eceg431/12/Keyboard.jack

// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/12/Keyboard.jack
/**
 * A library for handling user input from the keyboard.
 */
class Keyboard {

    /** Initializes the keyboard. */
    function void init() {
        return;
    }

    /**
     * Returns the character of the currently pressed key on the keyboard;
     * if no key is currently pressed, returns 0.
     *
     * Recognizes all ASCII characters, as well as the following keys:
     * new line = 128 = String.newline()
     * backspace = 129 = String.backspace()
     * left arrow = 130
     * up arrow = 131
     * right arrow = 132
     * down arrow = 133
     * home = 134
     * End = 135
     * page up = 136
     * page down = 137
     * insert = 138
     * delete = 139
     * ESC = 140
     * F1 - F12 = 141 - 152
     */
    function char keyPressed() {
        return Memory.peek(24576);
    }

    /**	Waits until a key is pressed on the keyboard and released,
     *  then echoes the key to the screen, and returns the character
     *  of the pressed key. */
    function char readChar() {
        var char key;

        // Wait for key press
        while (Keyboard.keyPressed() = 0) {}

        let key = Keyboard.keyPressed();

        // Wait for release
        while (~(Keyboard.keyPressed() = 0)) {}

        // Echo (except backspace)
        if (key < 129) {
             // Handle newline specially for cleaner output?
             if (key = 128) {
                 do Output.println();
             } else {
                 do Output.printChar(key);
             }
        }
        // If key > 129 (arrows etc), printChar might print garbage or square.

        return key;
    }

    /**	Displays the message on the screen, reads from the keyboard the entered
     *  text until a newline character is detected, echoes the text to the screen,
     *  and returns its value. Also handles user backspaces. */
    function String readLine(String message) {
        var String s;
        var char c;

        do Output.printString(message);
        let s = String.new(64); // Assume max line 64

        while (true) {
            let c = Keyboard.readChar();

            if (c = 128) { // Newline
                do Output.println();
                return s;
            }

            if (c = 129) { // Backspace
                if (s.length() > 0) {
                    do s.eraseLastChar();
                    do Output.backSpace();
                    // Erase not supported by Output, so we print space and back up again?
                    // But printChar sends cursor forward.
                    // To visually erase: Backspace (move left), Print Space (overwrite, move right), Backspace (move left).
                    // My output implementation doesn't support 'erasing' naturally.
                    // But this trick works.
                     do Output.printChar(32); // Space
                     do Output.backSpace();
                }
            } else {
                do s.appendChar(c);
            }
        }
        return s;
    }

    /** Displays the message on the screen, reads from the keyboard the entered
     *  text until a newline character is detected, echoes the text to the screen,
     *  and returns its integer value (until the first non-digit character in the
     *  entered text is detected). Also handles user backspaces. */
    function int readInt(String message) {
        var String s;
        var int val;

        let s = Keyboard.readLine(message);
        let val = s.intValue();
        do s.dispose();

        return val;
    }
}