#include "thread/Thread.h"
#include "Log.h"
#include "memory/MemoryManager.h"
#include "thread/Scheduler.h"
#include <bits/atfile.h>
#include <bits/open-flags.h>
#include <bits/signal.h>
#include <bits/waitpid.h>
#include <luna/Alloc.h>
#include <luna/Atomic.h>
#include <luna/PathParser.h>

static Atomic<u64> g_next_id;

LinkedList<Thread> g_threads;

void Thread::init()
{
    g_next_id = 2;
}

Result<Thread*> new_thread()
{
    Thread* const thread = TRY(make<Thread>());

    thread->id = g_next_id++;

    return thread;
}

Result<int> Thread::allocate_fd(int min)
{
    if (min < 0 || min >= FD_MAX) return err(EINVAL);
    for (int i = min; i < FD_MAX; i++)
    {
        // FIXME: Possible race condition if multiple threads share a FileDescriptorTable? Let's not worry about it for
        // now, we're still a long way away from reaching that point.
        if (!fd_table[i].has_value()) { return i; }
    }

    return err(EMFILE);
}

Result<FileDescriptor*> Thread::resolve_fd(int fd)
{
    if (fd < 0 || fd >= FD_MAX) return err(EBADF);

    Option<FileDescriptor>& maybe_descriptor = fd_table[fd];

    if (!maybe_descriptor.has_value()) return err(EBADF);

    return maybe_descriptor.value_ptr();
}

Result<SharedPtr<VFS::Inode>> Thread::resolve_atfile(int dirfd, const String& path, bool allow_empty_path,
                                                     bool follow_last_symlink, SharedPtr<VFS::Inode>* parent_inode)
{
    if (parent_inode) *parent_inode = this->current_directory;

    if (PathParser::is_absolute(path.view()))
        return VFS::resolve_path(path.chars(), this->auth, {}, follow_last_symlink);

    if (dirfd == AT_FDCWD)
        return VFS::resolve_path(path.chars(), this->auth, this->current_directory, follow_last_symlink);

    auto descriptor = TRY(resolve_fd(dirfd));

    if (parent_inode) *parent_inode = descriptor->inode;

    if (path.is_empty() && allow_empty_path) return descriptor->inode;

    return VFS::resolve_path(path.chars(), this->auth, descriptor->inode, follow_last_symlink);
}

[[noreturn]] void Thread::exit_and_signal_parent(int _status)
{
    if (this->id == 1) fail("the init process exited");
    if (is_kernel) state = ThreadState::Dying;
    else
    {
        Scheduler::for_each_child(this, [](Thread* child) {
            child->parent = Scheduler::init_thread();
            return true;
        });

        if (parent)
        {
            if (parent->state == ThreadState::Waiting)
            {
                auto child = *parent->child_being_waited_for;
                if (child == -1 || child == (pid_t)id)
                {
                    parent->child_being_waited_for = (pid_t)id;
                    parent->wake_up();
                }
            }
            else { parent->send_signal(SIGCHLD); }
        }

        state = ThreadState::Exited;
    }
    status = _status;
    kernel_yield();
    unreachable();
}

enum class DefaultSignalAction
{
    Ignore,
    Terminate,
};

// FIXME: Implement coredumps for some signals.
static constexpr DefaultSignalAction default_actions[] = {
    DefaultSignalAction::Terminate, // SIGHUP
    DefaultSignalAction::Terminate, // SIGINT
    DefaultSignalAction::Terminate, // SIGQUIT (dump core)
    DefaultSignalAction::Terminate, // SIGILL  (dump core)
    DefaultSignalAction::Terminate, // SIGTRAP (dump core)
    DefaultSignalAction::Terminate, // SIGABRT (dump core)
    DefaultSignalAction::Ignore,    // SIGCHLD
    DefaultSignalAction::Terminate, // SIGFPE  (dump core)
    DefaultSignalAction::Terminate, // SIGKILL
    DefaultSignalAction::Terminate, // SIGSTOP (FIXME: Support stopping and continuing)
    DefaultSignalAction::Terminate, // SIGSEGV (dump core)
    DefaultSignalAction::Ignore,    // SIGCONT (FIXME: Support stopping and continuing)
    DefaultSignalAction::Terminate, // SIGPIPE
    DefaultSignalAction::Terminate, // SIGALRM
    DefaultSignalAction::Terminate, // SIGTERM
    DefaultSignalAction::Terminate, // SIGTTIN
    DefaultSignalAction::Terminate, // SIGTTOU
};

void Thread::process_pending_signals(Registers* current_regs)
{
    interrupted = false;
    for (int i = 0; i < NSIG; i++)
    {
        int signo = i + 1;
        if (signo != SIGKILL && signo != SIGSTOP && signal_mask & (1 << i)) continue;
        if (pending_signals & (1 << i))
        {
            pending_signals &= ~(1 << i);
            kinfoln("signal: executing signal %d for thread %ld", signo, id);
            auto handler = signal_handlers[i];
            if (signo != SIGKILL && signo != SIGSTOP && handler.sa_handler == SIG_IGN)
            {
                kinfoln("signal: ignoring signal (handler=SIG_IGN)");
                return;
            }
            if (handler.sa_handler == SIG_DFL || signo == SIGKILL || signo == SIGSTOP)
            {
            default_signal:
                if (id == 1)
                {
                    kwarnln("signal: init got a signal it has no handler for, ignoring");
                    return;
                }

                kinfoln("signal: using default behavior (handler=SIG_DFL)");

                auto action = default_actions[i];
                switch (action)
                {
                case DefaultSignalAction::Ignore: return;
                // FIXME: Add signal exit codes.
                case DefaultSignalAction::Terminate: exit_and_signal_parent(signo | _SIGBIT);
                default: return;
                }
            }
            // If we fail to deliver the signal (usually because there's not enough space on the stack), execute the
            // default action.
            if (!deliver_signal(signo, current_regs)) goto default_signal;
            return;
        }
    }
}

bool Thread::will_invoke_signal_handler()
{
    for (int i = 0; i < NSIG; i++)
    {
        if (pending_signals & (1 << i))
        {
            int signo = i + 1;
            if (signo != SIGKILL && signo != SIGSTOP && signal_mask & (1 << i)) continue;
            auto handler = signal_handlers[i];
            if (handler.sa_handler == SIG_IGN || handler.sa_handler == SIG_DFL) return false;
            if (signo == SIGKILL || signo == SIGSTOP) return false;
            return true;
        }
    }
    return false;
}

void Thread::send_signal(int signo)
{
    check(signo > 0 && signo <= NSIG);
    pending_signals |= 1 << (signo - 1);

    if (state == ThreadState::Waiting || state == ThreadState::Sleeping)
    {
        interrupted = true;
        wake_up();
    }
}

bool FileDescriptor::should_append()
{
    return flags & O_APPEND;
}

bool FileDescriptor::should_block()
{
    return !(flags & O_NONBLOCK);
}

bool FileDescriptor::is_readable()
{
    return flags & O_RDONLY;
}

bool FileDescriptor::is_writable()
{
    return flags & O_WRONLY;
}