const std = @import("std");

// --- Protocol Definitions (Match core/ion.nim) ---

pub const CmdPacket = extern struct {
    kind: u32,
    arg: u32,
    id: [16]u8, // SipHash Provenance (Matches Nim array[16, byte])
};

pub const IonPacket = extern struct {
    data: u64, // ptr
    phys: u64,
    len: u16,
    id: u16,
};

// Generic Lock-Free Ring Buffer (Single Producer / Single Consumer safe)
pub fn RingBuffer(comptime T: type) type {
    return extern struct {
        head: u32,
        tail: u32,
        mask: u32,
        data: [256]T,

        pub fn push(self: *volatile @This(), item: T) bool {
            const head = self.head;
            const tail = self.tail;
            const mask = self.mask;

            // Check full
            if (((head + 1) & mask) == (tail & mask)) {
                return false;
            }

            // Write data
            self.data[head & mask] = item;

            // Commit
            asm volatile ("fence" ::: .{ .memory = true });
            self.head = (head + 1) & mask;
            return true;
        }
    };
}

// System Table Layout (Located at 0x83000000)
pub const SysTable = extern struct {
    magic: u32,
    s_rx: *RingBuffer(IonPacket),
    s_tx: *RingBuffer(IonPacket),
    s_event: *RingBuffer(IonPacket),
    s_cmd: *RingBuffer(CmdPacket),
    s_input: *RingBuffer(IonPacket),
};

const SYSTABLE_ADDR: usize = 0x83000000;

// --- API ---

pub fn sys_cmd_push(pkt: CmdPacket) bool {
    const sys = @as(*const volatile SysTable, @ptrFromInt(SYSTABLE_ADDR));

    // Safety check magic (0x4E585553 = "NXUS")
    if (sys.magic != 0x4E585553) return false;

    // Push to Command Ring
    return sys.s_cmd.push(pkt);
}

pub fn sys_input_pop(out_pkt: *IonPacket) bool {
    const sys = @as(*const volatile SysTable, @ptrFromInt(SYSTABLE_ADDR));
    if (sys.magic != 0x4E585553) return false;

    const ring = sys.s_input;
    const head = @atomicLoad(u32, &ring.head, .acquire);
    const tail = @atomicLoad(u32, &ring.tail, .monotonic);

    if (head == tail) return false;

    out_pkt.* = ring.data[tail & ring.mask];
    @atomicStore(u32, &ring.tail, tail + 1, .release);
    return true;
}