WIP: parse command line

cpm/cxx/cpm.cxx

@@ -1,14 +1,40 @@
+#include <algorithm>
+#include <format>
 #include <iostream>
 
-int main (int argc, char* argv[])
-{
-  using namespace std;
-
-  if (argc < 2)
-  {
-    cerr << "error: missing name" << endl;
-    return 1;
-  }
-
-  cout << "Hello, " << argv[1] << '!' << endl;
+// From https://stackoverflow.com/questions/865668
+bool cmdOptionExists(char** begin, char** end, const std::string& option) {
+   return std::find(begin, end, option) != end;
+}
+
+int main (int argc, char* argv[]) {
+   const std::string stdflag = "-";
+   std::string infile = stdflag;
+   std::string outfile = "";
+   bool showHelp = false;
+
+   if (cmdOptionExists(argv, argv+argc, "-h")) showHelp = true;
+   else if (cmdOptionExists(argv, argv+argc, "--help")) showHelp = true;
+   else switch (argc) {
+         case 3: outfile = argv[2]; /* DROP */
+         case 2: infile = argv[1]; /* DROP */
+         case 1: break;
+         default: showHelp = true;
+      }
+   if (showHelp) {
+      std::cerr << R"(
+Usage: cpm [infile [outfile]]
+   If infile is not specified or is '-', stdin is used.
+   If outfile is '-' or unspecified and infile is stdin, stdout is used.
+   Otherwise if outfile is unspecified, the name of the infile with its
+   final '.' extension (if any) removed and '.cxx' added is used.
+)";
+      return 1;
+   }
+   if (outfile.length() == 0) {
+      if (infile == stdflag) outfile = stdflag;
+      else outfile = infile.substr(0, infile.rfind('.')) + ".cxx";
+   }
+
+   std::cout << std::format("Transforming from {} to {}.\n", infile, outfile);
 }