1 files changed, 35 insertions, 1 deletions
diff --git a/build.c b/build.c
index b8740fc..56c4d74 100644
--- a/build.c
+++ b/build.c
@@ -1,7 +1,41 @@
 #include <sys/wait.h>
+#include <sys/stat.h>
 #include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include <time.h>
+#include <string.h>
+
+// https://github.com/tsoding/nob.h/blob/0a08926d8094fc4ae678155c5d73ae21d1f96f3f/nob.h#L2413
+int needs_rebuild(char* bin_file, char* source_file) {
+  struct stat statbuf = {0};
+  if (stat(bin_file, &statbuf) < 0) {
+    if (errno == ENOENT) return 1;
+    return -1;
+  }
+  time_t output_path_time = statbuf.st_mtime;
+
+  if (stat(source_file, &statbuf) < 0) {
+    fprintf(stderr, "could not stat %s: %s", source_file, strerror(errno));
+    return -1;
+  }
+
+  time_t input_path_time = statbuf.st_mtime;
+  return input_path_time > output_path_time;
+}
+
+int main(int argc, char** argv) {
+  if (needs_rebuild(argv[0], __FILE__)) {
+    if (fork() == 0) {
+      char* args[] = {"gcc", __FILE__, "-o", argv[0], NULL};
+      execvp(args[0], args);
+      return 0;
+    } else {
+      wait(NULL);
+      execvp(argv[0], argv);
+    }
+  }
 
-int main() {
   if (fork() == 0) {
     char* args[] = {"gcc", "src/main.c", "-o", "main.o", NULL};
     execvp(args[0], args);