#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <linux/uhid.h>

/*
 * HID Report Desciptor
 * We emulate a basic 3 button mouse with wheel and 3 keyboard LEDs. This is
 * the report-descriptor as the kernel will parse it:
 *
 * INPUT(1)[INPUT]
 *   Field(0)
 *     Physical(GenericDesktop.Pointer)
 *     Application(GenericDesktop.Mouse)
 *     Usage(3)
 *       Button.0001
 *       Button.0002
 *       Button.0003
 *     Logical Minimum(0)
 *     Logical Maximum(1)
 *     Report Size(1)
 *     Report Count(3)
 *     Report Offset(0)
 *     Flags( Variable Absolute )
 *   Field(1)
 *     Physical(GenericDesktop.Pointer)
 *     Application(GenericDesktop.Mouse)
 *     Usage(3)
 *       GenericDesktop.X
 *       GenericDesktop.Y
 *       GenericDesktop.Wheel
 *     Logical Minimum(-128)
 *     Logical Maximum(127)
 *     Report Size(8)
 *     Report Count(3)
 *     Report Offset(8)
 *     Flags( Variable Relative )
 * OUTPUT(2)[OUTPUT]
 *   Field(0)
 *     Application(GenericDesktop.Keyboard)
 *     Usage(3)
 *       LED.NumLock
 *       LED.CapsLock
 *       LED.ScrollLock
 *     Logical Minimum(0)
 *     Logical Maximum(1)
 *     Report Size(1)
 *     Report Count(3)
 *     Report Offset(0)
 *     Flags( Variable Absolute )
 *
 * This is the mapping that we expect:
 *   Button.0001 ---> Key.LeftBtn
 *   Button.0002 ---> Key.RightBtn
 *   Button.0003 ---> Key.MiddleBtn
 *   GenericDesktop.X ---> Relative.X
 *   GenericDesktop.Y ---> Relative.Y
 *   GenericDesktop.Wheel ---> Relative.Wheel
 *   LED.NumLock ---> LED.NumLock
 *   LED.CapsLock ---> LED.CapsLock
 *   LED.ScrollLock ---> LED.ScrollLock
 *
 * This information can be verified by reading /sys/kernel/debug/hid/<dev>/rdesc
 * This file should print the same information as showed above.
 */

static unsigned char rdesc[] = {
	0x05, 0x01,	/* USAGE_PAGE (Generic Desktop) */
	0x09, 0x02,	/* USAGE (Mouse) */
	0xa1, 0x01,	/* COLLECTION (Application) */
	0x09, 0x01,		/* USAGE (Pointer) */
	0xa1, 0x00,		/* COLLECTION (Physical) */
	0x85, 0x01,			/* REPORT_ID (1) */
	0x05, 0x09,			/* USAGE_PAGE (Button) */
	0x19, 0x01,			/* USAGE_MINIMUM (Button 1) */
	0x29, 0x03,			/* USAGE_MAXIMUM (Button 3) */
	0x15, 0x00,			/* LOGICAL_MINIMUM (0) */
	0x25, 0x01,			/* LOGICAL_MAXIMUM (1) */
	0x95, 0x03,			/* REPORT_COUNT (3) */
	0x75, 0x01,			/* REPORT_SIZE (1) */
	0x81, 0x02,			/* INPUT (Data,Var,Abs) */
	0x95, 0x01,			/* REPORT_COUNT (1) */
	0x75, 0x05,			/* REPORT_SIZE (5) */
	0x81, 0x01,			/* INPUT (Cnst,Var,Abs) */
	0x05, 0x01,			/* USAGE_PAGE (Generic Desktop) */
	0x09, 0x30,			/* USAGE (X) */
	0x09, 0x31,			/* USAGE (Y) */
	0x09, 0x38,			/* USAGE (WHEEL) */
	0x15, 0x81,			/* LOGICAL_MINIMUM (-127) */
	0x25, 0x7f,			/* LOGICAL_MAXIMUM (127) */
	0x75, 0x08,			/* REPORT_SIZE (8) */
	0x95, 0x03,			/* REPORT_COUNT (3) */
	0x81, 0x06,			/* INPUT (Data,Var,Rel) */
	0xc0,			/* END_COLLECTION */
	0xc0,		/* END_COLLECTION */
	0x05, 0x01,	/* USAGE_PAGE (Generic Desktop) */
	0x09, 0x06,	/* USAGE (Keyboard) */
	0xa1, 0x01,	/* COLLECTION (Application) */
	0x85, 0x02,		/* REPORT_ID (2) */
	0x05, 0x08,		/* USAGE_PAGE (Led) */
	0x19, 0x01,		/* USAGE_MINIMUM (1) */
	0x29, 0x03,		/* USAGE_MAXIMUM (3) */
	0x15, 0x00,		/* LOGICAL_MINIMUM (0) */
	0x25, 0x01,		/* LOGICAL_MAXIMUM (1) */
	0x95, 0x03,		/* REPORT_COUNT (3) */
	0x75, 0x01,		/* REPORT_SIZE (1) */
	0x91, 0x02,		/* Output (Data,Var,Abs) */
	0x95, 0x01,		/* REPORT_COUNT (1) */
	0x75, 0x05,		/* REPORT_SIZE (5) */
	0x91, 0x01,		/* Output (Cnst,Var,Abs) */
	0xc0,		/* END_COLLECTION */
};

void print_uhid_event(struct uhid_event ev, const char * var_name)
{
	size_t size_bytes = sizeof(ev);
	printf("let mut %s: [u8; %u] = [0; %u];\n", var_name, size_bytes, size_bytes);
	for (size_t offset = 0; offset < size_bytes; ++offset)
	{
		unsigned char byte = ((unsigned char*)&ev)[offset];
		if (byte != 0)
		{
			printf("%s[%u] = 0x%02x;\n", var_name, offset, byte);
			// printf("%s[%u] = %u;\n", var_name, offset, byte);
		}
	}
	printf("\n");
}

int main(int argc, char **argv)
{
	{
		const char *name = "input";
		struct uhid_event ev;
		memset(&ev, 0, sizeof(ev));
		ev.type = UHID_INPUT;
		ev.u.input.size = 5;
		ev.u.input.data[0] = 0x1;
		ev.u.input.data[1] |= 0x1;
		ev.u.input.data[1] |= 0x2;
		ev.u.input.data[1] |= 0x4;
		ev.u.input.data[2] = 5;
		ev.u.input.data[3] = -5;
		ev.u.input.data[4] = 1;
		print_uhid_event(ev, name);
	}

	{
		const char *name = "create";
		struct uhid_event ev;
		memset(&ev, 0, sizeof(ev));
		ev.type = UHID_CREATE2;
		strcpy((char*)ev.u.create2.name, "test-uhid-device");
		memcpy(ev.u.create2.rd_data, rdesc, sizeof(rdesc));
		ev.u.create2.rd_size = sizeof(rdesc);
		ev.u.create2.bus = BUS_USB;
		ev.u.create2.vendor = 0x15d9;
		ev.u.create2.product = 0x0a37;
		ev.u.create2.version = 0;
		ev.u.create2.country = 0;
		print_uhid_event(ev, name);
	}

	{
		const char *name = "destroy";
		struct uhid_event ev;
		memset(&ev, 0, sizeof(ev));
		ev.type = UHID_DESTROY;		
		print_uhid_event(ev, name);
	}
	
	return EXIT_SUCCESS;
}