Update spotify config handling

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

lib/runtime/merge/default.nix

@@ -0,0 +1,13 @@
+{ lib, pkgs, ... }:
+{
+  keyValue = lib.meta.getExe (
+    pkgs.writeShellApplication {
+      name = "merge-key-value";
+      runtimeInputs = with pkgs; [
+        gnugrep
+        coreutils
+      ];
+      text = builtins.readFile ./key-value.sh;
+    }
+  );
+}

lib/runtime/merge/key-value.sh

@@ -0,0 +1,19 @@
+SOURCE_FILE=$(realpath -m "$1")
+TARGET_FILE=$(realpath -m "$2")
+
+mkdir -p "$(dirname "${TARGET_FILE}")"
+
+TEMP_FILE=$(mktemp)
+cat "${SOURCE_FILE}" > "${TEMP_FILE}"
+
+if [[ -f "${TARGET_FILE}" ]]; then
+  while IFS='=' read -r key value; do
+    if ! grep -q "^${key}=" "${TEMP_FILE}"; then
+      echo "${key}=${value}" >> "${TEMP_FILE}"
+    fi
+  done < "${TARGET_FILE}"
+fi
+
+mv "${TEMP_FILE}" "${TARGET_FILE}"
+
+echo "Configuration file ${TARGET_FILE} has been updated."