slist.c

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

void split(struct dns_list* head, struct dns_list** a, struct dns_list** b);
struct dns_list* merge(struct dns_list* a, struct dns_list* b);
int comp_times(struct dns_list* a, struct dns_list* b);

int add_hosts_server(struct hosts_list** head, char* server)
{
	struct hosts_list* end;
	if (!(*head)) {
		*head = malloc(sizeof(struct hosts_list));
		end = *head;
	} else {
		end = *head;
		while (end->next)
			end = end->next;
		end->next = malloc(sizeof(struct hosts_list));
		end = end->next;
	}
	end->next = NULL;
	end->server = server;
	return 0;
}

int free_hosts_list(struct hosts_list** head)
{
	struct hosts_list* temp;
	while (*head) {
		temp = (*head)->next;
		free(*head);
		*head = temp;
	}
	return 0;
}

int add_dns_server(struct dns_list** head, char* server)
{
	struct dns_list* end;
	if (!(*head)) {
		*head = malloc(sizeof(struct dns_list));
		end = *head;
	} else {
		end = *head;
		while (end->next)
			end = end->next;
		end->next = malloc(sizeof(struct dns_list));
		end = end->next;
	}
	end->next = NULL;
	end->server = server;
	end->time.tv_nsec = 0;
	end->time.tv_sec = 0;
	return 0;
}

int free_dns_list(struct dns_list** head)
{
	struct dns_list* temp;
	while (*head) {
		temp = (*head)->next;
		free(*head);
		*head = temp;
	}
	return 0;
}

// Sort with merge sort as works well for linked lists
// Copied from https://www.geeksforgeeks.org/merge-sort-for-linked-list/
int sort_servers(struct dns_list** headRef)
{
	struct dns_list* head = *headRef;
	struct dns_list *a, *b;
	if (!head || !(head->next)) { // Empty list or containing one element
		return 0;
	}
	split(head, &a, &b);
	sort_servers(&a);
	sort_servers(&b);
	*headRef = merge(a, b);
	return 0;
}

void split(struct dns_list* head, struct dns_list** a, struct dns_list** b)
{
	struct dns_list *fast = head->next, *slow = head;
	while (fast) {
		fast = fast->next;
		if (fast) {
			slow = slow->next;
			fast = fast->next;
		}
	}
	*a = head;
	*b = slow->next;
	slow->next = NULL;
}

struct dns_list* merge(struct dns_list* a, struct dns_list* b)
{
	struct dns_list* out = NULL;
	if (!a) return b;
	if (!b) return a;

	if (comp_times(a, b) > 0) {
		out = b;
		out->next = merge(a, b->next);
	} else {
		out = a;
		out->next = merge(a->next, b);
	}
	return out;
}

int comp_times(struct dns_list* a, struct dns_list* b)
{
	if (a->errors != b->errors) {
		return a->errors > b->errors;
	} else if (a->time.tv_sec == b->time.tv_sec) {
		if (a->time.tv_nsec >= b->time.tv_nsec)
			return 1;
		else
			return -1;
	} else if (a->time.tv_sec > b->time.tv_sec) {
		return 1;
	} else
		return -1;
}

int print_servers(struct dns_list* head)
{
	printf("%-16s | %-11s | %s\n", "Server", "Time", "Errors");
	while (head) {
		printf("%-16s | %ld.%09ld | %d\n", head->server, head->time.tv_sec,
		       head->time.tv_nsec, head->errors);
		head = head->next;
	}
	return 0;
}