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use std::default::Default;
use std::ops::{Add, AddAssign, Div, Mul};
//use std::iter::Product;

mod tests;

pub struct Matrix<T> {
    r: usize,
    c: usize,
    buf: Vec<T>,
}

impl<T> Matrix<T>
where
    T: Copy + Add<Output = T> + Div<Output = T>,
{
    // Accepts the row and the column size of the matrix
    // and the data vector (of which it takes ownership) as parameters
    pub fn new(r: usize, c: usize, v: Vec<T>) -> Matrix<T> {
        assert_eq!(r * c, v.len(), "Matrix dimensions and data size differ");

        Matrix { r, c, buf: v }
    }

    // Same as self::new() but does not take ownership
    // of the data vector
    pub fn from_vec(r: usize, c: usize, v: &Vec<T>) -> Matrix<T> {
        assert_eq!(r * c, v.len(), "Matrix dimensions and data size differ");

        Matrix {
            r,
            c,
            buf: v.clone(),
        }
    }

    pub fn rows(&self) -> usize {
        self.r
    }

    pub fn cols(&self) -> usize {
        self.c
    }

    // Returns the element at the r-th row and c-th column,
    // provided those are within bounds
    pub fn at(&self, r: usize, c: usize) -> &T {
        assert!(r < self.r && c < self.c, "Out of bounds");

        &self.buf[r * self.c + c]
    }

    pub fn at_mut(&mut self, r: usize, c: usize) -> &mut T {
        &mut self.buf[r * self.c + c]
    }

    // TODO: implement this
    // pub fn determinant(&self) -> T {
    //     assert_eq!(self.r, self.c, "Matrix is not square");

    //     let mut v = self.buf.clone();

    //     for i in 0..self.r {
    //         for j in i + 1..self.r {

    //         }
    //     }

    //     self.diagonal()
    //         .iter()
    //         .fold(1, |l, r| l * r)
    // }

    // Returns a reference to the matrix data vector
    pub fn data(&self) -> &Vec<T> {
        &self.buf
    }

    // Map over the elements of the matrix
    pub fn map<U, F>(&self, f: F) -> Matrix<U>
    where
        U: Copy + Add<Output = U> + Div<Output = U>,
        F: Fn(&T) -> U,
    {
        let new_v = self.buf.iter().map(f).collect();

        Matrix::new(self.r, self.c, new_v)
    }

    // Get the diagonal of an 'm x m' matrix
    pub fn diagonal(&self) -> Vec<T> {
        self.check_square();

        self.buf
            .iter()
            .zip(0..self.buf.len())
            .filter(|(_, i)| i % self.c == i / self.r)
            .map(|(&elem, _)| elem)
            .collect()
    }

    fn check_square(&self) {
        assert_eq!(self.r, self.c, "Matrix is not square");
    }
}

// Matrix addition works with references to the matrices
// as to not take ownership
impl<'a, T> Add<&'a Matrix<T>> for &'a Matrix<T>
where
    T: Copy + Add<Output = T> + Div<Output = T>,
{
    type Output = Matrix<T>;

    fn add(self, other: Self) -> Self::Output {
        assert!(
            self.r == other.rows() && self.c == other.cols(),
            "Matrices are not of the same size"
        );

        let new_v = self
            .buf
            .iter()
            .zip(other.data())
            .map(|(&x, &y)| x + y)
            .collect();

        Matrix::new(self.r, self.c, new_v)
    }
}

impl<'a, T> Mul<&'a Matrix<T>> for &'a Matrix<T>
where
    T: Copy + Add<Output = T> + AddAssign<T> + Mul<Output = T> + Div<Output = T> + Default,
{
    type Output = Matrix<T>;

    fn mul(self, other: Self) -> Self::Output {
        assert_eq!(self.c, other.r);

        let mut v: Vec<T> = vec![Default::default(); self.r * other.c];

        for i in 0..self.r {
            for j in 0..other.c {
                for k in 0..self.c {
                    v[i * self.r + j] += self.buf[i * self.c + k] * other.buf[k * other.c + j];
                }
            }
        }

        Matrix::new(self.r, other.c, v)
    }
}