// 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 int key, key1;
        let key = 0;
        while (key = 0) {
            key = Memory.peek(24576);
        }
        key1 = key;
        while (key1 = key) {
            key1 = Memory.peek(24576);
        }
        Output.printChar(key);
        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 int c;
        var String s;
        let s = "";
        Output.printString(message);
        let c = Keyboard.readChar();
        while (~(c = 128)) {
            if (c = 129) {
                if (s.length() > 0) {
                    do s.eraseLastChar();
                }
            } else {
                do s.appendChar(c);
            }
            let c = Keyboard.readChar();
        }
        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 int n, i;
        var char t;
        var String s;
        let n = 0;
        let neg = false;
        let s = Keyboard.readLine("");
        let i = 0;
        if (s.charAt(0) = 45) {
            let i = 1;
            let neg = true;
        }
        let t = s.charAt(i);
        if ((t < 48) | (t > 57)) {
            do Sys.error(3);
            Output.printString("Keyboard.readInt: the input data is not number!");
        }
        let done = false;
        while (~done) {
            if ((s.charAt(i) > 47) & (s.charAt(i) < 58)) {
                n = n * 10 + (t - 48);
            } else {
                done = true;
            }
            let i = i + 1;
            done = done | (i < s.length());
        }
        if (neg) {
            n = - n;
        }
        return n;
    }
}