use std::{
    cmp::{Eq, Ord, Ordering, PartialEq, PartialOrd},
    convert::From,
    fmt,
    ops::{Add, Mul, Sub},
};

use crate::lisp::error::{EvalError, LispError};

#[derive(Debug, Copy, Clone)]
pub enum LispNumber {
    Integer(i64),
    Float(f64),
}

impl LispNumber {
    pub fn div(self, rhs: Self) -> Result<LispNumber, LispError> {
        use LispNumber::*;
        if rhs == Integer(0) || rhs == Float(0.) {
            Err(EvalError::DivByZero.into())
        } else {
            Ok(match (self, rhs) {
                (Integer(a), Integer(b)) => Float(a as f64 / b as f64),
                (Float(a), Integer(b)) => Float(a / b as f64),
                (Integer(a), Float(b)) => Float(a as f64 / b),
                (Float(a), Float(b)) => Float(a / b),
            })
        }
    }
    pub fn unwrap_integer(self) -> i64 {
        match self {
            Self::Integer(x) => x,
            Self::Float(x) => x.floor() as i64, // lossy
        }
    }
}

impl Add for LispNumber {
    type Output = Self;
    fn add(self, rhs: Self) -> Self::Output {
        use LispNumber::*;
        match (self, rhs) {
            (Integer(a), Integer(b)) => Integer(a + b),
            (Float(a), Integer(b)) => Float(a + b as f64),
            (Integer(a), Float(b)) => Float(a as f64 + b),
            (Float(a), Float(b)) => Float(a + b),
        }
    }
}

impl Sub for LispNumber {
    type Output = Self;
    fn sub(self, rhs: Self) -> Self::Output {
        use LispNumber::*;
        match (self, rhs) {
            (Integer(a), Integer(b)) => Integer(a - b),
            (Float(a), Integer(b)) => Float(a - b as f64),
            (Integer(a), Float(b)) => Float(a as f64 - b),
            (Float(a), Float(b)) => Float(a - b),
        }
    }
}

impl Mul for LispNumber {
    type Output = Self;
    fn mul(self, rhs: Self) -> Self::Output {
        use LispNumber::*;
        match (self, rhs) {
            (Integer(a), Integer(b)) => Integer(a * b),
            (Float(a), Integer(b)) => Float(a * b as f64),
            (Integer(a), Float(b)) => Float(a as f64 * b),
            (Float(a), Float(b)) => Float(a * b),
        }
    }
}

impl PartialEq for LispNumber {
    fn eq(&self, other: &Self) -> bool {
        use LispNumber::*;
        match (self, other) {
            (Integer(a), Integer(b)) => *a == *b,
            (Float(a), Integer(b)) => *a == *b as f64,
            (Integer(a), Float(b)) => *a as f64 == *b,
            (Float(a), Float(b)) => *a == *b,
        }
    }
}

impl Eq for LispNumber {}

impl Ord for LispNumber {
    fn cmp(&self, other: &Self) -> Ordering {
        use LispNumber::*;
        match (*self, *other) {
            (Integer(a), Integer(b)) => a.cmp(&b),
            (Float(a), Integer(b)) => (a as i64).cmp(&b),
            (Integer(a), Float(b)) => a.cmp(&(b as i64)),
            (Float(a), Float(b)) => (a as i64).cmp(&(b as i64)),
        }
    }
}

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

impl fmt::Display for LispNumber {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            LispNumber::Integer(v) => write!(f, "{}", v),
            LispNumber::Float(v) => write!(f, "{}", v),
        }
    }
}

impl From<i64> for LispNumber {
    fn from(target: i64) -> Self {
        LispNumber::Integer(target)
    }
}