ircd:Ⓜ️ Improve room::messages interface as a bidirectional STL iterator.

include/ircd/m/room.h

@@ -106,23 +106,41 @@ struct ircd::m::room
 
 /// Interface to room messages
 ///
-/// This interface focuses on room messages (state and ephemeral) from all
-/// integrated timelines. Most queries to this interface respond in linear
-/// time.
+/// This interface has the form of an STL-style iterator over room messages
+/// which are state and non-state events from all integrated timelines.
+/// Moving the iterator is cheap, but the dereference operators fetch a
+/// full event. One can iterate just event_id's by using event_id() instead
+/// of the dereference operators.
 ///
 struct ircd::m::room::messages
 {
 	m::room room;
+	db::index::const_iterator it;
+	event::id _event_id;
+	event::fetch _event;
 
-	void for_each(const event::id::closure &) const;
-	void for_each(const event::closure &) const;
+  public:
+	operator bool() const              { return bool(it);                      }
+	bool operator!() const             { return !it;                           }
 
-	bool test(const event::id::closure_bool &view) const;
-	bool test(const event::closure_bool &view) const;
+	const event::id &event_id();
+	const m::event &fetch(std::nothrow_t);
+	const m::event &fetch();
 
-	messages(const m::room &room)
-	:room{room}
-	{}
+	bool seek(const uint64_t &depth);
+	bool seek(const event::id &);
+	bool seek();
+
+	// These are reversed on purpose
+	auto &operator++()                 { return --it;                          }
+	auto &operator--()                 { return ++it;                          }
+
+	const m::event &operator*();
+	const m::event *operator->()       { return &operator*();                  }
+
+	messages(const m::room &room, const uint64_t &depth);
+	messages(const m::room &room, const event::id &);
+	messages(const m::room &room);
 };
 
 /// Interface to room state.

ircd/m/room.cc

@@ -369,75 +369,106 @@ const
 // room::messages
 //
 
-void
-ircd::m::room::messages::for_each(const event::closure &closure)
-const
+ircd::m::room::messages::messages(const m::room &room)
+:room{room}
 {
-	event::fetch event;
-	for_each(event::id::closure{[&closure, &event]
-	(const event::id &event_id)
-	{
-		if(seek(event, event_id, std::nothrow))
-			closure(event);
-	}});
+	seek();
 }
 
-void
-ircd::m::room::messages::for_each(const event::id::closure &closure)
-const
+ircd::m::room::messages::messages(const m::room &room,
+                                  const event::id &event_id)
+:room{room}
 {
-	test(event::id::closure_bool{[&closure]
-	(const event::id &event_id)
-	{
-		closure(event_id);
-		return false;
-	}});
+	seek(event_id);
 }
 
-bool
-ircd::m::room::messages::test(const event::closure_bool &closure)
-const
+ircd::m::room::messages::messages(const m::room &room,
+                                  const uint64_t &depth)
+:room{room}
 {
-	event::fetch event;
-	return test(event::id::closure_bool{[&closure, &event]
-	(const m::event::id &event_id)
-	{
-		if(seek(event, event_id, std::nothrow))
-			if(closure(event))
-				return true;
-
-		return false;
-	}});
+	seek(depth);
 }
 
-bool
-ircd::m::room::messages::test(const event::id::closure_bool &closure)
-const
+const ircd::m::event &
+ircd::m::room::messages::operator*()
 {
-	auto it
-	{
-		dbs::room_events.begin(room.room_id)
+	return fetch(std::nothrow);
 };
 
-	if(it) do
+bool
+ircd::m::room::messages::seek()
 {
+	this->it = dbs::room_events.begin(room.room_id);
+	return bool(*this);
+}
+
+bool
+ircd::m::room::messages::seek(const event::id &event_id)
+{
+	static constexpr auto idx
+	{
+		json::indexof<event, "depth"_>()
+	};
+
+	auto &column
+	{
+		dbs::event_column.at(idx)
+	};
+
+	uint64_t depth;
+	column(event_id, [&](const string_view &binary)
+	{
+		assert(size(binary) == sizeof(depth));
+		depth = byte_view<uint64_t>(binary);
+	});
+
+	char buf[m::state::KEY_MAX_SZ];
+	const auto seek_key
+	{
+		dbs::room_events_key(buf, room.room_id, depth, event_id)
+	};
+
+	this->it = dbs::room_events.begin(seek_key);
+	return bool(*this);
+}
+
+bool
+ircd::m::room::messages::seek(const uint64_t &depth)
+{
+	char buf[m::state::KEY_MAX_SZ];
+	const auto seek_key
+	{
+		dbs::room_events_key(buf, room.room_id, depth)
+	};
+
+	this->it = dbs::room_events.begin(seek_key);
+	return bool(*this);
+}
+
+const ircd::m::event::id &
+ircd::m::room::messages::event_id()
+{
+	assert(bool(*this));
 	const auto &key{it->first};
-		const auto part
-		{
-			dbs::room_events_key(key)
-		};
-
-		const auto event_id
-		{
-			std::get<1>(part)
-		};
-
-		if(closure(event_id))
-			return true;
+	const auto part{dbs::room_events_key(key)};
+	_event_id = std::get<1>(part);
+	return _event_id;
 }
-	while(++it);
 
-	return false;
+const ircd::m::event &
+ircd::m::room::messages::fetch()
+{
+	m::seek(_event, event_id());
+	return _event;
+}
+
+const ircd::m::event &
+ircd::m::room::messages::fetch(std::nothrow_t)
+{
+	if(!m::seek(_event, event_id(), std::nothrow))
+		_event = m::event::fetch{};
+
+	return _event;
 }
 
 //