//! Relibc Threads, or RLCT.

use core::{
    cell::UnsafeCell,
    ptr,
    sync::atomic::{AtomicBool, AtomicUsize, Ordering},
};

use alloc::collections::BTreeMap;

use crate::{
    error::Errno,
    header::{errno::*, pthread as header, sched::sched_param, sys_mman},
    ld_so::{ExpectTlsFree, tcb::Tcb},
    platform::{Pal, Sys, types::*},
};

use crate::sync::{Mutex, waitval::Waitval};

/// Called only by the main thread, as part of relibc_start.
#[allow(unused_mut)]
pub unsafe fn init() {
    let mut thread = Pthread {
        waitval: Waitval::new(),
        has_enabled_cancelation: AtomicBool::new(false),
        has_queued_cancelation: AtomicBool::new(false),
        flags: PthreadFlags::empty().bits().into(),

        //index: FIRST_THREAD_IDX,

        // TODO: set these values on Linux as well
        stack_base: ptr::null_mut(),
        stack_size: 0,

        os_tid: UnsafeCell::new(Sys::current_os_tid()),

        robust_list_head: UnsafeCell::new(core::ptr::null_mut()),
    };

    #[cfg(target_os = "redox")]
    {
        //TODO: what is the best way to get these values?
        use redox_rt::arch::{STACK_SIZE, STACK_TOP};
        thread.stack_base = (STACK_TOP - STACK_SIZE) as *mut c_void;
        thread.stack_size = STACK_SIZE;
    }

    unsafe { Tcb::current() }
        .expect_notls("no TCB present for main thread")
        .pthread = thread;
}

//static NEXT_INDEX: AtomicU32 = AtomicU32::new(FIRST_THREAD_IDX + 1);
//const FIRST_THREAD_IDX: usize = 1;

pub unsafe fn terminate_from_main_thread() {
    for (_, tcb) in OS_TID_TO_PTHREAD.lock().iter() {
        let _ = unsafe { cancel(&(*tcb.0).pthread) };
    }
}

bitflags::bitflags! {
    pub struct PthreadFlags: usize {
        const DETACHED = 1;
        const FINISHED = 2;
    }
}

#[derive(Debug)]
pub struct Pthread {
    pub(crate) waitval: Waitval<Retval>,
    pub(crate) has_queued_cancelation: AtomicBool,
    pub(crate) has_enabled_cancelation: AtomicBool,
    pub(crate) flags: AtomicUsize,

    pub(crate) stack_base: *mut c_void,
    pub(crate) stack_size: usize,

    pub os_tid: UnsafeCell<OsTid>,

    /// Head of the per-thread robust mutex list, used by the kernel
    /// during thread exit to mark any held robust mutexes with
    /// `FUTEX_OWNER_DIED` so a future `pthread_mutex_lock` on a
    /// dead-owner mutex can recover via `EOWNERDEAD`. Maintained as
    /// an `UnsafeCell<*mut RobustMutexNode>` because the kernel walks
    /// it during thread exit. `null` = empty list.
    pub(crate) robust_list_head: UnsafeCell<*mut crate::sync::pthread_mutex::RobustMutexNode>,
}

#[derive(Clone, Copy, Debug, Default, Ord, Eq, PartialOrd, PartialEq)]
pub struct OsTid {
    #[cfg(target_os = "redox")]
    pub thread_fd: usize,
    #[cfg(target_os = "linux")]
    pub thread_id: usize,
}

unsafe impl Send for Pthread {}
unsafe impl Sync for Pthread {}

#[derive(Clone, Copy, Debug)]
pub struct Retval(pub *mut c_void);

struct MmapGuard {
    page_start: *mut c_void,
    mmap_size: usize,
}
impl Drop for MmapGuard {
    fn drop(&mut self) {
        unsafe {
            let _ = Sys::munmap(self.page_start, self.mmap_size);
        }
    }
}

#[allow(unused_mut)]
pub(crate) unsafe fn create(
    attrs: Option<&header::RlctAttr>,
    start_routine: extern "C" fn(arg: *mut c_void) -> *mut c_void,
    arg: *mut c_void,
) -> Result<pthread_t, Errno> {
    let attrs = attrs.cloned().unwrap_or_default();

    let mut current_sigmask = 0_u64;
    #[cfg(target_os = "redox")]
    {
        current_sigmask =
            redox_rt::signal::get_sigmask().expect("failed to obtain sigprocmask for caller");
    }

    // Create a locked mutex, unlocked by the thread after it has started.
    let synchronization_mutex = unsafe { Mutex::locked(current_sigmask) };
    let synchronization_mutex = &synchronization_mutex;

    let stack_size = attrs.stacksize.next_multiple_of(Sys::getpagesize());

    let stack_base = if attrs.stack != 0 {
        attrs.stack as *mut c_void
    } else {
        let ret = unsafe {
            sys_mman::mmap(
                core::ptr::null_mut(),
                stack_size,
                sys_mman::PROT_READ | sys_mman::PROT_WRITE,
                sys_mman::MAP_PRIVATE | sys_mman::MAP_ANONYMOUS,
                -1,
                0,
            )
        };
        if ret as isize == -1 {
            // "Insufficient resources"
            return Err(Errno(EAGAIN));
        }
        ret
    };

    let mut flags = PthreadFlags::empty();
    match i32::from(attrs.detachstate) {
        header::PTHREAD_CREATE_DETACHED => flags |= PthreadFlags::DETACHED,
        header::PTHREAD_CREATE_JOINABLE => (),

        other => unreachable!("unknown detachstate {}", other),
    }

    let stack_raii = MmapGuard {
        page_start: stack_base,
        mmap_size: stack_size,
    };

    let current_tcb = unsafe { Tcb::current() }.expect("no TCB!");
    let new_tcb = unsafe { Tcb::new(current_tcb.tls_len) }.map_err(|_| Errno(ENOMEM))?;
    new_tcb.pthread.flags = flags.bits().into();
    new_tcb.pthread.stack_base = stack_base;
    new_tcb.pthread.stack_size = stack_size;
    // Initialize the robust mutex list head to null. The
    // Pthread struct is zero-initialized in Tcb::new but we
    // set this explicitly for documentation/clarity, and to
    // guard against future changes that might not zero the
    // struct (e.g. a switch to Box<MaybeUninit<Pthread>>).
    // Without this, the first pthread_mutex_lock of a
    // ROBUST mutex would dereference an uninitialized pointer.
    new_tcb.pthread.robust_list_head = UnsafeCell::new(core::ptr::null_mut());

    new_tcb.masters_ptr = current_tcb.masters_ptr;
    new_tcb.masters_len = current_tcb.masters_len;
    new_tcb.linker_ptr = current_tcb.linker_ptr;
    new_tcb.mspace = current_tcb.mspace;

    let stack_end = unsafe { stack_base.add(stack_size) };
    let mut stack = stack_end.cast::<usize>();
    {
        let mut push = |value: usize| {
            stack = unsafe { stack.sub(1) };
            unsafe { stack.write(value) };
        };

        if cfg!(target_arch = "aarch64") {
            // Aarch64 requires the stack to be 16 byte aligned after
            // the call instruction, unlike x86 which requires it to be
            // aligned before the call instruction. As such push an
            // extra word on the stack to align the stack to 16 bytes.
            push(0);
        }
        push(0);
        push(0);
        push(ptr::from_ref(synchronization_mutex) as usize);
        push(ptr::from_mut(new_tcb) as usize);

        push(arg as usize);
        push(start_routine as usize);

        push(new_thread_shim as *const () as usize);
    }

    let Ok(os_tid) = (unsafe { Sys::rlct_clone(stack, &mut new_tcb.os_specific) }) else {
        return Err(Errno(EAGAIN));
    };
    core::mem::forget(stack_raii);

    let _ = synchronization_mutex.lock();

    OS_TID_TO_PTHREAD
        .lock()
        .insert(os_tid, ForceSendSync(new_tcb));

    Ok(&raw const new_tcb.pthread as *mut _)
}

/// A shim to wrap thread entry points in logic to set up TLS, for example
unsafe extern "C" fn new_thread_shim(
    entry_point: unsafe extern "C" fn(*mut c_void) -> *mut c_void,
    arg: *mut c_void,
    tcb: *mut Tcb,
    synchronization_mutex: *const Mutex<u64>,
) -> ! {
    let tcb = unsafe { tcb.as_mut() }.expect_notls("non-null TLS is required");

    #[cfg(not(target_os = "redox"))]
    {
        unsafe { tcb.activate() };
    }
    #[cfg(target_os = "redox")]
    {
        // `thr_fd` in `tcb` is set by [`Sys::rlct_clone`] *before* jumping to
        // the entry point of the new thread.
        unsafe {
            tcb.activate(None);
        }
        redox_rt::signal::setup_sighandler(&tcb.os_specific, false);
    }

    let procmask = unsafe { (&*synchronization_mutex).as_ptr().read() };

    unsafe { tcb.copy_masters() }.unwrap();

    unsafe { (*tcb).pthread.os_tid.get().write(Sys::current_os_tid()) };

    unsafe { (&*synchronization_mutex).manual_unlock() };

    #[cfg(target_os = "redox")]
    {
        redox_rt::signal::set_sigmask(Some(procmask), None)
            .expect("failed to set procmask in child thread");
    }

    let retval = unsafe { entry_point(arg) };

    unsafe { exit_current_thread(Retval(retval)) }
}
pub unsafe fn join(thread: &Pthread) -> Result<Retval, Errno> {
    // We don't have to return EDEADLK, but unlike e.g. pthread_t lifetime checking, it's a
    // relatively easy check.
    if core::ptr::eq(
        thread,
        current_thread().expect("current thread not present"),
    ) {
        return Err(Errno(EDEADLK));
    }

    // Waitval starts locked, and is unlocked when the thread finishes.
    let retval = *thread.waitval.wait();

    // We have now awaited the thread and received its return value. POSIX states that the
    // pthread_t of this thread, will no longer be valid. In practice, we can thus deallocate the
    // thread state.

    unsafe { dealloc_thread(thread) };

    Ok(retval)
}

pub unsafe fn detach(thread: &Pthread) -> Result<(), Errno> {
    thread
        .flags
        .fetch_or(PthreadFlags::DETACHED.bits(), Ordering::AcqRel);
    Ok(())
}

pub fn current_thread() -> Option<&'static Pthread> {
    unsafe { Tcb::current().map(|p| &p.pthread) }
}

pub unsafe fn testcancel() {
    let this_thread = current_thread().expect("current thread not present");

    if this_thread.has_queued_cancelation.load(Ordering::Acquire)
        && this_thread.has_enabled_cancelation.load(Ordering::Acquire)
    {
        unsafe { cancel_current_thread() };
    }
}

pub unsafe fn exit_current_thread(retval: Retval) -> ! {
    // Run pthread_cleanup_push/pthread_cleanup_pop destructors.
    unsafe { header::run_destructor_stack() };

    unsafe { header::tls::run_all_destructors() };

    let this = current_thread().expect("failed to obtain current thread when exiting");
    let stack_base = this.stack_base;
    let stack_size = this.stack_size;

    if this.flags.load(Ordering::Acquire) & PthreadFlags::DETACHED.bits() != 0 {
        // When detached, the thread state no longer makes any sense, and can immediately be
        // deallocated.
        unsafe { dealloc_thread(this) };
    } else {
        // Mark the thread as finished so that pthread_kill() can return ESRCH
        // instead of delivering a signal to a thread that has already exited.
        this.flags.fetch_or(PthreadFlags::FINISHED.bits(), Ordering::AcqRel);
        // When joinable, the return value should be made available to other threads.
        unsafe { this.waitval.post(retval) };
    }

    unsafe { Sys::exit_thread(stack_base.cast(), stack_size) }
}

unsafe fn dealloc_thread(thread: &Pthread) {
    // TODO: How should this be handled on Linux?
    unsafe {
        OS_TID_TO_PTHREAD.lock().remove(&thread.os_tid.get().read());
    }
}
pub const SIGRT_RLCT_CANCEL: usize = 33;
pub const SIGRT_RLCT_TIMER: usize = 34;

unsafe extern "C" fn cancel_sighandler(_: c_int) {
    unsafe { cancel_current_thread() };
}
unsafe fn cancel_current_thread() {
    // Terminate the thread
    unsafe { exit_current_thread(Retval(header::PTHREAD_CANCELED)) };
}

pub unsafe fn cancel(thread: &Pthread) -> Result<(), Errno> {
    // TODO: What order should these atomic bools be accessed in?
    thread.has_queued_cancelation.store(true, Ordering::Release);

    if thread.has_enabled_cancelation.load(Ordering::Acquire) {
        (unsafe { Sys::rlct_kill(thread.os_tid.get().read(), SIGRT_RLCT_CANCEL) })?;
    }

    Ok(())
}

pub fn set_sched_param(
    _thread: &Pthread,
    _policy: c_int,
    _param: &sched_param,
) -> Result<(), Errno> {
    // TODO
    Ok(())
}
pub fn set_sched_priority(_thread: &Pthread, _prio: c_int) -> Result<(), Errno> {
    // TODO
    Ok(())
}
pub fn set_cancel_state(state: c_int) -> Result<c_int, Errno> {
    let this_thread = current_thread().expect("current thread not present");

    let was_cancelable = match state {
        header::PTHREAD_CANCEL_ENABLE => {
            let old = this_thread
                .has_enabled_cancelation
                .swap(true, Ordering::Release);

            if this_thread.has_queued_cancelation.load(Ordering::Acquire) {
                unsafe {
                    cancel_current_thread();
                }
            }
            old
        }
        header::PTHREAD_CANCEL_DISABLE => this_thread
            .has_enabled_cancelation
            .swap(false, Ordering::Release),

        _ => return Err(Errno(EINVAL)),
    };

    Ok(match was_cancelable {
        true => header::PTHREAD_CANCEL_ENABLE,
        false => header::PTHREAD_CANCEL_DISABLE,
    })
}
pub fn set_cancel_type(ty: c_int) -> Result<c_int, Errno> {
    let this_thread = current_thread().expect("current thread not present");

    // TODO
    match ty {
        header::PTHREAD_CANCEL_DEFERRED => (),
        header::PTHREAD_CANCEL_ASYNCHRONOUS => (),

        _ => return Err(Errno(EINVAL)),
    }
    Ok(header::PTHREAD_CANCEL_DEFERRED)
}
pub fn get_cpu_clkid(thread: &Pthread) -> Result<clockid_t, Errno> {
    // TODO
    Err(Errno(ENOENT))
}
pub fn get_sched_param(thread: &Pthread) -> Result<(clockid_t, sched_param), Errno> {
    todo!()
}

// TODO: Hash map?
// TODO: RwLock to improve perf?
static OS_TID_TO_PTHREAD: Mutex<BTreeMap<OsTid, ForceSendSync<*mut Tcb>>> =
    Mutex::new(BTreeMap::new());

#[derive(Clone, Copy)]
struct ForceSendSync<T>(T);
unsafe impl<T> Send for ForceSendSync<T> {}
unsafe impl<T> Sync for ForceSendSync<T> {}

/*pub(crate) fn current_thread_index() -> u32 {
    current_thread().expect("current thread not present").index
}*/

#[derive(Clone, Copy, Default, Debug)]
pub enum Pshared {
    #[default]
    Private,

    Shared,
}
impl Pshared {
    pub const fn from_raw(raw: c_int) -> Option<Self> {
        Some(match raw {
            header::PTHREAD_PROCESS_PRIVATE => Self::Private,
            header::PTHREAD_PROCESS_SHARED => Self::Shared,

            _ => return None,
        })
    }
    pub const fn raw(self) -> c_int {
        match self {
            Self::Private => header::PTHREAD_PROCESS_PRIVATE,
            Self::Shared => header::PTHREAD_PROCESS_SHARED,
        }
    }
}

/// Return `true` if the given mutex owner ID refers to a thread that
/// is still alive in this process. Used by `pthread_mutex_lock` to
/// detect robust-mutex dead-owner recovery (a thread exited while
/// holding a robust mutex; the kernel marked it with `FUTEX_OWNER_DIED`
/// and a future lock can recover via `EOWNERDEAD`).
///
/// On Redox, the owner ID is the kernel's `thread_fd` for the
/// thread. The kernel's `proc:` scheme lets us query whether a thread
/// handle is still alive by attempting an `open` on its name handle
/// (EOPNOTSUPP / EBADF / ENOENT -> dead).
///
/// On Linux, the owner ID is the `tid` (kernel task ID). A pthread
/// has not exited when its `tid` is in the live-process set; we
/// approximate this by checking our own `OS_TID_TO_PTHREAD` map,
/// which is populated at thread creation and removed at thread exit.
///
/// The fallback `false` is safe: a `false` return causes the lock
/// path to fall back to `EOWNERDEAD` recovery (treating the lock as
/// orphaned), which is the POSIX-allowed behavior for robust mutexes.
pub fn mutex_owner_id_is_live(owner: u32) -> bool {
    if owner == 0 {
        return false;
    }
    #[cfg(target_os = "redox")]
    {
        // For Redox, attempt to open the thread's "name" handle via
        // the proc scheme. If the thread is alive, the open succeeds;
        // if it has exited and been reaped, the open returns ENOENT.
        let path = alloc::format!("proc:{}/name\0", owner);
        let cstr = match crate::c_str::CStr::from_bytes_with_nul(path.as_bytes()) {
            Ok(c) => c,
            Err(_) => return false,
        };
        let fd = crate::platform::Sys::open(cstr, crate::header::fcntl::O_RDONLY, 0);
        match fd {
            Ok(fd) => {
                let _ = crate::platform::Sys::close(fd);
                true
            }
            Err(_) => false,
        }
    }
    #[cfg(target_os = "linux")]
    {
        // For Linux, the OS_TID_TO_PTHREAD map is maintained at
        // thread creation (insert) and exit (remove). If owner is
        // in the map, the thread is alive. We acquire the map lock
        // briefly to avoid a TOCTOU race.
        crate::pthread::OS_TID_TO_PTHREAD
            .lock()
            .iter()
            .any(|(_os_tid, pthread)| {
                let tid = unsafe { (*pthread).os_tid.get().read() };
                tid.thread_id as u32 == owner
            })
    }
}