#![allow(unused_variables)]
//! \[WIP\] Arbitrarily large integers
use crate::num::Sign::*;
use crate::num::*;
use core::ops::{
    Add, AddAssign, Div, DivAssign, Mul, MulAssign, Neg, Not, Rem, RemAssign, Sub, SubAssign,
};
use core::usize;
use std::convert::TryInto;

#[derive(Clone, Debug, PartialEq)]
pub struct BigInt {
    inner: Vec<usize>,
    sign: Sign,
}

impl Default for BigInt {
    fn default() -> Self {
        Self {
            inner: vec![0],
            sign: Sign::default(),
        }
    }
}

impl From<usize> for BigInt {
    fn from(n: usize) -> Self {
        Self {
            inner: vec![n],
            sign: Sign::default(),
        }
    }
}

impl From<&str> for BigInt {
    fn from(s: &str) -> Self {
        Self::from_str_radix(s, 10)
    }
}

impl From<String> for BigInt {
    fn from(s: String) -> Self {
        Self::from_str_radix(s, 10)
    }
}

impl BigInt {
    /// Create a new Bigint, of value 0
    ///
    /// The various `From` implementations are more useful in most cases
    pub fn new() -> Self {
        Self::default()
    }

    fn new_empty() -> Self {
        Self {
            inner: Vec::new(),
            sign: Sign::Positive,
        }
    }

    /// Create a new BigInt, with the specified inner capacity
    pub fn with_capacity(size: usize) -> Self {
        Self {
            inner: Vec::with_capacity(size),
            sign: Positive,
        }
    }

    /// Remove digits that are zero from the internal representation.
    ///
    /// Similar to 007 -> 7 in base 10
    pub fn trim_zeros(&mut self) {
        let current_len = self.inner.len();
        if current_len < 2 {
            return;
        }

        let mut trailing_zeros = 0usize;
        for val in self.inner.iter().rev() {
            if *val != 0 {
                break;
            }

            trailing_zeros += 1;
        }

        // Always keep at least one digit
        if trailing_zeros == current_len {
            trailing_zeros -= 1;
        }

        let new_len = current_len - trailing_zeros;

        self.inner.truncate(new_len);
    }

    /// Remove unused digits, and shrink the internal vector
    pub fn shrink_to_fit(&mut self) {
        self.trim_zeros();
        self.inner.shrink_to_fit();
    }

    /// Convert a `&str` or a `String` representing a number in the specified radix to a Bigint.
    ///
    /// For radix 10, use the `from` associated function instead.
    pub fn from_str_radix<T: ToString>(s: T, radix: usize) -> BigInt {
        todo!();
    }

    fn get_digit_count(a: &Self, b: &Self) -> usize {
        let a_digits = a.inner.len();
        let b_digits = b.inner.len();

        let digits = if b_digits > a_digits {
            b_digits
        } else {
            a_digits
        };

        if digits > 0 {
            digits
        } else {
            1
        }
    }
}

impl Add for BigInt {
    type Output = Self;

    // @TODO: handle signs
    fn add(self, rhs: Self) -> Self::Output {
        if self.sign == Positive && rhs.sign == Negative {
            return self - -rhs;
        }

        let digits = Self::get_digit_count(&self, &rhs) + 1;
        let mut out = BigInt::with_capacity(digits);

        let mut carry = 0usize;
        for i in 0..digits {
            let a = *self.inner.get(i).unwrap_or(&0usize);
            let b = *rhs.inner.get(i).unwrap_or(&0usize);

            let (res, overflowed) = a.overflowing_add(b);
            if res == 0 && !overflowed {
                out.inner.push(res + carry);
                carry = 0;
                continue;
            }

            if overflowed {
                out.inner.push(res + carry);
                carry = 1;
            } else if res < core::usize::MAX {
                out.inner.push(res + carry);
                carry = 0;
            } else {
                out.inner.push(0usize);
                carry = 1;
            }
        }

        out.trim_zeros();

        out
    }
}

impl Sub for BigInt {
    type Output = Self;

    // @TODO: handle signs
    fn sub(self, rhs: Self) -> Self::Output {
        let digits = Self::get_digit_count(&self, &rhs);
        let mut out = BigInt::with_capacity(digits);

        let mut borrow = 0usize;
        for i in 0..digits {
            let a = *self.inner.get(i).unwrap_or(&0usize);
            let b = *rhs.inner.get(i).unwrap_or(&0usize);

            if a >= borrow && (a - borrow) >= b {
                let res = a - b - borrow;

                out.inner.push(res);
                borrow = 0;
            } else {
                // To prevent subtraction overflow, the max borrowed
                // value is usize::MAX. The rest of the borrowed value
                // will be added on afterwords.
                // In base ten, this would be like:
                // 18 - 9 = 9-9 + 9
                let rem = (a + 1) - borrow;
                let res = (core::usize::MAX - b) + rem;
                out.inner.push(res);

                borrow = 1;
            }
        }

        out.trim_zeros();

        out
    }
}

impl Mul for BigInt {
    type Output = Self;

    fn mul(self, rhs: Self) -> Self::Output {
        // Multiplication can result in twice the number of digits
        let digits = Self::get_digit_count(&self, &rhs) * 2;
        let mut out = BigInt::with_capacity(digits);

        let mut carry = 0usize;
        for i in 0..digits {
            let a = *self.inner.get(i).unwrap_or(&0usize);
            let b = *rhs.inner.get(i).unwrap_or(&0usize);

            if a == 0 || b == 0 {
                out.inner.push(0);
                continue;
            }

            let (res, overflowed) = a.overflowing_mul(b);

            if overflowed {
                todo!()
            } else {
                match res.checked_add(carry) {
                    Some(res) => {
                        out.inner.push(res);
                        carry = 0;
                    }
                    None => {
                        // Well, we have to deal with overflow again
                        todo!();
                    }
                }
            }
        }

        out.trim_zeros();

        out
    }
}

impl Div for BigInt {
    type Output = Self;

    fn div(self, rhs: Self) -> Self::Output {
        todo!()
    }
}

impl Rem for BigInt {
    type Output = Self;

    fn rem(self, rhs: Self) -> Self::Output {
        todo!()
    }
}

impl AddAssign for BigInt {
    fn add_assign(&mut self, rhs: Self) {
        *self = self.clone() + rhs;
    }
}

impl SubAssign for BigInt {
    fn sub_assign(&mut self, rhs: Self) {
        *self = self.clone() - rhs;
    }
}

impl MulAssign for BigInt {
    fn mul_assign(&mut self, rhs: Self) {
        *self = self.clone() * rhs;
    }
}

impl DivAssign for BigInt {
    fn div_assign(&mut self, rhs: Self) {
        *self = self.clone() / rhs;
    }
}

impl RemAssign for BigInt {
    fn rem_assign(&mut self, rhs: Self) {
        *self = self.clone() % rhs;
    }
}

impl Neg for BigInt {
    type Output = Self;

    /// Flip the sign of the current `BigInt` value
    fn neg(mut self) -> Self::Output {
        self.sign = !self.sign;

        self
    }
}

impl Not for BigInt {
    type Output = Self;

    /// Do a bitwise negation of every digit's value
    fn not(self) -> Self::Output {
        let mut flipped: Vec<usize> = Vec::with_capacity(self.inner.len());

        for val in self.inner.iter() {
            let rev = !*val;
            flipped.push(rev);
        }

        BigInt {
            sign: self.sign,
            inner: flipped,
        }
    }
}

macro_rules! impl_from_smaller {
    ($(($s: ty, $u: ty)),* ) => {
        $(
            impl From<$s> for BigInt {
                /// Create a `BigInt` from a signed integer primitive
                fn from(n: $s) -> Self {
                    let sign = if n < 0 { Sign::Negative } else { Sign::Positive };
                    let n = n.abs();
                    let raw: usize = <$s>::try_into(n).unwrap();

                    Self {
                        inner: vec![raw],
                        sign,
                    }
                }
            }

            impl From<$u> for BigInt {
                /// Create a `BigInt` from an unsigned integer primitive
                fn from(n: $u) -> Self {
                    let mut new = Self::new_empty();
                    new.inner.push(n as usize);

                    new
                }
            }
        )*
    }
}

macro_rules! impl_from_larger {
    ($(($s: ty, $u: ty)),* ) => {
        $(
            impl From<$s> for BigInt {
                /// Create a `BigInt` from a signed integer primitive
                fn from(n: $s) -> Self {
                    todo!();
                }
            }

            impl From<$u> for BigInt {
                /// Create a `BigInt` from an unsigned integer primitive
                fn from(n: $u) -> Self {
                    use core::usize::MAX;

                    let base_usize_value = n / MAX as $u;
                    let rem = n % MAX as $u;

                    if base_usize_value == 0 {
                        Self::from(rem as usize)
                    } else {
                        todo!();
                    }
                }
            }
        )*
    };
}

#[cfg(target_pointer_width = "32")]
impl_from_larger!((i64, u64), (i128, u128));
#[cfg(target_pointer_width = "32")]
impl_from_smaller!((i8, u8), (i16, u16), (i32, u32));
#[cfg(target_pointer_width = "32")]
static BITS: usize = 32;

#[cfg(target_pointer_width = "64")]
impl_from_larger!((i128, u128));
#[cfg(target_pointer_width = "64")]
impl_from_smaller!((i8, u8), (i16, u16), (i32, u32), (i64, u64));
#[cfg(target_pointer_width = "64")]
static BITS: usize = 64;

#[cfg(test)]
#[cfg_attr(tarpaulin, skip)]
mod tests {
    use super::*;

    #[test]
    fn sanity_checks() {
        let int = BigInt::from(45u8);
        assert_eq!(int.inner[0], 45usize)
    }

    #[test]
    fn test_trim_zeros() {
        let mut lotsoftrailing = BigInt {
            inner: vec![1, 0, 0, 0, 0, 0, 0, 0, 0],
            sign: Positive,
        };

        lotsoftrailing.trim_zeros();

        assert_eq!(BigInt::from(1), lotsoftrailing);
    }

    #[test]
    fn test_add() {
        // MAX is 2^Bitsize - 1,
        // so the sum should be
        // [MAX -1, 1]
        // Compare base 10: 9 + 9 = 18
        let a = BigInt::from(core::usize::MAX);
        let b = BigInt::from(core::usize::MAX);

        let sum = a + b;

        assert_eq!(
            sum.inner[0],
            core::usize::MAX - 1,
            "least significant place should be MAX - 1"
        );
        assert_eq!(sum.inner[1], 1usize, "most significant place should be 1");

        let a = BigInt::from(core::usize::MAX);
        let b = BigInt::from(1usize);
        let sum = a + b;
        assert_eq!(sum.inner[0], 0usize);
        assert_eq!(sum.inner[1], 1usize);
    }

    #[test]
    fn test_sub() {
        let a = BigInt::from(core::usize::MAX);
        let b = BigInt::from(core::u16::MAX);

        let diff = a - b;
        assert_eq!(
            diff.clone().inner[0],
            core::usize::MAX - core::u16::MAX as usize
        );
        assert_eq!(diff.inner.len(), 1);
    }

    #[test]
    fn test_sub_borrow() {
        let a = BigInt {
            inner: vec![0, 1],
            sign: Positive,
        };

        let b = BigInt::from(2);
        let diff = a - b;
        assert_eq!(diff.clone().inner.len(), 1, "{:#?}", diff.clone());
        assert_eq!(diff.inner[0], core::usize::MAX - 1);
    }

    #[test]
    fn test_sub_assign() {
        let mut a = BigInt {
            inner: vec![1, 0, 1],
            sign: Positive,
        };
        let b = BigInt::from(2);

        a -= b;

        assert_eq!(a.inner, vec![core::usize::MAX, core::usize::MAX]);
    }

    #[test]
    fn test_zeros() {
        let a = BigInt::new();
        let b = BigInt::new();

        let c = a.clone() - b.clone();
        assert_eq!(a.clone(), b.clone());
        assert_eq!(c, a.clone());

        let c = a.clone() + b.clone();
        assert_eq!(a.clone(), b.clone());
        assert_eq!(c, a.clone());
    }

    #[test]
    fn test_not() {
        let a = BigInt::from(0u8);
        let b = !a;

        assert_eq!(b.inner[0], core::usize::MAX);
    }

    #[test]
    fn test_add_assign() {
        let mut a = BigInt::from(core::usize::MAX);
        let b = BigInt::from(core::usize::MAX);

        a += b;

        assert_eq!(
            a.inner[0],
            core::usize::MAX - 1,
            "least significant place should be MAX - 1"
        );
        assert_eq!(a.inner[1], 1usize, "most significant place should be 1");
    }

    #[test]
    fn test_from() {
        // Signed numbers
        assert_eq!(-BigInt::from(2), BigInt::from(-2));

        // Larger than usize
        assert_eq!(BigInt::from(45u128), BigInt::from(45usize));
    }
}