#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include "bmp.h"

uint32_t calc_bitmap_pixel_array_size_bytes(bitmap *bitmap_in) {
	/* We will assume that the bitmap bits per pixel is always a multiple of 8 and sizeof byte is always 8 */
	uint32_t bytes_unpadded = (bitmap_in->image_width * bitmap_in->image_height * bitmap_in->bits_per_pixel) / 8;
	return bytes_unpadded + (bytes_unpadded % 8); /* Add padding to ensure 4 byte allignment */
};

uint32_t calc_bitmap_file_size_bytes(bitmap *bitmap_in) {
	/* We will assume that the bitmap bits per pixel is always a multiple of 8 and sizeof byte is always 8 */
	return sizeof(bitmap) + calc_bitmap_pixel_array_size_bytes(bitmap_in) - 2 ; /* Take away two to account for compiler padding struct */
};

bitmap init_bitmap(int32_t image_width_in, int32_t image_height_in) {
	bitmap new_bitmap;
	/* Bitmap Info Header */
	new_bitmap.info_header_size_bytes = 40;
	new_bitmap.image_width = image_width_in;
	new_bitmap.image_height = image_height_in;
	new_bitmap.color_planes_used = 1;
	new_bitmap.bits_per_pixel = 24;
	new_bitmap.compression_method = 0;
	
	new_bitmap.image_size = calc_bitmap_pixel_array_size_bytes(&new_bitmap);
	new_bitmap.horizontal_resolution_pixels_per_metre = 2835; /* Approx 72DPI */
	new_bitmap.vertical_resolution_pixels_per_metre = 2835;
	new_bitmap.colors_in_palette = 0;
	new_bitmap.important_colors = 0;

	/* File Header */
	new_bitmap.header_field[0] = 'B'; 
	new_bitmap.header_field[1] = 'M'; 
	new_bitmap.file_size_bytes = calc_bitmap_file_size_bytes(&new_bitmap);
	new_bitmap.reserved1 = 0;
	new_bitmap.reserved2 = 0;
	new_bitmap.image_data_start_offset = 54;		

	return new_bitmap;
};

int write_to_bitmap(bitmap *bitmap_in, char *filename) {
	int8_t write_status;
	uint8_t *bitmap_in_byte_ptr = (uint8_t *)bitmap_in + 2; /* Offset by two to account for padding */
	int8_t fd = open(filename, O_WRONLY | O_CREAT);
	if (fd == -1)
		return -1;
	/* This is writing out of bounds (bitmap < bitmap_file_size), please fix */
	write_status = write(fd, bitmap_in_byte_ptr, calc_bitmap_file_size_bytes(bitmap_in));
	if (fd == -1) {
		close(fd);
		return -1;
	}
	close(fd);
	return 0;
};