/*
 # Copyright (c) 2009 - OpenSLX Project, Computer Center University of Freiburg
 #
 # This program is free software distributed under the GPL version 2.
 # See http://openslx.org/COPYING
 #
 # If you have any feedback please consult http://openslx.org/feedback and
 # send your suggestions, praise, or complaints to feedback@openslx.org
 #
 # General information about OpenSLX can be found at http://openslx.org/
 # --------------------------------------------------------------------------
 # inputEventHandler.h:
 #  - Common definitions for input event handlers
 # --------------------------------------------------------------------------
 */

#ifndef INPUTEVENTHANDLER_H_
#define INPUTEVENTHANDLER_H_

#include <QtGlobal>
#include <QtDebug>
#include <QList>
#include <QString>
#include <QCoreApplication>
#include <src/input/inputEvent.h>
#include "detail/policyChain.h"
#include "detail/systemTraits.h"

struct InputEventContext
{
	InputEventContext()
	{
		hasBeenDenied = false;
	}

	virtual pid_t senderPid() const = 0;
	virtual uid_t senderUid() const = 0;
	virtual gid_t senderGid() const = 0;

	mutable bool hasBeenDenied;
};

namespace input_policy
{

/////////////////////////////////////////////////////////////////////////
// Policy:
//  Modifies the behaviour of an input handler class.
//
//  There are several kinds of policy:
//   - Security Policy (When to allow a certain action)
//   - System Requirements (When to enable a certain handler)
//   - Applicability (When to consider a certain handler)
//
//  Policies are tied together using the detail::PolicyChain class.
/////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////////////////////////////////
// Security Policy:
//  At the moment there are two security policies:
//  1. If the user is on a local seat, allow. If the user is privileged,
//     allow. Else deny.
//  2. Allow everybody.
//  Additional security policies can be added by following the example
//  set by AllowLocalOrPrivileged
/////////////////////////////////////////////////////////////////////////
template<typename PolicyImpl>
BEGIN_POLICY_CLASS(Security)
{
	bool allow(InputEventContext const* context)
	{
		return PolicyImpl::allow(context);
	}
}
END_POLICY_CLASS

struct AllowLocalOrPrivileged
{
	static bool allow(InputEventContext const*);
};

struct AllowEverybody
{
	static bool allow(InputEventContext const*);
};

typedef Security<AllowEverybody> Unprivileged;

/////////////////////////////////////////////////////////////////////////
// System Requirements:
//  At the moment, this is trivial, as PVS only runs on Linux. But,
//  as porting efforts are already underway, we include the necessary
//  machinery anyway.
/////////////////////////////////////////////////////////////////////////
template<IMPLICIT_TYPE_LIST_PARAMS(Trait)>
BEGIN_POLICY_CLASS(Require)
{
	static const bool areSystemRequirementsFulfilled =
			NextPolicy::areSystemRequirementsFulfilled ||
			detail::Matches<AllOf<IMPLICIT_TYPE_LIST_ARGS(Trait)>, detail::SystemTraits>::value;
}
END_POLICY_CLASS

/////////////////////////////////////////////////////////////////////////
// System Requirements:
//  At the moment, this is trivial, as PVS only runs on Linux. But,
//  as porting efforts are already underway, we include the necessary
//  machinery anyway.
/////////////////////////////////////////////////////////////////////////
enum {
	HANDLER_CODE_DONT_CARE = 0xffff,
	HANDLER_VALUE_DONT_CARE = 0xffffffff
};

struct T;

template<unsigned short EventType,
		unsigned short EventCode = HANDLER_CODE_DONT_CARE,
		unsigned int EventValue = HANDLER_VALUE_DONT_CARE>
BEGIN_POLICY_CLASS(Match)
{
	bool isApplicable(InputEvent const& evt)
	{
		if(evt.type() != EventType)
			return NextPolicy::isApplicable(evt);
		if(EventCode != HANDLER_CODE_DONT_CARE && evt.code() != EventCode)
			return NextPolicy::isApplicable(evt);
		if(EventValue != HANDLER_VALUE_DONT_CARE && evt.value() != EventValue)
			return NextPolicy::isApplicable(evt);
		return true;
	}
};
END_POLICY_CLASS

namespace detail
{

/////////////////////////////////////////////////////////////////////////
// Base case: If no policies are given:
/////////////////////////////////////////////////////////////////////////
struct InputEventHandlerPolicyBase
{
	// The default security policy applies
	typedef AllowLocalOrPrivileged DefaultSecurityPolicyImpl;

	bool allow(InputEventContext const* context)
	{
		return DefaultSecurityPolicyImpl::allow(context);
	}

	// A handler that does not specify requirements works
	// everywhere
	static const bool areSystemRequirementsFulfilled = true;

	// Generate an error when no match policy is given.
	bool isApplicable(InputEvent const&)
	{
		return false;
	}

	// If any policy implementation needs an initialization hook:
	// Don't forget to call NextPolicy::initialize() in your
	// implementation!
	void initialize()
	{
	}
};

}
}

/////////////////////////////////////////////////////////////////////////
// We want a nice non-generic base so we can make a list of polymorphic
// handlers.
//
// The actual handler class need to provide doHandle and can override
// allow and isApplicable.
/////////////////////////////////////////////////////////////////////////
class InputEventHandlerBase
{
public:
	enum HandlerStatus
	{
		HANDLER_MATCHED,
		HANDLER_NOT_ALLOWED,
		HANDLER_NOT_APPLICABLE
	};

	virtual void initialize() = 0;
	HandlerStatus handle(InputEvent const& evt, InputEventContext const* context = 0);

protected:
	virtual bool allow(InputEvent const& event, InputEventContext const* context = 0) = 0;
	virtual bool isApplicable(InputEvent const& event, InputEventContext const* context = 0) = 0;
	virtual void doHandle(InputEvent const& event, InputEventContext const* context = 0) = 0;
};

/////////////////////////////////////////////////////////////////////////
// Now that the machinery is in place, we can finally define what it
// is like to be an input event handler:
/////////////////////////////////////////////////////////////////////////
template<POLICY_PARAMS>
class InputEventHandler : public InputEventHandlerBase
{
protected:
	typedef USE_POLICY(input_policy::detail::InputEventHandlerPolicyBase) policy_type;
	policy_type policy;

public:
	void initialize()
	{
		policy.initialize();
	}

	// Export this so the handler chain can decide whether to include this handler
	static const bool areSystemRequirementsFulfilled = policy_type::areSystemRequirementsFulfilled;

protected:

	typedef InputEventHandler super;

	// allow and isApplicable are actually provided by Policy. If the
	// handler class wishes to override any of them, the policy implementation
	// can be called by means of super.
	bool allow(InputEvent const&, InputEventContext const* context = 0)
	{
		return policy.allow(context);
	}

	bool isApplicable(InputEvent const& event, InputEventContext const* = 0)
	{
		return policy.isApplicable(event);
	}
};

/////////////////////////////////////////////////////////////////////////
// And we can chain input handlers together:
/////////////////////////////////////////////////////////////////////////
class InputEventHandlerChain
{
private:
	QList<InputEventHandlerBase*> handlers;

	/////////////////////////////////////////////////////////////////////////
	// We need to statically dispatch on a static member of HandlerType.
	// Unfortunately, we cannot specialize member functions of a template.
	// So, we need to make this a class with a static non-template member.
	/////////////////////////////////////////////////////////////////////////
	template<bool Compatible, typename HandlerType>
	struct ConditionallyAppend
	{
		/////////////////////////////////////////////////////////////////////////
		// This method will never be instantiated for handlers that are
		// not Compatible, thus generating no reference to HandlerType
		// and permitting compilation to proceed without
		// tedious nested preprocessor conditionals.
		/////////////////////////////////////////////////////////////////////////
		static void doIt(InputEventHandlerChain* chain)
		{
			chain->handlers.append(new HandlerType);
		}
	};

	template<typename HandlerType>
	struct ConditionallyAppend<false, HandlerType>
	{
		static void doIt(InputEventHandlerChain*)
		{
		}
	};

public:
	// Add an event handler to the chain. The argument is only for
	// compilers which cannot handle template member functions
	// correctly.
	template<typename HandlerType>
	InputEventHandlerChain& add(HandlerType const* = 0)
	{
		ConditionallyAppend<HandlerType::areSystemRequirementsFulfilled, HandlerType>::doIt(this);
		return *this;
	}

	void initialize()
	{
		QListIterator<InputEventHandlerBase*> i(handlers);
		while(i.hasNext())
		{
			i.next()->initialize();
		}
	}

	void handle(InputEvent const& event, InputEventContext const* context = 0)
	{
		QListIterator<InputEventHandlerBase*> i(handlers);
		while(i.hasNext())
		{
			switch(i.next()->handle(event, context))
			{
			case InputEventHandlerBase::HANDLER_MATCHED:
				break;
			case InputEventHandlerBase::HANDLER_NOT_ALLOWED:
				context->hasBeenDenied = true;
			case InputEventHandlerBase::HANDLER_NOT_APPLICABLE:
				continue;
			}
		}
	}
};

#endif /* INPUTEVENTHANDLER_H_ */