// SPDX-License-Identifier: Apache-2.0
// Sealed with Magistamp.

use core::ops::{Add, AddAssign, Mul, MulAssign};

use crate::number::Number;
use crate::one::One;



/// A Natural number is a counting number from one to infinity.
/// 1, 2, 3, 4, 5, 6, ...
///
/// Rust types that are in this category are:
/// u8, u16, u32, u64, u128, usize
pub trait Natural: Number + One +
                   Add<Output=Self> + AddAssign +
                   Mul<Output=Self> + MulAssign +
{
   /// Attempts to subtract a number from itself.
   ///
   /// Since subtraction isn't closed under this set (1 - 2 = -1) the trait
   /// doesn't enforce that Sub and SubAssign are implemented. This function,
   /// however, allows for subtraction and handles the case where the result is
   /// no longer within the `Natural` numbers domain.
   ///
   /// # Arguments
   /// `rhs`: The number to subtract.
   ///
   /// # Returns
   /// `None` if the subtraction would fall below 1.  
   /// `Some` if their is a valid result.
   ///
   /// # Examples
   /// ```rust
   /// use sigils::Natural;
   ///
   /// let x = 3u8 as Natural;
   ///
   /// assert_eq!(x.try_sub(2), Some(1));
   /// assert_eq!(x.try_sub(7), None);
   /// ```
   fn try_sub(self, rhs: Self) -> Option<Self>;
/*
   ///
   fn try_div(self, rhs: Self) -> Option<Self>;

   ///
   fn try_rem(self, rhs: Self) -> Option<Self>;

   /// Performs division and returns both the quotient and remainder.
   #[inline]
   fn try_div_rem(self, rhs: Self) -> Option<(Self, Self)>
   {
      Some((self.try_div(rhs)?, self.try_rem(rhs)?))
   }
*/
}



/// A macro to make implementing the `Natural` trait easier for all the
/// base types in Rust.
macro_rules! natural_trait_impl
{
   ($($varType:ty),*) =>
   {
      $(
         impl Natural for $varType
         {
            #[inline]
            fn try_sub(self, rhs: Self) -> Option<Self>
            {
               self.checked_sub(rhs).filter(|x| *x >= Self::one())
            }
         }
      )*
   }
}

// Implement the Number trait for the types that are Numbers.
natural_trait_impl!(u8, u16, u32, u64, u128, usize);