/*  Mycelium Scheme
 *  Copyright (C) 2025 Ava Affine
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#![cfg_attr(not(test), no_std)]
extern crate alloc;

use alloc::string::String;
use alloc::format;
use alloc::fmt::Debug;
use core::{cmp::Ordering, f64, ops::{Add, Div, Mul, Sub}, str::FromStr};
use num::{integer::{gcd}, pow::Pow};

pub const E_INCOMPREHENSIBLE:       &str = "could not comprehend number literal";
pub const E_BASE_PARSE_FAIL:        &str = "failed to parse explicit base literal";
pub const E_POUND_TRUNCATED:        &str = "pound sign implies additional input";
pub const E_UNKNOWN_CONTROL:        &str = "unknown character in number literal";
pub const E_EMPTY_INPUT:            &str = "empty string cannot be a number";
pub const E_UNKNOWN_SYMBOL:         &str = "unknown symbolic number repr";
pub const E_NO_DENOMINATOR:         &str = "fraction is missing a denominator";
pub const E_MULTI_DENOMINATOR:      &str = "fraction has too many denominators";
pub const E_ZERO_DENOMINATOR:       &str = "denominator cannot be zero";
pub const E_NUMERATOR_PARSE_FAIL:   &str = "couldnt parse numerator";
pub const E_DENOMINATOR_PARSE_FAIL: &str = "couldnt parse denominator";
pub const E_FLOAT_PARSE_FAIL:       &str = "couldnt parse float";
pub const E_SCIENTIFIC_E:           &str = "scientific notation implies an 'e'";
pub const E_SCIENTIFIC_MULTI_E:     &str = "scientific notation implies only a single 'e'";
pub const E_SCIENTIFIC_OPERAND:     &str = "couldnt parse 32 bit float operand";
pub const E_SCIENTIFIC_POWER:       &str = "couldnt parse integer power";

pub trait Numeric: Copy + Clone + Debug + FromStr + Into<String> {
    fn is_exact(&self) -> bool;
    fn make_inexact(&self) -> Float;
    fn make_exact(&self) -> Fraction;
}


#[derive(Copy, Clone, Debug, PartialEq)]
pub struct ScientificNotation (pub f32, pub isize);

#[derive(Copy, Clone, Debug, PartialEq)]
pub enum SymbolicNumber {
    Inf,
    NegInf,
    NaN,
    NegNan,
}

#[derive(Copy, Clone, Debug, PartialEq)]
pub struct Fraction (pub isize, pub isize);

#[derive(Copy, Clone, Debug, PartialEq)]
pub struct Float (pub f64);

#[derive(Copy, Clone, Debug)]
pub enum Number {
    Sci(ScientificNotation),
    Fra(Fraction),
    Flt(Float),
    Sym(SymbolicNumber)
}

impl From<SymbolicNumber> for Number {
    fn from(value: SymbolicNumber) -> Self {
        Number::Sym(value)
    }
}

impl From<ScientificNotation> for Number {
    fn from(value: ScientificNotation) -> Self {
        Number::Sci(value)
    }
}

impl From<Fraction> for Number {
    fn from(value: Fraction) -> Self {
        Number::Fra(value)
    }
}

impl From<Float> for Number {
    fn from(value: Float) -> Self {
        Number::Flt(value)
    }
}

// TODO: both the following impls should be done with a macro
impl Into<String> for Number {
    fn into(self) -> String {
        match self {
            Number::Sci(x) => x.into(),
            Number::Fra(x) => x.into(),
            Number::Flt(x) => x.into(),
            Number::Sym(x) => x.into(),
        }
    }
}

impl Numeric for Number {
    fn is_exact(&self) -> bool {
        match self {
            Number::Sci(x) => x.is_exact(),
            Number::Fra(x) => x.is_exact(),
            Number::Flt(x) => x.is_exact(),
            Number::Sym(x) => x.is_exact(),
        }
    }

    fn make_exact(&self) -> Fraction {
        match self {
            Number::Sci(x) => x.make_exact(),
            Number::Fra(x) => x.make_exact(),
            Number::Flt(x) => x.make_exact(),
            Number::Sym(x) => x.make_exact(),
        }
    }

    fn make_inexact(&self) -> Float {
        match self {
            Number::Sci(x) => x.make_inexact(),
            Number::Fra(x) => x.make_inexact(),
            Number::Flt(x) => x.make_inexact(),
            Number::Sym(x) => x.make_inexact(),
        }
    }
}

impl From<f64> for Number {
    fn from(value: f64) -> Self {
        match value {
            f64::INFINITY => Number::Sym(SymbolicNumber::Inf),
            f64::NEG_INFINITY => Number::Sym(SymbolicNumber::NegInf),
            _ if value.is_nan() => Number::Sym(SymbolicNumber::NaN),
            _ if value.fract() == 0.0 => Number::Fra(Fraction(value as isize, 1)),
            _ => Number::Flt(Float(value))
        }
    }
}

impl FromStr for Number {
    type Err = &'static str;

    /* Number forms 
     * - 1.3
     * - 1e100
     * - 1.3e100
     * - +1.3
     * - -2.3
     * - #d124
     * - #o2535 // base 8
     * - #x8A3D // base 16
     * - #b1011 // base 2
     * - 2/4    // inexact
     * - #e1/5  // exact (fraction is as is)
     * - #e1e1  // exact 1e1 (= 10)
     * - #i1/5  // inexact (collapse fraction to decimal)
     * - +inf.0, -inf.0, +nan.0, -nan.0
     */

    fn from_str(value: &str) -> Result<Self, Self::Err> {
        let maybe_sym = value.parse::<SymbolicNumber>();
        if maybe_sym.is_ok() {
            return Ok(Number::Sym(maybe_sym.unwrap()))
        }

        /* Only two things that we need to handle here.
         * 1. leading with a +/-
         * 2. leading with a #i or a #e
         * These are mutually exclusive options.
         *
         * Once they have been managed or ruled out we can
         * just try each number type
         */

        let mut force_exact = false;
        let mut force_inexact = false;
        let mut base = 0;
        let mut iter = value.chars();
        let mut start_idx: usize = 0;

        match iter.next() {
            Some('+') => start_idx = 1,
            Some('-') => start_idx = 0,
            Some('#') => {
                start_idx = 2;
                match iter.next() {
                    None => return Err(E_POUND_TRUNCATED),
                    Some('i') => force_inexact = true,
                    Some('e') => force_exact = true,
                    Some('x') => base = 16,
                    Some('d') => base = 10,
                    Some('o') => base = 8,
                    Some('b') => base = 2,
                    _ => return Err(E_UNKNOWN_CONTROL),
                }
            },
            None => return Err(E_EMPTY_INPUT),
            _ => ()
        }

        let substr = &value[start_idx..];
        let res;

        if base > 0 {
            let num = isize::from_str_radix(substr, base)
                .or(Err(E_BASE_PARSE_FAIL))?;
            return Ok(Number::Fra(Fraction(num, 1)));

        } else if let Ok(num) = substr.parse::<ScientificNotation>() {
            res = Number::Sci(num);

        } else if let Ok(num) = substr.parse::<Fraction>() {
            res = Number::Fra(num);

        } else if let Ok(num) = substr.parse::<Float>() {
            res = Number::Flt(num);

        } else {
            return Err(E_INCOMPREHENSIBLE)
        }

        if force_exact {
            return Ok(Number::Fra(res.make_exact()))
        }

        if force_inexact {
            return Ok(Number::Flt(res.make_inexact()))
        }

        Ok(res)
   }
}

impl Add for Number {
    type Output = Number;
    fn add(self, rhs: Self) -> Self::Output {
        if self.is_exact() && rhs.is_exact() {
            let Fraction(lnum, lden) = self.make_exact();
            let Fraction(rnum, rden) =  rhs.make_exact();
            let num = (lnum * rden) + (rnum * lden);
            let den = lden * rden;
            Number::Fra(Fraction(num, den).simplify())

        } else {
            let Float(l) = self.make_inexact();
            let Float(r) =  rhs.make_inexact();
            let res = l + r;
            res.into()
        }
    }
}

impl Sub for Number {
    type Output = Number;
    fn sub(self, rhs: Self) -> Self::Output {
        if self.is_exact() && rhs.is_exact() {
            let Fraction(lnum, lden) = self.make_exact();
            let Fraction(rnum, rden) =  rhs.make_exact();
            let num = (lnum * rden) - (rnum * lden);
            let den = lden * rden;
            Number::Fra(Fraction(num, den).simplify())

        } else {
            let Float(l) = self.make_inexact();
            let Float(r) =  rhs.make_inexact();
            let res = l - r;
            res.into()
        }
    }
}

impl Mul for Number {
    type Output = Number;
    fn mul(self, rhs: Self) -> Self::Output {
        if self.is_exact() && rhs.is_exact() {
            let Fraction(lnum, lden) = self.make_exact();
            let Fraction(rnum, rden) =  rhs.make_exact();
            let num = lnum * rnum;
            let den = lden * rden;
            Number::Fra(Fraction(num, den).simplify())

        } else {
            let Float(l) = self.make_inexact();
            let Float(r) =  rhs.make_inexact();
            let res = l * r;
            res.into()
        }
    }
}

impl Div for Number {
    type Output = Number;
    fn div(self, rhs: Self) -> Self::Output {
        if self.is_exact() && rhs.is_exact() {
            let Fraction(lnum, lden) = self.make_exact();
            let Fraction(rnum, rden) =  rhs.make_exact();
            let num = lnum * rden;
            let den = rnum * lden;
            Number::Fra(Fraction(num, den).simplify())

        } else {
            let Float(l) = self.make_inexact();
            let Float(r) =  rhs.make_inexact();
            let res = l / r;
            res.into()
        }
    }
}

impl Pow<Number> for Number {
    type Output = Number;
    fn pow(self, rhs: Number) -> Self::Output {
        if self.is_exact() && rhs.is_exact() {
            let Fraction(mut lnum, mut lden) = self
                .make_exact()
                .simplify();
            let Fraction(rnum, rden) = rhs
                .make_exact()
                .simplify();

            // flip first frac if second one is negative
            if rnum < 0 {
                let tmp = lnum;
                lnum = lden;
                lden = tmp;
            }

            // apply fractional exponent (denominator)
            let mut intermediate_numer = f64::powf(lnum as f64, 1.0 / rden as f64);
            let mut intermediate_denom = f64::powf(lden as f64, 1.0 / rden as f64);

            // apply whole exponent (numerator)
            intermediate_numer =
                f64::powf(intermediate_numer, rnum.abs() as f64);
            intermediate_denom =
                f64::powf(intermediate_denom, rnum.abs() as f64);

            if intermediate_numer.fract() == 0.0 && intermediate_denom.fract() == 0.0 {
                Number::Fra(Fraction(intermediate_numer as isize, intermediate_denom as isize)
                                .simplify())
            } else {
                (intermediate_numer / intermediate_denom).into()
            }

        // one or both are already inexact
        } else {
            let Float(l) = self.make_inexact();
            let Float(r) =  rhs.make_inexact();
            let res = f64::powf(l, r);
            res.into()
        }
    }
}

impl PartialEq for Number {
    fn eq(&self, other: &Number) -> bool {
        //if self.is_exact() && other.is_exact() {
            // TODO: Figure out a way to comp two fractions without reducing
            // to a float and losing the precision of exact numbers
        //} else {
        self.make_inexact() == other.make_inexact()
        //}
    }
}

impl PartialOrd for Number{
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        //if self.is_exact() && other.is_exact() {
            // TODO: Figure out a way to comp two fractions without reducing
            // to a float and losing the precision of exact numbers
        //} else {
        self.make_inexact().0.partial_cmp(&other.make_inexact().0)
        //}
    }
}

impl FromStr for SymbolicNumber {
    type Err = &'static str;

    fn from_str(value: &str) -> Result<Self, Self::Err> {
        match value {
            "+inf.0" => Ok(SymbolicNumber::Inf),
            "-inf.0" => Ok(SymbolicNumber::NegInf),
            "+nan.0" => Ok(SymbolicNumber::NaN),
            "-nan.0" => Ok(SymbolicNumber::NegNan),
            _ => Err(E_UNKNOWN_SYMBOL)
        }
    }
}

impl Into<String> for SymbolicNumber {
    fn into(self) -> String {
        match self {
            SymbolicNumber::Inf    => format!("+inf.0"),
            SymbolicNumber::NegInf => format!("-inf.0"),
            SymbolicNumber::NaN    => format!("+nan.0"),
            SymbolicNumber::NegNan => format!("-nan.0"),
        }
    }
}

impl Numeric for SymbolicNumber {
    fn is_exact(&self) -> bool {
        false
    }

    fn make_inexact(&self) -> Float {
        match self {
            SymbolicNumber::Inf => Float(f64::INFINITY),
            SymbolicNumber::NegInf => Float(f64::NEG_INFINITY),
            SymbolicNumber::NaN | SymbolicNumber::NegNan => Float(f64::NAN),
        }
    }

    fn make_exact(&self) -> Fraction {
        panic!("attempted to make inf or nan into fraction")
    }
}

impl Fraction {
    fn simplify(&self) -> Fraction {
        let mut n = self.0;
        let mut d = self.1;
        /* normalize negative to numerator
         * if numerator is also negative this becomes a positive frac
         */
        if self.1 < 0 {
            d = 0 - self.1;
            n = 0 - self.0;
        }

        /* divide both by their greatest common divisor
         * leading to simplest possible form
         */
        let g = gcd(n, d);
        Fraction(n / g, d / g)
    }
}

impl FromStr for Fraction {
    type Err = &'static str;

    fn from_str(value: &str) -> Result<Self, Self::Err> {
        let part: usize;
        if let Some(idx) = value.find('/') {
            part = idx;
        } else {
            return Err(E_NO_DENOMINATOR)
        }

        // make sure there is ONLY ONE slash
        if let Some(idx) = value.rfind('/') && idx != part {
            return Err(E_MULTI_DENOMINATOR)
        }

        let numerator_text   = &value[..part];
        let denominator_text = &value[part+1..];

        let numerator   = numerator_text.parse::<isize>()
            .or(Err(E_NUMERATOR_PARSE_FAIL))?;
        let denominator = denominator_text.parse::<isize>()
            .or(Err(E_DENOMINATOR_PARSE_FAIL))?;

        if denominator == 0 {
            return Err(E_ZERO_DENOMINATOR)
        }

        Ok(Fraction(numerator, denominator))
    }
}

impl Into<String> for Fraction {
    fn into(self) -> String {
        format!("{}/{}", self.0, self.1)
    }
}

impl Numeric for Fraction {
    fn is_exact(&self) -> bool {
        true
    }

    fn make_inexact(&self) -> Float {
        Float(self.0 as f64 / self.1 as f64)
    }

    fn make_exact(&self) -> Fraction {
        *self
    }
}

impl FromStr for Float {
    type Err = &'static str;
    fn from_str(value: &str) -> Result<Self, Self::Err> {
        Ok(Float(value.parse::<f64>().or(Err(E_FLOAT_PARSE_FAIL))?))
    }
}

impl Into<String> for Float {
    fn into(self) -> String {
        if self.is_exact() {
            format!("{}", self.0)
        } else {
            format!("#i{}", self.0)
        }
    }
}

impl Numeric for Float {
    fn is_exact(&self) -> bool {
        self.0.fract() == 0.0
    }

    fn make_inexact(&self) -> Float {
        *self
    }

    fn make_exact(&self) -> Fraction {
        if self.0.fract() == 0.0 {
            Fraction(self.0 as isize, 1)
        } else {
            todo!("rational approximation implementation")
        }
    }
}

impl FromStr for ScientificNotation {
    type Err = &'static str;

    fn from_str(value: &str) -> Result<Self, Self::Err> {
        let part: usize;
        if let Some(idx) = value.find('e') {
            part = idx;
        } else {
            return Err(E_SCIENTIFIC_E)
        }

        // make sure there is ONLY ONE slash
        if let Some(idx) = value.rfind('e') && idx != part {
            return Err(E_SCIENTIFIC_MULTI_E)
        }

        let operand_text   = &value[..part];
        let power_text = &value[part+1..];

        let operand   = operand_text.parse::<f32>()
            .or(Err(E_SCIENTIFIC_OPERAND))?;
        let power = power_text.parse::<isize>()
            .or(Err(E_SCIENTIFIC_POWER))?;

        Ok(ScientificNotation(operand, power))
    }
}

impl Into<String> for ScientificNotation {
    fn into(self) -> String {
        format!("{}e{}", self.0, self.1)
    }
}

impl Numeric for ScientificNotation {
    fn is_exact(&self) -> bool {
        self.0.fract() == 0.0 && self.1 >= 0
    }

    fn make_inexact(&self) -> Float {
        Float(self.0 as f64 * f64::powi(10.0, self.1 as i32) as f64)
    }

    fn make_exact(&self) -> Fraction {
        self.make_inexact().make_exact()
    }
}


#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn parse_fraction_tests() {
        assert_eq!("2/3".parse::<Fraction>(),
            Ok(Fraction(2, 3)));

        assert_eq!("0/1".parse::<Fraction>(),
            Ok(Fraction(0, 1)));

        assert_eq!("-1/34".parse::<Fraction>(),
            Ok(Fraction(-1, 34)));

        assert_eq!("2".parse::<Fraction>(),
            Err(E_NO_DENOMINATOR));

        assert_eq!("2/2/2".parse::<Fraction>(),
            Err(E_MULTI_DENOMINATOR));

        assert_eq!("2/0".parse::<Fraction>(),
            Err(E_ZERO_DENOMINATOR));

        assert_eq!("3.3/3".parse::<Fraction>(),
            Err(E_NUMERATOR_PARSE_FAIL));

        assert_eq!("2/two".parse::<Fraction>(),
            Err(E_DENOMINATOR_PARSE_FAIL));
    }

    #[test]
    fn parse_scientific_notation_tests() {
        assert_eq!("2e3".parse::<ScientificNotation>(),
            Ok(ScientificNotation(2.0, 3)));

        assert_eq!("0e1".parse::<ScientificNotation>(),
            Ok(ScientificNotation(0.0, 1)));

        assert_eq!("-1e34".parse::<ScientificNotation>(),
            Ok(ScientificNotation(-1.0, 34)));

        assert_eq!("3.3e3".parse::<ScientificNotation>(),
            Ok(ScientificNotation(3.3, 3)));

        assert_eq!("2".parse::<ScientificNotation>(),
            Err(E_SCIENTIFIC_E));

        assert_eq!("2e2e2".parse::<ScientificNotation>(),
            Err(E_SCIENTIFIC_MULTI_E));

        assert_eq!("2etwo".parse::<ScientificNotation>(),
            Err(E_SCIENTIFIC_POWER));

        assert_eq!("twoe2".parse::<ScientificNotation>(),
            Err(E_SCIENTIFIC_OPERAND));
    }

    #[test]
    fn parse_number_tests() {
        assert_eq!("1.3".parse::<Number>(),
            Ok(Number::Flt(Float(1.3))));

        assert_eq!("1".parse::<Number>(),
            Ok(Number::Flt(Float(1 as f64))));

        assert_eq!("1.3e3".parse::<Number>(),
            Ok(Number::Sci(ScientificNotation(1.3, 3))));

        assert_eq!("+1.3".parse::<Number>(),
            Ok(Number::Flt(Float(1.3))));

        assert_eq!("-1.3".parse::<Number>(),
            Ok(Number::Flt(Float(-1.3))));

        assert_eq!("#d234".parse::<Number>(),
            Ok(Number::Flt(Float(234.0))));

        assert_eq!("#o17".parse::<Number>(),
            Ok(Number::Fra(Fraction(15, 1))));

        assert_eq!("#xAA".parse::<Number>(),
            Ok(Number::Fra(Fraction(170, 1))));

        assert_eq!("#b101".parse::<Number>(),
            Ok(Number::Flt(Float(5.0))));

        assert_eq!("2/4".parse::<Number>(),
            Ok(Number::Fra(Fraction(2, 4))));

        assert_eq!("#e1/5".parse::<Number>(),
            Ok(Number::Fra(Fraction(1, 5))));

        assert_eq!("#i1/5".parse::<Number>(),
            Ok(Number::Flt(Float(0.2))));

        assert_eq!("#e1e1".parse::<Number>(),
            Ok(Number::Sci(ScientificNotation(1.0, 1))));

        assert_eq!("+inf.0".parse::<Number>(),
            Ok(Number::Sym(SymbolicNumber::Inf)));
    }

    #[test]
    fn test_number_addition_subtraction_cases() {
        let cases = vec![
            vec!["1/5", "4/5", "1/1"],
            vec!["1/5", "0.8", "1/1"],
            vec!["1e1", "2.0", "12/1"],
            vec!["1e1", "2/1", "12/1"],
            vec!["1e1", "1/2", "10.5"],
        ];

        cases.iter().for_each(|case| {
            println!("+ {:#?}", case);
            let x = case[0].parse::<Number>().unwrap();
            let y = case[1].parse::<Number>().unwrap();
            let z = case[2].parse::<Number>().unwrap();

            // test some mathematical properties
            assert_eq!(x + y, z);
            assert_eq!(x + y, y + x);
            assert_eq!(z - x, y);
            assert_eq!(x + y - x, y);
        });

        // theres no reason this should adhere to all the other rules
        let x = "+inf.0".parse::<Number>().unwrap();
        let y = "1e1".parse::<Number>().unwrap();
        let z = "+inf.0".parse::<Number>().unwrap();
        assert_eq!(x + y, z);
    }

    #[test]
    fn test_number_multiplication_division_cases() {
        let cases = vec![
            vec!["1/5", "5e0", "1/1"],
            vec!["1/5", "5", "1/1"],
            vec!["1/5", "2/1", "2/5"],
            vec!["4.4", "1/2", "2.2"],
            vec!["12.0", "1/2", "6/1"],
            vec!["1e1", "2.0", "20/1"],
            vec!["1e1", "2/1", "20/1"],
            vec!["1e1", "1/2", "5/1"],
        ];

        cases.iter().for_each(|case| {
            println!("+ {:#?}", case);
            let x = case[0].parse::<Number>().unwrap();
            let y = case[1].parse::<Number>().unwrap();
            let z = case[2].parse::<Number>().unwrap();

            // test some mathematical properties
            assert_eq!(x * y, z);
            assert_eq!(x * y, y * x);
            assert_eq!(z / x, y);
            assert_eq!(x * y / x, y);
        });
    }

    #[test]
    fn test_number_pow_cases() {
        // TODO: add scientific notation cases
        let cases = vec![
            vec!["2", "2", "4"],
            vec!["2/1", "2/1", "4/1"],
            vec!["2/1", "2/-1", "1/4"],
            vec!["2/1", "2/2", "2/1"],
            vec!["2/1", "2.0", "4/1"],
            vec!["27/8", "2/-3", "4/9"]
        ];

        cases.iter().for_each(|case| {
            println!("+ {:#?}", case);
            let x = case[0].parse::<Number>().unwrap();
            let y = case[1].parse::<Number>().unwrap();
            let z = case[2].parse::<Number>().unwrap();
            assert_eq!(x.pow(y), z);
        });
    }

    #[test]
    fn test_number_ord_cases() {
        // TODO: add more cases
        let cases = vec![
            vec!["1/2", "1.0", "1e1"],
        ];

        cases.iter().for_each(|case| {
            println!("+ {:#?}", case);
            let x = case[0].parse::<Number>().unwrap();
            let y = case[1].parse::<Number>().unwrap();
            let z = case[2].parse::<Number>().unwrap();
            assert!(x < y);
            assert!(y < z);
            assert!(x < z);
        });
    }

    #[test]
    fn float_negative_exponent_case() {
        if let Float(0.1) = "1e-1"
            .parse::<Number>()
            .unwrap()
            .make_inexact() {
                return
        }

        assert!(false)
    }
}