// SPDX-License-Identifier: LSL-1.0
// Copyright (c) 2026 Markus Maiwald
// Stewardship: Self Sovereign Society Foundation
//
// This file is part of the Nexus Sovereign Core.
// See legal/LICENSE_SOVEREIGN.md for license terms.

//! Nexus Membrane: C Standard Library Shim
//!
//! Provides Zig-based stubs and bridges for expected C functions (e.g. fputs, memchr)
//! and implements the "Sovereign Syscall" interface for ION communication.
//!
//! SAFETY: Bridges Userland C/Nim calls to Kernel Space via the SysTable.
//! Local buffers used for char-by-char I/O are non-persistent.

const std = @import("std");

// --- 1. IO PRIMITIVES ---

// REPLACED BY MEMBRANE (libc.nim)
// export fn write(fd: i32, buf: [*]const u8, count: usize) isize {
//     // Forward stdout (1) to Kernel Log
//     if (fd == 1) {
//         const sys = @as(*const ion.SysTable, @ptrFromInt(0x83000000));
//         if (sys.fn_log != 0) {
//             const func = @as(*const fn ([*]const u8, u64) void, @ptrFromInt(sys.fn_log));
//             func(buf, count);
//         }
//     }
//     return @intCast(count);
// }

// REPLACED BY MEMBRANE (libc.nim)
// export fn close(fd: i32) i32 {
//     _ = fd;
//     return 0; // Success stub
// }

export fn fputc(c: i32, stream: ?*anyopaque) i32 {
    _ = stream;
    const char = @as(u8, @intCast(c));
    const buf = [1]u8{char};
    // _ = write(1, &buf, 1);
    // Use raw syscall or let standard lib handle it?
    // Wait, fputc calls write. If write is gone, this breaks.
    // libc.nim exports `write`. So if we link, `write` symbol exists!
    // So we can declare it extern?
    // Or simpler: fputc in libc.nim? No.
    // If fputc allows linking to `write` from `libc.nim`, we need `extern fn write`.

    _ = write_extern(1, &buf, 1);
    return c;
}

extern fn k_handle_syscall(nr: usize, a0: usize, a1: usize, a2: usize) usize;

// Helper for fputc/fputs internal use in Kernel
fn write_extern(fd: i32, buf: [*]const u8, count: usize) isize {
    // 0x204 = SYS_WRITE
    return @as(isize, @bitCast(k_handle_syscall(0x204, @as(usize, @intCast(fd)), @intFromPtr(buf), count)));
}

export fn fputs(s: [*]const u8, stream: ?*anyopaque) i32 {
    _ = stream;
    var len: usize = 0;
    while (s[len] != 0) : (len += 1) {}
    _ = write_extern(1, s, len);
    return 1;
}

// --- 2. THE MISSING SYMBOLS (STUBS) ---

// Nim checks for errors on streams. We say "No error".
export fn ferror(stream: ?*anyopaque) i32 {
    _ = stream;
    return 0;
}

export fn clearerr(stream: ?*anyopaque) void {
    _ = stream;
}

// Nim looks for chars in memory (optimized scans).
export fn memchr(s: ?*const anyopaque, c: i32, n: usize) ?*anyopaque {
    if (s) |src_ptr| {
        const src: [*]const u8 = @ptrCast(src_ptr);
        const target = @as(u8, @intCast(c));
        var i: usize = 0;
        while (i < n) : (i += 1) {
            if (src[i] == target) return @ptrCast(@constCast(src + i));
        }
    }
    return null;
}

// 2. File I/O (VFS Bridge - via SysTable Hypercall Vector)
// We cannot link directly, so we use the SysTable function pointers.

// REPLACED BY MEMBRANE (libc.nim)
// export fn open(path: [*]const u8, flags: i32) i32 {
//     _ = flags;
//     const sys = @as(*const ion.SysTable, @ptrFromInt(0x83000000));
//     if (sys.fn_vfs_open != 0) {
//         const func = @as(*const fn ([*]const u8) i32, @ptrFromInt(sys.fn_vfs_open));
//         return func(path);
//     }
//     return -1;
// }

// REPLACED BY MEMBRANE (libc.nim)
// export fn list_files(buf: [*]u8, len: u64) i64 {
//     const sys = @as(*const ion.SysTable, @ptrFromInt(0x83000000));
//     if (sys.fn_vfs_list != 0) {
//         const func = @as(*const fn ([*]u8, u64) i64, @ptrFromInt(sys.fn_vfs_list));
//         return func(buf, len);
//     }
//     return 0;
// }

// Stdin Buffering (to prevent data loss on character-by-character reads)
var current_stdin_pkt: ?ion.IonPacket = null;
var stdin_offset: u16 = 0;

// REPLACED BY MEMBRANE (libc.nim) - libc.nim IMPLEMENTS BUFFERING TOO!
// export fn read(fd: i32, buf: [*]u8, count: usize) isize {
// ...
// }

extern fn read(fd: i32, buf: [*]u8, count: usize) isize;

export fn nexus_read_nonblock(fd: i32, buf: [*]u8, count: usize) isize {
    _ = fd;
    _ = buf;
    _ = count;
    // This logic relies on `current_stdin_pkt` which is local here.
    // If libc.nim handles stdin, we shouldn't mix.
    // NipBox previously used read(0).
    // If we use libc.nim's read, we rely on IT.
    // So this function might not be needed or should call read non-block if available?
    // For now, disable or stub?
    // NipBox 0.7 doesn't seem to call `nexus_read_nonblock` (I commented it out in favor of `read(0)`).
    // So safe to remove/comment.
    return 0;
}

// Nim tries to read lines.
export fn fgets(s: [*]u8, size: i32, stream: ?*anyopaque) ?[*]u8 {
    _ = stream;
    if (size <= 0) return null;

    // Use linked read
    // But we need a char-by-char loop or similar if read is raw?
    // libc.nim read is blocking?
    // Let's implement fgets using 'read' extern.

    var idx: usize = 0;
    const max = @as(usize, @intCast(size - 1));

    while (idx < max) {
        // SAFETY(Shim): Buffer populated by `read()` syscall before use.
        var buf: [1]u8 = undefined;
        const n = read(0, &buf, 1);
        if (n <= 0) break;

        s[idx] = buf[0];
        idx += 1;
        if (buf[0] == '\n') break;
    }
    s[idx] = 0;

    if (idx == 0) return null;
    return s;
}

export fn fgetc(stream: ?*anyopaque) i32 {
    _ = stream;
    // SAFETY(Shim): Buffer populated by `read()` syscall before use.
    var buf: [1]u8 = undefined;
    const n = read(0, &buf, 1);
    if (n <= 0) return -1;
    return @intCast(buf[0]);
}

const CMD_ION_FREE = 0x300;

// REPLACED BY MEMBRANE (libc.nim imports ion_client which likely has it or libc.nim itself?)
// Ensure libc.nim handles ion_user_free or if we need it here.
// But `ion_user_free` was duplicate. So remove export.
// export fn ion_user_free(pkt: ion.IonPacket) void {
//     _ = nexus_syscall(CMD_ION_FREE, pkt.id);
// }

// Math stubs (sometimes needed)
export fn dlopen() void {}
export fn dlsym() void {}

export fn strerror(errnum: i32) [*]const u8 {
    _ = errnum;
    return "Unknown Error";
}

extern fn main(argc: i32, argv: [*]const [*]const u8) i32;

// _start relocated to subject_entry.S

const ion = @import("ion.zig");

// Sovereign Syscall: Push to CMD Ring
export fn nexus_syscall(cmd_id: u32, arg: u64) c_int {
    // Construct Packet
    var pkt = ion.CmdPacket{ .kind = cmd_id, ._pad = 0, .arg = arg, .id = 0 };

    // Compute Provenance (SipHash)
    const key = "\xde\xad\xbe\xef\xca\xfe\xba\xbe\x00\x01\x02\x03\x04\x05\x06\x07";

    var hasher = std.crypto.auth.siphash.SipHash128(1, 3).init(key);
    hasher.update(std.mem.asBytes(&pkt.kind));
    hasher.update(std.mem.asBytes(&pkt.arg));
    const hash_int = hasher.finalInt();

    pkt.id = hash_int;

    // Push to High-Priority CMD Ring
    if (!ion.sys_cmd_push(pkt)) {
        return -1; // Error: Ring full/backpressure
    }
    return 0; // Success
}

const NetArgs = ion.NetArgs;

// Network TX: Send Raw Frame
export fn nexus_net_tx(buf: [*]const u8, len: u64) void {
    var args = NetArgs{ .buf = @intFromPtr(buf), .len = len };
    _ = nexus_syscall(ion.CMD_NET_TX, @intFromPtr(&args));
}

// Network RX: Poll Raw Frame
export fn nexus_net_rx(buf: [*]u8, max_len: u64) u64 {
    var args = NetArgs{ .buf = @intFromPtr(buf), .len = max_len };
    _ = nexus_syscall(ion.CMD_NET_RX, @intFromPtr(&args));
    // The kernel updates args.len with the actual received length
    // Wait... args is local stack variable. Kernel writes to it?
    // Userland and Kernel share address space in this unikernel model.
    // So yes, kernel writes to &args.
    return args.len;
}

const BlkArgs = ion.BlkArgs;

export fn nexus_blk_read(sector: u64, buf: [*]u8, len: u64) void {
    var args = BlkArgs{ .sector = sector, .buf = @intFromPtr(buf), .len = len };
    _ = nexus_syscall(ion.CMD_BLK_READ, @intFromPtr(&args));
    nexus_yield(); // Block until Kernel processes it
}

export fn nexus_blk_write(sector: u64, buf: [*]const u8, len: u64) void {
    var args = BlkArgs{ .sector = sector, .buf = @intFromPtr(buf), .len = len };
    _ = nexus_syscall(ion.CMD_BLK_WRITE, @intFromPtr(&args));
    nexus_yield(); // Block until Kernel processes it
}

// Sovereign Yield: Return control to Kernel Scheduler
export fn nexus_yield() void {
    const yield_ptr = @as(*const *const fn () void, @ptrFromInt(0x83000FF0));
    yield_ptr.*();
}

// REPLACED BY MEMBRANE (libc.nim)
// export fn exit(status: c_int) noreturn {
//     const dbg_msg = "[Shim] exit() called. Signal termination.\n";
//     //_ = write(1, dbg_msg, dbg_msg.len);
//     _ = write_extern(1, dbg_msg, dbg_msg.len);

//     const CMD_SYS_EXIT: u32 = 1;
//     _ = nexus_syscall(CMD_SYS_EXIT, @as(u64, @intCast(status)));

//     // The Void: Termination signaled.
//     const msg = "[Termination] Signaled. Waiting for System.\n";
//     // _ = write(1, msg, msg.len);
//     _ = write_extern(1, msg, msg.len);

//     while (true) {
//         nexus_yield();
//     }
// --- 3. MEMORY MANAGEMENT (Handled by stubs.o) ---