#ifndef _INCLUDE_SOURCEMOD_FORWARDINTERFACE_H_

#define _INCLUDE_SOURCEMOD_FORWARDINTERFACE_H_

#include <IForwardSys.h>

#include <IPluginSys.h>

#define SMINTERFACE_FORWARDMANAGER_NAME		"IForwardManager"

#define SMINTERFACE_FORWARDMANAGER_VERSION	1

/**

 * There is some very important documentation at the bottom of this file.

 * Readers interested in knowing more about the forward system, scrolling down is a must!

 */

namespace SourceMod

{

	enum ResultType

	{

		Pl_Continue = 0,	/* No result */

		Pl_Handled = 1,		/* Result was handled, stop at the end */

		Pl_Stop = 2,		/* Result was handled, stop now */

	};

	enum ExecType

	{

		ET_Ignore = 0,		/* Ignore all return values, return 0 */

		ET_Single = 1,		/* Only return the first exec, ignore all others */

		ET_Event = 2,		/* Acts as an event with the ResultTypes above, no mid-Stops allowed, returns highest */

		ET_Hook = 3,		/* Acts as a hook with the ResultTypes above, mid-Stops allowed, returns highest */

	};

	/**

	 * :TODO: finish this spec

	 * @brief Abstracts multiple function calling.

	 * NOTE: Parameters should be pushed in forward order, unlike

	 * the virtual machine/IPluginContext order.

	 * NOTE: Some functions are repeated in here because their documentation differs

	 * from their IPluginFunction equivalents.

	 */

	class IForward : public ICallable

	{

	public:

		/**

		 * @brief Returns the name of the forward.

		 *

		 * @return			Forward name.

		 */

		virtual const char *GetForwardName() =0;

		/**

		 * @brief Returns the number of functions in this forward.

		 *

		 * @return			Number of functions in forward.

		 */

		virtual unsigned int GetFunctionCount() =0;

		/**

		 * @brief Returns the method of multi-calling this forward has.

		 *

		 * @return			ExecType of the forward.

		 */

		virtual ExecType GetExecType() =0;

		/**

		 * @brief Executes the forward.

		 *

		 * @param result		Pointer to store result in.

		 * @param num_functions	Optionally filled with the number of function sucessfully executed.

		 * @return				Error code, if any.

		 */

		virtual int Execute(cell_t *result, unsigned int *num_functions) =0;

	};

	class IChangeableForward : public IForward

	{

	public:

		/** 

		 * @brief Removes a function from the call list.

		 *

		 * @param func		Function to remove.

		 */

		virtual void RemoveFunction(IPluginFunction *func) =0;

		/** 

		 * @brief Removes all instances of a plugin from the call list.

		 *

		 * @param plugin	Plugin to remove instances of.

		 * @return			Number of functions removed therein.

		 */

		virtual unsigned int RemoveFunctionsOfPlugin(IPlugin *plugin) =0;

		/**

		 * @brief Adds a function to the call list.

		 * NOTE: Cannot be used during a call.

		 *

		 * @param func		Function to add.

		 * @return			True on success, otherwise false.

		 */

		virtual bool AddFunction(IPluginFunction *func) =0;

		/**

		 * @brief Adds a function to the call list.

		 * NOTE: Cannot be used during a call.

		 *

		 * @param ctx		Context to use as a look-up.

		 * @param funcid	Function id to add.

		 * @return			True on success, otherwise false.

		 */

		virtual bool AddFunction(sp_context_t *ctx, funcid_t index) =0;

	};

	enum ParamType

	{

		Param_Any = 0,		//Any type will be accepted

		Param_Cell = 1,		//Only a cell will be accepted

		Param_Float = 2,	//Only a float value will be accepted

		Param_String = 3,	//Only a string will be accepted

		Param_Array = 4,	//Only a 1D array will be accepted

		Param_VarArgs = 5,	//Anything will be accepted

		ParamTypes_Total = 6,

	};

	class IForwardManager : public SMInterface

	{

	public:

		virtual const char *GetInterfaceName()

		{

			return SMINTERFACE_FORWARDMANAGER_NAME;

		}

		virtual unsigned int GetInterfaceVersion()

		{

			return SMINTERFACE_FORWARDMANAGER_VERSION;

		}

	public:

		/**

		 * @brief Creates a managed forward.  This forward exists globally.

		 *  The name used to create the forward is used as its public function in all target plugins.

		 *  As new non-private plugins become loaded or unloaded, they will be automatically added

		 * or removed.  This is ideal for global, static forwards that are never changed.

		 *

		 * @param name			Name of public function to use in forward.

		 * @param et			Execution type to be used.

		 * @param num_params	Number of parameter this function will have.

		 *						NOTE: For varargs, this should include the vararg parameter.

		 * @param types			Array of type information about each parameter.  If NULL, types

		 *						are read off the vararg stream.

		 * @param ...			If types is NULL, num_params ParamTypes should be pushed.

		 * @return				A new IForward on success, NULL if type combination is impossible.

		 */

		virtual IForward *CreateForward(const char *name, 

										ExecType et, 

										unsigned int num_params, 

										ParamType *types, 

										...) =0;

		/**

		 * @brief Creates an unmanaged forward.  This forward exists privately.

		 * Unlike managed forwards, no functions are ever added by the Manager.

		 * However, functions will be removed automatically if their parent plugin is unloaded.

		 *

		 * @param name			Name of forward (unused except for lookup, can be NULL for anonymous).

		 * @param et			Execution type to be used.

		 * @param num_params	Number of parameter this function will have.

		 *						NOTE: For varargs, this should include the vararg parameter.

		 * @param types			Array of type information about each parameter.  If NULL, types

		 *						are read off the vararg stream.

		 * @param ...			If types is NULL, num_params ParamTypes should be pushed.

		 * @return				A new IChangeableForward on success, NULL if type combination is impossible.

		 */

		virtual IChangeableForward *CreateForwardEx(const char *name, 

													ExecType et, 

													int num_params, 

													ParamType *types, 

													...) =0;

		/**

		 * @brief Finds a forward by name.  Does not return anonymous forwards (named NULL or "").

		 *

		 * @param name			Name of forward.

		 * @param ifchng		Optionally store either NULL or an IChangeableForward pointer

		 *                      depending on type of forward.

		 * @return				IForward pointer, or NULL if none found matching the name.

		 */

		virtual IForward *FindForward(const char *name, IChangeableForward **ifchng) =0;

	};

};

/**

 *  In the AMX Mod X model of forwarding, each forward contained a list of pairs, each pair containing

 * a function ID and an AMX structure.  The forward structure itself did very little but hold parameter types.

 * An execution call worked like this:

 *  - executeForward() took in a function id and a list of parameters

 *  - for each contained plugin:

 *   - the list of parameters was preprocessed and pushed

 *   - the call was made

 *   - the list was freed and copybacks were made

 *  - return

 * 

 *  The advantages to this is that the system is very easy to implement, and it's fast. The disadvantage is 

 * varargs tend to be very unforgiving and inflexible, and thus weird problems arose with casting.  You also 

 * lose flexibility, type checking, and the ability to reasonably use variable arguments lists in the VM.

 *

 *  SourceMod replaces this forward system with a far more advanced, but a bit bulkier one. The idea is that 

 * each plugin has a table of functions, and each function is an ICallable object.  As well as being an ICallable, 

 * each function is an IPluginFunction.  An ICallable simply describes the process of adding parameters to a 

 * function call.  An IPluginFunction describes the process of actually calling a function and performing allocation, 

 * copybacks, and deallocations.

 *

 * A very powerful forward system emerges: a Forward is just a collection of IPluginFunctions.  Thus, the same 

 * API can be easily wrapped around a simple list, and it will look transparent to the user.

 * Advantages:

 * 1) "SP Forwards" from AMX Mod X are simply IPluginFunctions without a collection.

 * 2) Forwards are function based, rather than plugin based, and are thus far more flexible at runtime..

 * 3) [2] Individual functions can be paused and more than one function from the same plugin can be hooked.

 * 4) [2] One hook type that used to map to many SP Forwards can now be centralized as one Forward.

 *    This helps alleviate messes like Fakemeta.

 * 5) Parameter pushing is type-checked and allows for variable arguments.

 *

 *  Note that while #2,3,4 could be added to AMX Mod X, the real binding property is #1, which makes the system

 * object oriented, rather than AMX Mod X, which hides the objects behind static functions.  It is entirely a design

 * issue, rather than a usability one.  The interesting part is when it gets to implementation, which is when the 

 * problems for SourceMod arise.  Specifically, the implementation is easier in GENERAL -- the tough part is the oddball

 * cases.

 *

 * Observe the calling process:

 * - Each parameter is pushed using the ICallable interface.  For each parameter:

 *  - For each function in the collection, the parameter is processed and pushed.

 * - For each function in the collection:

 *  - The call is made.

 *  - Copy backs are performed.

 * - Return

 *

 *  Astute readers will note the problems - the parameters are processed individually for each push,

 * rather than for each call.  This means:

 * 1) More memory is used.  Specifically, rather than N params of memory, you now have N params * M plugins.

 *    This is because, again, parameters are processed per function object, per-push, before the call.

 * 2) There are slightly more calls going around: one extra call for each parameter, since each push is manual.

 * 3) Copybacks won't work as expected.  

 *

 *  Number 3 is hard to see.  For example, say a forward has two functions, and an array is pushed with copyback.

 * The array gets pushed and copied into each plugin.  When the call is made, each plugin now has separate copies of 

 * the array.  When the copyback is performed, it gets mirrored to the originall address, but not to the next plugin!

 *  Implementing this is "difficult."  To be re-entrant, an IPluginFunction can't tell you anything

 * about its copybacks after it has returned, because its internal states were reset long ago.

 * 

 *  In order to implement this feature, IPluginFunction::Execute function now lets you pass a listener in.

 * This listener is notified each time an array parameter is about to be copied back.  Specifically, the forward 

 * uses this to detect when it needs to push a new parameter out to the next plugin.  When the forward gets the 

 * call back, it detects whether there is another plugin in the queue.  If there is, it grabs the address it will

 * be using for the same arrays, and specifies it as the new copy-back point.  If no plugins are left, it allows

 * the copyback to chain up to the original address.

 * 

 *  This wonderful little hack is somewhat reminiscent of how SourceHook parameter rewrite chains work.  It seems 

 * ugly at first, but it is actually the correct design pattern to apply to an otherwise awful problem.

 *

 *  Note that there are other solutions to this that aren't based on a visitor-like pattern.  For example, the Function

 * class could expose a "set new original address" function.  Then after arrays are pushed, the arrays are re-browsed,

 * and function #1 gets function #2's original address, function #2 gets function #3's original address, et cetera.

 * This extra browse step is a bit less efficient though, since the "visitor" method implies only taking action when

 * necessary.  Furthermore, it would require exposing such a "set address" function, which should fire a red flag 

 * that the API is doing something it shouldn't (namely, exposing the direct setting of very internal properties).

 */

#endif //_INCLUDE_SOURCEMOD_FORWARDINTERFACE_H_