const std = @import("std");

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();
    const allocator = gpa.allocator();

    var uxn = Uxn{
        .mem = try allocator.alloc(u8, 0xFFFF),
        .ws = try allocator.alloc(u8, 0xFF),
        .rs = try allocator.alloc(u8, 0xFF),
        .wsp = 0,
        .rsp = 0,
        .pc = 0x0100,
    };
    defer allocator.free(uxn.mem);
    defer allocator.free(uxn.ws);
    defer allocator.free(uxn.rs);

    while (true) uxn.loop();
}

pub const Uxn = struct {
    mem: [0xFFFF]u8,
    // ws: [0xFF]u8,
    // rs: [0xFF]u8,
    // wsp: u8,
    // rsp: u8,
    ws: Stack,
    rs: Stack,
    pc: u16,

    const Stack = struct {
        s: *[0xFF]u8,
        sp: *u8,

        pub fn peek(self: *Stack, comptime T: type) T {
            return switch (T) {
                u8 => self.s[self.sp],
                u16 => @intCast(self.s[self.sp]), // but actually do the conversion
                else => unreachable,
            };
        }

        pub fn poke(self: *Stack, comptime T: type, v: T) void {
            switch (T) {
                u8 => self.s[self.sp] = v,
                u16 => {},
                else => unreachable,
            }
        }

        pub fn pop(self: *Stack, comptime T: type) T {
            switch (T) {
                u8 => {
                    self.sp -%= 1;
                    return self.s[self.sp +% 1];
                },
                u16 => {
                    self.sp -%= 2;
                    return self.s[self.sp +% 1];
                },
                else => unreachable,
            }
        }

        pub fn push(self: *Stack, comptime T: type, v: T) void {
            switch (T) {
                u8 => {
                    self.sp +%= 1;
                    self.s[self.sp] = v;
                },
                u16 => {
                    self.sp +%= 2;
                    self.s[self.sp] = v;
                },
                else => unreachable,
            }
        }
    };

    pub fn loop(self: *Uxn) void {
        switch (self.mem[self.pc]) {
            0x00 => {}, // BRK
            0x01 => inc(&self.ws, false, false), // INC
            0x02 => pop(&self.ws, false, false), // POP
            0x03 => nip(&self.ws, false, false), // NIP
            0x04 => swp(&self.ws, false, false), // SWP
            0x05 => rot(&self.ws, false, false), // ROT
            0x06 => dup(&self.ws, false, false), // DUP
            0x07 => ovr(&self.ws, false, false), // OVR
            0x08 => equ(&self.ws, false, false), // EQU
            0x09 => neq(&self.ws, false, false), // NEQ
            0x0A => gth(&self.ws, false, false), // GTH
            0x0B => lth(&self.ws, false, false), // LTH
            0x0C => self.jmp(&self.ws, u8, false), // JMP
            0x0D => self.jcn(&self.ws, u8, false), // JCN
            0x0E => self.jsr(&self.ws, u8, false), // JSR
            0x0F => self.sth(false, u8, false), // STH
            0x10 => {}, // LDZ
            0x11 => {}, // STZ
            0x12 => {}, // LDR
            0x13 => {}, // STR
            0x14 => {}, // LDA
            0x15 => {}, // STA
            0x16 => {}, // DEI
            0x17 => {}, // DEO
            0x18 => {}, // ADD
            0x19 => {}, // SUB
            0x1A => {}, // MUL
            0x1B => {}, // DIV
            0x1C => {}, // AND
            0x1D => {}, // ORA
            0x1E => {}, // EOR
            0x1F => {}, // SFT
        }
    }

    fn brk() void {}

    fn inc(stack: *Stack, comptime T: type, comptime keep: bool) void {
        const a = if (keep) stack.peek(T) else stack.pop(T);
        stack.push(T, a +% 1);
        // if (keep) {
        //     stack.s[stack.sp +% 1] = stack.s[stack.sp] +% 1;
        //     stack.sp +%= 1;
        // } else {
        //     stack.s[stack.sp] +%= 1;
        // }
    }

    fn pop(stack: *Stack, comptime T: type, comptime keep: bool) void {
        if (keep) return;
        _ = stack.pop(T);
        // if (!keep) {
        //     if (short) stack.sp -%= 2 else stack.sp -%= 1;
        // }
    }

    fn nip(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = if (keep) stack.peek(T) else stack.pop(T);
        const b = if (keep) stack.peek(T) else stack.pop(T);
        stack.push(T, b);
        // if (!keep) {
        //     stack.sp -%= 1;
        //     stack.s[stack.sp] = stack.s[stack.sp +% 1];
        // }
    }

    fn swp(stack: *Stack, comptime T: type, comptime keep: bool) void {
        const a = if (keep) stack.peek(T) else stack.pop(T);
        const b = if (keep) stack.peek(T) else stack.pop(T);
        stack.push(T, b);
        stack.push(T, a);
        // if (keep) {
        //     stack.s[stack.sp +% 1] = stack.s[stack.sp];
        //     stack.s[stack.sp +% 2] = stack.s[stack.sp -% 1];
        // } else {
        //     const a = stack.s[stack.sp -% 1];
        //     stack.s[stack.sp -% 1] = stack.s[stack.sp];
        //     stack.sp = a;
        // }
    }

    fn rot(stack: *Stack, comptime T: type, comptime keep: bool) void {
        const a = if (keep) stack.peek(T) else stack.pop(T);
        const b = if (keep) stack.peek(T) else stack.pop(T);
        const c = if (keep) stack.peek(T) else stack.pop(T);
        stack.push(T, b);
        stack.push(T, c);
        stack.push(T, a);
    }

    fn dup(stack: *Stack, comptime T: type, comptime keep: bool) void {
        const a = if (keep) stack.peek(T) else stack.pop(T);
        stack.push(T, a);
        // stack.s[stack.sp +% 1] = stack.s[stack.sp];
        // if (keep) {
        //     stack.s[stack.sp +% 2] = stack.s[stack.sp];
        //     stack.sp +%= 2;
        // } else stack.sp +%= 1;
    }

    fn ovr(stack: *Stack, comptime T: type, comptime keep: bool) void {
        const a = if (keep) stack.peek(T) else stack.pop(T);
        const b = if (keep) stack.peek(T) else stack.pop(T);
        stack.push(T, a);
        stack.push(T, b);
        stack.push(T, a);
        // if (keep) {
        //     stack.s[stack.sp +% 1] = stack.s[stack.sp -% 1];
        //     stack.s[stack.sp +% 2] = stack.s[stack.sp];
        //     stack.s[stack.sp +% 3] = stack.s[stack.sp -% 1];
        //     stack.sp +%= 3;
        // } else {
        //     stack.s[stack.sp +% 1] = stack.s[stack.sp -% 1];
        //     stack.sp +%= 1;
        // }
    }

    fn equ(stack: *Stack, comptime T: type, comptime keep: bool) void {
        const a = if (keep) stack.peek(T) else stack.pop(T);
        const b = if (keep) stack.peek(T) else stack.pop(T);
        if (a == b) stack.push(T, 1) else stack.push(T, 0);
        // if (keep) {} else {
        //     if (stack.s[stack.sp -% 1] == stack.s[stack.sp])
        //         stack.s[stack.sp +% 1] = 1
        //     else
        //         stack.s[stack.sp +% 1] = 0;
        //     stack.sp +%= 1;
        // }
    }

    fn neq(stack: *Stack, comptime T: type, comptime keep: bool) void {
        const a = if (keep) stack.peek(T) else stack.pop(T);
        const b = if (keep) stack.peek(T) else stack.pop(T);
        if (a != b) stack.push(T, 1) else stack.push(T, 0);
    }

    fn gth(stack: *Stack, comptime T: type, comptime keep: bool) void {
        const a = if (keep) stack.peek(T) else stack.pop(T);
        const b = if (keep) stack.peek(T) else stack.pop(T);
        if (a > b) stack.push(T, 1) else stack.push(T, 0);
    }

    fn lth(stack: *Stack, comptime T: type, comptime keep: bool) void {
        const a = if (keep) stack.peek(T) else stack.pop(T);
        const b = if (keep) stack.peek(T) else stack.pop(T);
        if (a < b) stack.push(T, 1) else stack.push(T, 0);
    }

    fn jmp(self: *Uxn, stack: *Stack, comptime T: type, comptime keep: bool) void {
        const addr = if (keep) stack.peek(T) else stack.pop(T);
        switch (T) {
            u8 => self.pc +%= @as(i8, @bitCast(addr)),
            u16 => self.pc = addr,
            else => unreachable,
        }
    }

    fn jcn(self: *Uxn, stack: *Stack, comptime T: type, comptime keep: bool) void {
        const cond = if (keep) stack.peek(T) else stack.pop(T);
        const addr = if (keep) stack.peek(T) else stack.pop(T);
        if (cond == 0) return;
        switch (T) {
            u8 => self.pc +%= @as(i8, @bitCast(addr)),
            u16 => self.pc = addr,
            else => unreachable,
        }
    }

    fn jsr(self: *Uxn, stack: *Stack, comptime T: type, comptime keep: bool) void {
        self.rs.push(u16, self.pc);
        const addr = if (keep) stack.peek(T) else stack.pop(T);
        switch (T) {
            u8 => self.pc +%= @as(i8, @bitCast(addr)),
            u16 => self.pc = addr,
            else => unreachable,
        }
    }

    fn sth(self: *Uxn, comptime swap: bool, comptime T: type, comptime keep: bool) void {
        const src = if (swap) self.rs else self.ws;
        const dst = if (swap) self.ws else self.rs;
        const a = if (keep) src.peek(T) else src.pop(T);
        dst.push(T, a);
    }

    fn ldz(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn stz(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn ldr(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn str(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn lda(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn sta(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn dei(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn deo(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn add(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn sub(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn mul(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn div(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn @"and"(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn ora(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn eor(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }

    fn sft(stack: *Stack, comptime T: type, comptime keep: bool) void {
        _ = short;
    }
};