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// Copyright © 2024 Mikhail Hogrefe
//
// This file is part of Malachite.
//
// Malachite is free software: you can redistribute it and/or modify it under the terms of the GNU
// Lesser General Public License (LGPL) as published by the Free Software Foundation; either version
// 3 of the License, or (at your option) any later version. See <https://www.gnu.org/licenses/>.

use crate::InnerFloat::{Finite, Infinity, NaN, Zero};
use crate::{significand_bits, Float};
use core::cmp::Ordering::{self, *};
use malachite_base::num::arithmetic::traits::Sign;
use malachite_base::num::conversion::traits::ExactFrom;
use malachite_q::Rational;

pub fn float_partial_cmp_rational_alt(x: &Float, other: &Rational) -> Option<Ordering> {
    match (x, other) {
        (float_nan!(), _) => None,
        (float_infinity!(), _) => Some(Greater),
        (float_negative_infinity!(), _) => Some(Less),
        (float_either_zero!(), y) => 0u32.partial_cmp(y),
        (
            Float(Finite {
                sign: s_x,
                exponent: e_x,
                ..
            }),
            y,
        ) => Some(if *y == 0u32 {
            if *s_x {
                Greater
            } else {
                Less
            }
        } else {
            let s_cmp = s_x.cmp(&(*y > 0));
            if s_cmp != Equal {
                return Some(s_cmp);
            }
            let ord_cmp = (e_x - 1).cmp(&other.floor_log_base_2_abs());
            if ord_cmp == Equal {
                Rational::try_from(x).unwrap().cmp(other)
            } else if *s_x {
                ord_cmp
            } else {
                ord_cmp.reverse()
            }
        }),
    }
}

impl PartialOrd<Rational> for Float {
    /// Compares a [`Float`] to a [`Rational`].
    ///
    /// NaN is not comparable to any [`Rational`]. Infinity is greater than any [`Rational`], and
    /// negative infinity is less. Both the [`Float`] zero and the [`Float`] negative zero are equal
    /// to the [`Rational`] zero.
    ///
    /// # Worst-case complexity
    /// $T(n) = O(n \log n \log\log n)$
    ///
    /// $M(n) = O(n \log n)$
    ///
    /// where $T$ is time, $M$ is additional memory, and $n$ is `max(self.significant_bits(),
    /// other.significant_bits())`.
    ///
    /// # Examples
    /// ```
    /// use malachite_base::num::basic::traits::{Infinity, NegativeInfinity};
    /// use malachite_float::Float;
    /// use malachite_q::Rational;
    ///
    /// assert!(Float::from(80) < Rational::from(100));
    /// assert!(Float::from(-80) > Rational::from(-100));
    /// assert!(Float::INFINITY > Rational::from(100));
    /// assert!(Float::NEGATIVE_INFINITY < Rational::from(-100));
    /// assert!(Float::from(1.0f64 / 3.0) < Rational::from_unsigneds(1u8, 3));
    /// ```
    fn partial_cmp(&self, other: &Rational) -> Option<Ordering> {
        match (self, other) {
            (float_nan!(), _) => None,
            (float_infinity!(), _) => Some(Greater),
            (float_negative_infinity!(), _) => Some(Less),
            (float_either_zero!(), y) => 0u32.partial_cmp(y),
            (
                Float(Finite {
                    sign: s_x,
                    exponent: e_x,
                    significand: significand_x,
                    ..
                }),
                y,
            ) => Some(if *y == 0u32 {
                if *s_x {
                    Greater
                } else {
                    Less
                }
            } else {
                let s_cmp = s_x.cmp(&(*y > 0));
                if s_cmp != Equal {
                    return Some(s_cmp);
                }
                let ord_cmp = (e_x - 1).cmp(&other.floor_log_base_2_abs());
                if ord_cmp == Equal {
                    let shift = e_x - i64::exact_from(significand_bits(significand_x));
                    let abs_shift = shift.unsigned_abs();
                    let prod_cmp = match shift.sign() {
                        Equal => {
                            (significand_x * other.denominator_ref()).cmp(other.numerator_ref())
                        }
                        Greater => ((significand_x * other.denominator_ref()) << abs_shift)
                            .cmp(other.numerator_ref()),
                        Less => {
                            let n_trailing_zeros = significand_x.trailing_zeros().unwrap();
                            if abs_shift <= n_trailing_zeros {
                                ((significand_x >> abs_shift) * other.denominator_ref())
                                    .cmp(other.numerator_ref())
                            } else {
                                ((significand_x >> n_trailing_zeros) * other.denominator_ref())
                                    .cmp(&(other.numerator_ref() << (abs_shift - n_trailing_zeros)))
                            }
                        }
                    };
                    if *s_x {
                        prod_cmp
                    } else {
                        prod_cmp.reverse()
                    }
                } else if *s_x {
                    ord_cmp
                } else {
                    ord_cmp.reverse()
                }
            }),
        }
    }
}

impl PartialOrd<Float> for Rational {
    /// Compares an [`Rational`] to a [`Float`].
    ///
    /// No [`Rational`] is comparable to NaN. Every [`Rational`] is smaller than infinity and
    /// greater than negative infinity. The [`Rational`] zero is equal to both the [`Float`] zero
    /// and the [`Float`] negative zero.
    ///
    /// # Worst-case complexity
    /// $T(n) = O(n \log n \log\log n)$
    ///
    /// $M(n) = O(n \log n)$
    ///
    /// where $T$ is time, $M$ is additional memory, and $n$ is `max(self.significant_bits(),
    /// other.significant_bits())`.
    ///
    /// # Examples
    /// ```
    /// use malachite_base::num::basic::traits::{Infinity, NegativeInfinity};
    /// use malachite_float::Float;
    /// use malachite_q::Rational;
    ///
    /// assert!(Rational::from(100) > Float::from(80));
    /// assert!(Rational::from(-100) < Float::from(-80));
    /// assert!(Rational::from(100) < Float::INFINITY);
    /// assert!(Rational::from(-100) > Float::NEGATIVE_INFINITY);
    /// assert!(Rational::from_unsigneds(1u8, 3) > Float::from(1.0f64 / 3.0));
    /// ```
    #[inline]
    fn partial_cmp(&self, other: &Float) -> Option<Ordering> {
        other.partial_cmp(self).map(Ordering::reverse)
    }
}