Arraylist - Text File Reader - C# Programming Exercise

// Importing necessary namespaces for file handling and console manipulation
using System;  // For basic input/output and handling console operations
using System.Collections;  // To use ArrayList for dynamic list handling
using System.IO;  // For file input/output operations

class Program
{
    // The list to store the lines from the text file
    static ArrayList lines = new ArrayList();  // ArrayList to hold all the lines from the text file
    // The current position (index of the first line to be shown)
    static int currentLineIndex = 0;  // Keeps track of the current position in the file

    // Method to read the file and store its lines in the 'lines' ArrayList
    static void ReadFile(string filePath)
    {
        // Try to open and read the file
        try
        {
            // Read all lines from the text file and store them in the ArrayList
            string[] fileLines = File.ReadAllLines(filePath);
            lines.AddRange(fileLines);  // Add all lines to the 'lines' ArrayList
        }
        catch (Exception ex)
        {
            // Display error if the file cannot be read
            Console.WriteLine("Error reading file: " + ex.Message);  // Show error message if file can't be read
        }
    }

    // Method to show the menu and set up the display
    static void ShowMenu()
    {
        // Clear the console screen
        Console.Clear();  // Clears the console screen for refreshing the display
        
        // Set up background and foreground colors for the menu
        Console.BackgroundColor = ConsoleColor.Black;  // Set background color to black
        Console.ForegroundColor = ConsoleColor.White;  // Set text color to white

        // Set the cursor to the top row (row 1)
        Console.SetCursorPosition(0, 0);  // Move cursor to the top-left corner of the console
        
        // Display a simple header
        Console.WriteLine("Text File Reader - Use UP/DOWN arrows to navigate, ESC to exit.");  // Display instructions at the top
    }

    // Method to show the 21 lines starting from the current index
    static void ShowFrom(int startLineIndex)
    {
        // Ensure we don't go beyond the file's end
        int endLineIndex = Math.Min(startLineIndex + 21, lines.Count);  // Calculate the end line index based on current position

        // Display lines from the 'lines' array starting from 'startLineIndex'
        for (int i = startLineIndex; i < endLineIndex; i++)
        {
            // Adjust cursor position to display lines one by one starting from row 2 (skip the header)
            Console.SetCursorPosition(0, i - startLineIndex + 2);  // Set the cursor position dynamically for each line
            Console.WriteLine(lines[i]);  // Display the current line
        }
    }

    // Main method to execute the program logic
    static void Main(string[] args)
    {
        // Ask the user for the file path
        Console.Write("Enter the file path: ");  // Prompt the user for the file path
        string filePath = Console.ReadLine();  // Read the user input as the file path

        // Read the file contents
        ReadFile(filePath);  // Call ReadFile method to load the file into memory

        // Main program loop to handle navigation and display
        while (true)
        {
            // Show the menu and the lines from the current position
            ShowMenu();  // Call ShowMenu to display the navigation instructions
            ShowFrom(currentLineIndex);  // Call ShowFrom to display the lines starting from currentLineIndex

            // Get user input for navigation
            var key = Console.ReadKey(true).Key;  // Read key input without echoing to console

            // If the ESC key is pressed, break out of the loop and exit
            if (key == ConsoleKey.Escape)
            {
                break;  // Exit the program if ESC is pressed
            }
            // If the DOWN arrow key is pressed, move to the next 21 lines (if possible)
            else if (key == ConsoleKey.DownArrow)
            {
                if (currentLineIndex + 21 < lines.Count)  // Check if there are more lines to show
                {
                    currentLineIndex += 21;  // Move the index forward by 21 lines
                }
            }
            // If the UP arrow key is pressed, move to the previous 21 lines (if possible)
            else if (key == ConsoleKey.UpArrow)
            {
                if (currentLineIndex - 21 >= 0)  // Ensure we don't move past the beginning of the file
                {
                    currentLineIndex -= 21;  // Move the index backward by 21 lines
                }
            }
        }

        // Exiting the program
        Console.WriteLine("\nProgram terminated.");  // Inform the user that the program has ended
    }
}