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use super::SparseMatrix;
use crate::number::Number;
use std::ops::Mul;

fn mul<T>(slf: &SparseMatrix<T>, rhs: &SparseMatrix<T>) -> SparseMatrix<T>
where
  T: Number,
{
  if slf.cols != rhs.rows {
    panic!("Dimension mismatch.");
  }
  let mut new_matrix = SparseMatrix::new(slf.rows, rhs.cols);

  for (&(i, j), &s) in slf.elems.iter() {
    for (&(_, k), &r) in rhs.elems.iter().filter(|&(&(jr, _), _)| j == jr) {
      let sr = s * r;
      if sr == T::default() {
        continue;
      }

      *new_matrix.elems.entry((i, k)).or_insert(T::default()) += sr;
    }
  }

  new_matrix
}

impl<T> Mul<SparseMatrix<T>> for SparseMatrix<T>
where
  T: Number,
{
  type Output = SparseMatrix<T>;

  fn mul(self, rhs: SparseMatrix<T>) -> Self::Output {
    mul(&self, &rhs)
  }
}

impl<T> Mul<&SparseMatrix<T>> for SparseMatrix<T>
where
  T: Number,
{
  type Output = SparseMatrix<T>;

  fn mul(self, rhs: &SparseMatrix<T>) -> Self::Output {
    mul(&self, rhs)
  }
}

impl<T> Mul<SparseMatrix<T>> for &SparseMatrix<T>
where
  T: Number,
{
  type Output = SparseMatrix<T>;

  fn mul(self, rhs: SparseMatrix<T>) -> Self::Output {
    mul(self, &rhs)
  }
}

impl<T> Mul<&SparseMatrix<T>> for &SparseMatrix<T>
where
  T: Number,
{
  type Output = SparseMatrix<T>;

  fn mul(self, rhs: &SparseMatrix<T>) -> Self::Output {
    mul(self, rhs)
  }
}