use std::{fmt::{self, Write},
          ops};

pub struct Fx32(i32);

impl Fx32
{
   const FRACBITS: u32 = 16;
   const FRACMASK: u32 = 0xFFFF;
   const ONE:      i32 = 1 << Fx32::FRACBITS;

   pub fn to_bits(&self) -> u32
   {
      self.0 as u32
   }

   pub fn set_bits(&mut self, bits: u32)
   {
      self.0 = bits as i32
   }

   pub fn from_bits(bits: u32) -> Fx32
   {
      Fx32(bits as i32)
   }

   pub fn integ(&self) -> i16
   {
      (self.0 >> Fx32::FRACBITS) as i16
   }

   pub fn fract(&self) -> u16
   {
      (self.0 as u32 & Fx32::FRACMASK) as u16
   }

   pub fn mul_i(&self, n: i32) -> Fx32
   {
      Fx32(self.0 * n)
   }

   pub fn div_i(&self, n: i32) -> Fx32
   {
      Fx32(self.0 / n)
   }
}

impl From<i32> for Fx32
{
   fn from(n: i32) -> Fx32
   {
      Fx32(n << Fx32::FRACBITS)
   }
}

impl ops::Add for Fx32
{
   type Output = Fx32;

   fn add(self, o: Fx32) -> Fx32
   {
      Fx32(self.0 + o.0)
   }
}

impl ops::Sub for Fx32
{
   type Output = Fx32;

   fn sub(self, o: Fx32) -> Fx32
   {
      Fx32(self.0 - o.0)
   }
}

impl ops::Mul for Fx32
{
   type Output = Fx32;

   fn mul(self, o: Fx32) -> Fx32
   {
      Fx32((self.0 as i64 * o.0 as i64 / Fx32::ONE as i64) as i32)
   }
}

impl ops::Div for Fx32
{
   type Output = Fx32;

   fn div(self, o: Fx32) -> Fx32
   {
      Fx32((self.0 as i64 * Fx32::ONE as i64 / o.0 as i64) as i32)
   }
}

impl ops::Neg for Fx32
{
   type Output = Fx32;

   fn neg(self) -> Fx32
   {
      Fx32(-self.0)
   }
}

impl ops::Not for Fx32
{
   type Output = Fx32;

   fn not(self) -> Fx32
   {
      Fx32(!self.0)
   }
}

impl fmt::Display for Fx32
{
   fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result
   {
      let prec = f.precision().unwrap_or(1);
      let widt = f.width().unwrap_or(0);
      write!(f, "{:widt$}.", self.integ(), widt = widt)?;

      let mut k = self.to_bits();
      for _ in 0..prec {
         k &= Fx32::FRACMASK;
         k *= 10;
         let d = k >> Fx32::FRACBITS;
         let d = d % 10;
         f.write_char((d as u8 + b'0') as char)?;
      }

      Ok(())
   }
}

impl fmt::Debug for Fx32
{
   fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result
   {
      fmt::Display::fmt(self, f)
   }
}

#[test]
fn fx32_basic_ops()
{
   let seven_div_2 = 3 << Fx32::FRACBITS | Fx32::FRACMASK / 2 + 1;
   assert_eq!((Fx32::from(1) + 1.into()).to_bits(), 2 << Fx32::FRACBITS);
   assert_eq!((Fx32::from(2) - 1.into()).to_bits(), 1 << Fx32::FRACBITS);
   assert_eq!((Fx32::from(6) * 2.into()).to_bits(), 12 << Fx32::FRACBITS);
   assert_eq!((Fx32::from(6).mul_i(2)).to_bits(), 12 << Fx32::FRACBITS);
   assert_eq!((Fx32::from(7) / 2.into()).to_bits(), seven_div_2);
   assert_eq!((Fx32::from(7).div_i(2)).to_bits(), seven_div_2);
}

#[test]
#[should_panic]
#[allow(unused_must_use)]
fn fx32_overflow()
{
   Fx32::from(32767) + 1.into();
}

#[test]
fn fx32_printing()
{
   assert_eq!(format!("{}", Fx32::from(6)), "6.0");
   assert_eq!(format!("{}", Fx32::from(7).div_i(2)), "3.5");
   assert_eq!(format!("{:7.7}", Fx32::from_bits(0xDEAD_BEEF)),
              "  -8531.7458343");
}

// EOF