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use crate::atomic::{Ordering, PyAtomic, Radium};

// State layout (usize):

// [1 bit: destructed] [1 bit: reserved] [1 bit: leaked] [N bits: weak_count] [M bits: strong_count]

// 64-bit: N=30, M=31. 32-bit: N=14, M=15.

const FLAG_BITS: u32 = 3;

const DESTRUCTED: usize = 1 << (usize::BITS - 1);

const LEAKED: usize = 1 << (usize::BITS - 3);

const TOTAL_COUNT_WIDTH: u32 = usize::BITS - FLAG_BITS;

const WEAK_WIDTH: u32 = TOTAL_COUNT_WIDTH / 2;

const STRONG_WIDTH: u32 = TOTAL_COUNT_WIDTH - WEAK_WIDTH;

const STRONG: usize = (1 << STRONG_WIDTH) - 1;

const COUNT: usize = 1;

const WEAK_COUNT: usize = 1 << STRONG_WIDTH;

#[inline(never)]

#[cold]

fn refcount_overflow() -> ! {

#[cfg(feature = "std")]

std::process::abort();

#[cfg(not(feature = "std"))]

core::panic!("refcount overflow");

}

/// State wraps reference count + flags in a single word (platform usize)

#[derive(Clone, Copy)]

struct State {

inner: usize,

}

impl State {

#[inline]

fn from_raw(inner: usize) -> Self {

Self { inner }

}

#[inline]

fn as_raw(self) -> usize {

self.inner

}

#[inline]

fn strong(self) -> u32 {

((self.inner & STRONG) / COUNT) as u32

}

#[inline]

fn destructed(self) -> bool {

(self.inner & DESTRUCTED) != 0

}

#[inline]

fn leaked(self) -> bool {

(self.inner & LEAKED) != 0

}

#[inline]

fn add_strong(self, val: u32) -> Self {

Self::from_raw(self.inner + (val as usize) * COUNT)

}

#[inline]

fn with_leaked(self, leaked: bool) -> Self {

Self::from_raw((self.inner & !LEAKED) | if leaked { LEAKED } else { 0 })

}

/// Reference count using state layout with LEAKED support.

///

/// State layout (usize):

/// 64-bit: [1 bit: destructed] [1 bit: reserved] [1 bit: leaked] [30 bits: weak_count] [31 bits: strong_count]

/// 32-bit: [1 bit: destructed] [1 bit: reserved] [1 bit: leaked] [14 bits: weak_count] [15 bits: strong_count]

pub struct RefCount {

state: PyAtomic<usize>,

}

impl Default for RefCount {

fn default() -> Self {

Self::new()

}

impl RefCount {

/// Create a new RefCount with strong count = 1

pub fn new() -> Self {

// Initial state: strong=1, weak=1 (implicit weak for strong refs)

Self {

state: Radium::new(COUNT + WEAK_COUNT),

}

/// Get current strong count

#[inline]

pub fn get(&self) -> usize {

State::from_raw(self.state.load(Ordering::Relaxed)).strong() as usize

}

/// Increment strong count

#[inline]

pub fn inc(&self) {

let val = State::from_raw(self.state.fetch_add(COUNT, Ordering::Relaxed));

if val.destructed() || (val.strong() as usize) > STRONG - 1 {

refcount_overflow();

}

if val.strong() == 0 {

// The previous fetch_add created a permission to run decrement again

self.state.fetch_add(COUNT, Ordering::Relaxed);

}

#[inline]

pub fn inc_by(&self, n: usize) {

debug_assert!(n <= STRONG);

let val = State::from_raw(self.state.fetch_add(n * COUNT, Ordering::Relaxed));

if val.destructed() || (val.strong() as usize) > STRONG - n {

refcount_overflow();

}

/// Returns true if successful

#[inline]

#[must_use]

pub fn safe_inc(&self) -> bool {

let mut old = State::from_raw(self.state.load(Ordering::Relaxed));

loop {

if old.destructed() || old.strong() == 0 {

return false;

}

if (old.strong() as usize) >= STRONG {

refcount_overflow();

}

let new_state = old.add_strong(1);

match self.state.compare_exchange_weak(

old.as_raw(),

new_state.as_raw(),

Ordering::Relaxed,

) {

Ok(_) => return true,

Err(curr) => old = State::from_raw(curr),

}

/// Decrement strong count. Returns true when count drops to 0.

#[inline]

#[must_use]

pub fn dec(&self) -> bool {

let old = State::from_raw(self.state.fetch_sub(COUNT, Ordering::Release));

// LEAKED objects never reach 0

if old.leaked() {

return false;

}

if old.strong() == 1 {

core::sync::atomic::fence(Ordering::Acquire);

return true;

}

false

}

/// Mark this object as leaked (interned). It will never be deallocated.

pub fn leak(&self) {

debug_assert!(!self.is_leaked());

let mut old = State::from_raw(self.state.load(Ordering::Relaxed));

loop {

let new_state = old.with_leaked(true);

match self.state.compare_exchange_weak(

old.as_raw(),

new_state.as_raw(),

Ordering::AcqRel,

Ordering::Relaxed,

) {

Ok(_) => return,

Err(curr) => old = State::from_raw(curr),

}

/// Check if this object is leaked (interned).

pub fn is_leaked(&self) -> bool {

State::from_raw(self.state.load(Ordering::Acquire)).leaked()

}

// Deferred Drop Infrastructure

// This mechanism allows untrack_object() calls to be deferred until after

// the GC collection phase completes, preventing deadlocks that occur when

// clear (pop_edges) triggers object destruction while holding the tracked_objects lock.

#[cfg(feature = "std")]

use core::cell::{Cell, RefCell};

#[cfg(feature = "std")]

thread_local! {

/// Flag indicating if we're inside a deferred drop context.

/// When true, drop operations should defer untrack calls.

static IN_DEFERRED_CONTEXT: Cell<bool> = const { Cell::new(false) };

/// Queue of deferred untrack operations.

/// No Send bound needed - this is thread-local and only accessed from the same thread.

static DEFERRED_QUEUE: RefCell<Vec<Box<dyn FnOnce()>>> = const { RefCell::new(Vec::new()) };

}

#[cfg(feature = "std")]

struct DeferredDropGuard {

was_in_context: bool,

}

#[cfg(feature = "std")]

impl Drop for DeferredDropGuard {

fn drop(&mut self) {

IN_DEFERRED_CONTEXT.with(|in_ctx| {

in_ctx.set(self.was_in_context);

});

// Only flush if we're the outermost context and not already panicking

// (flushing during unwinding risks double-panic → process abort).

if !self.was_in_context && !std::thread::panicking() {

flush_deferred_drops();

}

/// Execute a function within a deferred drop context.

/// Any calls to `try_defer_drop` within this context will be queued

/// and executed when the context exits (even on panic).

#[cfg(feature = "std")]

#[inline]

pub fn with_deferred_drops<F, R>(f: F) -> R

where

F: FnOnce() -> R,

{

let _guard = IN_DEFERRED_CONTEXT.with(|in_ctx| {

let was_in_context = in_ctx.get();

in_ctx.set(true);

DeferredDropGuard { was_in_context }

});

f()

}

/// Try to defer a drop-related operation.

/// If inside a deferred context, the operation is queued.

/// Otherwise, it executes immediately.

#[cfg(feature = "std")]

#[inline]

pub fn try_defer_drop<F>(f: F)

where

F: FnOnce() + 'static,

{

let should_defer = IN_DEFERRED_CONTEXT.with(|in_ctx| in_ctx.get());

if should_defer {

DEFERRED_QUEUE.with(|q| {

q.borrow_mut().push(Box::new(f));

});

} else {

f();

}

/// Flush all deferred drop operations.

/// This is automatically called when exiting a deferred context.

#[cfg(feature = "std")]

#[inline]

pub fn flush_deferred_drops() {

DEFERRED_QUEUE.with(|q| {

// Take all queued operations

let ops: Vec<_> = q.borrow_mut().drain(..).collect();

// Execute them outside the borrow

for op in ops {

op();

}

});

}

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