[refactor] reorganize platform and wire sources

apps/desktop/src/platform/linux/path_backend.cpp

@@ -0,0 +1,51 @@
+#include "platform/path_backend.h"
+
+#include <limits.h>
+#include <unistd.h>
+
+#include <cstdlib>
+#include <vector>
+
+namespace crossdesk::platform {
+namespace {
+
+std::filesystem::path Home() {
+  const char* value = std::getenv("HOME");
+  return value ? std::filesystem::path(value) : std::filesystem::path();
+}
+
+std::filesystem::path EnvOrDefault(const char* name,
+                                   const std::filesystem::path& fallback) {
+  const char* value = std::getenv(name);
+  return value ? std::filesystem::path(value) : fallback;
+}
+
+}  // namespace
+
+std::filesystem::path GetExecutableDirectory() {
+  std::vector<char> buffer(PATH_MAX);
+  while (true) {
+    const ssize_t length =
+        readlink("/proc/self/exe", buffer.data(), buffer.size() - 1);
+    if (length <= 0) return {};
+    if (static_cast<size_t>(length) < buffer.size() - 1) {
+      buffer[static_cast<size_t>(length)] = '\0';
+      return std::filesystem::path(buffer.data()).parent_path();
+    }
+    buffer.resize(buffer.size() * 2);
+  }
+}
+
+std::filesystem::path GetConfigPath(const std::string& app_name) {
+  return EnvOrDefault("XDG_CONFIG_HOME", Home() / ".config") / app_name;
+}
+
+std::filesystem::path GetCachePath(const std::string& app_name) {
+  return EnvOrDefault("XDG_CACHE_HOME", Home() / ".cache") / app_name;
+}
+
+std::filesystem::path GetLogPath(const std::string& app_name) {
+  return GetCachePath(app_name) / "logs";
+}
+
+}  // namespace crossdesk::platform