#include<stdio.h>
#include<stdint.h>
#include<stdlib.h>
#include<errno.h>
#include<string.h>

typedef struct {
	FILE *file;
	long int size_of_file;
	char *contents;
} TEXTFILE;

long int filesize(FILE *fp) {
    long int size_of_file;
    fseek(fp, 0, SEEK_END);
    size_of_file = ftell(fp);
    fseek(fp, 0, SEEK_SET);
    return(size_of_file);
}

TEXTFILE* init_file(char* path) {
	TEXTFILE *buf;
	buf = malloc(sizeof(TEXTFILE));
	if (buf == NULL) {
		fprintf(stderr, "Error allocating structure");
		return NULL;
	}
	buf -> file = fopen(path, "r");
	if (buf -> file == NULL) {
		fprintf(stderr, "Error opening file");
		free(buf);
		return NULL;
	}
	buf -> size_of_file = filesize(buf -> file);
	buf -> contents = (char *)malloc(buf -> size_of_file);
	if (buf -> contents == NULL) {
		fprintf(stderr, "Error allocating contents array");
		fclose(buf -> file);
		free(buf);
		return NULL;
	}
	fread(buf -> contents, sizeof(char), buf -> size_of_file, buf -> file);
	return buf;
}

void close_file(TEXTFILE* file) {
	free(file -> contents);
	fclose(file -> file);
	free(file);
}

int main(int argc, char* argv[]) {
	if (argc < 3) {
            	printf("Некорректные аргументы. Требуется файл для чтения и файл для записи.\n");
        	return 1;
	} else {
		TEXTFILE* input_file = init_file(argv[1]);
		if (input_file == NULL) { return 1;}
		char* pos;
		pos = strstr(input_file -> contents, "777");
		while (pos != NULL) {
			*pos = 'M';
			*(pos+1) = 'A';
			*(pos+2) = 'I';
			pos = strstr(pos, "777");
		}
		FILE* output_file = fopen(argv[2], "w");
		if (output_file == NULL) {
			fprintf(stderr, "Error opening output file");
		} else {
			fwrite(input_file -> contents, sizeof(char), input_file -> size_of_file, output_file);
			fclose(output_file);
		}
		close_file(input_file);
		return 0;
	}
}