#include <libimg.h>

static void img_rotate_ip90(img_t img)
{
	if(img.width != img.height) return;

	img_pixel_t *tl = img.pixels;
	img_pixel_t *tr = img.pixels + img.width - 1;
	img_pixel_t *bl = tl + (img.height - 1) * img.stride;
	img_pixel_t *br = tr + (img.height - 1) * img.stride;

	for(int y=0; y < img.height >> 1; y++)
	{
		for(int x=y, dx=0, dy=0; x < img.width-1 - y; x++, dx++,
			dy+=img.stride)
		{
			int swp = tl[dx];
			tl[dx]  = bl[-dy];
			bl[-dy] = br[-dx];
			br[-dx] = tr[dy];
			tr[dy]  = swp;
		}

		tl += img.stride + 1;
		tr += img.stride - 1;
		bl -= img.stride - 1;
		br -= img.stride + 1;
	}
}

static void img_rotate_ip180(img_t img)
{
	img_pixel_t *tl = img.pixels;
	img_pixel_t *br = tl + (img.height - 1) * img.stride + img.width - 1;

	for(int y = 0; y < (img.height+1) >> 1; y++)
	{
		/* If both pointers reach the same line (height is odd), we
		   must stop at half of the width */
		int limit = img.width;
		if(tl+img.stride-1 == br) limit >>= 1;

		for(int x = 0; x < limit; x++)
		{
			int swp = tl[x];
			tl[x]   = br[-x];
			br[-x]  = swp;
		}

		tl += img.stride;
		br -= img.stride;
	}
}

static void img_rotate_ip270(img_t img)
{
	/* Same as img_rotate_ip90, except for the order of assignments */
	if(img.width != img.height) return;

	img_pixel_t *tl = img.pixels;
	img_pixel_t *tr = img.pixels + img.width - 1;
	img_pixel_t *bl = tl + (img.height - 1) * img.stride;
	img_pixel_t *br = tr + (img.height - 1) * img.stride;

	for(int y=0; y < img.height >> 1; y++)
	{
		for(int x=y, dx=0, dy=0; x < img.width-1 - y; x++, dx++,
			dy+=img.stride)
		{
			/* Only difference with img_rotate_ip90 */
			int swp = tl[dx];
			tl[dx]  = tr[dy];
			tr[dy]  = br[-dx];
			br[-dx] = bl[-dy];
			bl[-dy] = swp;
		}

		tl += img.stride + 1;
		tr += img.stride - 1;
		bl -= img.stride - 1;
		br -= img.stride + 1;
	}
}

void img_rotate_inplace(img_t img, int angle)
{
	if(angle == 90)  img_rotate_ip90(img);
	if(angle == 180) img_rotate_ip180(img);
	if(angle == 270) img_rotate_ip270(img);
}