macro_rules! then_inc {
    ($v:expr) => {{
        $v = $v.wrapping_add(1);
        $v as usize
    }};
}

pub struct ScratchDevice {
    memory: Vec<u8>,
    pub max_capacity: u32,
    pub pointer_1: u32,
    pub pointer_2: u32,
}

impl ScratchDevice {
    pub fn new() -> Self {
        Self {
            memory: Vec::new(),
            max_capacity: 16 * 65536,

            pointer_1: 0,
            pointer_2: 0,
        }
    }

    pub fn read_head_1(&mut self) -> u8 {
        let i = then_inc!(self.pointer_1);
        self.read_byte(i)
    }

    pub fn read_head_2(&mut self) -> u8 {
        let i = then_inc!(self.pointer_2);
        self.read_byte(i)
    }

    pub fn write_head_1(&mut self, value: u8) {
        let i = then_inc!(self.pointer_1);
        self.write_byte(i, value);
    }

    pub fn write_head_2(&mut self, value: u8) {
        let i = then_inc!(self.pointer_2);
        self.write_byte(i, value);
    }

    fn read_byte(&self, pointer: usize) -> u8 {
        match self.memory.get(pointer as usize) {
            Some(value) => *value,
            None => 0,
        }
    }

    fn write_byte(&mut self, pointer: usize, value: u8) {
        if pointer < self.max_capacity as usize {
            if pointer >= self.memory.len() {
                self.memory.resize(pointer + 1, 0);
            }
            self.memory[pointer] = value;
        }
    }
}