is to indicate to nix that we're
+      # handling the error ourselves, which simply indicates that the operation
+      # finished successfully.
+      if ! cp ${firmware}/*"$([ -n "$part" ] && echo "_$part")".uf2 "$mountpoint/" 2>/dev/null; then
+        echo "Done"
+      else
+        echo "ERROR"
+        echo "There was a failure during firmware copy. Your keyboard might still be in 'bootload' mode!"
+        exit 1
+      fi
+
+      sleep 1
+
+      mountpoint=""
+    done
+  '';
+
+  meta = with lib; {
+    description = "ZMK UF2 firmware flasher";
+    license = licenses.mit;
+    platforms = platforms.darwin;
+    maintainers = with maintainers; [lilyinstarlight];
+  };
+}

nix/flash.nix → nix/flash-linux.nix

@@ -2,10 +2,11 @@
 , writeShellApplication
 , util-linux
 , firmware
+, script-name ? "zmk-uf2-flash"
 }:
 
 writeShellApplication {
-  name = "zmk-uf2-flash";
+  name = script-name;
 
   runtimeInputs = [
     util-linux