#include "ff.h"

#include <arpa/inet.h>
#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define MAGIC "farbfeld"
#define MAGICLEN 8

#define BUFSIZE 4096

#define MIN(x, y) ((x) < (y) ? (x) : (y))

static uint8_t buf[BUFSIZE];

static uint8_t *loadpix(uint8_t *p, const pix_t *pix, unsigned n)
{
	for (unsigned i = 0; i < n; ++i) {
		*((uint16_t *)p) = htons(pix[i].r);
		p += sizeof(uint16_t);
		*((uint16_t *)p) = htons(pix[i].g);
		p += sizeof(uint16_t);
		*((uint16_t *)p) = htons(pix[i].b);
		p += sizeof(uint16_t);
		*((uint16_t *)p) = htons(pix[i].a);
		p += sizeof(uint16_t);
	}
	return p;
}

static void writebuf(int fd, size_t size)
{
	while (1) {
		errno = 0;
		const ssize_t res = write(fd, buf, size);

		if (res == (ssize_t)size) {
			return;
		} else if (res > 0) {
			fputs(
			    "Error writing image: Couldn't write entire buffer"
			    " (storage may be full)\n",
			    stderr);
			exit(1);
		} else {
			if (errno == EINTR) {
				continue;
			} else {
				perror("Error writing image");
				exit(1);
			}
		}
	}
}

void ff_write(int fd, img_t img)
{
	uint8_t *p = buf;

	memcpy(p, MAGIC, MAGICLEN);
	p += MAGICLEN;
	*((uint32_t *)p) = htonl(img.w);
	p += sizeof(uint32_t);
	*((uint32_t *)p) = htonl(img.h);
	p += sizeof(uint32_t);

	const pix_t *pix = img.pix;
	unsigned rem = img.w * img.h;
	while (rem > 0) {
		const unsigned cap = (BUFSIZE - (p - buf)) / sizeof(pix_t);
		const unsigned n = MIN(rem, cap);

		p = loadpix(p, pix, n);
		pix += n;
		rem -= n;

		writebuf(fd, p - buf);
		p = buf;
	}
}