check for existance using stat

include/perfect/detail/fs.hpp

@@ -3,15 +3,28 @@
 #include <fstream>
 #include <string>
 
-#include "perfect/result.hpp"
+#include "../result.hpp"
+
+#ifdef __linux__
+#include "fs/linux.hpp"
+#else
+#error "unsupported platform"
+#endif
 
 namespace perfect {
 namespace detail {
+
 Result write_str(const std::string &path, const std::string &val) {
+
+  if (!path_exists(path)) {
+    std::cerr << "write_str(): does not exist: " << path << "\n";
+    return Result::NOT_SUPPORTED;
+  }
+
   std::ofstream ofs(path);
   if (ofs.fail()) {
     std::cerr << "failed to open " << path << "\n";
-    return Result::NOT_SUPPORTED;
+    return Result::NO_PERMISSION;
   }
 
   ofs << val;

include/perfect/detail/fs/linux.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <string>
+#include <cerrno>
+#include <iostream>
+#include <cassert>
+
+
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+namespace perfect {
+    namespace detail {
+        bool path_exists(const std::string &path) {
+            struct stat sb;
+            if (stat(path.c_str(), &sb)) {
+                switch (errno) {
+                    case ENOENT: return false;
+                    case ENOTDIR: return false;
+                    default: {
+                        std::cerr << "unhandled error in stat() for " << path << "\n";
+                        assert(0);
+                    }
+                }
+            }
+            return true;
+        }
+    }
+}