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use std::{
    default::Default,
    fmt::{Debug, Display, Error},
    i64,
    iter::Sum,
    num::IntErrorKind,
    ops::{Add, Div, Mul, Neg},
    str::FromStr,
};

use num::{Num, NumCast, Signed};

/// Trait pattern to allow only **numbers** for generic value
pub trait MonomialValue:
    Num + NumCast + Signed + Copy + Default + Debug + Display + FromStr + PartialOrd
{
}

impl<T> MonomialValue for T where
    T: Num + NumCast + Signed + Copy + Default + Debug + Display + FromStr + PartialOrd
{
}

/// [Monomial](https://en.wikipedia.org/wiki/Monomial) representation
#[derive(Default, Debug, PartialEq, PartialOrd, Clone, Copy)]
pub struct Monomial<T> {
    pub(crate) value: T,
    pub(crate) exp: i32,
}

impl<T: MonomialValue> Monomial<T> {
    ///  - `value`: Coefficient
    ///  - `exp`: Exponent
    pub fn new(value: T, mut exp: i32) -> Monomial<T> {
        if T::is_zero(&value) {
            exp = 0;
        }

        Monomial { value, exp }
    }

    pub fn get_value(&self) -> T {
        self.value
    }

    pub fn get_exp(&self) -> i32 {
        self.exp
    }

    /// Check if other `Monomial` has same **exponent**
    pub fn is_operable(&self, other: &Self) -> bool {
        self.exp == other.exp
    }
}

/// # Example expresion
///
///```rust
/// let str = "4x^2";
///```
impl<T: MonomialValue> TryFrom<&str> for Monomial<T> {
    type Error = &'static str;

    fn try_from(value: &str) -> Result<Self, Self::Error> {
        let clean_value = value
            .trim()
            .to_lowercase()
            .replace(" ", "")
            .replace("^", "")
            .replace("+", "");

        let mut split: Vec<&str> = clean_value.split("x").collect();

        if split.is_empty() {
            return Ok(Monomial::default());
        }

        if "-" == split[0] {
            split[0] = "-1";
        }

        let base = match split[0].parse::<T>() {
            Ok(v) => v,
            Err(_) if split[0].is_empty() => T::one(),
            Err(_) => return Err("Not valid base"),
        };

        let exp = match split.len() {
            1 => 0,
            2 => match split[1].parse::<i32>() {
                Ok(v) => v,
                Err(err) if err.kind() == &IntErrorKind::Empty => 1,
                Err(_) => return Err("Not valid exponent"),
            },
            _ => return Err("To much symbols"),
        };

        Ok(Monomial { value: base, exp })
    }
}

impl<T: MonomialValue> Neg for Monomial<T> {
    type Output = Self;

    fn neg(self) -> Self::Output {
        Monomial::new(-self.value, self.exp)
    }
}

impl<T: MonomialValue> Add for Monomial<T> {
    type Output = Result<Self, &'static str>;

    fn add(self, rhs: Self) -> Self::Output {
        if !self.is_operable(&rhs) {
            return Err("Monomials only allow add same exponent");
        }

        Ok(Monomial::new(self.value + rhs.value, self.exp))
    }
}

impl<T: MonomialValue> Mul for Monomial<T> {
    type Output = Self;

    fn mul(self, rhs: Self) -> Self::Output {
        Monomial::new(self.value * rhs.value, self.exp + rhs.exp)
    }
}

impl<T: MonomialValue> Div for Monomial<T> {
    type Output = Self;

    fn div(self, rhs: Self) -> Self::Output {
        Monomial::new(self.value / rhs.value, self.exp - rhs.exp)
    }
}

impl<T: MonomialValue> Sum<Self> for Monomial<T> {
    fn sum<I: Iterator<Item = Self>>(iter: I) -> Self {
        let mut exp = 0;
        let mut sum = T::zero();
        for mono in iter {
            exp = mono.get_exp();
            sum = sum + mono.get_value();
        }

        Monomial::new(sum, exp)
    }
}

/// # Example expresion
///
///```rust
/// let str = "4x^2";
///```
impl<T: MonomialValue> Display for Monomial<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let val: i64 = T::to_i64(&self.value).ok_or(Error)?;
        let base: String = match val {
            -1 if self.exp == 0 => "-1".to_string(),
            -1 => "-".to_string(),
            1 if self.exp == 0 => "1".to_string(),
            1 => "".to_string(),
            _ => format!("{}", self.value),
        };

        let exp: String = match self.exp {
            0 => "".to_string(),
            1 => "x".to_string(),
            _ => format!("x^{}", self.exp),
        };

        write!(f, "{}{}", base, exp)
    }
}