// TODO: handle big/little endian ?

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <fcntl.h>

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

uint16_t engine_color_32_to_16(uint8_t r, uint8_t g, uint8_t b, uint8_t a) {
	uint16_t color16;
	r = r >> 4;
	g = g >> 4;
	b = b >> 4;
	a = a >> 4;
	color16 = (a << 12) | (r << 8) | (g << 4) | b;
	return color16;
}

int main(int argc, char **argv) {
	if (argc != 3) {
		fprintf(stderr,"Not the right number of arguments, syntax: tex <file> <outfile>\n");
		return 1;
	}
	
	int width;
	int height;
	int components;
	unsigned char * data = stbi_load(argv[1],&width,&height,&components,4);
	if (data == NULL) {
		fprintf(stderr,"stb_image could not decode input file.\n");
		return 1;	
	}
	
	int file = open(argv[2],O_WRONLY | O_CREAT | O_TRUNC,0644);
	if (file == -1) {
		fprintf(stderr,"Could not open output file (No permissions? Does not exist?).\n");
		return 1;
	}
	
	uint16_t width2 = (uint16_t)width;
	uint16_t height2 = (uint16_t)height;
	if (write(file,&width2,sizeof(uint16_t)) != sizeof(uint16_t)) {
		fprintf(stderr,"Could not write image to output file.\n");
	}
	
	if (write(file,&height2,sizeof(uint16_t)) != sizeof(uint16_t)) {
		fprintf(stderr,"Could not write image to output file.\n");
	}
	uint16_t * outbuffer = malloc(sizeof(uint16_t) * width * height);
	if (outbuffer == NULL) {
		fprintf(stderr,"Could not allocate output buffer in memory.\n");
		return 1;	
	}
	
	uint32_t pixelIndex = 0;
	while (pixelIndex < width * height * 4) {
		uint16_t color = engine_color_32_to_16(
			data[pixelIndex],
			data[pixelIndex + 1],
			data[pixelIndex + 2],
			data[pixelIndex + 3]
		);
		
		outbuffer[pixelIndex / 4] = color;
		pixelIndex += 4;
	}
	
	if (write(file,outbuffer,sizeof(uint16_t) * width * height) != sizeof(uint16_t) * width * height) {
		fprintf(stderr,"Could not write image to output file.\n");
	}
	close(file);
	
	return 0;
}