use std::cmp::{min, Ordering};
use std::error::Error;
use std::fmt::{Display, Formatter};
use std::iter::zip;
use std::ops::{Add, Div, Mul, Rem, Sub};

#[derive(Clone, Debug, Eq, PartialEq, Hash)]
pub enum Sign {
    Positif,
    Negatif,
}

#[derive(Clone, Debug, Eq, PartialEq, Hash)]
pub struct Number {
    pub digits: Vec<isize>,
    pub sign: Sign,
}

impl Number {
    pub fn get_digit(n: isize, pos: usize) -> isize {
        let modulo = 10isize.pow(pos as u32 + 1);
        let divisor = modulo / 10;
        (n % modulo) / divisor
    }

    pub const fn byte_to_digit(b: u8) -> isize {
        // wrapping_sub('0' as u32) same as - 48 but less magical
        (b as isize).wrapping_sub('0' as isize)
    }

    fn handle_overflows(&mut self) {
        let new_digits = &mut self.digits;
        let digits_len = new_digits.len();
        let mut digits_idx = digits_len - 1;
        loop {
            let digit_or_num = new_digits[digits_idx];
            let digit_len = if digit_or_num != 0 {
                (digit_or_num.abs() as f64 + 1.0).log10().ceil() as usize
            } else {
                1
            };
            for i in 0..digit_len {
                let new_digit = Self::get_digit(digit_or_num, i);
                let (digit_idx, is_overflow) = digits_idx.overflowing_sub(i);
                if is_overflow {
                    new_digits.insert(0, new_digit);
                    digits_idx += 1;
                } else {
                    let digit = new_digits.get_mut(digit_idx).unwrap();
                    if i == 0 {
                        *digit = new_digit;
                    } else {
                        *digit += new_digit;
                    }
                }
            }
            if digits_idx == 0 {
                break;
            }
            digits_idx -= 1;
        }
    }

    fn handle_underflows(&mut self) {
        let new_digits = &mut self.digits;
        let mut digits_len = new_digits.len();
        for digit in new_digits.clone() {
            match digit.cmp(&0) {
                Ordering::Equal => {
                    if digits_len == 1 {
                        return;
                    }
                    digits_len -= 1;
                    new_digits.remove(0);
                }
                Ordering::Less => {
                    self.sign = Sign::Negatif;
                    break;
                }
                _ => break,
            };
        }
        let mut digits_idx = digits_len - 1;
        loop {
            let digit = new_digits[digits_idx];
            if self.sign == Sign::Positif && digit < 0 && digits_idx > 0 {
                let mut_digit = new_digits.get_mut(digits_idx).unwrap();
                *mut_digit = 10 - digit.abs();
                let mut_digit = new_digits.get_mut(digits_idx - 1).unwrap();
                *mut_digit -= 1;
            } else {
                let mut_digit = new_digits.get_mut(digits_idx).unwrap();
                *mut_digit = digit.abs();
            }
            if digits_idx == 0 {
                break;
            }
            digits_idx -= 1;
        }
        for digit in new_digits.clone() {
            match digit.cmp(&0) {
                Ordering::Equal => {
                    new_digits.remove(0);
                }
                _ => break,
            };
        }
    }

    pub fn pow(self, n: u32) -> Self {
        let mut result = self.clone();
        if ((self.digits.len() * 8) as u32) < isize::BITS {
            let number = isize::from(self);
            for _i in 1..n {
                result = result * number;
            }
            result
        } else {
            let number = self.clone();
            for _i in 1..n {
                result = result * number.clone();
            }
            result
        }
    }

    pub fn fact(self) -> Self {
        let mut fact = Number::from(1);
        if ((self.digits.len() * 8) as u32) < isize::BITS {
            let max = isize::from(self);
            for n in 1..=max {
                fact = fact * n;
            }
            fact
        } else {
            panic!("starting number too big")
        }
    }

    pub fn fib(n: u64) -> Self {
        let mut last_two = (Self::from(1), Self::from(1));
        let mut iteration = 1;
        while iteration < n {
            last_two = (last_two.1.clone(), last_two.0 + last_two.1);
            iteration += 1;
        }

        last_two.0
    }

    pub fn div_with_rem(n1: Number, n2: Number) -> Result<(Number, Number), Box<dyn Error>> {
        if n2 == 0.into() {
            return Err(Box::from("Division by 0"));
        }
        let n1_len = n1.digits.len();
        let n2_len = n2.digits.len();
        if n2_len > n1_len {
            return Ok((Number::from(0), n2));
        }
        let dividend = n1.digits[..n2_len].to_vec();
        let mut quotient = vec![];
        let mut remainder = Number {
            digits: dividend.clone(),
            sign: Sign::Positif,
        };
        let mut iteration = 1;
        loop {
            let mut factor = 0;
            loop {
                let temp_remainder = remainder.clone() - n2.clone();
                if temp_remainder.sign == Sign::Negatif {
                    quotient.push(factor);
                    break;
                }
                remainder = temp_remainder;
                factor += 1;
            }
            if n1_len == n2_len + iteration - 1 {
                break;
            }
            remainder.digits.push(n1.digits[n2_len + iteration - 1]);
            iteration += 1;
        }
        let mut res = Number {
            digits: quotient,
            sign: Sign::Positif,
        };
        res.handle_overflows();
        for digit in res.clone().digits {
            if digit != 0 || res.digits.len() == 1 {
                break;
            }
            res.digits.remove(0);
        }
        for digit in remainder.clone().digits {
            if digit != 0 || remainder.digits.len() == 1 {
                break;
            }
            remainder.digits.remove(0);
        }
        Ok((res, remainder))
    }

    pub fn gcd(mut a: Number, mut b: Number) -> Number {
        loop {
            let t = b.clone();
            b = a % b;
            a = t;
            if b == Number::from(0) {
                return a;
            }
        }
    }
}

impl From<Number> for isize {
    fn from(value: Number) -> Self {
        let mut num = 0;
        for (pos, &digit) in value.digits.iter().rev().enumerate() {
            num += digit * 10isize.pow(pos as u32);
        }
        num
    }
}

impl From<Number> for String {
    fn from(value: Number) -> Self {
        let string_vec: Vec<String> = value
            .digits
            .iter()
            .map(|&digit| digit.to_string())
            .collect();
        string_vec.concat()
    }
}

impl From<&str> for Number {
    fn from(value: &str) -> Self {
        let bytes = value.as_bytes();
        let (sign, idx_start) = match bytes[0] {
            b'-' => (Sign::Negatif, 1),
            _ => (Sign::Positif, 0),
        };
        let mut digits = vec![];
        for &byte in &bytes[idx_start..] {
            let digit = Self::byte_to_digit(byte);
            digits.push(digit);
        }
        Self { digits, sign }
    }
}

impl From<isize> for Number {
    fn from(mut value: isize) -> Self {
        let mut sign = Sign::Positif;
        if value < 0 {
            sign = Sign::Negatif;
            value *= -1;
        }
        if value == 0 {
            return Self {
                digits: vec![0],
                sign: Sign::Positif,
            };
        }
        let num_len = (value as f64 + 1.0).log10().ceil() as usize;
        let mut digits = vec![];
        for digit_idx in 0..num_len {
            let digit = Self::get_digit(value, digit_idx);
            digits.push(digit);
        }
        let digits = digits.iter().rev().copied().collect();
        Self { digits, sign }
    }
}

impl Display for Number {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        let number_string = self
            .digits
            .iter()
            .map(|&digit| digit.to_string())
            .collect::<Vec<String>>()
            .join("");
        match self.sign {
            Sign::Positif => write!(f, "{number_string}"),
            Sign::Negatif => write!(f, "-{number_string}"),
        }
    }
}

impl Add for Number {
    type Output = Self;

    fn add(self, rhs: Self) -> Self::Output {
        let self_len = self.digits.len();
        let rhs_len = rhs.digits.len();
        let mut self_digits = self.digits.clone();
        let mut rhs_digits = rhs.digits.clone();
        if self_len != rhs_len {
            let difference = (self_len).abs_diff(rhs_len);
            let pad = vec![0isize; difference];
            if min(self_len, rhs_len) == self_len {
                self_digits = [pad, self.digits].concat();
            } else {
                rhs_digits = [pad, rhs.digits].concat();
            }
        }
        let zipped = zip(self_digits.iter(), rhs_digits.iter());
        let added = zipped
            .map(|(self_digit, rhs_digit)| self_digit + rhs_digit)
            .collect();
        let mut overflown_number = Self {
            digits: added,
            sign: Sign::Positif,
        };
        overflown_number.handle_overflows();
        overflown_number
    }
}

impl Sub for Number {
    type Output = Self;

    fn sub(self, rhs: Self) -> Self::Output {
        let self_len = self.digits.len();
        let rhs_len = rhs.digits.len();
        let mut self_digits = self.digits.clone();
        let mut rhs_digits = rhs.digits.clone();
        if self_len != rhs_len {
            let difference = (self_len).abs_diff(rhs_len);
            let pad = vec![0isize; difference];
            if min(self_len, rhs_len) == self_len {
                self_digits = [pad, self.digits].concat();
            } else {
                rhs_digits = [pad, rhs.digits].concat();
            }
        }
        let zipped = zip(self_digits.iter(), rhs_digits.iter());
        let added = zipped
            .map(|(self_digit, rhs_digit)| self_digit - rhs_digit)
            .collect();
        let mut underflown_number = Self {
            digits: added,
            sign: Sign::Positif,
        };
        underflown_number.handle_underflows();
        underflown_number
    }
}

impl Mul for Number {
    type Output = Self;

    fn mul(self, rhs: Self) -> Self::Output {
        let multiplied = self.digits.iter().rev().enumerate().map(|(pos, &digit)| {
            let mut mult = digit * rhs.clone();
            mult.digits = [mult.digits, vec![0; pos]].concat();
            mult
        });
        let mut overflown_number = multiplied.reduce(|acc, num| acc + num).unwrap();
        overflown_number.handle_overflows();
        overflown_number
    }
}

impl Mul<Number> for isize {
    type Output = Number;

    fn mul(self, rhs: Number) -> Self::Output {
        let multiplied = rhs.digits.iter().map(|digit| digit * self).collect();
        let mut overflown_number = Number {
            digits: multiplied,
            sign: Sign::Positif,
        };
        overflown_number.handle_overflows();
        overflown_number
    }
}

impl Mul<isize> for Number {
    type Output = Self;

    fn mul(self, rhs: isize) -> Self::Output {
        let multiplied = self.digits.iter().map(|digit| digit * rhs).collect();
        let mut overflown_number = Self {
            digits: multiplied,
            sign: Sign::Positif,
        };
        overflown_number.handle_overflows();
        overflown_number
    }
}

impl Div for Number {
    type Output = Self;

    fn div(self, rhs: Self) -> Self::Output {
        Self::div_with_rem(self, rhs).unwrap().0
    }
}

impl Rem for Number {
    type Output = Self;

    fn rem(self, rhs: Self) -> Self::Output {
        Self::div_with_rem(self, rhs).unwrap().1
    }
}

#[cfg(test)]
mod number_tests {
    use crate::number::{Number, Sign};

    #[test]
    fn test_from_isize() {
        let number = Number::from(-1234);
        assert_eq!(
            number,
            Number {
                digits: vec![1, 2, 3, 4],
                sign: Sign::Negatif
            }
        );
    }

    #[test]
    fn test_from_0isize() {
        let number = Number::from(0);
        assert_eq!(
            number,
            Number {
                digits: vec![0],
                sign: Sign::Positif
            }
        );
    }

    #[test]
    fn test_get_digit() {
        let num = 12345;
        let digit_1 = Number::get_digit(num, 0);
        let digit_2 = Number::get_digit(num, 1);
        let digit_3 = Number::get_digit(num, 2);
        let digit_4 = Number::get_digit(num, 3);
        let digit_5 = Number::get_digit(num, 4);
        assert_eq!(digit_1, 5);
        assert_eq!(digit_2, 4);
        assert_eq!(digit_3, 3);
        assert_eq!(digit_4, 2);
        assert_eq!(digit_5, 1);
    }
}