#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include "assert.h"


struct list_node {
  int data;
  struct list_node *next;
};
typedef struct list_node list_node_t;

struct list {
  list_node_t * head;
};
typedef struct list list_t;

void list_init (list_t * list) {
  list->head = NULL;
}

int list_length(list_t * list) {
  list_node_t *cur;
  int count = 0;

  cur = list->head;
  while (cur != NULL) {
    count++;
    cur = cur->next;
  }

  return count;
}

bool list_empty(list_t * list) {
  return (list->head == NULL);
}

void list_print(list_t * list) {
  list_node_t *cur;

  cur = list->head;
  while (cur != NULL) {
    printf("%d ", cur->data);
    cur = cur->next;
  }
  printf("\n");
}

void list_add(list_t * list, list_node_t * item) {
  list_node_t *cur;

  assert(item->next == NULL);

  if (list_empty(list)) {
    list->head = item;
  } else {
    cur = list->head;
    while (cur->next != NULL) {
      cur = cur->next;
    }
    cur->next = item;
  }
}

list_node_t * list_remove(list_t * list, list_node_t * item) {
  list_node_t *cur;

  if (list_empty(list))
    return NULL;

  if (list->head->data == item->data) {
    list_node_t * removed = list->head;
    list->head = list->head->next;
    return removed;
  }

  cur = list->head;
  assert(cur != NULL);

  while (cur->next != NULL) {
    if (cur->next->data == item->data) {
      list_node_t * removed = cur->next;
      cur->next = cur->next->next;
      return removed;                   /* just the first */
    }
    cur = cur->next;
  }

  return NULL;
}

void list_revert(list_t *list) {
  /* FIXME: work without 'reverted?' */
  list_t reverted;
  reverted.head = NULL;

  list_node_t *cur = list->head;
  while (cur != NULL) {
    list_node_t *next = cur->next;
    list_node_t *headbefore = reverted.head;

    reverted.head = cur;
    cur->next = headbefore;

    cur = next;
  }

  list->head = reverted.head;
}

list_node_t* list_elementat(list_t *list, int i) {
  if (list_empty(list) || i > list_length(list)-1) {
    return NULL;
  }

  list_node_t *cur = list->head;
  for (int j=0; j < i; j++) {
    cur = cur->next;
  }

  return cur;
}

int main(int argc, char *argv[]) {

  /* Test empty list */
  list_t *emptylist = malloc(sizeof(list_t));
  list_init(emptylist);
  assert(list_length(emptylist) == 0);
  assert(list_empty(emptylist) == true);
  list_print(emptylist);
  printf("list_length = %d\n", list_length(emptylist));
  assert(list_elementat(emptylist, 0) == NULL);
  assert(list_elementat(emptylist, 1) == NULL);
  assert(list_elementat(emptylist, 2) == NULL);
  free(emptylist);

  /* Setup foolist for the following tests. */
  list_t *foolist = malloc(sizeof(list_t));
  list_init(foolist);

  /* Add one element */
  list_node_t * foo = malloc(sizeof(list_node_t));
  assert(foo != NULL);
  *foo = (list_node_t) { 1, NULL };
  list_add(foolist, foo);

  assert(list_length(foolist) == 1);
  assert(list_empty(foolist) == false);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  // append something to foo
  list_node_t * bar = malloc(sizeof(list_node_t));
  *bar = (list_node_t) { 23, NULL };
  list_add(foolist, bar);

  assert(list_length(foolist) == 2);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  // append more
  const int howmany = 100;
  for (int i = 0; i < howmany; i++) {
    list_node_t *newnode = malloc(sizeof(list_node_t));
    *newnode = (list_node_t) { i, NULL };

    list_add(foolist, newnode);
  }
  assert(list_length(foolist) == 2 + howmany);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  // remove something
  list_node_t toremove = { 23, NULL };
  free(list_remove(foolist, &toremove));
  assert(list_length(foolist) == 2 + howmany - 1);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  // remove last item
  toremove.data = howmany - 1;
  free(list_remove(foolist, &toremove));
  assert(list_length(foolist) == 2 + howmany - 2);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  // remove something
  toremove.data = 1;
  free(list_remove(foolist, &toremove));
  assert(list_length(foolist) == 2 + howmany - 3);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  // remove something
  toremove.data = 1;
  free(list_remove(foolist, &toremove));
  assert(list_length(foolist) == 2 + howmany - 4);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  /* remove everything */
  for (int i = 0; i < howmany; i++) {
    toremove.data = i;
    free(list_remove(foolist, &toremove));
  }
  assert(list_length(foolist) == 0);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  /* remove last remaining item */
  toremove.data = 2;
  list_remove(foolist, &toremove);
  assert(list_length(foolist) == 0);
  assert(list_empty(foolist) == true);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  /* revert a list */
  const int howmany2 = 10;
  for (int i = 0; i < howmany2; i++) {
    list_node_t *newnode = malloc(sizeof(list_node_t));
    newnode->data = i;
    newnode->next = NULL;

    list_add(foolist, newnode);
  }

  for (int i = 0; i < howmany2; i++) {
    list_node_t *el = list_elementat(foolist, i);
    assert(el->data == i);
  }

  assert(list_length(foolist) == howmany2);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  list_revert(foolist);

  for (int i = 0; i < howmany2; i++) {
    list_node_t *el = list_elementat(foolist, i);
    assert(el->data == howmany2-i-1);
  }

  assert(list_length(foolist) == howmany2);
  list_print(foolist);
  printf("list_length = %d\n", list_length(foolist));

  /* Test upper bound */
  assert(list_elementat(foolist, list_length(foolist)-1) != NULL);
  assert(list_elementat(foolist, list_length(foolist)  ) == NULL);
  assert(list_elementat(foolist, list_length(foolist)+1) == NULL);
  assert(list_elementat(foolist, list_length(foolist)+2) == NULL);

  /* Free up remaining items and the list. */
  while(!list_empty(foolist)) {
    list_node_t *el = list_elementat(foolist, 0);
    free(list_remove(foolist, el));
  }
  free(foolist);
}