// io_bmp.c

#include <stdio.h>
#include "io_bmp.h"

struct BMP_HEADER {
	unsigned char BM[2];
	unsigned long f_sz;
	unsigned long pd0;
	unsigned long p_ofs;
	unsigned long bhs;
	long w;
	long h;
	unsigned short pl;
	unsigned short bit;
	unsigned long cmp;
	unsigned long isz;
	unsigned long xppm;
	unsigned long yppm;
	unsigned long cltu;
	unsigned long clti;
} __attribute__ ((packed));

void read_BMP(struct BMP* a, char* file_name)
{
	FILE* fp = fopen(file_name, "rb");
	
	struct BMP_HEADER hd;
	fseek(fp, 0, SEEK_SET);
	fread(&hd, sizeof(struct BMP_HEADER), 1, fp);
	
	a->w = hd.w;
	a->h = hd.h;
	const unsigned long p_ofs = hd.p_ofs;
	
	int q = 4 - ((a->w * 3) % 4);
	q = (q == 4) ? 0 : q;
	
	struct PIXEL* p;
	int j = a->h; while (j-- > 0) {
		fseek(fp, p_ofs + (((a->w * 3) + q) * j), SEEK_SET);
		
		p = a->p + (a->w * j);
		fread(p, sizeof(struct PIXEL), a->w, fp);
	}
}

void write_BMP(struct BMP* a, char* file_name)
{
	FILE* fp=fopen(file_name, "wb");

	int q = 4 - ((a->w * 3) % 4);
	q = (q == 4) ? 0 : q;
	
	const unsigned long p_ofs=54;
	const unsigned long i_sz=((a->w * 3) + q) * a->h;
	struct BMP_HEADER hd = {
		'B','M',
		p_ofs + i_sz,
		0,
		p_ofs,
		40,
		a->w,
		a->h,
		1,
		24,
		0,
		i_sz, 3780, 3780,
		0, 0
	};
	fseek(fp, 0, SEEK_SET);
	fwrite(&hd, sizeof(struct BMP_HEADER), 1, fp);
	
	struct PIXEL* p;
	int j = a->h; while (j-- > 0) {
		fseek(fp, p_ofs + ((a->w * 3) + q) * j, SEEK_SET);

		p = a->p + (a->w * j);
		fwrite(p, sizeof(unsigned char), (a->w * 3) + q, fp);
	}
}