use core::mem;

mod convert;
mod math;
#[cfg(feature = "num-traits")]
mod num;
mod ops;

#[derive(Clone, Copy, Default, PartialEq, Eq, PartialOrd, Hash)]
pub struct P16E1(i16);

impl P16E1 {
    pub const SIZE: usize = 16;
    pub const ES: usize = 1;

    /// Machine epsilon (2.44140625e-4).
    pub const EPSILON: Self = Self::new(0x_100);

    /// Smallest finite value (-268435456).
    pub const MIN: Self = Self::new(-0x_7FFF);

    /// Smallest positive normal value (3.725290298_e-9).
    pub const MIN_POSITIVE: Self = Self::new(0x_1);

    /// Largest finite value (268435456).
    pub const MAX: Self = Self::new(0x_7FFF);

    /// Not a Number (NaN).
    pub const NAN: Self = Self::new(-0x_8000);

    /// Infinity (∞).
    pub const INFINITY: Self = Self::new(-0x_8000);

    /// Zero.
    pub const ZERO: Self = Self::new(0);

    /// Identity.
    pub const ONE: Self = Self::new(0x_4000);

    #[inline]
    pub const fn new(i: i16) -> Self {
        Self(i)
    }
    #[inline]
    pub fn from_bits(v: u16) -> Self {
        unsafe { mem::transmute(v) }
    }
    #[inline]
    pub fn to_bits(self) -> u16 {
        unsafe { mem::transmute(self) }
    }
    #[inline]
    pub fn abs(self) -> Self {
        let i = self.to_bits() as i16;
        Self::from_bits((if i < 0 { -i } else { i }) as u16)
    }
    #[inline]
    pub fn is_nan(self) -> bool {
        self == Self::NAN
    }
    #[inline]
    pub fn is_infinite(self) -> bool {
        self == Self::INFINITY
    }
    #[inline]
    pub fn is_finite(self) -> bool {
        !self.is_nan()
    }
    #[inline]
    pub fn to_degrees(self) -> Self {
        const PIS_IN_180: P16E1 = P16E1::new(0x_7729);
        self * PIS_IN_180
    }
    #[inline]
    pub fn to_radians(self) -> Self {
        const PIS_O_180: P16E1 = P16E1::new(0x_0878);
        self * PIS_O_180
    }
    #[inline]
    pub fn max(self, other: Self) -> Self {
        if self.is_nan() || (self < other) {
            other
        } else {
            self
        }
    }
    #[inline]
    pub fn min(self, other: Self) -> Self {
        if other.is_nan() || (self < other) {
            self
        } else {
            other
        }
    }
}

impl P16E1 {
    pub const SIGN_MASK: u16 = 0x_8000;
    pub const REGIME_SIGN_MASK: u16 = 0x_4000;

    #[inline]
    pub(crate) fn sign_ui(a: u16) -> bool {
        (a & Self::SIGN_MASK) != 0
    }

    #[inline]
    fn sign_reg_ui(a: u16) -> bool {
        (a & Self::REGIME_SIGN_MASK) != 0
    }

    #[inline]
    fn pack_to_ui(regime: u16, reg_a: u8, exp_a: u16, frac_a: u16) -> u16 {
        regime
            + (if reg_a == 14 {
                0
            } else {
                exp_a << (13 - reg_a)
            })
            + frac_a
    }

    #[inline]
    pub(crate) fn separate_bits(bits: u16) -> (i8, i8, u16) {
        let (k, tmp) = Self::separate_bits_tmp(bits);
        (k, (tmp >> 14) as i8, (tmp | 0x4000))
    }
    #[inline]
    pub(crate) fn separate_bits_tmp(bits: u16) -> (i8, u16) {
        let mut k = 0;
        let mut tmp = bits << 2;
        if Self::sign_reg_ui(bits) {
            while (tmp & 0x_8000) != 0 {
                k += 1;
                tmp <<= 1;
            }
        } else {
            k = -1;
            while (tmp & 0x_8000) == 0 {
                k -= 1;
                tmp <<= 1;
            }
            tmp &= 0x7FFF;
        }
        (k, tmp)
    }

    #[inline]
    fn calculate_scale(mut bits: u16) -> (u16, u16) {
        let mut scale = 0_u16;
        // Decode the posit, left-justifying as we go.
        bits -= 0x4000; // Strip off first regime bit (which is a 1).
        while (0x2000 & bits) != 0 {
            // Increment scale by 2 for each regime sign bit.
            scale += 2; // Regime sign bit is always 1 in this range.
            bits = (bits - 0x2000) << 1; // Remove the bit; line up the next regime bit.
        }
        bits <<= 1; // Skip over termination bit, which is 0.
        if (0x2000 & bits) != 0 {
            scale += 1; // If exponent is 1, increment the scale.
        }
        (scale, bits)
    }

    #[inline]
    fn calculate_regime(k: i8) -> (u16, bool, u8) {
        let reg;
        if k < 0 {
            reg = (-k) as u8;
            (if reg > 15 { 0 } else { 0x4000_u16 >> reg }, false, reg)
        } else {
            reg = (k + 1) as u8;
            (
                if reg > 15 {
                    0x7FFF
                } else {
                    0x7FFF - (0x7FFF >> reg)
                },
                true,
                reg,
            )
        }
    }
}

#[derive(Clone, Debug)]
pub struct Q16E1(i64, u64);

impl Q16E1 {
    pub const ZERO: Self = Self(0, 0);
    pub const NAN: Self = Self(-0x8000_0000_0000_0000, 0);

    #[inline]
    pub const fn new() -> Self {
        Self::ZERO
    }

    #[inline]
    pub fn from_bits(v: [u64; 2]) -> Self {
        unsafe { mem::transmute(v) }
    }

    #[inline]
    pub fn to_bits(&self) -> [u64; 2] {
        unsafe { mem::transmute(self.clone()) }
    }

    #[inline]
    pub fn is_zero(&self) -> bool {
        self.to_bits() == [0, 0]
    }

    #[inline]
    pub fn is_nan(&self) -> bool {
        self.to_bits() == [0x8000_0000, 0]
    }

    #[inline]
    pub fn qma(&mut self, p_a: P16E1, p_b: P16E1) {
        ops::q16_fdp_add(self, p_a, p_b);
    }

    #[inline]
    pub fn qms(&mut self, p_a: P16E1, p_b: P16E1) {
        ops::q16_fdp_sub(self, p_a, p_b);
    }

    #[inline]
    pub fn roundp(self) -> P16E1 {
        P16E1::from(self)
    }

    #[inline]
    pub fn clear(&mut self) {
        *self = Self::ZERO;
    }

    #[inline]
    pub fn neg(&mut self) {
        self.0 = -(self.0);
    }
}

impl core::str::FromStr for P16E1 {
    type Err = core::num::ParseFloatError;
    #[inline]
    fn from_str(src: &str) -> Result<Self, core::num::ParseFloatError> {
        Ok(Self::from(f64::from_str(src)?))
    }
}

use core::fmt;
impl fmt::Display for P16E1 {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", f64::from(*self))
    }
}

impl fmt::Display for Q16E1 {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", f64::from(self.clone().roundp()))
    }
}

impl fmt::Debug for P16E1 {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "P16E1({})", self.0)
    }
}

use crate::MathConsts;
impl MathConsts for P16E1 {
    const E: Self = Self::new(0x_55bf);
    const FRAC_1_PI: Self = Self::new(0x_245f);
    const FRAC_1_SQRT_2: Self = Self::new(0x_36a1);
    const FRAC_2_PI: Self = Self::new(0x_345f);
    const FRAC_2_SQRT_PI: Self = Self::new(0x_420e);
    const FRAC_PI_2: Self = Self::new(0x_4922);
    const FRAC_PI_3: Self = Self::new(0x_40c1);
    const FRAC_PI_4: Self = Self::new(0x_3922);
    const FRAC_PI_6: Self = Self::new(0x_30c1);
    const FRAC_PI_8: Self = Self::new(0x_2922);
    const LN_10: Self = Self::new(0x_526c);
    const LN_2: Self = Self::new(0x_362e);
    const LOG10_E: Self = Self::new(0x_2bcb);
    const LOG2_E: Self = Self::new(0x_2344);
    const PI: Self = Self::new(0x_5922);
    const SQRT_2: Self = Self::new(0x_46a1);
    const LOG2_10: Self = Self::new(0x_5a93);
    const LOG10_2: Self = Self::new(0x_2344);
}

impl crate::Quire for P16E1 {
    type Q = Q16E1;
}

impl crate::Poly for P16E1 {
    #[inline]
    fn poly1k(x: Self, c: &[Self]) -> Self {
        let mut q = Q16E1::new(); // QCLR.S
        q += (c[1], x); // QMADD.S
        q += (c[0], Self::ONE);
        q.into() // QROUND.S
    }
    #[inline]
    fn poly2k(x: Self, x2: Self, c: &[Self], p: Self) -> Self {
        let mut q = Q16E1::new();
        q += (p, x2);
        q += (c[1], x);
        q += (c[0], Self::ONE);
        q.into()
    }
    #[inline]
    fn poly3k(x: Self, x2: Self, x3: Self, c: &[Self], p: Self) -> Self {
        let mut q = Q16E1::new();
        q += (p, x3);
        q += (c[2], x2);
        q += (c[1], x);
        q += (c[0], Self::ONE);
        q.into()
    }
    #[inline]
    fn poly4k(x: Self, x2: Self, x3: Self, x4: Self, c: &[Self], p: Self) -> Self {
        let mut q = Q16E1::new();
        q += (p, x4);
        q += (c[3], x3);
        q += (c[2], x2);
        q += (c[1], x);
        q += (c[0], Self::ONE);
        q.into()
    }
}

impl crate::Polynom for P16E1 {}