#include <stdio.h>
#include <stdlib.h>

typedef struct PBM
{
	int width;
	int height;
	int *pixel;
} PBM;

int *PBM_at(PBM *img, int i, int j)
{
	return img->pixel + img->width * i + j;
}

// アスキーフォーマットのみ
// コメント未対応
int read_pbm(const char *path, PBM *img)
{
	char header[2];
	FILE *fp;
	int r;
	int i;
	
	fp = fopen(path, "r");
	if (!fp) {
		goto FILE_ERROR;
	}
	
	r = fscanf(fp, "%c%c", &header[0], &header[1]);
	if (r != 2) {
		goto HEADER_ERROR;
	}
	if (header[0] != 'P' || header[1] != '1') {
		goto HEADER_ERROR;
	}
	r = fscanf(fp, "%d%d", &img->width, &img->height);
	if (r != 2) {
		goto HEADER_ERROR;
	}

	img->pixel = (int *)malloc(img->width * img->height * sizeof(int));
	if (!img->pixel) {
		goto MEMORY_ERROR;
	}

	for (i = 0; i < img->width * img->height; ++i) {
		r = fscanf(fp, "%d", &img->pixel[i]);
		if (r != 1) {
			goto DATA_ERROR;
		}
		if (img->pixel[i] != 0 && img->pixel[i] != 1) {
			goto DATA_ERROR;
		}
	}

	fclose(fp);
	return 0;
	
FILE_ERROR:
	return -1;

HEADER_ERROR:
	fclose(fp);
	return -2;

MEMORY_ERROR:
	fclose(fp);
	return -3;

DATA_ERROR:
	free(img->pixel);
	fclose(fp);
	return -4;
}

void free_pbm(PBM *img)
{
	img->width = 0;
	img->height = 0;
	free(img->pixel);
}

int output_pbm(const char *path, const PBM *img)
{
	FILE *fp;
	int i;

	fp = fopen(path, "w");

	if (!fp) {
		return - 1;
	}

	fprintf(fp, "P1\n%d %d\n", img->width, img->height);
	for (i = 0; i < img->width * img->height; ++i) {
		fprintf(fp, "%d", img->pixel[i]);
		if ((i + 1) % img->width != 0) {
			fputc(' ', fp);
		} else {
			fputc('\n', fp);
		}
	}
	return 0;
}

void swap_int(int *x, int *y)
{
	int t = *x;
	*x = *y;
	*y = t;
}

void flip_horizontal(PBM *img)
{
	int i, j;
	for (i = 0; i < img->height; ++i) {
		for (j = 0; j < img->width / 2; ++j) {
			swap_int(PBM_at(img, i, j), PBM_at(img, i, img->width - 1 - j));
		}
	}
}

int main(void)
{
	PBM img;
	if (read_pbm("in.pbm", &img) != 0) {
		printf("読み込み失敗！\n");
		return 0;
	}
	flip_horizontal(&img);
	if (output_pbm("out.pbm", &img) == 0) {
		printf("処理成功！\n");	
	} else {
		printf("処理失敗！\n");	
	}
	free_pbm(&img);
	return 0;
}