From a7aadafc8d6842fb960786d4840dc29c490d3071 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@gmail.com>
Date: Thu, 18 Jun 2026 16:42:03 +0200
Subject: lib: add simple echo router

---
 ttwhy/scanner.cppm | 127 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 ttwhy/scanner.cppm

(limited to 'ttwhy/scanner.cppm')

diff --git a/ttwhy/scanner.cppm b/ttwhy/scanner.cppm
new file mode 100644
index 0000000..86a8493
--- /dev/null
+++ b/ttwhy/scanner.cppm
@@ -0,0 +1,127 @@
+module;
+
+#include <algorithm>
+#include <boost/sml.hpp>
+
+#include <cctype>
+#include <span>
+#include <vector>
+
+export module ttwhy:scanner;
+
+import :event;
+
+namespace ttwhy::detail
+{
+
+  /// Events
+
+  struct byte_received
+  {
+    char value;
+  };
+
+  /// States
+
+  auto const idle = boost::sml::state<class idle>;
+  auto const escape_sequence = boost::sml::state<class escape_sequence>;
+  auto const csi_sequence = boost::sml::state<class csi_sequence>;
+
+  /// Actions
+
+  auto push_character = [](byte_received const & event, std::vector<input_event> & queue) {
+    queue.push_back(character_event{event.value});
+  };
+
+  auto push_backspace = [](std::vector<input_event> & queue) {
+    queue.push_back(control_event{control_key::backspace});
+  };
+
+  auto push_delete = [](std::vector<input_event> & queue) {
+    queue.push_back(navigation_event{navigation_key::delete_key});
+  };
+
+  auto fallback_escape = [](byte_received const & event, std::vector<input_event> & queue) {
+    queue.push_back(control_event{control_key::escape});
+    if (event.value >= 0x20 && event.value <= 0x7e)
+    {
+      queue.push_back(character_event{event.value});
+    }
+  };
+
+  /// Guards
+
+  auto is_backspace = [](byte_received e) {
+    return e.value == '\x08' || e.value == '\x7f';
+  };
+
+  auto is_escape = [](byte_received e) {
+    return e.value == '\x1b';
+  };
+
+  auto is_printable = [](byte_received e) {
+    return e.value >= 0x20 && e.value <= 0x7e;
+  };
+
+  auto is_csi_introducer = [](byte_received e) {
+    return e.value == '[';
+  };
+
+  auto is_csi_param = [](byte_received e) {
+    return e.value >= 0x20 && e.value <= 0x3f;
+  };
+
+  auto is_csi_terminator = [](byte_received e) {
+    return e.value >= 0x40 && e.value <= 0x7e;
+  };
+
+  auto is_tilde = [](byte_received e) {
+    return e.value == '~';
+  };
+
+  /// Transitions
+
+  struct transition_table
+  {
+    auto operator()() const noexcept
+    {
+      using namespace boost::sml;
+
+      // clang-format off
+      return make_transition_table(
+          *idle +            event<byte_received>[is_escape]                            = escape_sequence,
+           idle +            event<byte_received>[is_backspace]       / push_backspace  = idle,
+           idle +            event<byte_received>[is_printable]       / push_character  = idle,
+
+           escape_sequence + event<byte_received>[is_csi_introducer]                    = csi_sequence,
+           escape_sequence + event<byte_received>[!is_csi_introducer] / fallback_escape = idle,
+
+           csi_sequence +    event<byte_received>[is_csi_param]                         = csi_sequence,
+           csi_sequence +    event<byte_received>[is_tilde]           / push_delete     = idle,
+           csi_sequence +    event<byte_received>[is_csi_terminator]                    = idle
+      );
+      // clang-format on
+    }
+  };
+
+}  // namespace ttwhy::detail
+
+export namespace ttwhy
+{
+
+  struct ansi_scanner
+  {
+    explicit ansi_scanner(std::vector<input_event> & queue)
+        : m_state_machine{queue}
+    {}
+
+    auto process(std::span<char const> buffer) -> void
+    {
+      std::ranges::for_each(buffer, [&](auto byte) { m_state_machine.process_event(detail::byte_received{byte}); });
+    }
+
+  private:
+    boost::sml::sm<detail::transition_table> m_state_machine;
+  };
+
+}  // namespace ttwhy
-- 
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