Hogmaker: Only rebuild the hog file if any input file changed

tools/HogMaker/HogMaker.cpp

@@ -25,28 +25,22 @@
 #include "d3_version.h"
 #include "HogFormat.h"
 
-// TODO: To our descendants from the future: remove it when code will support C++20
-template <typename TP> std::time_t to_time_t(TP tp) {
-  auto sctp = std::chrono::duration_cast<std::chrono::system_clock::duration>(tp - TP::clock::now()) +
-              std::chrono::system_clock::now();
-  return std::chrono::system_clock::to_time_t(sctp);
-}
-
 // Find requested file in search paths
 std::filesystem::path resolve_path(const std::vector<std::filesystem::path> &search_path,
                                    const std::filesystem::path &file) {
   for (const auto &i : search_path) {
-    if (is_regular_file((i / file))) {
-      return (i / file);
+    std::filesystem::path testfile = (i / file);
+    if (is_regular_file(testfile)) {
+      return testfile;
     }
   }
   // Return empty path
   return std::filesystem::path{};
 }
 
 int main(int argc, char *argv[]) {
-  std::vector<std::filesystem::path> input_files;
 
+  // Print usage information on demand
   if (argc < 3) {
     std::cout << "HogMaker v" << D3_MAJORVER << "." << D3_MINORVER << "." << D3_BUILD << "-g" << D3_GIT_HASH << "\n"
               << "Usage:\n"
@@ -55,8 +49,26 @@ int main(int argc, char *argv[]) {
     return 1;
   }
 
+  // Filenames
+  std::filesystem::path hogmaker_filename{argv[0]};
   std::filesystem::path hog_filename{argv[1]};
   std::filesystem::path input_filename{argv[2]};
+
+  // Check if the input file is usable
+  if (!is_regular_file(input_filename)) {
+    std::cout << input_filename << " is not a regular file!" << std::endl;
+    return 1;
+  }
+
+  // Timestamps
+  auto hog_timestamp = std::filesystem::file_time_type::min();
+  if (std::filesystem::is_regular_file(hog_filename)) {
+    hog_timestamp = std::filesystem::last_write_time(hog_filename);
+  }
+  auto newer_than_hog = [&hog_timestamp](const std::filesystem::path &file) {
+    return (std::filesystem::last_write_time(file) >= hog_timestamp);
+  };
+
   // Default search path
   std::vector<std::filesystem::path> search_paths{input_filename.parent_path()};
   // Additional search paths
@@ -66,12 +78,9 @@ int main(int argc, char *argv[]) {
     }
   }
 
-  if (!is_regular_file(input_filename)) {
-    std::cout << input_filename << " is not a regular file!" << std::endl;
-    return 1;
-  }
-
   D3::HogFormat hog_table;
+  // Check if the hogmaker or the input file is newer than the hog file
+  bool file_changed = (newer_than_hog(hogmaker_filename) || newer_than_hog(input_filename));
 
   try {
     create_directories(absolute(hog_filename).parent_path());
@@ -80,28 +89,38 @@ int main(int argc, char *argv[]) {
       auto resolved_file = resolve_path(search_paths, line);
       if (resolved_file.empty()) {
         std::cout << "Warning! File " << line << " from " << input_filename << " not found! Skipping..." << std::endl;
+        file_changed = true;
       } else if (line.size() > 36) {
         std::cout << "Warning! Length of name of file " << line << " is more than 36 symbols! Skipping..." << std::endl;
       } else {
         hog_table.AddEntry(D3::HogFileEntry(resolved_file));
+        // Check if this file is newer than the hog file
+        if (newer_than_hog(resolved_file)) {
+          file_changed = true;
+        }
       }
     }
-
   } catch (std::exception &e) {
     std::cout << "Exception: " << e.what() << std::endl;
     return 1;
   }
 
+  // Don't do anything if there are no changed files
+  if (!file_changed) {
+    std::cout << "Already up to date" << std::endl;
+    return 0;
+  }
+
   hog_table.SortEntries();
 
   std::cout << "Creating " << absolute(hog_filename) << "..." << std::endl;
-  std::fstream ofs(hog_filename, std::ios_base::out | std::ios_base::binary);
+  std::ofstream ofs(hog_filename, std::ios_base::out | std::ios_base::binary);
 
   ofs << hog_table;
-  for (const auto& i : hog_table.GetEntries()) {
+  for (const auto &i : hog_table.GetEntries()) {
     std::cout << "Adding " << i.GetName() << "... ";
     try {
-      std::fstream ifs(i.GetRealPath(), std::ios_base::in | std::ios_base::binary);
+      std::ifstream ifs(i.GetRealPath(), std::ios_base::in | std::ios_base::binary);
       std::copy((std::istreambuf_iterator<char>(ifs)), std::istreambuf_iterator<char>(),
                 std::ostreambuf_iterator<char>(ofs));
     } catch (std::exception &e) {