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

struct string {
	char *data;
	size_t length;
	char own_data;
};

void safe_free(struct string s){
	if(s.own_data)
		free(s.data);
}

struct string make_string(char* data){
	struct string new_string = {data, strlen(data), 0};
	return new_string;
}

void print_string(struct string s){
	write(1, s.data, s.length);
	write(1, "\n", 1);
}

void append(struct string *s, struct string addition){
	if(s->own_data){
		s->data = realloc(s->data, s->length + addition.length);
	} else {
		char *old_data = s->data;
		s->data = malloc(s->length + addition.length);
		memcpy(s->data, old_data, s->length);
		s->own_data = 1;
	}
	memcpy(s->data + s->length, addition.data, addition.length);
	s->length += addition.length;
}

struct string substr(const struct string original, size_t beginning, size_t end){
	struct string substring;
	substring.data = original.data + beginning;
	substring.length = end - beginning;
	substring.own_data = 0;
	return substring;
}

char* c_substr(const char *original, size_t beginning, size_t end){
	char* new_string = malloc(1 + end - beginning);
	memcpy(new_string, original + beginning, end - beginning);
	new_string[end - beginning] = 0;
	return new_string;
}

int main(){
	/* Old way */ {
		char *our_string = "The slug went across the street in the middle of the night in the rain because there weren't any cars then.";

		char *slug = c_substr(our_string, 4, 9);
		printf("substring:  %s\n", slug);
		printf("original:  %s\n", our_string);
		free(slug);
	}

	/* With string "class" */ {
		struct string our_string = make_string("The slug went across the street in the middle of the night in the rain because there weren't any cars then.");
		struct string slug = substr(our_string, 4, 9);
		printf("substring, then original, with string \"class\"\n");
		print_string(slug);
		print_string(our_string);
		append(&our_string, make_string("  The rain is good for their skin."));
		print_string(our_string);
		append(&slug, make_string(" is a unit of mass in the english system, and a creature, and a type of shotgun ammunition"));
		print_string(slug);
		print_string(our_string);


		safe_free(our_string);
		safe_free(slug);
	}
}