use prolog_parser_rebis::ast::*;
use prolog_parser_rebis::{atom, clause_name};

use crate::clause_types::*;
use crate::fixtures::*;
use crate::forms::*;
use crate::instructions::*;
use crate::iterators::*;

use crate::machine::heap::*;
use crate::machine::machine_errors::*;
use crate::machine::machine_indices::*;

use crate::rug::ops::PowAssign;
use crate::rug::{Assign, Integer, Rational};
use ordered_float::*;

use std::cell::Cell;
use std::cmp::{max, min, Ordering};
use std::convert::TryFrom;
use std::f64;
use std::num::FpCategory;
use std::ops::{Add, Div, Mul, Neg, Sub};
use std::rc::Rc;
use std::vec::Vec;

#[derive(Debug)]
pub struct ArithInstructionIterator<'a> {
    state_stack: Vec<TermIterState<'a>>,
}

pub type ArithCont = (Code, Option<ArithmeticTerm>);

impl<'a> ArithInstructionIterator<'a> {
    fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
        self.state_stack
            .push(TermIterState::subterm_to_state(lvl, term));
    }

    fn new(term: &'a Term) -> Result<Self, ArithmeticError> {
        let state = match term {
            &Term::AnonVar => return Err(ArithmeticError::UninstantiatedVar),
            &Term::Clause(ref cell, ref name, ref terms, ref fixity) => {
                match ClauseType::from(name.clone(), terms.len(), fixity.clone()) {
                    ct @ ClauseType::Named(..) | ct @ ClauseType::Op(..) => {
                        Ok(TermIterState::Clause(Level::Shallow, 0, cell, ct, terms))
                    }
                    ClauseType::Inlined(InlinedClauseType::IsFloat(_)) => {
                        let ct = ClauseType::Named(clause_name!("float"), 1, CodeIndex::default());
                        Ok(TermIterState::Clause(Level::Shallow, 0, cell, ct, terms))
                    }
                    _ => Err(ArithmeticError::NonEvaluableFunctor(
                        Constant::Atom(name.clone(), fixity.clone()),
                        terms.len(),
                    )),
                }?
            }
            &Term::Constant(ref cell, ref cons) => {
                TermIterState::Constant(Level::Shallow, cell, cons)
            }
            &Term::Cons(_, _, _) => {
                return Err(ArithmeticError::NonEvaluableFunctor(atom!("'.'"), 2))
            }
            &Term::Var(ref cell, ref var) => TermIterState::Var(Level::Shallow, cell, var.clone()),
        };

        Ok(ArithInstructionIterator {
            state_stack: vec![state],
        })
    }
}

#[derive(Debug)]
pub enum ArithTermRef<'a> {
    Constant(&'a Constant),
    Op(ClauseName, usize), // name, arity.
    Var(&'a Cell<VarReg>, Rc<Var>),
}

impl<'a> Iterator for ArithInstructionIterator<'a> {
    type Item = Result<ArithTermRef<'a>, ArithmeticError>;

    fn next(&mut self) -> Option<Self::Item> {
        while let Some(iter_state) = self.state_stack.pop() {
            match iter_state {
                TermIterState::AnonVar(_) => return Some(Err(ArithmeticError::UninstantiatedVar)),
                TermIterState::Clause(lvl, child_num, cell, ct, subterms) => {
                    let arity = subterms.len();

                    if child_num == arity {
                        return Some(Ok(ArithTermRef::Op(ct.name(), arity)));
                    } else {
                        self.state_stack.push(TermIterState::Clause(
                            lvl,
                            child_num + 1,
                            cell,
                            ct,
                            subterms,
                        ));
                        self.push_subterm(lvl, subterms[child_num].as_ref());
                    }
                }
                TermIterState::Constant(_, _, c) => return Some(Ok(ArithTermRef::Constant(c))),
                TermIterState::Var(_, cell, var) => {
                    return Some(Ok(ArithTermRef::Var(cell, var.clone())))
                }
                _ => return Some(Err(ArithmeticError::NonEvaluableFunctor(atom!("'.'"), 2))),
            };
        }

        None
    }
}

#[derive(Debug)]
pub struct ArithmeticEvaluator<'a> {
    bindings: &'a AllocVarDict,
    interm: Vec<ArithmeticTerm>,
    interm_c: usize,
}

pub trait ArithmeticTermIter<'a> {
    type Iter: Iterator<Item = Result<ArithTermRef<'a>, ArithmeticError>>;

    fn iter(self) -> Result<Self::Iter, ArithmeticError>;
}

impl<'a> ArithmeticTermIter<'a> for &'a Term {
    type Iter = ArithInstructionIterator<'a>;

    fn iter(self) -> Result<Self::Iter, ArithmeticError> {
        ArithInstructionIterator::new(self)
    }
}

impl<'a> ArithmeticEvaluator<'a> {
    pub fn new(bindings: &'a AllocVarDict, target_int: usize) -> Self {
        ArithmeticEvaluator {
            bindings,
            interm: Vec::new(),
            interm_c: target_int,
        }
    }

    fn get_unary_instr(
        name: ClauseName,
        a1: ArithmeticTerm,
        t: usize,
    ) -> Result<ArithmeticInstruction, ArithmeticError> {
        match name.as_str() {
            "abs" => Ok(ArithmeticInstruction::Abs(a1, t)),
            "-" => Ok(ArithmeticInstruction::Neg(a1, t)),
            "+" => Ok(ArithmeticInstruction::Plus(a1, t)),
            "cos" => Ok(ArithmeticInstruction::Cos(a1, t)),
            "sin" => Ok(ArithmeticInstruction::Sin(a1, t)),
            "tan" => Ok(ArithmeticInstruction::Tan(a1, t)),
            "log" => Ok(ArithmeticInstruction::Log(a1, t)),
            "exp" => Ok(ArithmeticInstruction::Exp(a1, t)),
            "sqrt" => Ok(ArithmeticInstruction::Sqrt(a1, t)),
            "acos" => Ok(ArithmeticInstruction::ACos(a1, t)),
            "asin" => Ok(ArithmeticInstruction::ASin(a1, t)),
            "atan" => Ok(ArithmeticInstruction::ATan(a1, t)),
            "float" => Ok(ArithmeticInstruction::Float(a1, t)),
            "truncate" => Ok(ArithmeticInstruction::Truncate(a1, t)),
            "round" => Ok(ArithmeticInstruction::Round(a1, t)),
            "ceiling" => Ok(ArithmeticInstruction::Ceiling(a1, t)),
            "floor" => Ok(ArithmeticInstruction::Floor(a1, t)),
            "sign" => Ok(ArithmeticInstruction::Sign(a1, t)),
            "\\" => Ok(ArithmeticInstruction::BitwiseComplement(a1, t)),
            _ => Err(ArithmeticError::NonEvaluableFunctor(
                Constant::Atom(name, None),
                1,
            )),
        }
    }

    fn get_binary_instr(
        name: ClauseName,
        a1: ArithmeticTerm,
        a2: ArithmeticTerm,
        t: usize,
    ) -> Result<ArithmeticInstruction, ArithmeticError> {
        match name.as_str() {
            "+" => Ok(ArithmeticInstruction::Add(a1, a2, t)),
            "-" => Ok(ArithmeticInstruction::Sub(a1, a2, t)),
            "/" => Ok(ArithmeticInstruction::Div(a1, a2, t)),
            "//" => Ok(ArithmeticInstruction::IDiv(a1, a2, t)),
            "max" => Ok(ArithmeticInstruction::Max(a1, a2, t)),
            "min" => Ok(ArithmeticInstruction::Min(a1, a2, t)),
            "div" => Ok(ArithmeticInstruction::IntFloorDiv(a1, a2, t)),
            "rdiv" => Ok(ArithmeticInstruction::RDiv(a1, a2, t)),
            "*" => Ok(ArithmeticInstruction::Mul(a1, a2, t)),
            "**" => Ok(ArithmeticInstruction::Pow(a1, a2, t)),
            "^" => Ok(ArithmeticInstruction::IntPow(a1, a2, t)),
            ">>" => Ok(ArithmeticInstruction::Shr(a1, a2, t)),
            "<<" => Ok(ArithmeticInstruction::Shl(a1, a2, t)),
            "/\\" => Ok(ArithmeticInstruction::And(a1, a2, t)),
            "\\/" => Ok(ArithmeticInstruction::Or(a1, a2, t)),
            "xor" => Ok(ArithmeticInstruction::Xor(a1, a2, t)),
            "mod" => Ok(ArithmeticInstruction::Mod(a1, a2, t)),
            "rem" => Ok(ArithmeticInstruction::Rem(a1, a2, t)),
            "gcd" => Ok(ArithmeticInstruction::Gcd(a1, a2, t)),
            "atan2" => Ok(ArithmeticInstruction::ATan2(a1, a2, t)),
            _ => Err(ArithmeticError::NonEvaluableFunctor(
                Constant::Atom(name, None),
                2,
            )),
        }
    }

    fn incr_interm(&mut self) -> usize {
        let temp = self.interm_c;

        self.interm.push(ArithmeticTerm::Interm(temp));
        self.interm_c += 1;

        temp
    }

    fn instr_from_clause(
        &mut self,
        name: ClauseName,
        arity: usize,
    ) -> Result<ArithmeticInstruction, ArithmeticError> {
        match arity {
            1 => {
                let a1 = self.interm.pop().unwrap();

                let ninterm = if a1.interm_or(0) == 0 {
                    self.incr_interm()
                } else {
                    self.interm.push(a1.clone());
                    a1.interm_or(0)
                };

                Self::get_unary_instr(name, a1, ninterm)
            }
            2 => {
                let a2 = self.interm.pop().unwrap();
                let a1 = self.interm.pop().unwrap();

                let min_interm = min(a1.interm_or(0), a2.interm_or(0));

                let ninterm = if min_interm == 0 {
                    let max_interm = max(a1.interm_or(0), a2.interm_or(0));

                    if max_interm == 0 {
                        self.incr_interm()
                    } else {
                        self.interm.push(ArithmeticTerm::Interm(max_interm));
                        self.interm_c = max_interm + 1;
                        max_interm
                    }
                } else {
                    self.interm.push(ArithmeticTerm::Interm(min_interm));
                    self.interm_c = min_interm + 1;
                    min_interm
                };

                Self::get_binary_instr(name, a1, a2, ninterm)
            }
            _ => Err(ArithmeticError::NonEvaluableFunctor(
                Constant::Atom(name, None),
                arity,
            )),
        }
    }

    fn push_constant(&mut self, c: &Constant) -> Result<(), ArithmeticError> {
        match c {
            &Constant::Fixnum(n) => self.interm.push(ArithmeticTerm::Number(Number::Fixnum(n))),
            &Constant::Integer(ref n) => self
                .interm
                .push(ArithmeticTerm::Number(Number::Integer(n.clone()))),
            &Constant::Float(ref n) => self
                .interm
                .push(ArithmeticTerm::Number(Number::Float(n.clone()))),
            &Constant::Rational(ref n) => self
                .interm
                .push(ArithmeticTerm::Number(Number::Rational(n.clone()))),
            &Constant::Atom(ref name, _) if name.as_str() == "pi" => {
                self.interm
                    .push(ArithmeticTerm::Number(Number::Float(OrderedFloat(
                        f64::consts::PI,
                    ))))
            }
            _ => return Err(ArithmeticError::NonEvaluableFunctor(c.clone(), 0)),
        }

        Ok(())
    }

    pub fn eval<Iter>(&mut self, src: Iter) -> Result<ArithCont, ArithmeticError>
    where
        Iter: ArithmeticTermIter<'a>,
    {
        let mut code = vec![];

        for term_ref in src.iter()? {
            match term_ref? {
                ArithTermRef::Constant(c) => self.push_constant(c)?,
                ArithTermRef::Var(cell, name) => {
                    let r = if cell.get().norm().reg_num() == 0 {
                        match self.bindings.get(&name) {
                            Some(&VarData::Temp(_, t, _)) if t != 0 => RegType::Temp(t),
                            Some(&VarData::Perm(p)) if p != 0 => RegType::Perm(p),
                            _ => return Err(ArithmeticError::UninstantiatedVar),
                        }
                    } else {
                        cell.get().norm()
                    };

                    self.interm.push(ArithmeticTerm::Reg(r));
                }
                ArithTermRef::Op(name, arity) => {
                    code.push(Line::Arithmetic(self.instr_from_clause(name, arity)?));
                }
            }
        }

        Ok((code, self.interm.pop()))
    }
}

// integer division rounding function -- 9.1.3.1.
pub fn rnd_i<'a>(n: &'a Number) -> RefOrOwned<'a, Number> {
    match n {
        &Number::Integer(_) => RefOrOwned::Borrowed(n),
        &Number::Float(OrderedFloat(f)) => RefOrOwned::Owned(Number::from(
            Integer::from_f64(f.floor()).unwrap_or_else(|| Integer::from(0)),
        )),
        &Number::Fixnum(n) => RefOrOwned::Owned(Number::from(n)),
        &Number::Rational(ref r) => {
            let r_ref = r.fract_floor_ref();
            let (mut fract, mut floor) = (Rational::new(), Integer::new());
            (&mut fract, &mut floor).assign(r_ref);

            RefOrOwned::Owned(Number::from(floor))
        }
    }
}

// floating point rounding function -- 9.1.4.1.
pub fn rnd_f(n: &Number) -> f64 {
    match n {
        &Number::Fixnum(n) => n as f64,
        &Number::Integer(ref n) => n.to_f64(),
        &Number::Float(OrderedFloat(f)) => f,
        &Number::Rational(ref r) => r.to_f64(),
    }
}

// floating point result function -- 9.1.4.2.
pub fn result_f<Round>(n: &Number, round: Round) -> Result<f64, EvalError>
where
    Round: Fn(&Number) -> f64,
{
    let f = rnd_f(n);
    classify_float(f, round)
}

fn classify_float<Round>(f: f64, round: Round) -> Result<f64, EvalError>
where
    Round: Fn(&Number) -> f64,
{
    match f.classify() {
        FpCategory::Normal | FpCategory::Zero => Ok(round(&Number::Float(OrderedFloat(f)))),
        FpCategory::Infinite => {
            let f = round(&Number::Float(OrderedFloat(f)));

            if OrderedFloat(f) == OrderedFloat(f64::MAX) {
                Ok(f)
            } else {
                Err(EvalError::FloatOverflow)
            }
        }
        FpCategory::Nan => Err(EvalError::Undefined),
        _ => Ok(round(&Number::Float(OrderedFloat(f)))),
    }
}

#[inline]
fn float_fn_to_f(n: isize) -> Result<f64, EvalError> {
    classify_float(n as f64, rnd_f)
}

#[inline]
fn float_i_to_f(n: &Integer) -> Result<f64, EvalError> {
    classify_float(n.to_f64(), rnd_f)
}

#[inline]
fn float_r_to_f(r: &Rational) -> Result<f64, EvalError> {
    classify_float(r.to_f64(), rnd_f)
}

#[inline]
fn add_f(f1: f64, f2: f64) -> Result<OrderedFloat<f64>, EvalError> {
    Ok(OrderedFloat(classify_float(f1 + f2, rnd_f)?))
}

#[inline]
fn mul_f(f1: f64, f2: f64) -> Result<OrderedFloat<f64>, EvalError> {
    Ok(OrderedFloat(classify_float(f1 * f2, rnd_f)?))
}

#[inline]
fn div_f(f1: f64, f2: f64) -> Result<OrderedFloat<f64>, EvalError> {
    if FpCategory::Zero == f2.classify() {
        Err(EvalError::ZeroDivisor)
    } else {
        Ok(OrderedFloat(classify_float(f1 / f2, rnd_f)?))
    }
}

impl Add<Number> for Number {
    type Output = Result<Number, EvalError>;

    fn add(self, rhs: Number) -> Self::Output {
        match (self, rhs) {
            (Number::Fixnum(n1), Number::Fixnum(n2)) => {
                Ok(if let Some(result) = n1.checked_add(n2) {
                    Number::Fixnum(result)
                } else {
                    Number::from(Integer::from(n1) + Integer::from(n2))
                })
            }
            (Number::Fixnum(n1), Number::Integer(n2))
            | (Number::Integer(n2), Number::Fixnum(n1)) => {
                Ok(Number::from(Integer::from(n1) + &*n2))
            }
            (Number::Fixnum(n1), Number::Rational(n2))
            | (Number::Rational(n2), Number::Fixnum(n1)) => {
                Ok(Number::from(Rational::from(n1) + &*n2))
            }
            (Number::Fixnum(n1), Number::Float(OrderedFloat(n2)))
            | (Number::Float(OrderedFloat(n2)), Number::Fixnum(n1)) => {
                Ok(Number::Float(add_f(float_fn_to_f(n1)?, n2)?))
            }
            (Number::Integer(n1), Number::Integer(n2)) => {
                Ok(Number::from(Integer::from(&*n1) + &*n2)) // add_i
            }
            (Number::Integer(n1), Number::Float(OrderedFloat(n2)))
            | (Number::Float(OrderedFloat(n2)), Number::Integer(n1)) => {
                Ok(Number::Float(add_f(float_i_to_f(&n1)?, n2)?))
            }
            (Number::Integer(n1), Number::Rational(n2))
            | (Number::Rational(n2), Number::Integer(n1)) => {
                Ok(Number::from(Rational::from(&*n1) + &*n2))
            }
            (Number::Rational(n1), Number::Float(OrderedFloat(n2)))
            | (Number::Float(OrderedFloat(n2)), Number::Rational(n1)) => {
                Ok(Number::Float(add_f(float_r_to_f(&n1)?, n2)?))
            }
            (Number::Float(OrderedFloat(f1)), Number::Float(OrderedFloat(f2))) => {
                Ok(Number::Float(add_f(f1, f2)?))
            }
            (Number::Rational(r1), Number::Rational(r2)) => {
                Ok(Number::from(Rational::from(&*r1) + &*r2))
            }
        }
    }
}

impl Neg for Number {
    type Output = Number;

    fn neg(self) -> Self::Output {
        match self {
            Number::Fixnum(n) => {
                if let Some(n) = n.checked_neg() {
                    Number::Fixnum(n)
                } else {
                    Number::from(-Integer::from(n))
                }
            }
            Number::Integer(n) => Number::Integer(Rc::new(-Integer::from(&*n))),
            Number::Float(OrderedFloat(f)) => Number::Float(OrderedFloat(-f)),
            Number::Rational(r) => Number::Rational(Rc::new(-Rational::from(&*r))),
        }
    }
}

impl Sub<Number> for Number {
    type Output = Result<Number, EvalError>;

    fn sub(self, rhs: Number) -> Self::Output {
        self.add(-rhs)
    }
}

impl Mul<Number> for Number {
    type Output = Result<Number, EvalError>;

    fn mul(self, rhs: Number) -> Self::Output {
        match (self, rhs) {
            (Number::Fixnum(n1), Number::Fixnum(n2)) => {
                Ok(if let Some(result) = n1.checked_mul(n2) {
                    Number::Fixnum(result)
                } else {
                    Number::from(Integer::from(n1) * Integer::from(n2))
                })
            }
            (Number::Fixnum(n1), Number::Integer(n2))
            | (Number::Integer(n2), Number::Fixnum(n1)) => {
                Ok(Number::from(Integer::from(n1) * &*n2))
            }
            (Number::Fixnum(n1), Number::Rational(n2))
            | (Number::Rational(n2), Number::Fixnum(n1)) => {
                Ok(Number::from(Rational::from(n1) * &*n2))
            }
            (Number::Fixnum(n1), Number::Float(OrderedFloat(n2)))
            | (Number::Float(OrderedFloat(n2)), Number::Fixnum(n1)) => {
                Ok(Number::Float(mul_f(float_fn_to_f(n1)?, n2)?))
            }
            (Number::Integer(n1), Number::Integer(n2)) => {
                Ok(Number::Integer(Rc::new(Integer::from(&*n1) * &*n2))) // mul_i
            }
            (Number::Integer(n1), Number::Float(OrderedFloat(n2)))
            | (Number::Float(OrderedFloat(n2)), Number::Integer(n1)) => {
                Ok(Number::Float(mul_f(float_i_to_f(&n1)?, n2)?))
            }
            (Number::Integer(n1), Number::Rational(n2))
            | (Number::Rational(n2), Number::Integer(n1)) => {
                Ok(Number::Rational(Rc::new(Rational::from(&*n1) * &*n2)))
            }
            (Number::Rational(n1), Number::Float(OrderedFloat(n2)))
            | (Number::Float(OrderedFloat(n2)), Number::Rational(n1)) => {
                Ok(Number::Float(mul_f(float_r_to_f(&n1)?, n2)?))
            }
            (Number::Float(OrderedFloat(f1)), Number::Float(OrderedFloat(f2))) => {
                Ok(Number::Float(mul_f(f1, f2)?))
            }
            (Number::Rational(r1), Number::Rational(r2)) => {
                Ok(Number::Rational(Rc::new(Rational::from(&*r1) * &*r2)))
            }
        }
    }
}

impl Div<Number> for Number {
    type Output = Result<Number, EvalError>;

    fn div(self, rhs: Number) -> Self::Output {
        match (self, rhs) {
            (Number::Fixnum(n1), Number::Fixnum(n2)) => Ok(Number::Float(div_f(
                float_fn_to_f(n1)?,
                float_fn_to_f(n2)?,
            )?)),
            (Number::Fixnum(n1), Number::Integer(n2)) => Ok(Number::Float(div_f(
                float_fn_to_f(n1)?,
                float_i_to_f(&n2)?,
            )?)),
            (Number::Integer(n1), Number::Fixnum(n2)) => Ok(Number::Float(div_f(
                float_i_to_f(&n1)?,
                float_fn_to_f(n2)?,
            )?)),
            (Number::Fixnum(n1), Number::Rational(n2)) => Ok(Number::Float(div_f(
                float_fn_to_f(n1)?,
                float_r_to_f(&n2)?,
            )?)),
            (Number::Rational(n1), Number::Fixnum(n2)) => Ok(Number::Float(div_f(
                float_r_to_f(&n1)?,
                float_fn_to_f(n2)?,
            )?)),
            (Number::Fixnum(n1), Number::Float(OrderedFloat(n2))) => {
                Ok(Number::Float(div_f(float_fn_to_f(n1)?, n2)?))
            }
            (Number::Float(OrderedFloat(n1)), Number::Fixnum(n2)) => {
                Ok(Number::Float(div_f(n1, float_fn_to_f(n2)?)?))
            }
            (Number::Integer(n1), Number::Integer(n2)) => Ok(Number::Float(div_f(
                float_i_to_f(&n1)?,
                float_i_to_f(&n2)?,
            )?)),
            (Number::Integer(n1), Number::Float(OrderedFloat(n2))) => {
                Ok(Number::Float(div_f(float_i_to_f(&n1)?, n2)?))
            }
            (Number::Float(OrderedFloat(n2)), Number::Integer(n1)) => {
                Ok(Number::Float(div_f(n2, float_i_to_f(&n1)?)?))
            }
            (Number::Integer(n1), Number::Rational(n2)) => Ok(Number::Float(div_f(
                float_i_to_f(&n1)?,
                float_r_to_f(&n2)?,
            )?)),
            (Number::Rational(n2), Number::Integer(n1)) => Ok(Number::Float(div_f(
                float_r_to_f(&n2)?,
                float_i_to_f(&n1)?,
            )?)),
            (Number::Rational(n1), Number::Float(OrderedFloat(n2))) => {
                Ok(Number::Float(div_f(float_r_to_f(&n1)?, n2)?))
            }
            (Number::Float(OrderedFloat(n2)), Number::Rational(n1)) => {
                Ok(Number::Float(div_f(n2, float_r_to_f(&n1)?)?))
            }
            (Number::Float(OrderedFloat(f1)), Number::Float(OrderedFloat(f2))) => {
                Ok(Number::Float(div_f(f1, f2)?))
            }
            (Number::Rational(r1), Number::Rational(r2)) => Ok(Number::Float(div_f(
                float_r_to_f(&r1)?,
                float_r_to_f(&r2)?,
            )?)),
        }
    }
}

impl PartialEq for Number {
    fn eq(&self, rhs: &Self) -> bool {
        match (self, rhs) {
            (&Number::Fixnum(n1), &Number::Fixnum(n2)) => n1.eq(&n2),
            (&Number::Fixnum(n1), &Number::Integer(ref n2)) => n1.eq(&**n2),
            (&Number::Integer(ref n1), &Number::Fixnum(n2)) => (&**n1).eq(&n2),
            (&Number::Fixnum(n1), &Number::Rational(ref n2)) => n1.eq(&**n2),
            (&Number::Rational(ref n1), &Number::Fixnum(n2)) => (&**n1).eq(&n2),
            (&Number::Fixnum(n1), &Number::Float(n2)) => OrderedFloat(n1 as f64).eq(&n2),
            (&Number::Float(n1), &Number::Fixnum(n2)) => n1.eq(&OrderedFloat(n2 as f64)),
            (&Number::Integer(ref n1), &Number::Integer(ref n2)) => n1.eq(n2),
            (&Number::Integer(ref n1), Number::Float(n2)) => OrderedFloat(n1.to_f64()).eq(&n2),
            (&Number::Float(n1), &Number::Integer(ref n2)) => n1.eq(&OrderedFloat(n2.to_f64())),
            (&Number::Integer(ref n1), &Number::Rational(ref n2)) => {
                #[cfg(feature = "num")]
                {
                    &Rational::from(&**n1) == &**n2
                }
                #[cfg(not(feature = "num"))]
                {
                    &**n1 == &**n2
                }
            }
            (&Number::Rational(ref n1), &Number::Integer(ref n2)) => {
                #[cfg(feature = "num")]
                {
                    &**n1 == &Rational::from(&**n2)
                }
                #[cfg(not(feature = "num"))]
                {
                    &**n1 == &**n2
                }
            }
            (&Number::Rational(ref n1), &Number::Float(n2)) => OrderedFloat(n1.to_f64()).eq(&n2),
            (&Number::Float(n1), &Number::Rational(ref n2)) => n1.eq(&OrderedFloat(n2.to_f64())),
            (&Number::Float(f1), &Number::Float(f2)) => f1.eq(&f2),
            (&Number::Rational(ref r1), &Number::Rational(ref r2)) => r1.eq(&r2),
        }
    }
}

impl Eq for Number {}

impl PartialOrd for Number {
    fn partial_cmp(&self, rhs: &Number) -> Option<Ordering> {
        Some(self.cmp(rhs))
    }
}

impl Ord for Number {
    fn cmp(&self, rhs: &Number) -> Ordering {
        match (self, rhs) {
            (&Number::Fixnum(n1), &Number::Fixnum(n2)) => n1.cmp(&n2),
            (&Number::Fixnum(n1), Number::Integer(n2)) => Integer::from(n1).cmp(&*n2),
            (Number::Integer(n1), &Number::Fixnum(n2)) => (&**n1).cmp(&Integer::from(n2)),
            (&Number::Fixnum(n1), Number::Rational(n2)) => Rational::from(n1).cmp(&*n2),
            (Number::Rational(n1), &Number::Fixnum(n2)) => (&**n1).cmp(&Rational::from(n2)),
            (&Number::Fixnum(n1), &Number::Float(n2)) => OrderedFloat(n1 as f64).cmp(&n2),
            (&Number::Float(n1), &Number::Fixnum(n2)) => n1.cmp(&OrderedFloat(n2 as f64)),
            (&Number::Integer(ref n1), &Number::Integer(ref n2)) => n1.cmp(n2),
            (&Number::Integer(ref n1), Number::Float(n2)) => OrderedFloat(n1.to_f64()).cmp(&n2),
            (&Number::Float(n1), &Number::Integer(ref n2)) => n1.cmp(&OrderedFloat(n2.to_f64())),
            (&Number::Integer(ref n1), &Number::Rational(ref n2)) => {
                #[cfg(feature = "num")]
                {
                    Rational::from(&**n1).cmp(n2)
                }
                #[cfg(not(feature = "num"))]
                {
                    (&**n1).partial_cmp(&**n2).unwrap_or(Ordering::Less)
                }
            }
            (&Number::Rational(ref n1), &Number::Integer(ref n2)) => {
                #[cfg(feature = "num")]
                {
                    (&**n1).cmp(&Rational::from(&**n2))
                }
                #[cfg(not(feature = "num"))]
                {
                    (&**n1).partial_cmp(&**n2).unwrap_or(Ordering::Less)
                }
            }
            (&Number::Rational(ref n1), &Number::Float(n2)) => OrderedFloat(n1.to_f64()).cmp(&n2),
            (&Number::Float(n1), &Number::Rational(ref n2)) => n1.cmp(&OrderedFloat(n2.to_f64())),
            (&Number::Float(f1), &Number::Float(f2)) => f1.cmp(&f2),
            (&Number::Rational(ref r1), &Number::Rational(ref r2)) => r1.cmp(&r2),
        }
    }
}

impl<'a> TryFrom<(Addr, &'a Heap)> for Number {
    type Error = ();

    fn try_from((addr, heap): (Addr, &'a Heap)) -> Result<Number, Self::Error> {
        match addr {
            Addr::Fixnum(n) => Ok(Number::from(n)),
            Addr::Float(n) => Ok(Number::Float(n)),
            Addr::Usize(n) => {
                if let Ok(n) = isize::try_from(n) {
                    Ok(Number::from(n))
                } else {
                    Ok(Number::from(Integer::from(n)))
                }
            }
            Addr::Con(h) => Number::try_from(&heap[h]),
            _ => Err(()),
        }
    }
}

impl<'a> TryFrom<&'a HeapCellValue> for Number {
    type Error = ();

    fn try_from(value: &'a HeapCellValue) -> Result<Number, Self::Error> {
        match value {
            HeapCellValue::Addr(addr) => match addr {
                &Addr::Fixnum(n) => Ok(Number::from(n)),
                &Addr::Float(n) => Ok(Number::Float(n)),
                &Addr::Usize(n) => {
                    if let Ok(n) = isize::try_from(n) {
                        Ok(Number::from(n))
                    } else {
                        Ok(Number::from(Integer::from(n)))
                    }
                }
                _ => Err(()),
            },
            HeapCellValue::Integer(n) => Ok(Number::Integer(n.clone())),
            HeapCellValue::Rational(n) => Ok(Number::Rational(n.clone())),
            _ => Err(()),
        }
    }
}

impl<'a> From<&'a Integer> for Number {
    #[inline]
    fn from(src: &'a Integer) -> Self {
        Number::Integer(Rc::new(Integer::from(src)))
    }
}

// Computes n ^ power. Ignores the sign of power.
pub fn binary_pow(mut n: Integer, power: &Integer) -> Integer {
    let mut power = Integer::from(power.abs_ref());

    if power == 0 {
        return Integer::from(1);
    }

    let mut oddand = Integer::from(1);

    while power > 1 {
        if power.is_odd() {
            oddand *= &n;
        }

        n.pow_assign(2);
        power >>= 1;
    }

    n * oddand
}