add cli main

src/main_cli.cpp

@@ -0,0 +1,24 @@
+#include <filesystem>
+#include <iostream>
+
+namespace fs = std::filesystem;
+
+int main(int argc, const char* argv[]) {
+    // We take an image path and a list of points (grouped by 4 to define
+    // bounding boxes).
+    if (argc < 6 or (argc - 2) % 4 != 0) {
+        std::cerr
+            << "Usage: " << argv[0] << " path/to/image"
+            << " x1 y1 x2 y2 [...]\n"
+            << "x/y points must be grouped by 4 to define bounding boxes\n";
+        return 1;
+    }
+
+    const fs::path input(argv[1]);
+    if (!fs::exists(input)) {
+        std::cerr << "Input file " << input << " does not exist.\n";
+        return 1;
+    }
+
+    return 0;
+}