//! # Rusty Numbers
//!
//! Playin' with Numerics in Rust
#![forbid(unsafe_code)]

#[cfg_attr(tarpaulin, skip)]
pub mod bigint;
pub mod num;
pub mod rational;

/// Calculate a number in the fibonacci sequence,
/// using a lookup table for better worst-case performance.
///
/// Can calculate up to 186 using native unsigned 128 bit integers.
///
/// Example:
/// ```rust
/// use rusty_numbers::fibonacci;
///
/// let valid = fibonacci(45); // Some(1134903170)
/// # assert_eq!(1134903170, fibonacci(45).unwrap());
/// # assert!(valid.is_some());
///
/// let invalid = fibonacci(187); // None
/// # assert!(invalid.is_none());
/// ```
#[inline]
pub fn fibonacci(n: usize) -> Option<u128> {
    let mut table: Vec<u128> = vec![0, 1, 1, 2, 3, 5];

    _fibonacci(n, &mut table)
}

/// Actual calculating function for `fibonacci`
#[inline]
fn _fibonacci(n: usize, table: &mut Vec<u128>) -> Option<u128> {
    match table.get(n) {
        Some(x) => Some(*x),
        None => {
            let a = _fibonacci(n - 1, table)?;
            let b = _fibonacci(n - 2, table)?;

            // Check for overflow when adding
            let attempt = a.checked_add(b);

            if let Some(current) = attempt {
                table.insert(n, current);
            }

            attempt
        }
    }
}

/// Calculate a number in the fibonacci sequence,
/// using naive recursion
///
/// Can calculate up to 186 using native unsigned 128 bit integers.
#[inline]
pub fn rec_fibonacci(n: usize) -> Option<u128> {
    match n {
        0 => Some(0),
        1 => Some(1),
        n => {
            let a = rec_fibonacci(n - 1)?;
            let b = rec_fibonacci(n - 2)?;

            a.checked_add(b)
        },
    }
}

#[inline]
pub fn it_fibonacci(n: usize) -> Option<u128> {
    let mut a:u128 = 0;
    let mut b:u128 = 1;

    match n {
        0 => Some(a),
        1 => Some(b),
        _ => {
            for _ in 0..n-1 {
                let c: u128 = a.checked_add(b)?;

                a = b;
                b = c;
            }

            Some(b)
        }
    }
}

/// Calculate the value of a factorial,
/// using a lookup table for better worst-case performance.
///
/// Can calculate up to 34! using native unsigned 128 bit integers.
///
/// Example:
/// ```rust
/// use rusty_numbers::factorial;
///
/// let valid = factorial(3); // Some(6)
/// # assert_eq!(6, valid.unwrap());
///
/// let invalid = factorial(35); // None
/// # assert!(invalid.is_none());
/// ```
#[inline]
pub fn factorial(n: usize) -> Option<u128> {
    let mut table: Vec<u128> = vec![1, 1, 2];

    _factorial(n, &mut table)
}

/// Actual Calculation function for factoral
#[inline]
fn _factorial(n: usize, table: &mut Vec<u128>) -> Option<u128> {
    match table.get(n) {
        // Vec<T>.get returns a Option with a reference to the value,
        // so deref and wrap in Some() for proper return type
        Some(x) => Some(*x),
        None => {
            // The ? suffix passes along the Option value
            // to be handled later
            // See: https://doc.rust-lang.org/reference/expressions/operator-expr.html#the-question-mark-operator
            let prev = _factorial(n - 1, table)?;

            // Do an overflow-checked multiply
            let attempt = (n as u128).checked_mul(prev);

            // If there isn't an overflow, add the result
            // to the calculation table
            if let Some(current) = attempt {
                table.insert(n, current);
            }

            attempt // Some(x) if no overflow
        }
    }
}

/// Calculate the value of a factorial using recursion
///
/// Can calculate up to 34! using native unsigned 128 bit integers.
#[inline]
pub fn rec_factorial(n: usize) -> Option<u128> {
    match n {
        0 => Some(1u128),
        1 => Some(1u128),
        _ => {
            let prev = rec_factorial(n - 1)?;

            (n as u128).checked_mul(prev)
        }
    }
}

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

    #[test]
    fn test_factorial() {
        assert_eq!(1, factorial(0).unwrap());
        assert_eq!(1, factorial(1).unwrap());
        assert_eq!(6, factorial(3).unwrap());

        let res = factorial(34);
        let res2 = rec_factorial(34);
        assert!(res.is_some());
        assert_eq!(res.unwrap(), res2.unwrap());

        let res = factorial(35);
        assert!(res.is_none());
    }

    #[test]
    fn test_fibonacci() {
        assert_eq!(0, fibonacci(0).unwrap());
        assert_eq!(1, fibonacci(1).unwrap());
        assert_eq!(1, fibonacci(2).unwrap());

        let res = fibonacci(186);
        let res2 = it_fibonacci(186);
        assert!(res.is_some());
        assert!(res2.is_some());
        assert_eq!(res.unwrap(), res2.unwrap());

        let res = fibonacci(187);
        assert!(res.is_none());
    }
}