From d24315268c11d435bb9accbce87b7f46dda6ed3e Mon Sep 17 00:00:00 2001
From: Lexi Winter <lexi@le-fay.org>
Date: Sun, 29 Jun 2025 00:42:31 +0100
Subject: cli: improve command dispatch a bit

---
 nihil.util/CMakeLists.txt         |  2 ++
 nihil.util/capture_stream.ccm     | 61 +++++++++++++++++++++++++++++++++++++++
 nihil.util/nihil.util.ccm         |  1 +
 nihil.util/test_capture_stream.cc | 44 ++++++++++++++++++++++++++++
 4 files changed, 108 insertions(+)
 create mode 100644 nihil.util/capture_stream.ccm
 create mode 100644 nihil.util/test_capture_stream.cc

(limited to 'nihil.util')

diff --git a/nihil.util/CMakeLists.txt b/nihil.util/CMakeLists.txt
index b809a68..a07ea7d 100644
--- a/nihil.util/CMakeLists.txt
+++ b/nihil.util/CMakeLists.txt
@@ -6,6 +6,7 @@ target_sources(nihil.util
 	PUBLIC FILE_SET modules TYPE CXX_MODULES FILES
 	nihil.util.ccm
 
+	capture_stream.ccm
 	ctype.ccm
 	parse_size.ccm
 	next_word.ccm
@@ -17,6 +18,7 @@ if(NIHIL_TESTS)
 	enable_testing()
 
 	add_executable(nihil.util.test
+		test_capture_stream.cc
 		test_ctype.cc
 		test_parse_size.cc
 		test_next_word.cc
diff --git a/nihil.util/capture_stream.ccm b/nihil.util/capture_stream.ccm
new file mode 100644
index 0000000..3333505
--- /dev/null
+++ b/nihil.util/capture_stream.ccm
@@ -0,0 +1,61 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+module;
+
+#include <iostream>
+
+export module nihil.util:capture_stream;
+
+namespace nihil {
+
+/*
+ * Capture output written to a stream and redirect it to an internal string
+ * buffer.  Call .str() to get the data written.  Call .release() to stop
+ * capturing (or simply delete the capture_stream object).
+ */
+export template<typename Char, typename Traits>
+struct capture_stream {
+	capture_stream(std::basic_ostream<Char, Traits> &stream)
+		: m_stream(&stream)
+	{
+		m_old_streambuf = m_stream->rdbuf();
+		m_stream->rdbuf(m_buffer.rdbuf());
+	}
+
+	~capture_stream() {
+		if (m_old_streambuf == nullptr)
+			return;
+		release();
+	}
+
+	/*
+	 * Release this capture, returning the stream to its previous state.
+	 */
+	auto release(this capture_stream &self) -> void
+	{
+		if (self.m_old_streambuf == nullptr)
+			throw std::logic_error(
+				"release() called on empty capture_stream");
+
+		self.m_stream->rdbuf(self.m_old_streambuf);
+		self.m_old_streambuf = nullptr;
+	}
+
+	/*
+	 * Get the data which has been written to the stream.
+	 */
+	[[nodiscard]] auto str(this capture_stream const &self)
+		-> std::basic_string_view<Char, Traits>
+	{
+		return self.m_buffer.view();
+	}
+
+private:
+	std::basic_ostringstream<Char, Traits>	 m_buffer;
+	std::basic_ostream<Char, Traits>	*m_stream;
+	std::streambuf				*m_old_streambuf;
+};
+
+} // namespace nihil
diff --git a/nihil.util/nihil.util.ccm b/nihil.util/nihil.util.ccm
index afd513a..89510c9 100644
--- a/nihil.util/nihil.util.ccm
+++ b/nihil.util/nihil.util.ccm
@@ -6,6 +6,7 @@ module;
 
 export module nihil.util;
 
+export import :capture_stream;
 export import :ctype;
 export import :parse_size;
 export import :next_word;
diff --git a/nihil.util/test_capture_stream.cc b/nihil.util/test_capture_stream.cc
new file mode 100644
index 0000000..27c8596
--- /dev/null
+++ b/nihil.util/test_capture_stream.cc
@@ -0,0 +1,44 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+#include <iostream>
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil.util;
+
+TEST_CASE("nihil.util: capture", "[nihil][nihil.util]")
+{
+	SECTION("std::cout with release()") {
+		auto cap = nihil::capture_stream(std::cout);
+
+		std::cout << 1 << '+' << 1 << '=' << (1 + 1) << '\n';
+		REQUIRE(cap.str() == "1+1=2\n");
+		
+		cap.release();
+		REQUIRE(cap.str() == "1+1=2\n");
+	}
+
+	SECTION("std::cout with dtor") {
+		auto cap = nihil::capture_stream(std::cout);
+		std::cout << 1 << '+' << 1 << '=' << (1 + 1) << '\n';
+		REQUIRE(cap.str() == "1+1=2\n");
+	}
+
+	SECTION("std::cerr with release()") {
+		auto cap = nihil::capture_stream(std::cerr);
+
+		std::cerr << 1 << '+' << 1 << '=' << (1 + 1) << '\n';
+		REQUIRE(cap.str() == "1+1=2\n");
+		
+		cap.release();
+		REQUIRE(cap.str() == "1+1=2\n");
+	}
+
+	SECTION("std::cerr with dtor") {
+		auto cap = nihil::capture_stream(std::cerr);
+		std::cerr << 1 << '+' << 1 << '=' << (1 + 1) << '\n';
+		REQUIRE(cap.str() == "1+1=2\n");
+	}
+}
-- 
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