/*
 * \brief  Input-event filter
 * \author Norman Feske
 * \date   2017-02-01
 */

/*
 * Copyright (C) 2017 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU Affero General Public License version 3.
 */

/* Genode includes */
#include <input/component.h>
#include <os/static_root.h>
#include <base/component.h>
#include <base/attached_rom_dataspace.h>
#include <base/heap.h>
#include <timer_session/connection.h>

/* local includes */
#include <input_source.h>
#include <remap_source.h>
#include <merge_source.h>
#include <chargen_source.h>

namespace Input_filter { struct Main; }


struct Input_filter::Main : Input_connection::Avail_handler,
                            Source::Factory
{
	Env &_env;

	Attached_rom_dataspace _config { _env, "config" };

	Heap _heap { _env.ram(), _env.rm() };

	Registry<Registered<Input_connection> > _input_connections;

	typedef String<Session_label::capacity()> Label;

	/*
	 * Mechanism to construct a 'Timer' on demand
	 *
	 * By lazily constructing the timer, the input-filter does not depend
	 * on a timer service unless its configuration defines time-related
	 * filtering operations like key repeat.
	 */
	struct Timer_accessor : Input_filter::Timer_accessor
	{
		struct Lazy
		{
			Timer::Connection timer;

			Lazy(Env &env) : timer(env) { }
		};

		Env &_env;

		Constructible<Lazy> lazy;

		Timer_accessor(Env &env) : _env(env) { }

		/**
		 * Timer_accessor interface
		 */
		Timer::Connection &timer() override
		{
			if (!lazy.constructed())
				lazy.construct(_env);

			return lazy->timer;
		}
	} _timer_accessor { _env };

	/**
	 * Pool of configuration include snippets, obtained as ROM modules
	 */
	struct Include_accessor : Input_filter::Include_accessor
	{
		struct Rom
		{
			typedef Include_accessor::Name Name;

			Registry<Rom>::Element    _reg_elem;
			Name             const    _name;
			Attached_rom_dataspace    _dataspace;
			Signal_context_capability _reconfig_sigh;

			void _handle_rom_update()
			{
				_dataspace.update();

				/* trigger reconfiguration */
				Signal_transmitter(_reconfig_sigh).submit();
			}

			Signal_handler<Rom> _rom_update_handler;

			Rom(Registry<Rom> &registry, Env &env,
			    Name const &name, Type const &type,
			    Signal_context_capability reconfig_sigh)
			:
				_reg_elem(registry, *this), _name(name),
				_dataspace(env, name.string()), _reconfig_sigh(reconfig_sigh),
				_rom_update_handler(env.ep(), *this, &Rom::_handle_rom_update)
			{
				/* validate top-level node type */
				xml(type);

				/* respond to ROM updates */
				_dataspace.sigh(_rom_update_handler);
			}

			bool has_name(Name const &name) const { return _name == name; }

			/**
			 * Return ROM content as XML
			 *
			 * \throw Include_unavailable
			 */
			Xml_node xml(Include_accessor::Type const &type) const
			{
				Xml_node const node = _dataspace.xml();
				if (node.type() == type)
					return node;

				error("unexpected <", node.type(), "> node " "in included "
				      "ROM \"", _name, "\", expected, <", type, "> node");
				throw Include_unavailable();
			}
		};

		Env                      &_env;
		Allocator                &_alloc;
		Signal_context_capability _sigh;
		Registry<Rom>             _registry;

		/**
		 * Return true if registry contains an include with the given name
		 */
		bool _exists(Rom::Name const &name)
		{
			bool exists = false;
			_registry.for_each([&] (Rom const &rom) {
				if (rom.has_name(name))
					exists = true; });

			return exists;
		}

		/**
		 * Constructor
		 *
		 * \param sigh  signal handler that responds to new ROM versions
		 */
		Include_accessor(Env &env, Allocator &alloc, Signal_context_capability sigh)
		:
			_env(env), _alloc(alloc), _sigh(sigh)
		{ }

		~Include_accessor()
		{
			_registry.for_each([&] (Rom &rom) { destroy(_alloc, &rom); });
		}

		void _apply_include(Name const &name, Type const &type, Functor const &fn) override
		{
			/* populate registry on demand */
			if (!_exists(name)) {
				try { new (_alloc) Rom(_registry, _env, name, type, _sigh); }
				catch (...) {
					error("include \"", name, "\" unavailable");
					throw Include_unavailable();
				}
			}

			/* call 'fn' with the XML content of the named include */
			Rom const *matching_rom = nullptr;
			_registry.for_each([&] (Rom const &rom) {
				if (rom.has_name(name))
					matching_rom = &rom; });

			/* this condition should never occur */
			if (!matching_rom)
				throw Include_unavailable();

			fn.apply(matching_rom->xml(type));
		}
	};

	/**
	 * Maximum nesting depth of input sources, for limiting the stack usage
	 */
	unsigned _create_source_max_nesting_level = 16;

	/**
	 * Source::Factory interface
	 *
	 * \throw Source::Invalid_config
	 */
	Source &create_source(Source::Owner &owner, Xml_node node, Source::Sink &sink) override
	{
		/*
		 * Guard for the protection against too deep recursions while
		 * processing the configuration.
		 */
		struct Nesting_level_guard
		{
			unsigned &level;

			Nesting_level_guard(unsigned &level) : level(level)
			{
				if (level == 0) {
					error("too many nested input sources");
					throw Source::Invalid_config();
				}
				level--;
			}

			~Nesting_level_guard() { level++; }

		} nesting_level_guard { _create_source_max_nesting_level };

		/* return input source with the matching name */
		if (node.type() == Input_source::name()) {
			Label const label = node.attribute_value("name", Label());
			Input_connection *match = nullptr;

			_input_connections.for_each([&] (Input_connection &connection) {
				if (connection.label() == label)
					match = &connection; });

			if (match)
				return *new (_heap) Input_source(owner, *match, sink);

			error("input named '", label, "' does not exist");
			throw Source::Invalid_config();
		}

		/* create regular filter */
		if (node.type() == Remap_source::name())
			return *new (_heap) Remap_source(owner, node, sink, *this);

		if (node.type() == Merge_source::name())
			return *new (_heap) Merge_source(owner, node, sink, *this);

		if (node.type() == Chargen_source::name())
			return *new (_heap) Chargen_source(owner, node, sink, *this, _heap,
			                                   _timer_accessor, _include_accessor);

		error("unknown <", node.type(), "> input-source node type");
		throw Source::Invalid_config();
	}

	/**
	 * Source::Factory interface
	 */
	void destroy_source(Source &source) override { destroy(_heap, &source); }

	/*
	 * Flag used to defer configuration updates until all input sources are
	 * in their default state.
	 */
	bool _config_update_pending = false;

	/**
	 * Return true if all input sources are in their default state
	 */
	bool _input_connections_idle() const
	{
		bool idle = true;

		_input_connections.for_each([&] (Input_connection const &connection) {
			if (!connection.idle())
				idle = false; });

		return idle;
	}

	struct Output
	{
		Source::Owner  _owner;
		Source        &_top_level;

		/**
		 * Constructor
		 *
		 * \throw Source::Invalid_config
		 * \throw Genode::Out_of_memory
		 */
		Output(Xml_node output, Source::Sink &sink, Source::Factory &factory)
		:
			_owner(factory),
			_top_level(factory.create_source(_owner, Source::input_sub_node(output), sink))
		{ }

		void generate() { _top_level.generate(); }
	};

	Constructible<Output> _output;

	/*
	 * Input session provided to our client
	 */
	Input::Session_component _input_session { _env, _env.ram() };

	/* process events */
	struct Final_sink : Source::Sink
	{
		Input::Session_component &_input_session;

		Final_sink(Input::Session_component &input_session)
		: _input_session(input_session) { }

		void submit_event(Input::Event const &event) override {
			_input_session.submit(event); }

	} _final_sink { _input_session };

	/*
	 * Input_connection::Avail_handler
	 */
	void handle_input_avail() override
	{
		for (;;) {

			/* fetch events in input sources */
			_input_connections.for_each([&] (Input_connection &connection) {
				connection.flush(); });

			bool pending = false;

			_input_connections.for_each([&] (Input_connection &connection) {
				pending |= connection.pending(); });

			if (pending && _output.constructed())
				_output->generate();

			if (_config_update_pending && _input_connections_idle())
				Signal_transmitter(_config_handler).submit();

			/* stop if no events are pending */
			if (!pending)
				break;
		}
	}

	Static_root<Input::Session> _input_root { _env.ep().manage(_input_session) };

	void _handle_config()
	{
		_config.update();

		bool const force = _config.xml().attribute_value("force", false);
		bool const idle  = _input_connections_idle();

		/* defer reconfiguration until all sources are idle */
		if (!idle && !force) {
			_config_update_pending = true;
			return;
		}

		if (!idle)
			warning("force reconfiguration while input state is not idle");

		_apply_config();
	}

	void _apply_config()
	{
		_input_connections.for_each([&] (Registered<Input_connection> &conn) {
			destroy(_heap, &conn); });

		_config.xml().for_each_sub_node("input", [&] (Xml_node input_node) {

			try {
				Label const label =
					input_node.attribute_value("label", Label());

				try {
					new (_heap)
						Registered<Input_connection>(_input_connections, _env,
						                             label, *this, _heap);

				} catch (Genode::Service_denied) {
					error("parent denied input source '", label, "'");
				}
			} catch (Xml_node::Nonexistent_attribute) {
				error("ignoring invalid input node '", input_node);
			}
		});

		try {
			if (_config.xml().has_sub_node("output"))
				_output.construct(_config.xml().sub_node("output"),
				                  _final_sink, *this);

		} catch (Source::Invalid_config) {
			error("invalid <output> configuration");
		} catch (Allocator::Out_of_memory) {
			error("out of memory while constructing filter chain"); }

		_config_update_pending = false;
	}

	Signal_handler<Main> _config_handler
		{ _env.ep(), *this, &Main::_handle_config };

	Include_accessor _include_accessor { _env, _heap, _config_handler };

	/**
	 * Constructor
	 */
	Main(Genode::Env &env) : _env(env)
	{
		_input_session.event_queue().enabled(true);
		_config.sigh(_config_handler);

		/*
		 * Apply initial configuration
		 */
		_apply_config();

		/*
		 * Announce service
		 */
		_env.parent().announce(_env.ep().manage(_input_root));
	}
};


void Component::construct(Genode::Env &env) { static Input_filter::Main inst(env); }