// ilo.rs, (c) charles childers, (c) 2024 Matt Keeter

use std::convert::TryInto;
use std::fs::{File, OpenOptions};
use std::io;
use std::io::{Read, Seek, SeekFrom, Write};

struct Ilo {
    /// memory
    memory: [i32; 65536],
    /// data stack
    data: [i32; 33],
    /// address stack
    addr: [i32; 257],
    /// data stack pointer
    sp: usize,
    /// address stack pointer
    rp: usize,
    /// instruction pointer
    ip: usize,
}

impl Default for Ilo {
    fn default() -> Self {
        Self {
            memory: [0; 65536],
            data: [0; 33],
            addr: [0; 257],
            sp: 0,
            rp: 0,
            ip: 0,
        }
    }
}

impl Ilo {
    fn load_image(&mut self) {
        match std::fs::read("ilo.rom") {
            Ok(image) => {
                for (i, c) in image.chunks(4).enumerate() {
                    self.store(i32::from_le_bytes(c.try_into().unwrap()), i);
                }
            }
            Err(e) => {
                panic!("could not load 'ilo.rom': {}", e);
            }
        }
    }

    fn read_block(&mut self, block: i32, buffer: i32) -> io::Result<()> {
        let mut f = File::open("ilo.blocks")?;
        let mut data = [0; 4096];
        f.seek(SeekFrom::Start(4096 * (block as u64)))?;
        f.read_exact(&mut data)?;
        for (i, c) in data.chunks(4).enumerate() {
            let x = c[0] as i32;
            self.store(x, (buffer as usize) + i);
        }
        Ok(())
    }

    fn write_block(&self, block: i32, buffer: i32) -> io::Result<()> {
        let mut f = OpenOptions::new()
            .read(true)
            .write(true)
            .open("ilo.blocks")?;
        let mut data = [0; 4096];
        for x in 0..1024 {
            let v = self.fetch((buffer as usize) + x);
            data[(x * 4)..][..4].copy_from_slice(&v.to_le_bytes());
        }
        f.seek(SeekFrom::Start(4096 * (block as u64)))?;
        f.write_all(&data)?;
        Ok(())
    }

    fn push(&mut self, x: i32) {
        self.sp += 1;
        self.data[self.sp] = x;
    }
    fn pop(&mut self) -> i32 {
        self.sp -= 1;
        self.data[self.sp + 1]
    }

    fn fetch(&self, a: usize) -> i32 {
        self.memory[a]
    }
    fn store(&mut self, v: i32, a: usize) {
        self.memory[a] = v;
    }

    fn reset(&mut self) {
        self.ip = 0;
        self.sp = 0;
        self.rp = 0;
    }
    fn next(&mut self) {
        self.ip += 1;
    }

    fn li(&mut self) {
        self.next();
        self.push(self.fetch(self.here()));
    }
    fn du(&mut self) {
        self.push(self.data[self.sp]);
    }
    fn dr(&mut self) {
        self.pop();
    }
    fn sw(&mut self) {
        let x = self.pop();
        let y = self.pop();
        self.push(x);
        self.push(y);
    }
    fn pu(&mut self) {
        self.rp += 1;
        self.addr[self.rp] = self.pop();
    }
    fn po(&mut self) {
        self.push(self.addr[self.rp]);
        self.rp -= 1;
    }
    fn ju(&mut self) {
        self.ip = (self.pop() - 1) as usize;
    }
    fn ca(&mut self) {
        self.rp += 1;
        self.addr[self.rp] = (self.ip) as i32;
        self.ip = (self.pop() - 1) as usize;
    }
    fn cc(&mut self) {
        let t = self.pop();
        if self.pop() != 0 {
            self.push(t);
            self.ca();
        }
    }
    fn cj(&mut self) {
        let t = self.pop();
        if self.pop() != 0 {
            self.push(t);
            self.ju();
        }
    }
    fn re(&mut self) {
        self.ip = (self.addr[self.rp]) as usize;
        self.rp -= 1;
    }
    fn eq(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(if x == y { -1 } else { 0 });
    }
    fn ne(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(if x != y { -1 } else { 0 });
    }
    fn lt(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(if x < y { -1 } else { 0 });
    }
    fn gt(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(if x > y { -1 } else { 0 });
    }
    fn fe(&mut self) {
        let x = self.pop() as usize;
        self.push(self.fetch(x));
    }
    fn st(&mut self) {
        let x = self.pop() as usize;
        let v = self.pop();
        self.store(v, x);
    }
    fn ad(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(x.wrapping_add(y));
    }
    fn su(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(x.wrapping_sub(y));
    }
    fn mu(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(x.wrapping_mul(y));
    }
    fn di(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(x.wrapping_rem(y));
        self.push(x.wrapping_div(y));
    }
    fn an(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(x & y);
    }
    fn or(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(x | y);
    }
    fn xo(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(x ^ y);
    }
    fn sl(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(x.wrapping_shl(y.try_into().unwrap()));
    }
    fn sr(&mut self) {
        let y = self.pop();
        let x = self.pop();
        self.push(x.wrapping_shr(y.try_into().unwrap()));
    }
    fn cp(&mut self) {
        let len = self.pop() as usize;
        let dest = self.pop() as usize;
        let src = self.pop() as usize;
        let slice1 = &self.memory[src..(src + len)];
        let slice2 = &self.memory[dest..(dest + len)];
        if slice1 == slice2 {
            self.push(-1);
        } else {
            self.push(0);
        }
    }
    fn cy(&mut self) {
        let mut len = self.pop();
        let mut dest = self.pop() as usize;
        let mut src = self.pop() as usize;
        while len > 0 {
            self.store(self.fetch(src), dest);
            len -= 1;
            src += 1;
            dest += 1;
        }
    }
    fn io(&mut self) {
        let dev = self.pop();
        match dev {
            0 => {
                let mut c = self.pop();
                if c == 0 {
                    c = 32;
                }
                let mut stdout = std::io::stdout().lock();
                stdout.write_all(&[c as u8]).unwrap();
                stdout.flush().unwrap();
            }
            1 => match std::io::stdin().lock().bytes().next().unwrap() {
                Ok(127) => self.push(8),
                Ok(val) => self.push(val as i32),
                Err(_) => std::process::exit(1),
            },
            2 => {
                let buffer = self.pop();
                let block = self.pop();
                if let Err(e) = self.read_block(block, buffer) {
                    panic!("could not read 'ilo.blocks': {}", e);
                }
            }
            3 => {
                let buffer = self.pop();
                let block = self.pop();
                if let Err(e) = self.write_block(block, buffer) {
                    panic!("could not write 'ilo.blocks': {}", e);
                }
            }
            4 => {}
            5 => {
                self.load_image();
                self.ip = 70000;
            }
            6 => {
                self.ip = 65536;
            }
            7 => {
                self.push(self.sp as i32);
                self.push(self.rp as i32);
            }
            _ => (),
        }
    }

    fn process(&mut self, inst: u8) {
        match inst {
            0 => (), // nop
            1 => self.li(),
            2 => self.du(),
            3 => self.dr(),
            4 => self.sw(),
            5 => self.pu(),
            6 => self.po(),
            7 => self.ju(),
            8 => self.ca(),
            9 => self.cc(),
            10 => self.cj(),
            11 => self.re(),
            12 => self.eq(),
            13 => self.ne(),
            14 => self.lt(),
            15 => self.gt(),
            16 => self.fe(),
            17 => self.st(),
            18 => self.ad(),
            19 => self.su(),
            20 => self.mu(),
            21 => self.di(),
            22 => self.an(),
            23 => self.or(),
            24 => self.xo(),
            25 => self.sl(),
            26 => self.sr(),
            27 => self.cp(),
            28 => self.cy(),
            29 => self.io(),
            _ => (),
        }
    }

    fn not_done(&self) -> bool {
        self.ip < 65536
    }
    fn here(&self) -> usize {
        self.ip
    }

    fn execute(&mut self) {
        self.reset();
        while self.not_done() {
            let opcode = self.fetch(self.here());
            for op in opcode.to_le_bytes() {
                self.process(op);
            }
            if self.here() == 70000 {
                self.reset();
            } else {
                self.next();
            }
        }
    }

    fn dump_stack(&mut self) {
        while self.sp > 0 {
            let x = self.pop();
            println!("{x}");
        }
    }
}

fn main() {
    let mut ilo = Ilo::default();
    ilo.load_image();
    ilo.execute();
    ilo.dump_stack();
}