// MatrixCheck tests to see if all of the rows of the matrix inputted have similar size columns
const matrixCheck = (matrix)=>{
  let columnNumb;
  for (let index = 0; index < matrix.length; index++){
    if (index == 0){
      columnNumb = matrix[index].length;
    } else if (matrix[index].length != columnNumb){
      console.log('The columns in this array are not equal')
    } else {
      return columnNumb;
    }
  }
}

// tests to see if the matrices have a like side, i.e. the row length on the first matrix matches the column length on the second matrix, or vise versa.
const twoMatricesCheck = (first, second)=>{
  const [firstRowLength, secondRowLength, firstColLength, secondColLength] = [first.length, second.length, matrixCheck(first), matrixCheck(second)];
    if (firstRowLength != secondColLength || secondRowLength != firstColLength){
      console.log('These matrices do not have a common side');
      return false;
    } else {
      return true;
    }
}

// returns an empty array that has the same number of rows as the left matrix being multiplied.
  //Uses Array.prototype.map() to loop over the first (or left) matrix and returns an empty array on each iteration.
const initiateEmptyArray = (first, second)=>{
  if (twoMatricesCheck(first, second)){
    const emptyArray = first.map(()=>{
      return [''];
    })
    return emptyArray;
  }else{
    return false;
  }
}

// Finally, `matrixMult` uses `Array.prototype.push()`, multiple layers of nested `for` loops, the addition assignment `+=` operator and multiplication operator `*` to perform the dot product between two matrices of differing sizes.
    // Dot product, takes the row of the first matrix and multiplies it by the column of the second matrix, the `twoMatricesCheck` tested to see if they were the same size already.
    // The dot product for each iteration is then saved to its respective index into `multMatrix`.
const matrixMult = (firstArray, secondArray)=>{
  let multMatrix = initiateEmptyArray(firstArray, secondArray);
  for (let rm = 0; rm < firstArray.length; rm++){
    rowMult = [];
    for (let col = 0; col < firstArray[0].length; col++){
      rowMult.push(firstArray[rm][col]);
    }
    for (let cm = 0; cm < firstArray.length; cm++){
      colMult = [];
      for (let row = 0; row < secondArray.length; row++){
        colMult.push(secondArray[row][cm]);
      }
      let newNumb = 0;
      for (let index = 0; index < rowMult.length; index++){
        newNumb += rowMult[index] * colMult[index];
      }
      multMatrix[rm][cm] = newNumb;
    }
  }
  return multMatrix;
}

const firstMatrix = [
  [1, 2],
  [3, 4]
];

const secondMatrix = [
  [5, 6],
  [7, 8]
];

console.log(matrixMult(firstMatrix, secondMatrix)); // [ [ 19, 22 ], [ 43, 50 ] ]

const thirdMatrix = [
  [-1, 4, 1],
  [7, -6, 2],
];
const fourthMatrix = [
  [2, -2],
  [5, 3],
  [3, 2],
];

console.log(matrixMult(thirdMatrix, fourthMatrix)); // [ [ 21, 16 ], [ -10, -28 ] ]