import java.util.Scanner;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

public class MatrixMultiplication {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Choose an option:");
        System.out.println("1. Input matrices manually");
        System.out.println("2. Read matrices from a text file");
        int option = scanner.nextInt();

        int[][] matrixA, matrixB;

        if (option == 1) {
            matrixA = inputMatrix("first");
            matrixB = inputMatrix("second");
        } else if (option == 2) {
            matrixA = readMatrixFromFile("matrixA.txt");
            matrixB = readMatrixFromFile("matrixB.txt");
        } else {
            System.out.println("Invalid option. Exiting program.");
            return;
        }

        if (matrixA == null || matrixB == null) {
            System.out.println("Error in reading matrices. Exiting program.");
            return;
        }

        int rowsA = matrixA.length;
        int colsA = matrixA[0].length;
        int rowsB = matrixB.length;
        int colsB = matrixB[0].length;

        if (colsA != rowsB) {
            System.out.println("Error: The number of columns in the first matrix must be equal to the number of rows in the second matrix.");
            return;
        }

        // Perform matrix multiplication
        int[][] resultMatrix = multiplyMatrices(matrixA, matrixB);

        // Display the result
        System.out.println("Result of matrix multiplication:");
        displayMatrix(resultMatrix);

        // Save the result to a text file
        saveMatrixToFile(resultMatrix, "resultMatrix.txt");
    }

    // Function to input matrix from the user
    private static int[][] inputMatrix(String name) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter the number of rows for the " + name + " matrix: ");
        int rows = scanner.nextInt();
        System.out.print("Enter the number of columns for the " + name + " matrix: ");
        int cols = scanner.nextInt();

        if (rows <= 0 || cols <= 0) {
            System.out.println("Error: Matrix dimensions must be positive.");
            return null;
        }

        int[][] matrix = new int[rows][cols];

        System.out.println("Enter the elements for the " + name + " matrix:");
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                System.out.print("Element at position (" + (i + 1) + ", " + (j + 1) + "): ");
                matrix[i][j] = scanner.nextInt();
            }
        }

        return matrix;
    }

    // Function to read matrix from a text file
    private static int[][] readMatrixFromFile(String filename) {
        try {
            Scanner fileScanner = new Scanner(new File(filename));
            int rows = fileScanner.nextInt();
            int cols = fileScanner.nextInt();

            if (rows <= 0 || cols <= 0) {
                System.out.println("Error: Matrix dimensions must be positive.");
                return null;
            }

            int[][] matrix = new int[rows][cols];

            for (int i = 0; i < rows; i++) {
                for (int j = 0; j < cols; j++) {
                    if (fileScanner.hasNextInt()) {
                        matrix[i][j] = fileScanner.nextInt();
                    } else {
                        System.out.println("Error: Insufficient data in the file.");
                        return null;
                    }
                }
            }

            fileScanner.close();
            return matrix;
        } catch (IOException e) {
            System.out.println("Error: File not found or cannot be read.");
            return null;
        }
    }

    // Function to multiply two matrices
    private static int[][] multiplyMatrices(int[][] matrixA, int[][] matrixB) {
        int rowsA = matrixA.length;
        int colsA = matrixA[0].length;
        int colsB = matrixB[0].length;

        int[][] resultMatrix = new int[rowsA][colsB];

        for (int i = 0; i < rowsA; i++) {
            for (int j = 0; j < colsB; j++) {
                for (int k = 0; k < colsA; k++) {
                    resultMatrix[i][j] += matrixA[i][k] * matrixB[k][j];
                }
            }
        }

        return resultMatrix;
    }

    // Function to display a matrix
    private static void displayMatrix(int[][] matrix) {
        for (int[] row : matrix) {
            for (int value : row) {
                System.out.print(value + " ");
            }
            System.out.println();
        }
    }

    // Function to save a matrix to a text file
    private static void saveMatrixToFile(int[][] matrix, String filename) {
        try {
            FileWriter writer = new FileWriter(filename);

            writer.write(matrix.length + " " + matrix[0].length + "\n");

            for (int[] row : matrix) {
                for (int value : row) {
                    writer.write(value + " ");
                }
                writer.write("\n");
            }

            writer.close();
            System.out.println("Result matrix saved to " + filename);
        } catch (IOException e) {
            System.out.println("Error: Unable to save result matrix to file.");
        }
    }
}