use std::{fmt, ops};

#[derive(Debug, PartialEq, Eq)]
pub struct Fraction {
    num: i64,
    den: i64,
}

#[derive(Debug, PartialEq, Eq)]
pub enum FractionError {
    DivisionByZero,
    ZeroDenominator,
    Overflow,
    InvalidInteger,
}

impl fmt::Display for FractionError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            FractionError::DivisionByZero => write!(f, "Division by zero"),
            FractionError::ZeroDenominator => write!(f, "Denominator can't be zero"),
            FractionError::Overflow => write!(f, "Numeric overflow"),
            FractionError::InvalidInteger => write!(f, "Can't convert to integer"),
        }
    }
}

impl std::error::Error for FractionError {}

impl Fraction {
    pub fn new(num: i64, den: i64) -> Result<Self, FractionError> {
        if den == 0 {
            return Err(FractionError::ZeroDenominator);
        }

        let mut new = Fraction { num, den };

        new.reduce();
        new.correct_sign();

        Ok(new)
    }

    pub fn reciprocal(&self) -> Result<Self, FractionError> {
        Fraction::new(self.den, self.num)
    }

    pub fn abs(&self) -> Self {
        Fraction {
            num: self.num.abs(),
            den: self.den,
        }
    }

    pub fn is_zero(&self) -> bool {
        self.num == 0
    }

    pub fn is_integer(&self) -> bool {
        self.den == 1
    }

    fn gcd(a: i64, b: i64) -> i64 {
        if a == 0 {
            return b;
        }
        Fraction::gcd(b % a, a)
    }

    fn reduce(&mut self) {
        let gdc = Fraction::gcd(self.num, self.den);

        self.num /= gdc;
        self.den /= gdc;
    }

    fn correct_sign(&mut self) {
        if self.num < 0 && self.den < 0 {
            self.num = self.num.abs();
            self.den = self.den.abs();
        } else if self.den < 0 {
            self.num = -self.num;
            self.den = self.den.abs();
        }
    }
}

impl ops::Mul for Fraction {
    type Output = Self;

    fn mul(self, other: Self) -> Self::Output {
        let mut new = Fraction {
            num: self.num * other.num,
            den: self.den * other.den,
        };
        new.reduce();
        new
    }
}

impl ops::Add for Fraction {
    type Output = Self;

    fn add(self, other: Self) -> Self::Output {
        let mut new = Fraction {
            num: (self.num * other.den) + (self.den * other.num),
            den: self.den * other.den,
        };
        new.reduce();
        new.correct_sign();
        new
    }
}

impl ops::Div for Fraction {
    type Output = Result<Self, FractionError>;

    fn div(self, other: Self) -> Self::Output {
        if other.is_zero() {
            return Err(FractionError::DivisionByZero);
        }

        let mut new = Fraction {
            num: self.num * other.den,
            den: self.den * other.num,
        };
        new.reduce();
        new.correct_sign();
        Ok(new)
    }
}

impl ops::Sub for Fraction {
    type Output = Self;

    fn sub(self, other: Self) -> Self::Output {
        let mut new = Fraction {
            num: (self.num * other.den) - (self.den * other.num),
            den: self.den * other.den,
        };
        new.reduce();
        new.correct_sign();
        new
    }
}

impl ops::Neg for Fraction {
    type Output = Self;

    fn neg(self) -> Self::Output {
        Fraction {
            num: -self.num,
            den: self.den,
        }
    }
}

impl fmt::Display for Fraction {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{0}/{1}", self.num, self.den)
    }
}

impl From<i32> for Fraction {
    fn from(value: i32) -> Self {
        Fraction {
            num: value.into(),
            den: 1,
        }
    }
}

impl From<i64> for Fraction {
    fn from(value: i64) -> Self {
        Fraction { num: value, den: 1 }
    }
}

impl TryFrom<(i32, i32)> for Fraction {
    type Error = FractionError;

    fn try_from(value: (i32, i32)) -> Result<Self, Self::Error> {
        if value.1 == 0 {
            return Err(FractionError::ZeroDenominator);
        }

        Ok(Fraction {
            num: value.0.into(),
            den: value.1.into(),
        })
    }
}

impl TryFrom<(i64, i64)> for Fraction {
    type Error = FractionError;

    fn try_from(value: (i64, i64)) -> Result<Self, Self::Error> {
        if value.1 == 0 {
            return Err(FractionError::ZeroDenominator);
        }

        Ok(Fraction {
            num: value.0,
            den: value.1,
        })
    }
}

impl TryInto<i64> for Fraction {
    type Error = FractionError;

    fn try_into(self) -> Result<i64, Self::Error> {
        if self.den != 1 {
            return Err(FractionError::InvalidInteger);
        }

        Ok(self.num)
    }
}

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

    #[test]
    fn test_new_valid_fraction() {
        let f = Fraction::new(2, 4).unwrap();
        assert_eq!(f.num, 1);
        assert_eq!(f.den, 2);
    }

    #[test]
    fn test_new_zero_denominator_error() {
        let f = Fraction::new(2, 0);
        assert!(matches!(f, Err(FractionError::ZeroDenominator)));
    }

    #[test]
    fn test_new_reduces_fraction() {
        let f = Fraction::new(256, 512).unwrap();
        assert_eq!(f.num, 1);
        assert_eq!(f.den, 2);
    }

    #[test]
    fn test_new_normalizes_signs() {
        let f = Fraction::new(1, -2).unwrap();
        assert_eq!(f.num, -1);
        assert_eq!(f.den, 2);
    }

    #[test]
    fn test_add_basic() {
        let a = Fraction::new(7, 13).unwrap();
        let b = Fraction::new(4, 7).unwrap();
        let c = a + b;
        assert_eq!(c.num, 101);
        assert_eq!(c.den, 91);
    }

    #[test]
    fn test_add_with_common_denominator() {
        let a = Fraction::new(7, 13).unwrap();
        let b = Fraction::new(4, 13).unwrap();
        let c = a + b;
        assert_eq!(c.num, 11);
        assert_eq!(c.den, 13);
    }

    #[test]
    fn test_add_positive_and_negative() {
        let a = Fraction::new(-32, 237).unwrap();
        let b = Fraction::new(22, 44).unwrap();
        let c = a + b;
        assert_eq!(c.num, 173);
        assert_eq!(c.den, 474);
    }

    #[test]
    fn test_add_negative_and_negative() {
        let a = Fraction::new(-500, 12).unwrap();
        let b = Fraction::new(-22, 4).unwrap();
        let c = a + b;
        assert_eq!(c.num, -283);
        assert_eq!(c.den, 6);
    }

    #[test]
    fn test_add_with_zero() {
        let a = Fraction::new(0, 13).unwrap();
        let b = Fraction::new(4, 7).unwrap();
        let c = a + b;
        assert_eq!(c.num, 4);
        assert_eq!(c.den, 7);
    }

    #[test]
    fn test_sub_basic() {
        let a = Fraction::new(7, 13).unwrap();
        let b = Fraction::new(4, 7).unwrap();
        let c = a - b;
        assert_eq!(c.num, -3);
        assert_eq!(c.den, 91);
    }

    #[test]
    fn test_sub_with_common_denominator() {
        let a = Fraction::new(7, 13).unwrap();
        let b = Fraction::new(4, 13).unwrap();
        let c = a - b;
        assert_eq!(c.num, 3);
        assert_eq!(c.den, 13);
    }

    #[test]
    fn test_sub_positive_and_negative() {
        let a = Fraction::new(-32, 237).unwrap();
        let b = Fraction::new(22, 44).unwrap();
        let c = a - b;
        assert_eq!(c.num, -301);
        assert_eq!(c.den, 474);
    }

    #[test]
    fn test_sub_negative_and_negative() {
        let a = Fraction::new(-500, 12).unwrap();
        let b = Fraction::new(-22, 4).unwrap();
        let c = a - b;
        assert_eq!(c.num, -217);
        assert_eq!(c.den, 6);
    }

    #[test]
    fn test_sub_with_zero() {
        let a = Fraction::new(0, 13).unwrap();
        let b = Fraction::new(4, 7).unwrap();
        let c = a - b;
        assert_eq!(c.num, -4);
        assert_eq!(c.den, 7);
    }

    #[test]
    fn test_sub_result_zero() {
        let a = Fraction::new(5, 9).unwrap();
        let b = Fraction::new(5, 9).unwrap();
        let c = a - b;
        assert_eq!(c.num, 0);
        assert_eq!(c.den, 1);
    }
}