//! Nyash CounterBox Plugin - BID-FFI v1 Implementation

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

use once_cell::sync::Lazy;

// ===== Error Codes (BID-1 alignment) =====
const NYB_SUCCESS: i32 = 0;
const NYB_E_SHORT_BUFFER: i32 = -1;
const NYB_E_INVALID_TYPE: i32 = -2;
const NYB_E_INVALID_METHOD: i32 = -3;
const NYB_E_INVALID_ARGS: i32 = -4;
const NYB_E_PLUGIN_ERROR: i32 = -5;
const NYB_E_INVALID_HANDLE: i32 = -8;

// ===== Method IDs =====
const METHOD_BIRTH: u32 = 0; // constructor
const METHOD_INC: u32 = 1; // increments and returns new count
const METHOD_GET: u32 = 2; // returns current count
const METHOD_FINI: u32 = u32::MAX; // destructor

// Assign a unique type_id for CounterBox (distinct from FileBox=6)
const TYPE_ID_COUNTER: u32 = 7;

// ===== Instance state =====
struct CounterInstance {
    count: i32,
}

static INSTANCES: Lazy<Mutex<HashMap<u32, CounterInstance>>> =
    Lazy::new(|| Mutex::new(HashMap::new()));
static INSTANCE_COUNTER: AtomicU32 = AtomicU32::new(1);

// legacy v1 abi entry (kept for compatibility with host shim)
#[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_COUNTER {
        return NYB_E_INVALID_TYPE;
    }

    unsafe {
        match method_id {
            METHOD_BIRTH => {
                // Return new instance handle (u32 id)
                if result_len.is_null() {
                    return NYB_E_INVALID_ARGS;
                }
                if preflight(result, result_len, 4) {
                    return NYB_E_SHORT_BUFFER;
                }
                let id = INSTANCE_COUNTER.fetch_add(1, Ordering::Relaxed);
                if let Ok(mut map) = INSTANCES.lock() {
                    map.insert(id, CounterInstance { count: 0 });
                } else {
                    return NYB_E_PLUGIN_ERROR;
                }
                let bytes = id.to_le_bytes();
                std::ptr::copy_nonoverlapping(bytes.as_ptr(), result, 4);
                *result_len = 4;
                NYB_SUCCESS
            }
            METHOD_FINI => {
                if let Ok(mut map) = INSTANCES.lock() {
                    map.remove(&instance_id);
                    NYB_SUCCESS
                } else {
                    NYB_E_PLUGIN_ERROR
                }
            }
            METHOD_INC => {
                // increments and returns new count as I32 TLV
                if let Ok(mut map) = INSTANCES.lock() {
                    if let Some(inst) = map.get_mut(&instance_id) {
                        inst.count += 1;
                        let v = inst.count;
                        if preflight(result, result_len, 12) {
                            return NYB_E_SHORT_BUFFER;
                        }
                        return write_tlv_i32(v, result, result_len);
                    } else {
                        return NYB_E_INVALID_HANDLE;
                    }
                } else {
                    return NYB_E_PLUGIN_ERROR;
                }
            }
            METHOD_GET => {
                if let Ok(map) = INSTANCES.lock() {
                    if let Some(inst) = map.get(&instance_id) {
                        if preflight(result, result_len, 12) {
                            return NYB_E_SHORT_BUFFER;
                        }
                        return write_tlv_i32(inst.count, result, result_len);
                    } else {
                        return NYB_E_INVALID_HANDLE;
                    }
                } else {
                    return NYB_E_PLUGIN_ERROR;
                }
            }
            _ => NYB_E_INVALID_METHOD,
        }
    }
}

// ===== Nyash ABI v2 TypeBox FFI =====
#[allow(non_camel_case_types)]
type InvokeFn = extern "C" fn(
    u32, /* instance_id */
    u32, /* method_id */
    *const u8,
    usize,
    *mut u8,
    *mut usize,
) -> i32;

#[repr(C)]
pub struct NyashTypeBoxFfi {
    pub abi_tag: u32,
    pub version: u16,
    pub struct_size: u16,
    pub name: *const std::os::raw::c_char,
    pub resolve: Option<extern "C" fn(*const std::os::raw::c_char) -> u32>,
    pub invoke_id: Option<InvokeFn>,
    pub capabilities: u64,
}

// The FFI descriptor is immutable and contains only function pointers and a const c-string pointer.
// Mark it Sync to allow use as a shared static.
unsafe impl Sync for NyashTypeBoxFfi {}

extern "C" fn counter_resolve(name: *const std::os::raw::c_char) -> u32 {
    unsafe {
        if name.is_null() {
            return 0;
        }
        let s = std::ffi::CStr::from_ptr(name).to_string_lossy();
        match s.as_ref() {
            "birth" => METHOD_BIRTH,
            "inc" => METHOD_INC,
            "get" => METHOD_GET,
            "fini" => METHOD_FINI,
            _ => 0,
        }
    }
}

extern "C" fn counter_invoke(
    instance_id: u32,
    method_id: u32,
    _args: *const u8,
    _args_len: usize,
    result: *mut u8,
    result_len: *mut usize,
) -> i32 {
    unsafe {
        match method_id {
            METHOD_BIRTH => {
                // Return new instance handle (u32 id) as raw 4 bytes (not TLV)
                if result_len.is_null() {
                    return NYB_E_INVALID_ARGS;
                }
                if preflight(result, result_len, 4) {
                    return NYB_E_SHORT_BUFFER;
                }
                let id = INSTANCE_COUNTER.fetch_add(1, Ordering::Relaxed);
                if let Ok(mut map) = INSTANCES.lock() {
                    map.insert(id, CounterInstance { count: 0 });
                } else {
                    return NYB_E_PLUGIN_ERROR;
                }
                let bytes = id.to_le_bytes();
                std::ptr::copy_nonoverlapping(bytes.as_ptr(), result, 4);
                *result_len = 4;
                NYB_SUCCESS
            }
            METHOD_FINI => {
                if let Ok(mut map) = INSTANCES.lock() {
                    map.remove(&instance_id);
                    NYB_SUCCESS
                } else {
                    NYB_E_PLUGIN_ERROR
                }
            }
            METHOD_INC => {
                if let Ok(mut map) = INSTANCES.lock() {
                    if let Some(inst) = map.get_mut(&instance_id) {
                        inst.count += 1;
                        return write_tlv_i32(inst.count, result, result_len);
                    } else {
                        return NYB_E_INVALID_HANDLE;
                    }
                } else {
                    return NYB_E_PLUGIN_ERROR;
                }
            }
            METHOD_GET => {
                if let Ok(map) = INSTANCES.lock() {
                    if let Some(inst) = map.get(&instance_id) {
                        return write_tlv_i32(inst.count, result, result_len);
                    } else {
                        return NYB_E_INVALID_HANDLE;
                    }
                } else {
                    return NYB_E_PLUGIN_ERROR;
                }
            }
            _ => NYB_E_INVALID_METHOD,
        }
    }
}

#[no_mangle]
pub static nyash_typebox_CounterBox: NyashTypeBoxFfi = NyashTypeBoxFfi {
    abi_tag: 0x5459_4258, // 'TYBX'
    version: 1,
    struct_size: std::mem::size_of::<NyashTypeBoxFfi>() as u16,
    name: b"CounterBox\0".as_ptr() as *const std::os::raw::c_char,
    resolve: Some(counter_resolve),
    invoke_id: Some(counter_invoke),
    capabilities: 0,
};

// ===== TLV helpers =====
fn write_tlv_result(payloads: &[(u8, &[u8])], result: *mut u8, result_len: *mut usize) -> i32 {
    if result_len.is_null() {
        return NYB_E_INVALID_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()); // version
    buf.extend_from_slice(&(payloads.len() as u16).to_le_bytes()); // argc
    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 NYB_E_SHORT_BUFFER;
        }
        std::ptr::copy_nonoverlapping(buf.as_ptr(), result, needed);
        *result_len = needed;
    }
    NYB_SUCCESS
}

fn write_tlv_i32(v: i32, result: *mut u8, result_len: *mut usize) -> i32 {
    write_tlv_result(&[(2u8, &v.to_le_bytes())], result, result_len)
}

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
}