/**
 * @file event.h
 * @author Travis Vroman (travis@kohiengine.com)
 * @brief This file contains structures and functions specific to the
 * event system.
 * Events are a mechenism that allows the developer to send and recieve
 * data at critical points in the execution of the application in a non-
 * coupled way. For now, this follows a simple pub-sub model of event
 * transmission.
 * @version 1.0
 * @date 2022-01-10
 *
 * @copyright Kohi Game Engine is Copyright (c) Travis Vroman 2021-2022
 *
 */

#pragma once

#include "defines.h"

/**
 * @brief Represents event contextual data to be sent along with an
 * event code when an event is fired.
 * It is a union that is 128 bytes in size, meaning data can be mixed
 * and matched as required by the developer.
 * */
typedef struct event_context {
	// 128 bytes
	union {
		/** @brief An array of 2 64-bit signed integers. */
		i64 i64[2];
		/** @brief An array of 2 64-bit unsigned integers. */
		u64 u64[2];

		/** @brief An array of 2 64-bit floating-point numbers. */
		f64 f64[2];

		/** @brief An array of 4 32-bit signed integers. */
		i32 i32[4];
		/** @brief An array of 4 32-bit unsigned integers. */
		u32 u32[4];
		/** @brief An array of 4 32-bit floating-point numbers. */
		f32 f32[4];

		/** @brief An array of 8 16-bit signed integers. */
		i16 i16[8];

		/** @brief An array of 8 16-bit unsigned integers. */
		u16 u16[8];

		/** @brief An array of 16 8-bit signed integers. */
		i8 i8[16];
		/** @brief An array of 16 8-bit unsigned integers. */
		u8 u8[16];

		/**
		 * @brief Allows a pointer to arbitrary data to be passed. Also includes size info.
		 * NOTE: If used, should be freed by the sender or listener.
		 */
		struct {
			// The size of the data pointed to.
			u64 size;
			// A pointer to a memory block of data to be included with the event.
			void *data;
		} custom_data;

		/** @brief A free-form string. If used, should be freed by sender or listener. */
		const char *s;
	} data;
} event_context;

/**
 * @brief A function pointer typedef which is used for event subscriptions by the subscriber.
 * @param code The event code to be sent.
 * @param sender A pointer to the sender of the event. Can be 0.
 * @param listener_inst A pointer to the listener of the event. Can be 0.
 * @param data The event context to be passed with the fired event.
 * @returns True if the message should be considered handled, which means that it will not
 * be sent to any other consumers; otherwise false.
 */
typedef b8 (*PFN_on_event)(u16 code, void *sender, void *listener_inst, event_context data);

/**
 * @brief Initializes the event system.
 */
b8 event_system_initialize (u64 *memory_requirement, void *state, void *config);

/**
 * @brief Shuts the event system down.
 */
void event_system_shutdown (void *state);

/**
 * @brief Register to listen for when events are sent with the provided code. Events with duplicate
 * listener/callback combos will not be registered again and will cause this to return false.
 * @param code The event code to listen for.
 * @param listener A pointer to a listener instance. Can be 0/NULL.
 * @param on_event The callback function pointer to be invoked when the event code is fired.
 * @returns True if the event is successfully registered; otherwise false.
 */
KAPI b8 event_register (u16 code, void *listener, PFN_on_event on_event);

/**
 * @brief Register to listen for when a single event is sent with the provided code. Events with duplicate
 * listener/callback combos will not be registered again and will cause this to return false.
 * @note: the event is automatically unregistered once fired a single time.
 *
 * @param code The event code to listen for.
 * @param listener A pointer to a listener instance. Can be 0/NULL.
 * @param on_event The callback function pointer to be invoked when the event code is fired.
 * @returns True if the event is successfully registered; otherwise false.
 */
KAPI b8 event_register_single (u16 code, void *listener, PFN_on_event on_event);

/**
 * @brief Unregister from listening for when events are sent with the provided code. If no matching
 * registration is found, this function returns false.
 * @param code The event code to stop listening for.
 * @param listener A pointer to a listener instance. Can be 0/NULL.
 * @param on_event The callback function pointer to be unregistered.
 * @returns True if the event is successfully unregistered; otherwise false.
 */
KAPI b8 event_unregister (u16 code, void *listener, PFN_on_event on_event);

/**
 * @brief Fires an event to listeners of the given code. If an event handler returns
 * true, the event is considered handled and is not passed on to any more listeners.
 * @param code The event code to fire.
 * @param sender A pointer to the sender. Can be 0/NULL.
 * @param data The event data.
 * @returns True if handled, otherwise false.
 */
KAPI b8 event_fire (u16 code, void *sender, event_context context);

/** @brief System internal event codes. Application should use codes beyond 255. */
typedef enum system_event_code {
	/** @brief Shuts the application down on the next frame. */
	EVENT_CODE_APPLICATION_QUIT = 0x0001,

	/** @brief Keyboard key pressed.
	 * Context usage:
	 * u16 key_code = data.data.u16[0];
	 * u16 repeat_count = data.data.u16[1];
	 */
	EVENT_CODE_KEY_PRESSED = 0x0002,

	/** @brief Keyboard key released.
	 * Context usage:
	 * u16 key_code = data.data.u16[0];
	 * u16 repeat_count = data.data.u16[1];
	 */
	EVENT_CODE_KEY_RELEASED = 0x0003,

	/** @brief Mouse button pressed.
	 * Context usage:
	 * u16 x = data.data.i16[0];
	 * u16 y = data.data.i16[1];
	 * u16 delta_x = data.data.i16[2];
	 * u16 delta_y = data.data.i16[3];
	 * u16 button = data.data.u16[4];
	 */
	EVENT_CODE_BUTTON_PRESSED = 0x0004,

	/** @brief Mouse button released.
	 * Context usage:
	 * u16 x = data.data.i16[0];
	 * u16 y = data.data.i16[1];
	 * u16 delta_x = data.data.i16[2];
	 * u16 delta_y = data.data.i16[3];
	 * u16 button = data.data.u16[4];
	 */
	EVENT_CODE_BUTTON_RELEASED = 0x0005,

	/** @brief Mouse button pressed then released.
	 * Context usage:
	 * u16 x = data.data.i16[0];
	 * u16 y = data.data.i16[1];
	 * u16 delta_x = data.data.i16[2];
	 * u16 delta_y = data.data.i16[3];
	 * u16 button = data.data.u16[4];
	 */
	EVENT_CODE_BUTTON_CLICKED = 0x0006,

	/** @brief Mouse moved.
	 * Context usage:
	 * u16 x = data.data.i16[0];
	 * u16 y = data.data.i16[1];
	 * u16 delta_x = data.data.i16[2];
	 * u16 delta_y = data.data.i16[3];
	 */
	EVENT_CODE_MOUSE_MOVED = 0x0007,

	/** @brief Mouse moved.
	 * Context usage:
	 * u16 x = data.data.i16[0];
	 * u16 y = data.data.i16[1];
	 * u16 delta_x = data.data.i16[2];
	 * u16 delta_y = data.data.i16[3];
	 * ui z_delta = data.data.i8[8];
	 */
	EVENT_CODE_MOUSE_WHEEL = 0x0008,

	/** @brief Resized/resolution of a window changed from the OS.
	 * Context usage:
	 * u16 width = data.data.u16[0];
	 * u16 height = data.data.u16[1];
	 * Sender is the window itself.
	 */
	EVENT_CODE_WINDOW_RESIZED = 0x0009,

	// Change the render mode for debugging purposes.
	/* Context usage:
	 * i32 mode = context.data.i32[0];
	 */
	EVENT_CODE_SET_RENDER_MODE = 0x000A,

	/** @brief Clipboard content is ready to be retrieved.
	 * NOTE: data is freed by the platform immediately after this event is fired.
	 *
	 * Context usage:
	 * struct clipboard_context* = context.data.custom_data.data, (sizeof clipboard_context)
	 */
	EVENT_CODE_CLIPBOARD_PASTE = 0x000B,

	/** @brief Special-purpose debugging event. Context will vary over time. */
	EVENT_CODE_DEBUG0 = 0x0010,
	/** @brief Special-purpose debugging event. Context will vary over time. */
	EVENT_CODE_DEBUG1 = 0x0011,
	/** @brief Special-purpose debugging event. Context will vary over time. */
	EVENT_CODE_DEBUG2 = 0x0012,
	/** @brief Special-purpose debugging event. Context will vary over time. */
	EVENT_CODE_DEBUG3 = 0x0013,
	/** @brief Special-purpose debugging event. Context will vary over time. */
	EVENT_CODE_DEBUG4 = 0x0014,

	EVENT_CODE_DEBUG5 = 0x0015,
	EVENT_CODE_DEBUG6 = 0x0016,
	EVENT_CODE_DEBUG7 = 0x0017,
	EVENT_CODE_DEBUG8 = 0x0018,
	EVENT_CODE_DEBUG9 = 0x0019,
	EVENT_CODE_DEBUG10 = 0x001A,
	EVENT_CODE_DEBUG11 = 0x001B,
	EVENT_CODE_DEBUG12 = 0x001C,
	EVENT_CODE_DEBUG13 = 0x001D,
	EVENT_CODE_DEBUG14 = 0x001E,
	EVENT_CODE_DEBUG15 = 0x001F,

	/** @brief The hovered-over object id, if there is one.
	 * Context usage:
	 * i32 id = context.data.u32[0]; - will be INVALID ID if nothing is hovered over.
	 */
	EVENT_CODE_OBJECT_HOVER_ID_CHANGED = 0x0020,

	/**
	 * @brief An event fired by the renderer backend to indicate when any render targets
	 * associated with the default window resources need to be refreshed (i.e. a window resize)
	 */
	EVENT_CODE_DEFAULT_RENDERTARGET_REFRESH_REQUIRED = 0x0021,

	/**
	 * @brief An event fired by the kvar system when a kvar has been updated.
	 * Context usage:
	 * kvar_change* change = context.data.custom_data.data;
	 */
	EVENT_CODE_KVAR_CHANGED = 0x0022,

#if KOHI_HOT_RELOAD
	/**
	 * @brief An event fired from the asset system when a watched asset file has been written to.
	 * Context usage:
	 * u32 watch_id = context.data.u32[0];
	 * kasset* = sender;
	 */
	EVENT_CODE_ASSET_HOT_RELOADED = 0x0023,

	/**
	 * @brief An event fired when a watched file has written to disk.
	 * Context usage:
	 * u32 watch_id = context.data.u32[0];
	 * vfs_asset_data* = sender
	 */
	EVENT_CODE_VFS_FILE_WRITTEN_TO_DISK = 0x0024,

	/**
	 * @brief An event fired when a watched file has been removed from disk.
	 * No asset data is included (obviously)
	 * Context usage:
	 * u32 watch_id = context.data.u32[0];
	 */
	EVENT_CODE_VFS_FILE_DELETED_FROM_DISK = 0x0025,

#endif

	/**
	 * @brief An event fired while a button is being held down and the
	 * mouse is moved.
	 *
	 * Context usage:
	 * i16 x = context.data.i16[0]
	 * i16 y = context.data.i16[1]
	 * i16 delta_x = context.data.i16[2]
	 * i16 delta_y = context.data.i16[3]
	 * u16 button = context.data.u16[4]
	 */
	EVENT_CODE_MOUSE_DRAGGED = 0x0030,

	/**
	 * @brief An event fired when a button is pressed and a mouse movement
	 * is done while it is pressed.
	 *
	 * Context usage:
	 * i16 x = context.data.i16[0]
	 * i16 y = context.data.i16[1]
	 * i16 delta_x = context.data.i16[2]
	 * i16 delta_y = context.data.i16[3]
	 * u16 button = context.data.u16[4]
	 */
	EVENT_CODE_MOUSE_DRAG_BEGIN = 0x0031,

	/**
	 * @brief An event fired when a button is released was previously dragging.
	 *
	 * Context usage:
	 * i16 x = context.data.i16[0]
	 * i16 y = context.data.i16[1]
	 * i16 delta_x = context.data.i16[2]
	 * i16 delta_y = context.data.i16[3]
	 * u16 button = context.data.u16[4]
	 */
	EVENT_CODE_MOUSE_DRAG_END = 0x0032,

	/**
	 * @brief An event fired when an animation starts.
	 *
	 * Context usage:
	 * kname animation_name = context.data.u64[0]
	 */
	EVENT_CODE_ANIMATION_STARTED = 0x0033,

	/**
	 * @brief An event fired when an animation completes.
	 *
	 * Context usage:
	 * kname animation_name = context.data.u64[0]
	 */
	EVENT_CODE_ANIMATION_COMPLETE = 0x0034,

	/**
	 * @brief An event fired when an audio starts playing.
	 *
	 * Context usage:
	 * kname animation_name = context.data.u64[0]
	 */
	EVENT_CODE_AUDIO_STARTED = 0x0035,

	/**
	 * @brief An event fired when an audio completes.
	 *
	 * Context usage:
	 * kaudio base = context.data.u16[0]
	 * instance_id = context.data.u16[1]
	 */
	EVENT_CODE_AUDIO_COMPLETE = 0x0036,

	/**
	 * @brief An event fired when a scene entity is loaded.
	 *
	 * Context usage:
	 * kentity entity = context.data.u64[0]
	 *
	 * Sender is typically kscene*
	 */
	EVENT_CODE_SCENE_ENTITY_LOADED = 0x0037,

	/**
	 * @brief An event fired when a scene entity is unloaded.
	 *
	 * Context usage:
	 * kentity entity = context.data.u64[0]
	 *
	 * Sender is typically kscene*
	 */
	EVENT_CODE_SCENE_ENTITY_UNLOADED = 0x0038,

	/**
	 * @brief An event fired when a heightfield terrain is loaded.
	 *
	 * Context usage:
	 * addrof hf_terrain (cast to hf_terrain*) = context.data.u64[0]
	 *
	 * Sender is typically kscene*
	 */
	EVENT_CODE_HF_TERRAIN_LOADED = 0x0039,

	/**
	 * @brief An event fired when a heightfield terrain is loaded.
	 *
	 * Context usage:
	 * addrof hf_terrain (cast to hf_terrain*) = context.data.u64[0]
	 *
	 * Sender is typically kscene*
	 */
	EVENT_CODE_HF_TERRAIN_UNLOADED = 0x003A,

	/**
	 * @brief An event fired when a material is created.
	 *
	 * Context usage:
	 * addrof kmaterial_data (cast to kmaterial_data*) = context.custom_data.data
	 * sizeof kmaterial_data = context.custom_data.size
	 */
	EVENT_CODE_MATERIAL_CREATED = 0x003B,

	/**
	 * @brief An event fired when a material is destroyed.
	 *
	 * Context usage:
	 * addrof kmaterial_data (cast to kmaterial_data*) = context.custom_data.data
	 * sizeof kmaterial_data = context.custom_data.size
	 */
	EVENT_CODE_MATERIAL_DESTROYED = 0x003C,

	/** @brief The maximum event code that can be used internally. */
	MAX_EVENT_CODE = 0x00FF
} system_event_code;