#ifndef KNOTKIT_ALGEBRA_ZP_H
#define KNOTKIT_ALGEBRA_ZP_H

#include <iostream>
#include <tuple>
#include <cassert>

template<unsigned p>
class Zp
{
 public:
  using linear_combination = ::linear_combination<Zp<p>>;
  using linear_combination_const_iter = ::linear_combination_const_iter<Zp<p>>;
  
 private:
  unsigned v;
  
 public:
  Zp () : v(0) { }
  Zp (unsigned init) : v(init % p) { }
  Zp (int init)
  {
    int i = init % (int)p;
    if (i < 0)
      i += p;
    assert (i >= 0 && i < (int)p);
    v = i;
  }
  
  Zp (const Zp& x) : v(x.v) { }
  Zp (copy, const Zp& x) : v(x.v) {}
  Zp (Zp&& x) : v(std::move(x.v)) {
    x.v = 0;
  }
  ~Zp () { }
  
  Zp& operator = (const Zp& x) { v = x.v; return *this; }
  Zp& operator = (Zp&& x) { v = x.v; x.v = 0; return *this; }
  Zp& operator = (int x)
  {
    return operator = (Zp (x));
  }
  
  bool operator == (const Zp& x) const { return v == x.v; }
  bool operator != (const Zp& x) const { return !operator == (x); }
  
  bool operator == (int x) const { return operator == (Zp (x)); }
  bool operator != (int x) const { return !operator == (x); }
  
  bool operator < (const Zp& x) const { return v < x.v; }
  
  bool is_unit () const
  {
    return v != 0;
  }
  
  Zp operator + (const Zp& x) const { return Zp (v + x.v); }
  Zp operator - (const Zp& x) const { return Zp ((int)v - (int)x.v); }
  Zp operator - () const { return Zp (- (int)v);  }
  
  Zp operator * (const Zp& x) const { return Zp (v * x.v); }
  
  Zp operator / (const Zp& x) const
  {
    return operator * (x.recip ());
  }
  
  Zp recip () const
  {
    std::tuple<unsigned, int, int> t = unsigned_extended_gcd (v, p);
    assert (std::get<0> (t) == 1);
    assert ((int)std::get<0> (t) == std::get<1> (t)*(int)v  + std::get<2> (t)*(int)p);
    
    return Zp (std::get<1> (t));
  }
  
  Zp& operator += (const Zp& x)
  {
    v = (v + x.v) % p;
    return *this;
  }
  
  Zp& operator -= (const Zp& x) { return operator = (Zp ((int)v - (int)x.v)); }
  
  Zp& operator *= (const Zp& x)
  {
    v = (v * x.v) % p;
    return *this;
  }
  
  Zp& operator /= (const Zp& x)
  {
    return operator *= (x.recip ());
  }
  
  // d | n, d.divides (n)
  bool divides (const Zp& n) const
  {
    return v || !n.v;
  }
  
  bool operator | (const Zp& n) const { return divides (n); }
  
  Zp div (const Zp& d) const { return operator / (d); }
  
  std::tuple<Zp, Zp, Zp> extended_gcd (const Zp &x) const
  {
    if (v)
      return std::make_tuple (v, Zp (1), Zp (0));
    else
      return std::make_tuple (x, Zp (0), Zp (1));
  }
  
  Zp gcd (const Zp &x) const
  {
    assert (v || x.v);
    return 1;
  }
  friend std::ostream& operator << (std::ostream& os, const Zp& x) {
    return os << x.v;
  }
  static void show_ring () { std::cout << "Z" << p; }
  void show_self () const { std::cout << v << "(" << p << ")"; }
  void display_self () const { std::cout << *this << "\n"; }
};

#endif //KNOTKIT_ALGEBRA_ZP_H