//! Nyash IntegerBox Plugin - Minimal BID-FFI v1
//! Methods: birth(0), get(1), set(2), fini(u32::MAX)

use once_cell::sync::Lazy;
use std::collections::HashMap;
use std::sync::{Mutex, atomic::{AtomicU32, Ordering}};

// Error codes
const OK: i32 = 0;
const E_SHORT: i32 = -1;
const E_TYPE: i32 = -2;
const E_METHOD: i32 = -3;
const E_ARGS: i32 = -4;
const E_PLUGIN: i32 = -5;
const E_HANDLE: i32 = -8;

// Methods
const M_BIRTH: u32 = 0;
const M_GET:   u32 = 1;
const M_SET:   u32 = 2;
const M_FINI:  u32 = u32::MAX;

// Assigned type id (nyash.toml must match)
const TYPE_ID_INTEGER: u32 = 12;

struct IntInstance { value: i64 }

static INST: Lazy<Mutex<HashMap<u32, IntInstance>>> = Lazy::new(|| Mutex::new(HashMap::new()));
static NEXT_ID: AtomicU32 = AtomicU32::new(1);

#[no_mangle]
pub extern "C" fn nyash_plugin_abi() -> u32 { 1 }

#[no_mangle]
pub extern "C" fn nyash_plugin_init() -> i32 { OK }

#[no_mangle]
pub extern "C" fn nyash_plugin_invoke(
    type_id: u32,
    method_id: u32,
    instance_id: u32,
    args: *const u8,
    args_len: usize,
    result: *mut u8,
    result_len: *mut usize,
) -> i32 {
    if type_id != TYPE_ID_INTEGER { return E_TYPE; }
    unsafe {
        match method_id {
            M_BIRTH => {
                if result_len.is_null() { return E_ARGS; }
                if preflight(result, result_len, 4) { return E_SHORT; }
                // Optional initial value from first arg (i64/i32)
                let init = read_arg_i64(args, args_len, 0).unwrap_or(0);
                let id = NEXT_ID.fetch_add(1, Ordering::Relaxed);
                if let Ok(mut m) = INST.lock() { m.insert(id, IntInstance { value: init }); }
                else { return E_PLUGIN; }
                let b = id.to_le_bytes();
                std::ptr::copy_nonoverlapping(b.as_ptr(), result, 4); *result_len = 4; OK
            }
            M_FINI => {
                if let Ok(mut m) = INST.lock() { m.remove(&instance_id); OK } else { E_PLUGIN }
            }
            M_GET => {
                if let Ok(m) = INST.lock() { if let Some(inst) = m.get(&instance_id) { return write_tlv_i64(inst.value, result, result_len); } else { return E_HANDLE; } } else { return E_PLUGIN; }
            }
            M_SET => {
                let v = match read_arg_i64(args, args_len, 0) { Some(v) => v, None => return E_ARGS };
                if let Ok(mut m) = INST.lock() { if let Some(inst) = m.get_mut(&instance_id) { inst.value = v; return write_tlv_i64(inst.value, result, result_len); } else { return E_HANDLE; } } else { return E_PLUGIN; }
            }
            _ => E_METHOD,
        }
    }
}

fn preflight(result: *mut u8, result_len: *mut usize, needed: usize) -> bool {
    unsafe { if result_len.is_null() { return false; } if result.is_null() || *result_len < needed { *result_len = needed; return true; } }
    false
}

fn write_tlv_result(payloads: &[(u8, &[u8])], result: *mut u8, result_len: *mut usize) -> i32 {
    if result_len.is_null() { return E_ARGS; }
    let mut buf: Vec<u8> = Vec::with_capacity(4 + payloads.iter().map(|(_,p)| 4 + p.len()).sum::<usize>());
    buf.extend_from_slice(&1u16.to_le_bytes());
    buf.extend_from_slice(&(payloads.len() as u16).to_le_bytes());
    for (tag, payload) in payloads { buf.push(*tag); buf.push(0); buf.extend_from_slice(&(payload.len() as u16).to_le_bytes()); buf.extend_from_slice(payload); }
    unsafe { let needed = buf.len(); if result.is_null() || *result_len < needed { *result_len = needed; return E_SHORT; } std::ptr::copy_nonoverlapping(buf.as_ptr(), result, needed); *result_len = needed; }
    OK
}

fn write_tlv_i64(v: i64, result: *mut u8, result_len: *mut usize) -> i32 { write_tlv_result(&[(3u8, &v.to_le_bytes())], result, result_len) }

fn read_arg_i64(args: *const u8, args_len: usize, n: usize) -> Option<i64> {
    if args.is_null() || args_len < 4 { return None; }
    let buf = unsafe { std::slice::from_raw_parts(args, args_len) };
    let mut off = 4usize; // header
    for i in 0..=n {
        if buf.len() < off + 4 { return None; }
        let tag = buf[off]; let size = u16::from_le_bytes([buf[off+2], buf[off+3]]) as usize;
        if buf.len() < off + 4 + size { return None; }
        if i == n {
            match (tag, size) {
                (3, 8) => { let mut b=[0u8;8]; b.copy_from_slice(&buf[off+4..off+12]); return Some(i64::from_le_bytes(b)); }
                (2, 4) => { let mut b=[0u8;4]; b.copy_from_slice(&buf[off+4..off+8]); let v = i32::from_le_bytes(b) as i64; return Some(v); }
                _ => return None,
            }
        }
        off += 4 + size;
    }
    None
}