#![no_std]
#![no_main]

use core::panic::PanicInfo;
use riscv_rt::entry;

#[panic_handler]
fn panic_handler(_info: &PanicInfo) -> ! {
    unsafe {
        OUTPUT.write_volatile(0xDEADC0DE);
    }
    loop {}
}

const OUTPUT: *mut u32 = 0x2000_0000 as *mut u32;
const BTNS: *mut u8 = 0x2000_0008 as *mut u8;
const SCREEN: *mut u32 = 0x2000_0080 as *mut u32;

#[entry]
fn main() -> ! {
    let mut playerA: u8 = 1;
    let mut playerB: u8 = 1;
    let mut ballX: i8 = 16;
    let mut ballY: i8 = 16;
    let mut ballXvel: i8 = 1;

    let mut vram: [u32; 32] = [0; 32];

    vram[playerA as usize] |= 1 << 31;
    vram[playerB as usize] |= 1;
    vram[ballY as usize] |= 1 << ballX;

    loop {
        let btns;
        unsafe {
            btns = BTNS.read_volatile();
        }

        // left up
        if btns & (1 << 7) > 0 {
            vram[playerA as usize] &= !(1 << 31);
            playerA -= 1;
            vram[playerA as usize] |= 1 << 31;
        }
        // left down
        if btns & (1 << 5) > 0 {
            vram[playerA as usize] &= !(1 << 31);
            playerA += 1;
            vram[playerA as usize] |= 1 << 31;
        }

        // right up
        if btns & (1 << 3) > 0 {
            vram[playerB as usize] &= !1;
            playerB -= 1;
            vram[playerB as usize] |= 1;
        }
        // right down
        if btns & (1 << 1) > 0 {
            vram[playerB as usize] &= !1;
            playerB += 1;
            vram[playerB as usize] |= 1;
        }

        if ballX >= 31 {
            ballXvel = -1;
        } else if ballX == 0 {
            ballXvel = 1;
        }
        vram[ballY as usize] &= !(1 << ballX);
        ballX += ballXvel;
        vram[ballY as usize] |= 1 << ballX;

        draw(&vram);
    }
}

fn draw(vram: &[u32; 32]) {
    for row_index in 0..32 {
        unsafe {
            SCREEN
                .offset(row_index)
                .write_volatile(vram[row_index as usize]);
        }
    }
}