/* list.cpp
 * Date: 2021-11-20
 * Author: Aryadev Chavali
 */

#include <cstdio>
#include <cstdlib>
#include <iostream>

template <typename T>
struct List
{
  T value;
  List<T> *next;

  List(T val, List<T> *n)
  {
    value = val;
    next  = n;
  }

  ~List()
  {
    if (next == nullptr)
      return;
    delete next;
  }
};

template <typename T>
List<T> *append(List<T> *lst, T value)
{
  List<T> *node;
  if (lst == nullptr)
    return new List<T>(value, nullptr);

  for (node = lst; node->next != nullptr; node = node->next)
    continue;

  node->next = new List<T>(value, nullptr);
  return lst;
}

/** Reverse a list
 */
template <typename T>
List<T> *reverse(List<T> *lst, List<T> *prev = nullptr)
{
  auto next = lst->next;
  lst->next = prev;
  if (next == nullptr)
    return lst;
  return reverse(next, lst);
}

template <typename T, typename U>
List<U> *map(List<T> *lst, U (*f)(T))
{
  if (!lst)
    return nullptr;
  return new List<U>(f(lst->value), map(lst->next, f));
}

template <typename T>
T reduce(List<T> *lst, T (*reducer)(T, T), T init = 0)
{
  if (!lst)
    return init;
  else if (!init)
    init = lst->value;
  else
    init = reducer(init, lst->value);
  return reduce(lst->next, reducer, init);
}

template <typename T>
List<T> *filter(List<T> *lst, bool (*f)(T), List<T> *new_lst = nullptr)
{
  if (!lst)
    return new_lst;
  if (f(lst->value))
    new_lst = append(new_lst, lst->value);
  return filter(lst->next, f, new_lst);
}

template <typename T>
std::ostream &operator<<(std::ostream &ostream, const List<T> *lst)
{
  if (!lst)
    return ostream;
  ostream << "|" << lst->value << lst->next;
  return ostream;
}

int main(void)
{
  puts("Create linked list with 1..10");
  auto lst = append<int>(nullptr, 1);
  for (int i = 2; i <= 10; ++i)
    lst = append(lst, i);
  printf("Current output for list: ");
  std::cout << lst << std::endl;
  lst = reverse(lst);
  printf("Reverse list: ");
  std::cout << lst << std::endl;
  puts("Reverse list again...");
  printf("Map list with f(x) = 2x: ");
  auto mapped = map<int, int>(lst = reverse(lst),
                              [](int x)
                              {
                                return x * 2;
                              });
  std::cout << mapped << std::endl;
  delete mapped;
  printf("Sum all numbers in list: ");
  std::cout << reduce<int>(
    lst,
    [](int a, int b)
    {
      return a + b;
    },
                   0)
            << std::endl;
  printf("Print all even numbers 1..10: ");
  auto evens = filter<int>(lst,
                           [](int a)
                           {
                             return a % 2 == 0;
                           });
  std::cout << evens << std::endl;
  delete lst;
  delete evens;
  return 0;
}