// 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() {
        var char value;
        let value = Memory.peek(24576);

        if (value = 128) {
            return String.newLine();
        }

        if (value = 129) {
            return String.backSpace();
        }

        return value;
    }

    /**
     * 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, result;
        while (Keyboard.keyPressed() = 0) {}
        let key = Keyboard.keyPressed();
        while (~(Keyboard.keyPressed() = 0)) {}
        if (key = String.newLine()) {
            return key;
        }
        if (key = String.backSpace()) {
            return key;
        }
        do 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 String s;
        var char key, newline, backspace;
        var int i;
        let newline = String.newLine();
        let backspace = String.backSpace();
        let s = String.new(128);
        let key = 0;

        do Output.printString(message);
        let i = 0;
        while (~(key = newline)) {
            let key = Keyboard.readChar();
            if (key = newline) {
                do Output.println();
                return s;
            } else {
                if (key = backspace) {
                    if (i > 0) {
                        do s.eraseLastChar();
                        do Output.backSpace();
                        let i = i - 1;
                    }
                } else {
                    do s.appendChar(key);
                    let i = i + 1;
                }
            }
            // Prevent out of bound error.
            if (i = 128) {
                return s;
            }
        }
        return s;
    }

    function int textToInt(String s) {
        var int result, i, length, multiplier;
        var char c;
        var boolean isNegative, continue;
        let isNegative = false;
        let length = s.length();
        let i = 0;
        let result = 0;
        let multiplier = 1;

        if (length = 0) {
            return 0;
        }

        if (s.charAt(0) = 45) {
            let isNegative = true;
        }

        let i = length;
        while (true) { 
            let i = i - 1;
            let c = s.charAt(i);
            if ((s.charAt(i) > 47) & (s.charAt(i) < 58)) {
                let result = result + ((s.charAt(i) - 48) * multiplier);
                let multiplier =  multiplier * 10;
            } else {
                // could raise exception here;
            }

            if (isNegative) {
                if (i = 1) {
                    return -result;
                }
            } else {
                if (i = 0) {
                    return result;
                }
            }
        }
        return 0;
    }

    /**
     * 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 char key, newline, backspace;
        var int i;
        let newline = String.newLine();
        let backspace = String.backSpace();
        let s = String.new(128);
        let key = 0;

        do Output.printString(message);
        let i = 0;
        while (~(key = newline)) {
            let key = Keyboard.readChar();
            if (key = newline) {
                do Output.println();
            } else {
                if (key = backspace) {
                    if (i > 0) {
                        do s.eraseLastChar();
                        do Output.backSpace();
                        let i = i - 1;
                    }
                } else {
                    do s.appendChar(key);
                    let i = i + 1;
                }
            }
            // Prevent out of bound error.
            if (i = 128) {
                return s;
            }
        }
        let i = Keyboard.textToInt(s);
        do s.dispose();
        return i;
    }
}