/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * Copyright (c) 2021, sin-ack <sin-ack@protonmail.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/NonnullRefPtrVector.h>
#include <AK/Singleton.h>
#include <AK/StringBuilder.h>
#include <AK/StringView.h>
#include <Kernel/API/InodeWatcherEvent.h>
#include <Kernel/FileSystem/Custody.h>
#include <Kernel/FileSystem/FileDescription.h>
#include <Kernel/FileSystem/Inode.h>
#include <Kernel/FileSystem/InodeWatcher.h>
#include <Kernel/FileSystem/VirtualFileSystem.h>
#include <Kernel/KBufferBuilder.h>
#include <Kernel/Memory/SharedInodeVMObject.h>
#include <Kernel/Net/LocalSocket.h>
#include <Kernel/Process.h>

namespace Kernel {

static SpinLock s_all_inodes_lock;
static AK::Singleton<Inode::List> s_list;

static Inode::List& all_with_lock()
{
    VERIFY(s_all_inodes_lock.is_locked());

    return *s_list;
}

void Inode::sync()
{
    NonnullRefPtrVector<Inode, 32> inodes;
    {
        ScopedSpinLock all_inodes_lock(s_all_inodes_lock);
        for (auto& inode : all_with_lock()) {
            if (inode.is_metadata_dirty())
                inodes.append(inode);
        }
    }

    for (auto& inode : inodes) {
        VERIFY(inode.is_metadata_dirty());
        inode.flush_metadata();
    }
}

KResultOr<NonnullOwnPtr<KBuffer>> Inode::read_entire(FileDescription* description) const
{
    KBufferBuilder builder;

    size_t nread;
    u8 buffer[4096];
    off_t offset = 0;
    for (;;) {
        auto buf = UserOrKernelBuffer::for_kernel_buffer(buffer);
        auto result = read_bytes(offset, sizeof(buffer), buf, description);
        if (result.is_error())
            return result.error();
        nread = result.value();
        VERIFY(nread <= sizeof(buffer));
        if (nread == 0)
            break;
        builder.append((const char*)buffer, nread);
        offset += nread;
        if (nread < sizeof(buffer))
            break;
    }

    auto entire_file = builder.build();
    if (!entire_file)
        return ENOMEM;
    return entire_file.release_nonnull();
}

KResultOr<NonnullRefPtr<Custody>> Inode::resolve_as_link(Custody& base, RefPtr<Custody>* out_parent, int options, int symlink_recursion_level) const
{
    // The default implementation simply treats the stored
    // contents as a path and resolves that. That is, it
    // behaves exactly how you would expect a symlink to work.
    auto contents_or = read_entire();
    if (contents_or.is_error())
        return contents_or.error();

    auto& contents = contents_or.value();
    auto path = StringView(contents->data(), contents->size());
    return VirtualFileSystem::the().resolve_path(path, base, out_parent, options, symlink_recursion_level);
}

Inode::Inode(FileSystem& fs, InodeIndex index)
    : m_file_system(fs)
    , m_index(index)
{
    ScopedSpinLock all_inodes_lock(s_all_inodes_lock);
    all_with_lock().append(*this);
}

Inode::~Inode()
{
    ScopedSpinLock all_inodes_lock(s_all_inodes_lock);
    all_with_lock().remove(*this);

    for (auto& watcher : m_watchers) {
        watcher->unregister_by_inode({}, identifier());
    }
}

void Inode::will_be_destroyed()
{
    MutexLocker locker(m_inode_lock);
    if (m_metadata_dirty)
        flush_metadata();
}

KResult Inode::set_atime(time_t)
{
    return ENOTIMPL;
}

KResult Inode::set_ctime(time_t)
{
    return ENOTIMPL;
}

KResult Inode::set_mtime(time_t)
{
    return ENOTIMPL;
}

KResult Inode::increment_link_count()
{
    return ENOTIMPL;
}

KResult Inode::decrement_link_count()
{
    return ENOTIMPL;
}

void Inode::set_shared_vmobject(Memory::SharedInodeVMObject& vmobject)
{
    MutexLocker locker(m_inode_lock);
    m_shared_vmobject = vmobject;
}

bool Inode::bind_socket(LocalSocket& socket)
{
    MutexLocker locker(m_inode_lock);
    if (m_socket)
        return false;
    m_socket = socket;
    return true;
}

bool Inode::unbind_socket()
{
    MutexLocker locker(m_inode_lock);
    if (!m_socket)
        return false;
    m_socket = nullptr;
    return true;
}

void Inode::register_watcher(Badge<InodeWatcher>, InodeWatcher& watcher)
{
    MutexLocker locker(m_inode_lock);
    VERIFY(!m_watchers.contains(&watcher));
    m_watchers.set(&watcher);
}

void Inode::unregister_watcher(Badge<InodeWatcher>, InodeWatcher& watcher)
{
    MutexLocker locker(m_inode_lock);
    VERIFY(m_watchers.contains(&watcher));
    m_watchers.remove(&watcher);
}

NonnullRefPtr<FIFO> Inode::fifo()
{
    MutexLocker locker(m_inode_lock);
    VERIFY(metadata().is_fifo());

    // FIXME: Release m_fifo when it is closed by all readers and writers
    if (!m_fifo) {
        m_fifo = FIFO::try_create(metadata().uid);
        // FIXME: We need to be able to observe OOM here.
        VERIFY(!m_fifo.is_null());
    }

    VERIFY(m_fifo);
    return *m_fifo;
}

void Inode::set_metadata_dirty(bool metadata_dirty)
{
    MutexLocker locker(m_inode_lock);

    if (metadata_dirty) {
        // Sanity check.
        VERIFY(!fs().is_readonly());
    }

    if (m_metadata_dirty == metadata_dirty)
        return;

    m_metadata_dirty = metadata_dirty;
    if (m_metadata_dirty) {
        // FIXME: Maybe we should hook into modification events somewhere else, I'm not sure where.
        //        We don't always end up on this particular code path, for instance when writing to an ext2fs file.
        for (auto& watcher : m_watchers) {
            watcher->notify_inode_event({}, identifier(), InodeWatcherEvent::Type::MetadataModified);
        }
    }
}

void Inode::did_add_child(InodeIdentifier const&, String const& name)
{
    MutexLocker locker(m_inode_lock);

    for (auto& watcher : m_watchers) {
        watcher->notify_inode_event({}, identifier(), InodeWatcherEvent::Type::ChildCreated, name);
    }
}

void Inode::did_remove_child(InodeIdentifier const&, String const& name)
{
    MutexLocker locker(m_inode_lock);

    if (name == "." || name == "..") {
        // These are just aliases and are not interesting to userspace.
        return;
    }

    for (auto& watcher : m_watchers) {
        watcher->notify_inode_event({}, identifier(), InodeWatcherEvent::Type::ChildDeleted, name);
    }
}

void Inode::did_modify_contents()
{
    MutexLocker locker(m_inode_lock);
    for (auto& watcher : m_watchers) {
        watcher->notify_inode_event({}, identifier(), InodeWatcherEvent::Type::ContentModified);
    }
}

void Inode::did_delete_self()
{
    MutexLocker locker(m_inode_lock);
    for (auto& watcher : m_watchers) {
        watcher->notify_inode_event({}, identifier(), InodeWatcherEvent::Type::Deleted);
    }
}

KResult Inode::prepare_to_write_data()
{
    // FIXME: It's a poor design that filesystems are expected to call this before writing out data.
    //        We should funnel everything through an interface at the VirtualFileSystem layer so this can happen from a single place.
    MutexLocker locker(m_inode_lock);
    if (fs().is_readonly())
        return EROFS;
    auto metadata = this->metadata();
    if (metadata.is_setuid() || metadata.is_setgid()) {
        dbgln("Inode::prepare_to_write_data(): Stripping SUID/SGID bits from {}", identifier());
        return chmod(metadata.mode & ~(04000 | 02000));
    }
    return KSuccess;
}

RefPtr<Memory::SharedInodeVMObject> Inode::shared_vmobject() const
{
    MutexLocker locker(m_inode_lock);
    return m_shared_vmobject.strong_ref();
}

template<typename T>
static inline bool range_overlap(T start1, T len1, T start2, T len2)
{
    return ((start1 < start2 + len2) || len2 == 0) && ((start2 < start1 + len1) || len1 == 0);
}

static inline KResult normalize_flock(FileDescription const& description, flock& lock)
{
    off_t start;
    switch (lock.l_whence) {
    case SEEK_SET:
        start = lock.l_start;
        break;
    case SEEK_CUR:
        start = description.offset() + lock.l_start;
        break;
    case SEEK_END:
        // FIXME: Implement SEEK_END and negative lengths.
        return ENOTSUP;
    default:
        return EINVAL;
    }
    lock = { lock.l_type, SEEK_SET, start, lock.l_len, 0 };
    return KSuccess;
}

KResult Inode::can_apply_flock(FileDescription const& description, flock const& new_lock) const
{
    VERIFY(new_lock.l_whence == SEEK_SET);

    MutexLocker locker(m_inode_lock, Mutex::Mode::Shared);

    if (new_lock.l_type == F_UNLCK) {
        for (auto& lock : m_flocks) {
            if (&description == lock.owner && lock.start == new_lock.l_start && lock.len == new_lock.l_len)
                return KSuccess;
        }
        return EINVAL;
    }

    for (auto& lock : m_flocks) {
        if (!range_overlap(lock.start, lock.len, new_lock.l_start, new_lock.l_len))
            continue;

        if (new_lock.l_type == F_RDLCK && lock.type == F_WRLCK)
            return EAGAIN;

        if (new_lock.l_type == F_WRLCK)
            return EAGAIN;
    }
    return KSuccess;
}

KResult Inode::apply_flock(Process const& process, FileDescription const& description, Userspace<flock const*> input_lock)
{
    flock new_lock;
    if (!copy_from_user(&new_lock, input_lock))
        return EFAULT;

    auto rc = normalize_flock(description, new_lock);
    if (rc.is_error())
        return rc;

    MutexLocker locker(m_inode_lock);

    rc = can_apply_flock(description, new_lock);
    if (rc.is_error())
        return rc;

    if (new_lock.l_type == F_UNLCK) {
        for (size_t i = 0; i < m_flocks.size(); ++i) {
            if (&description == m_flocks[i].owner && m_flocks[i].start == new_lock.l_start && m_flocks[i].len == new_lock.l_len) {
                m_flocks.remove(i);
                return KSuccess;
            }
        }
        return EINVAL;
    }

    m_flocks.append(Flock { new_lock.l_type, new_lock.l_start, new_lock.l_len, &description, process.pid().value() });
    return KSuccess;
}

KResult Inode::get_flock(FileDescription const& description, Userspace<flock*> reference_lock) const
{
    flock lookup;
    if (!copy_from_user(&lookup, reference_lock))
        return EFAULT;

    auto rc = normalize_flock(description, lookup);
    if (rc.is_error())
        return rc;

    MutexLocker locker(m_inode_lock, Mutex::Mode::Shared);

    for (auto& lock : m_flocks) {
        if (!range_overlap(lock.start, lock.len, lookup.l_start, lookup.l_len))
            continue;

        if ((lookup.l_type == F_RDLCK && lock.type == F_WRLCK) || lookup.l_type == F_WRLCK) {
            lookup = { lock.type, SEEK_SET, lock.start, lock.len, lock.pid };
            if (!copy_to_user(reference_lock, &lookup))
                return EFAULT;
            return KSuccess;
        }
    }

    lookup.l_type = F_UNLCK;
    if (!copy_to_user(reference_lock, &lookup))
        return EFAULT;
    return KSuccess;
}

void Inode::remove_flocks_for_description(FileDescription const& description)
{
    MutexLocker locker(m_inode_lock);

    for (size_t i = 0; i < m_flocks.size(); ++i) {
        if (&description == m_flocks[i].owner)
            m_flocks.remove(i--);
    }
}
}