//File: Matrix.java
//Name: Trai Pham
//Date: 01/30/2020
//Course: CSE 8B
//This code would allow you to manipulate matrix/matrices, in which you can
//set elements of a matrix, add matrices together, multiple matrices, or
//transpose a matrix.


//#file header: this file contains the Matrix code and Matrixtester
//#class header: this class does a lot to an object matrix and it has methods
//that are able to manipulate the matrics




public class Matrix{
  private int row;
  private int column;
  private int[][] arr;
  private static final String ADD_ERROR = "Matrices cannot be added";
  private static final String MULTIPLY_ERROR = "Matrices cannot be multiplied";

//Constructor Method
  public Matrix(){
    row = 0;
    column = 0;
    arr = null;
  }
//Assigning the row and column to Matrix
/**
* @param int row and col
* @return Matrix object
*/
  public Matrix(int row, int column){
    this.row = row;
    this.column = column;

    if(row < 0 || column < 0){
      this.row = 0;
      this.column = 0;
      this.arr = null;
    }
    else{
      this.arr= new int[this.row][this.column];
    }
    return;
  }
//Create a deep copy of Matrix
/**
* @param Matrix object
* @return Matrix
*/
  public Matrix(Matrix mat){

    this.row = mat.row;
    this.column = mat.column;
    this.arr = new int[mat.row][mat.column];
//array of matrix has the same number of rows and Columns
//as the original
    for(int i = 0; i < mat.row; i++ ){
      for(int j = 0; j < mat.column; j++){
        this.arr[i][j] = mat.arr[i][j];
      }
    }
}
//Set the value for a Matrix at a specific index (r,c)
/**
* @param int r,c, element
* @return boolean
*/
    public boolean setElement(int r, int c, int element){
//invalid input/matrices
      if(r >= this.row){
        return false;
      }
      else if(c >= this.column){
        return false;
      }
      else if(r< 0){
        return false;
      }
      else if(c < 0){
        return false;
      }
  //assigning value to specific index
      else{
        this.arr[r][c] = element;
        return true;
      }
    }
//gets the Element/value of a Matrix at a specific index
/**
* @param int r,c
* @return Integer
*/
    public Integer getElement(int r, int c) {
//invalid inputs/matrices
      if(r >= this.row || c >= this.column || r < 0 || c < 0){
        return null;
      }
      else{
        return this.arr[r][c];
      }
    }
//Gets the row of the matrix
    public int getRows(){
      return this.row;
    }
//Gets the column of the matrix
    public int getColumns(){
      return this.column;
    }
//Convert a matrix that contains integers into a string
//This would help you print the matrix
/**
* @param void
* @return string
*/
    @Override
    public String toString(){
      String str = "";//declares and initialize a String variable

      for(int i = 0; i < this.row; i++){
        for( int j = 0; j < this.column; j++){
          str += (this.arr[i][j] + " " );
  //this would print a new line when you reach the end of column
          if( j >= this.column - 1){
            str += "\n";
          }
        }
      }
      return str;
    }
//This would let you add two matrices together
/**
* @param Matrix object
* @return Matrix
*/
    public Matrix add(Matrix y){
  // invalid inputs/matrices
      if( y == null){
        return null;
      }
      else if( this.arr == null){
        return null;
      }
      Matrix a = new Matrix(y);
//create a new Matrix to get the sum of values at specific index
      if( y.row == this.row && y.column == this.column){
        for( int i = 0; i < this.row; i++){
          for( int j = 0; j < this.column; j++){
            a.arr[i][j] = y.arr[i][j] + this.arr[i][j];
          }
        }
        return a;
      }
      else{
        System.out.println(ADD_ERROR);
        return null;
      }
    }
//This would let you multiply two matrices based on the multiplication
//rules of matrices, and you'll get the product of those two matrices
/**
* @param Matrix object
* @return Matrix
*/
    public Matrix multiply(Matrix y){
//null matrices
      if(y == null){//Null Matrix
        return null;
      }
      else if (this.column != y.getRows()){//Error message
        System.out.println(MULTIPLY_ERROR);
        return null;
      }
  //the new matrix should have the row of the first matrix, and
  //the column numbers of the called matrix
      Matrix newMat = new Matrix(this.row, y.getColumns());
      if(this.column == y.row){
        for( int i = 0; i < newMat.row; i++){//Get row of new Matrix
          for(int j = 0; j < newMat.column; j++){ //Get the column of new Matrix
            int num = 0;
            for(int a = 0; a < this.column; a++){
              num += (this.arr[i][a] * y.arr[a][j]); // this would get you
              //the sum when you multiply column of first matrix to row of
              //second matrix
            }
            newMat.arr[i][j] = num;
          }
        }
        return newMat;
      }
      else{
        return null;
      }
    }
//This would flip the rows and columns of a Matrix, though keeping
//the same value
/**
* @param void
* @return Matrix
*/
    public Matrix transpose (){
      Matrix tranMat = new Matrix(this.column, this.row);
      for(int i = 0; i < this.column; i++){
        for(int j = 0; j < this.row; j++){
//flip the rows and the columns in order to efficiently transpose
          tranMat.arr[i][j] = this.arr[j][i];
        }

      }
      return tranMat;
    }

}