#ifndef _KERNEL_h
#define _KERNEL_h

#include "Task.h"
#include "EventListener.h"

#define KERNEL_MAX_HANDLES 256
#define KERNEL_MAX_TASKS 32
#define KERNEL_MAX_EVENT_SUBSCRIPTIONS 64

typedef void (*kernel_handle_destructor_t)(kernel_handle_t, void*);

struct KernelHandle;
struct KernelTask;
struct KernelEventSubscription;

/// <summary>
/// WatchOS kernel providing the supervisor that makes it all go
/// </summary>
class Kernel
{
private:
	/// <summary>
	/// Holds the accounting of all handles the kernel has allocated
	/// </summary>
	KernelHandle* m_handle[KERNEL_MAX_HANDLES];
	/// <summary>
	/// Id of the next handle to allocate
	/// </summary>
	int m_next_handle = 1;
	/// <summary>
	/// Holds a reference and metadata for every task registered with the kernel
	/// </summary>
	KernelTask* m_task[KERNEL_MAX_TASKS];
	/// <summary>
	/// Holds a reference and metadata for every event subscription
	/// </summary>
	KernelEventSubscription* m_event_subscription[KERNEL_MAX_EVENT_SUBSCRIPTIONS];

	/// <summary>
	/// Perform the actual actions to free a handle
	/// </summary>
	/// <remarks>
	/// Calls the destructor (if set), and removes it from the kernel's internal tracking
	/// </remarks>
	/// <param name="handle">handle to free</param>
	void freeHandle(kernel_handle_t handle);

public:
	Kernel();

	/// <summary>
	/// Initialize the kernel on first boot and notify tasks to do the same
	/// </summary>
	void initialize();
	/// <summary>
	/// Have all tasks perform startup after booting
	/// </summary>
	void start();
	/// <summary>
	/// Notify all tasks and the kernel to prepare for deep sleep by saving any state
	/// required to persistent storage.
	/// </summary>
	void suspend();

	/// <summary>
	/// Create a new kernel handle pointing to an object
	/// </summary>
	/// <param name="type">type of the handle, one of WATCHOS_HANDLE_TYPE_ consts</param>
	/// <param name="object">pointer to the object this handle references</param>
	/// <param name="destructor">function to call when this handle has released all references</param>
	/// <param name="well_known">specify a 'well_known' value this pointer can be fetched by</param>
	/// <returns>a handle which can be used to fetch or release this object</returns>
	kernel_handle_t allocHandle(byte type, void* object, kernel_handle_destructor_t destructor = nullptr, uint32_t well_known = 0);

	/// <summary>
	/// Fetch the object referenced by this handle
	/// </summary>
	/// <param name="handle">handle to fetch</param>
	/// <returns>a pointer to the object the handle references</returns>
	void* getHandle(kernel_handle_t handle);

	/// <summary>
	/// Increase the reference count of a handle
	/// </summary>
	/// <param name="handle">handle to increase reference count on</param>
	void useHandle(kernel_handle_t handle);

	/// <summary>
	/// Decrease the reference count of a handle
	/// </summary>
	/// <param name="handle">handle to decrease reference count on</param>
	void releaseHandle(kernel_handle_t handle);

	/// <summary>
	/// Fetch the handle associated with a "well known" handle
	/// </summary>
	/// <param name="handle">a well known handle we're trying to locate</param>
	/// <returns>the kernel handle of the well known object</returns>
	kernel_handle_t getHandleForWellKnown(well_known_handle_t handle);

	/// <summary>
	/// Register a new task with the kernel
	/// </summary>
	/// <param name="task">task implementation to register</param>
	/// <param name="wk_handle">optionally, register this as a well known object</param>
	/// <returns>the handle of the registered task</returns>
	kernel_handle_t registerTask(Task* task, well_known_handle_t wk_handle = WATCHOS_HANDLE_NULL);
	/// <summary>
	/// Unregisters a task with the kernel
	/// </summary>
	/// <param name="task">task implementation to unregister</param>
	void unregisterTask(Task* task);

	/// <summary>
	/// Push an event to all relevant subscribers
	/// </summary>
	/// <remarks>
	/// This will look through all subscriptions and see which subscriptions' masks are
	/// set to receive events of this source/type, and push the event through to the
	/// applicable listeners.
	/// </remarks>
	/// <param name="source">handle of the sender</param>
	/// <param name="event">id of the event; what the event means</param>
	/// <param name="param1">event-defined data</param>
	/// <param name="param2">event-defined data</param>
	void pushEvent(well_known_handle_t source, uint16_t event, byte param1, byte param2);

	/// <summary>
	/// Subscribe a listener to an event
	/// </summary>
	/// <param name="listener">listener that should receive events</param>
	/// <param name="source_mask">a bitmask of the event sources that we want to receive</param>
	/// <param name="event_mask">a bitmask of the event types that we want to receive</param>
	/// <returns>a handle to the subscription</returns>
	kernel_handle_t subscribeEvent(EventListener* listener, well_known_handle_t source_mask, uint16_t event_mask);
	/// <summary>
	/// Remove an event subscription
	/// </summary>
	/// <param name="subscription">the subscription to remove</param>
	void unsubscribeEvent(KernelEventSubscription* subscription);

	/// <summary>
	/// Have the kernel and any runnable tasks do processing
	/// </summary>
	void tick();
};

#endif