cli: improve command dispatch a bit

1 files changed, 82 insertions, 0 deletions

diff --git a/nihil.cli/dispatch_command.cc b/nihil.cli/dispatch_command.cc
new file mode 100644
index 0000000..736e16e
--- /dev/null
+++ b/nihil.cli/dispatch_command.cc
@@ -0,0 +1,82 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+module;
+
+#include <cstdio>
+#include <functional>
+#include <iostream>
+#include <map>
+#include <print>
+#include <ranges>
+#include <string>
+#include <utility>
+
+#include <unistd.h>
+
+module nihil.cli;
+
+import nihil.core;
+
+namespace nihil {
+
+auto dispatch_command(int argc, char **argv) -> int
+{
+	auto tree = build_command_tree();
+
+	// The caller should have stripped argv[0] already.  find() will
+	// strip all the remaining elements except the last, which means
+	// argv[0] will be set to something reasonable for the next call
+	// to getopt().
+
+	// find() never returns nullptr; at worst it will return the
+	// root node.
+	auto const *node = tree.find(argc, argv);
+
+	// Get the command_node.
+	auto const &command = node->command();
+
+	// Reset getopt(3) for the command, in case main() used it already.
+	optreset = 1;
+	optind = 1;
+
+	/*
+	 * Set the program name to the existing progname plus the full path
+	 * to the command being invoked; this makes error messages nicer.
+	 */
+	auto *old_progname = ::getprogname();
+
+	{
+		auto cprogname = std::format("{} {}", ::getprogname(),
+					     command->path());
+		::setprogname(cprogname.c_str());
+	}
+
+	// Invoke the command see what it returns.
+	auto ret = command->invoke(argc, argv);
+
+	// Restore the old progname.
+	::setprogname(old_progname);
+
+	// If the command produced an exit code, return it.
+	if (ret)
+		return *ret;
+
+	/*
+	 * We have special handling for some errors.
+	 */
+
+	// Incomplete command: print the list of valid commands at this node.
+	if (ret.error() == errc::incomplete_command) {
+		std::print(std::cerr, "{}: usage:\n", ::getprogname());
+		node->print_commands();
+		return 1;
+	}
+
+	// We didn't recognise the error, so just print it and exit.
+	std::print(std::cerr, "{}\n", ret.error());
+	return 1;
+}
+
+} // namespace nihil