From 22f6534081acfabdab4956d337604a21e7da5b64 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@gmail.com>
Date: Tue, 22 Sep 2026 18:56:44 +0200
Subject: lib: generalize concepts

---
 ttwhy/io/readers.cppm                 |  6 +++---
 ttwhy/routers/concepts.cppm           |  7 ++-----
 ttwhy/routers/echo.cppm               |  2 --
 ttwhy/routers/echo.tests.cpp          | 20 +++++++++-----------
 ttwhy/scanners/concepts.cppm          | 13 ++++++++-----
 ttwhy/scanners/terminal_policies.cppm | 18 ++++++++----------
 ttwhy/scanners/terminal_scanner.cppm  |  6 +++---
 7 files changed, 33 insertions(+), 39 deletions(-)

diff --git a/ttwhy/io/readers.cppm b/ttwhy/io/readers.cppm
index d15cc7a..56ce2b0 100644
--- a/ttwhy/io/readers.cppm
+++ b/ttwhy/io/readers.cppm
@@ -16,7 +16,8 @@ import ttwhy.scanners;
 namespace ttwhy::io
 {
 
-  export template<typename InputStream, router AppRouter>
+  export template<typename TerminalPolicy = scanners::xterm_policy, typename InputStream,
+                  router<scanners::input_event> AppRouter>
   auto read_events(InputStream & stream, AppRouter & router) -> asio::awaitable<void>
   {
     using namespace asio::experimental::awaitable_operators;
@@ -32,8 +33,7 @@ namespace ttwhy::io
       queue.push_back(event);
     };
 
-    using terminal_policy = ttwhy::scanners::associated_terminal_policy_t<AppRouter>;
-    auto scanner = scanners::terminal_scanner<decltype(sink), terminal_policy>{sink};
+    auto scanner = scanners::terminal_scanner<decltype(sink), TerminalPolicy>{sink};
 
     auto raw_buffer = std::array<char, 64>{};
 
diff --git a/ttwhy/routers/concepts.cppm b/ttwhy/routers/concepts.cppm
index 9660afc..cfbcb5a 100644
--- a/ttwhy/routers/concepts.cppm
+++ b/ttwhy/routers/concepts.cppm
@@ -6,14 +6,11 @@ module;
 
 export module ttwhy.routers:concepts;
 
-import ttwhy.scanners;
-
 namespace ttwhy
 {
 
-  export template<typename Candidate>
-  concept router = requires(Candidate candidate, scanners::input_event event) {
-    typename Candidate::terminal_policy;
+  export template<typename Candidate, typename Event>
+  concept router = requires(Candidate candidate, Event event) {
     { candidate.process(event) } -> std::same_as<asio::awaitable<void>>;
   };
 
diff --git a/ttwhy/routers/echo.cppm b/ttwhy/routers/echo.cppm
index ff309c8..c9cd7c7 100644
--- a/ttwhy/routers/echo.cppm
+++ b/ttwhy/routers/echo.cppm
@@ -29,8 +29,6 @@ namespace ttwhy::routers
   export template<typename StreamType>
   struct echo
   {
-    using terminal_policy = scanners::xterm_policy;
-
     explicit echo(StreamType & stream)
         : m_output_stream{stream}
     {}
diff --git a/ttwhy/routers/echo.tests.cpp b/ttwhy/routers/echo.tests.cpp
index c6ea10a..da2db40 100644
--- a/ttwhy/routers/echo.tests.cpp
+++ b/ttwhy/routers/echo.tests.cpp
@@ -46,29 +46,27 @@ namespace
     }
   };
 
-  struct incomplete_router_no_policy
-  {
-    auto process(ttwhy::scanners::input_event) -> asio::awaitable<void>;
-  };
-
   struct incomplete_router_no_process
   {
-    using terminal_policy = ttwhy::scanners::xterm_policy;
   };
 
   struct incomplete_router_wrong_return
   {
-    using terminal_policy = ttwhy::scanners::xterm_policy;
     auto process(ttwhy::scanners::input_event) -> void;
   };
+
+  struct incomplete_router_wrong_event
+  {
+    auto process(int) -> asio::awaitable<void>;
+  };
 }  // namespace
 
 TEST_CASE("The router concept validates router candidate interfaces", "[router][concept]")
 {
-  STATIC_REQUIRE(ttwhy::router<ttwhy::routers::echo<mock_stream>>);
-  STATIC_REQUIRE_FALSE(ttwhy::router<incomplete_router_no_policy>);
-  STATIC_REQUIRE_FALSE(ttwhy::router<incomplete_router_no_process>);
-  STATIC_REQUIRE_FALSE(ttwhy::router<incomplete_router_wrong_return>);
+  STATIC_REQUIRE(ttwhy::router<ttwhy::routers::echo<mock_stream>, ttwhy::scanners::input_event>);
+  STATIC_REQUIRE_FALSE(ttwhy::router<incomplete_router_no_process, ttwhy::scanners::input_event>);
+  STATIC_REQUIRE_FALSE(ttwhy::router<incomplete_router_wrong_return, ttwhy::scanners::input_event>);
+  STATIC_REQUIRE_FALSE(ttwhy::router<incomplete_router_wrong_event, ttwhy::scanners::input_event>);
 }
 
 SCENARIO("The echo router handles terminal navigation within the valid printed area", "[router][echo]")
diff --git a/ttwhy/scanners/concepts.cppm b/ttwhy/scanners/concepts.cppm
index 69d6459..5c29b5f 100644
--- a/ttwhy/scanners/concepts.cppm
+++ b/ttwhy/scanners/concepts.cppm
@@ -17,11 +17,14 @@ namespace ttwhy
     { a.is_pending() } -> std::same_as<bool>;
   };
 
-  export template<typename Sink>
-  concept ansi_sink = requires(Sink sink) {
-    { sink(std::declval<ttwhy::scanners::character_event>()) } -> std::same_as<void>;
-    { sink(std::declval<ttwhy::scanners::control_event>()) } -> std::same_as<void>;
-    { sink(std::declval<ttwhy::scanners::navigation_event>()) } -> std::same_as<void>;
+  export template<typename Sink, typename Event>
+  concept event_sink = requires(Sink sink, Event event) {
+    { sink(event) } -> std::same_as<void>;
   };
 
+  export template<typename Sink>
+  concept terminal_event_sink =
+      event_sink<Sink, scanners::character_event> && event_sink<Sink, scanners::control_event> &&
+      event_sink<Sink, scanners::navigation_event>;
+
 }  // namespace ttwhy
diff --git a/ttwhy/scanners/terminal_policies.cppm b/ttwhy/scanners/terminal_policies.cppm
index 7af0d66..e3c889c 100644
--- a/ttwhy/scanners/terminal_policies.cppm
+++ b/ttwhy/scanners/terminal_policies.cppm
@@ -59,12 +59,9 @@ namespace ttwhy::scanners
 
   }  // namespace detail
 
-  export template<typename T>
-  using associated_terminal_policy_t = typename T::terminal_policy;
-
   export struct ansi_policy
   {
-    constexpr auto static resolve_vt220_keypad(std::string & buffer, ttwhy::ansi_sink auto & sink) -> void
+    constexpr auto static resolve_vt220_keypad(std::string & buffer, ttwhy::terminal_event_sink auto & sink) -> void
     {
       if (buffer.empty())
       {
@@ -78,7 +75,8 @@ namespace ttwhy::scanners
       buffer.clear();
     }
 
-    constexpr auto static resolve_vt100_cursor(char terminator, std::string &, ttwhy::ansi_sink auto & sink) -> void
+    constexpr auto static resolve_vt100_cursor(char terminator, std::string &, ttwhy::terminal_event_sink auto & sink)
+        -> void
     {
       if (auto key = detail::map_vt100_cursor(terminator))
       {
@@ -86,7 +84,7 @@ namespace ttwhy::scanners
       }
     }
 
-    constexpr auto static resolve_ss3(char terminator, ttwhy::ansi_sink auto & sink) -> void
+    constexpr auto static resolve_ss3(char terminator, ttwhy::terminal_event_sink auto & sink) -> void
     {
       if (auto key = detail::map_vt100_cursor(terminator))
       {
@@ -124,7 +122,7 @@ namespace ttwhy::scanners
       return static_cast<modifier_set>(modifier_value - 1);
     }
 
-    constexpr auto static resolve_vt220_keypad(std::string & buffer, ttwhy::ansi_sink auto & sink) -> void
+    constexpr auto static resolve_vt220_keypad(std::string & buffer, ttwhy::terminal_event_sink auto & sink) -> void
     {
       if (buffer.empty())
       {
@@ -140,8 +138,8 @@ namespace ttwhy::scanners
       buffer.clear();
     }
 
-    constexpr auto static resolve_vt100_cursor(char terminator, std::string & buffer, ttwhy::ansi_sink auto & sink)
-        -> void
+    constexpr auto static resolve_vt100_cursor(char terminator, std::string & buffer,
+                                               ttwhy::terminal_event_sink auto & sink) -> void
     {
       auto modifiers = parse_modifiers(buffer);
 
@@ -151,7 +149,7 @@ namespace ttwhy::scanners
       }
     }
 
-    constexpr auto static resolve_ss3(char terminator, ttwhy::ansi_sink auto & sink) -> void
+    constexpr auto static resolve_ss3(char terminator, ttwhy::terminal_event_sink auto & sink) -> void
     {
       if (auto key = detail::map_vt100_cursor(terminator))
       {
diff --git a/ttwhy/scanners/terminal_scanner.cppm b/ttwhy/scanners/terminal_scanner.cppm
index ec4a1a6..a791909 100644
--- a/ttwhy/scanners/terminal_scanner.cppm
+++ b/ttwhy/scanners/terminal_scanner.cppm
@@ -95,7 +95,7 @@ namespace ttwhy::scanners::detail
 
   /// Transitions
 
-  template<ansi_sink Sink, typename TerminalPolicy>
+  template<terminal_event_sink Sink, typename TerminalPolicy>
   struct transition_table
   {
     auto operator()() const noexcept
@@ -200,7 +200,7 @@ namespace ttwhy::scanners::detail
 export namespace ttwhy::scanners
 {
 
-  template<ansi_sink Sink, typename TerminalPolicy>
+  template<terminal_event_sink Sink, typename TerminalPolicy>
   struct terminal_scanner
   {
     explicit terminal_scanner(Sink & sink)
@@ -230,7 +230,7 @@ export namespace ttwhy::scanners
         m_state_machine;
   };
 
-  template<ansi_sink Sink>
+  template<terminal_event_sink Sink>
   using ansi = terminal_scanner<Sink, ansi_policy>;
 
 }  // namespace ttwhy::scanners
-- 
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