// 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.

//! Rumpk NPL: Benchmark (The Speed Freak)
//!
//! Measures raw ION ring transfer latency using the RISC-V cycle counter.
//! Tests the physics of shared-memory communication overhead.
//!
//! SAFETY: Uses inline assembly to read the hardware cycle counter (`rdcycle`).

const std = @import("std");

// 1. The SysTable Contract (Must match Kernel!)
const ION_BASE = 0x83000000;

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

const CmdPacket = extern struct {
    kind: u32,
    arg: u32,
};

const RingBufferPacket = extern struct {
    head: u32,
    tail: u32,
    mask: u32,
    data: [256]IonPacket,
};

const RingBufferCmd = extern struct {
    head: u32,
    tail: u32,
    mask: u32,
    data: [256]CmdPacket,
};

const SysTable = extern struct {
    magic: u32,
    s_rx: *RingBufferPacket,
    s_tx: *RingBufferPacket,
    s_event: *RingBufferPacket,
    s_cmd: *RingBufferCmd,
};

fn get_systable() *SysTable {
    return @ptrFromInt(ION_BASE);
}

inline fn read_cycles() u64 {
    // SAFETY(Bench): Cycles variable is populated by inline assembly before return.
    var cycles: u64 = undefined;
    // RISC-V 64-bit cycle counter
    asm volatile ("rdcycle %[cycles]"
        : [cycles] "=r" (cycles),
    );
    return cycles;
}

export fn main() c_int {
    const sys = get_systable();
    print("[BENCH] Warming up ION...\n");

    if (sys.magic != 0x4E585553) {
        print("[BENCH] Magic mismatch! 0x");
        print_hex(sys.magic);
        print("\n");
        return 1;
    }

    var i: usize = 0;
    const ITERATIONS = 100_000;

    // 1. Calibrate (Measure overhead of reading cycles)
    const t0 = read_cycles();
    const t1 = read_cycles();
    const overhead = t1 - t0;

    print("[BENCH] Timer Overhead: ");
    print_u64(overhead);
    print(" cycles\n");

    // 2. The Loop
    print("[BENCH] Starting 100k IO ops (Raw Ring Push - NO YIELD)...\n");
    const start = read_cycles();

    const cmd_ring = sys.s_cmd;
    while (i < ITERATIONS) : (i += 1) {
        // Measure Pure Ring Push (Physics)
        while (true) {
            const head = @atomicLoad(u32, &cmd_ring.head, .monotonic);
            const tail = @atomicLoad(u32, &cmd_ring.tail, .monotonic);

            const next = (head + 1) & cmd_ring.mask;
            if (next != tail) {
                cmd_ring.data[head & cmd_ring.mask] = .{ .kind = 0, .arg = @intCast(i) };
                @atomicStore(u32, &cmd_ring.head, next, .release);
                // fiber_yield(); // BYPASS FOR RAW SPEED
                break;
            } else {
                // Ring full - yield to let Kernel process
                fiber_yield();
            }
        }
    }

    const end = read_cycles();
    const total_cycles = (end - start) - overhead;
    const avg = total_cycles / ITERATIONS;

    print("[BENCH] Total Cycles: ");
    print_u64(total_cycles);
    print("\n");
    print("[BENCH] Result: ");
    print_u64(avg);
    print(" cycles/op\n");

    return 0;
}

// OS Shims
extern fn write(fd: c_int, buf: [*]const u8, count: usize) isize;

const YIELD_LOC = 0x83000FF0;
fn fiber_yield() void {
    const ptr: *const *const fn () callconv(.c) void = @ptrFromInt(YIELD_LOC);
    const func = ptr.*;
    func();
}

fn print(text: []const u8) void {
    _ = write(1, text.ptr, text.len);
}

fn print_u64(val: u64) void {
    // SAFETY(Bench): Buffer populated by `std.fmt.bufPrint` before use.
    var buf: [32]u8 = undefined;
    const s = std.fmt.bufPrint(&buf, "{}", .{val}) catch "ERR";
    print(s);
}

fn print_hex(val: u32) void {
    // SAFETY(Bench): Buffer populated by `std.fmt.bufPrint` before use.
    var buf: [16]u8 = undefined;
    const s = std.fmt.bufPrint(&buf, "{x}", .{val}) catch "ERR";
    print(s);
}

pub fn panic(msg: []const u8, error_return_trace: ?*std.builtin.StackTrace, ret_addr: ?usize) noreturn {
    _ = error_return_trace;
    _ = ret_addr;
    print("\n[BENCH] PANIC: ");
    print(msg);
    print("\n");
    while (true) {}
}