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// Copyright © 2018–2024 Trevor Spiteri

// This library is free software: you can redistribute it and/or
// modify it under the terms of either
//
//   * the Apache License, Version 2.0 or
//   * the MIT License
//
// at your option.
//
// You should have recieved copies of the Apache License and the MIT
// License along with the library. If not, see
// <https://www.apache.org/licenses/LICENSE-2.0> and
// <https://opensource.org/licenses/MIT>.

use crate::{
    int_helper,
    types::extra::{LeEqU128, LeEqU16, LeEqU32, LeEqU64, LeEqU8},
    FixedI128, FixedI16, FixedI32, FixedI64, FixedI8, FixedU128, FixedU16, FixedU32, FixedU64,
    FixedU8,
};
use core::cmp::Ordering;

// Unsigned can have 0 ≤ x < 2^128, that is its msb can be 0 or 1.
// Negative can have -2^127 ≤ x < 0, that is its msb must be 1.
pub enum Widest {
    Unsigned(u128),
    Negative(i128),
}

pub struct ToFixedHelper {
    pub(crate) bits: Widest,
    pub(crate) dir: Ordering,
    pub(crate) overflow: bool,
}

pub struct ToFloatHelper {
    pub(crate) neg: bool,
    pub(crate) abs: u128,
}

pub struct FromFloatHelper {
    pub(crate) kind: FloatKind,
}
pub enum FloatKind {
    NaN,
    Infinite { neg: bool },
    Finite { neg: bool, conv: ToFixedHelper },
}

pub struct Private;

pub trait Sealed: Copy {
    fn to_fixed_helper(self, _: Private, dst_frac_nbits: u32, dst_int_nbits: u32) -> ToFixedHelper;
    fn to_float_helper(self, _: Private) -> ToFloatHelper;
    fn saturating_from_float_helper(_: Private, src: FromFloatHelper) -> Self;
    fn overflowing_from_float_helper(_: Private, src: FromFloatHelper) -> (Self, bool);
}
macro_rules! impl_sealed {
    ($Fixed:ident($LeEqU:ident, $Signedness:ident, $Inner:ident)) => {
        impl<Frac: $LeEqU> Sealed for $Fixed<Frac> {
            #[inline]
            fn to_fixed_helper(
                self,
                _: Private,
                dst_frac_nbits: u32,
                dst_int_nbits: u32,
            ) -> ToFixedHelper {
                int_helper::$Inner::to_fixed_helper(
                    self.to_bits(),
                    Self::FRAC_NBITS as i32,
                    dst_frac_nbits,
                    dst_int_nbits,
                )
            }
            #[inline]
            fn to_float_helper(self, _: Private) -> ToFloatHelper {
                let (neg, abs) = int_helper::$Inner::neg_abs(self.to_bits());
                let abs = abs.into();
                ToFloatHelper { neg, abs }
            }
            #[inline]
            fn saturating_from_float_helper(_: Private, src: FromFloatHelper) -> Self {
                let neg = match src.kind {
                    FloatKind::NaN => panic!("NaN"),
                    FloatKind::Infinite { neg } => neg,
                    FloatKind::Finite { neg, .. } => neg,
                };
                let saturated = if neg { Self::MIN } else { Self::MAX };
                let FloatKind::Finite { conv, .. } = src.kind else {
                    return saturated;
                };
                if conv.overflow {
                    return saturated;
                }
                let bits = if_signed_unsigned!(
                    $Signedness,
                    match conv.bits {
                        Widest::Unsigned(bits) => {
                            let bits = bits as _;
                            if bits < 0 {
                                return Self::MAX;
                            }
                            bits
                        }
                        Widest::Negative(bits) => bits as _,
                    },
                    match conv.bits {
                        Widest::Unsigned(bits) => bits as _,
                        Widest::Negative(_) => return Self::MIN,
                    },
                );
                Self::from_bits(bits)
            }
            #[inline]
            #[track_caller]
            fn overflowing_from_float_helper(_: Private, src: FromFloatHelper) -> (Self, bool) {
                let conv = match src.kind {
                    FloatKind::NaN => panic!("NaN"),
                    FloatKind::Infinite { .. } => panic!("infinite"),
                    FloatKind::Finite { conv, .. } => conv,
                };
                let mut new_overflow = false;
                let bits = if_signed_unsigned!(
                    $Signedness,
                    match conv.bits {
                        Widest::Unsigned(bits) => {
                            let bits = bits as _;
                            if bits < 0 {
                                new_overflow = true;
                            }
                            bits
                        }
                        Widest::Negative(bits) => bits as _,
                    },
                    match conv.bits {
                        Widest::Unsigned(bits) => bits as _,
                        Widest::Negative(bits) => {
                            new_overflow = true;
                            bits as _
                        }
                    },
                );
                (Self::from_bits(bits), conv.overflow || new_overflow)
            }
        }
    };
}

impl_sealed! { FixedI8(LeEqU8, Signed, i8) }
impl_sealed! { FixedI16(LeEqU16, Signed, i16) }
impl_sealed! { FixedI32(LeEqU32, Signed, i32) }
impl_sealed! { FixedI64(LeEqU64, Signed, i64) }
impl_sealed! { FixedI128(LeEqU128, Signed, i128) }
impl_sealed! { FixedU8(LeEqU8, Unsigned, u8) }
impl_sealed! { FixedU16(LeEqU16, Unsigned, u16) }
impl_sealed! { FixedU32(LeEqU32, Unsigned, u32) }
impl_sealed! { FixedU64(LeEqU64, Unsigned, u64) }
impl_sealed! { FixedU128(LeEqU128, Unsigned, u128) }