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    //! File-locking support.
    //!
    //! This module defines the [`Filesystem`] type which is an abstraction over a
    //! filesystem, ensuring that access to the filesystem is only done through
    //! coordinated locks.
    //!
    //! The [`FileLock`] type represents a locked file, and provides access to the
    //! file.

    use std::fs::{File, OpenOptions};
    use std::io;
    use std::io::{Read, Seek, SeekFrom, Write};
    use std::path::{Display, Path, PathBuf};

    use crate::util::errors::CargoResult;
    use crate::util::style;
    use crate::util::GlobalContext;
    use anyhow::Context as _;
    use cargo_util::paths;
    use sys::*;

    /// A locked file.
    ///
    /// This provides access to file while holding a lock on the file. This type
    /// implements the [`Read`], [`Write`], and [`Seek`] traits to provide access
    /// to the underlying file.
    ///
    /// Locks are either shared (multiple processes can access the file) or
    /// exclusive (only one process can access the file).
    ///
    /// This type is created via methods on the [`Filesystem`] type.
    ///
    /// When this value is dropped, the lock will be released.
    #[derive(Debug)]
    pub struct FileLock {
        f: Option<File>,
        path: PathBuf,
    }

    impl FileLock {
        /// Returns the underlying file handle of this lock.
        pub fn file(&self) -> &File {
            self.f.as_ref().unwrap()
        }

        /// Returns the underlying path that this lock points to.
        ///
        /// Note that special care must be taken to ensure that the path is not
        /// referenced outside the lifetime of this lock.
        pub fn path(&self) -> &Path {
            &self.path
        }

        /// Returns the parent path containing this file
        pub fn parent(&self) -> &Path {
            self.path.parent().unwrap()
        }

        /// Removes all sibling files to this locked file.
        ///
        /// This can be useful if a directory is locked with a sentinel file but it
        /// needs to be cleared out as it may be corrupt.
        pub fn remove_siblings(&self) -> CargoResult<()> {
            let path = self.path();
            for entry in path.parent().unwrap().read_dir()? {
                let entry = entry?;
                if Some(&entry.file_name()[..]) == path.file_name() {
                    continue;
                }
                let kind = entry.file_type()?;
                if kind.is_dir() {
                    paths::remove_dir_all(entry.path())?;
                } else {
                    paths::remove_file(entry.path())?;
                }
            }
            Ok(())
        }
    }

    impl Read for FileLock {
        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
            self.file().read(buf)
        }
    }

    impl Seek for FileLock {
        fn seek(&mut self, to: SeekFrom) -> io::Result<u64> {
            self.file().seek(to)
        }
    }

    impl Write for FileLock {
        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
            self.file().write(buf)
        }

        fn flush(&mut self) -> io::Result<()> {
            self.file().flush()
        }
    }

    impl Drop for FileLock {
        fn drop(&mut self) {
            if let Some(f) = self.f.take() {
                if let Err(e) = unlock(&f) {
                    tracing::warn!("failed to release lock: {e:?}");
                }
            }
        }
    }

    /// A "filesystem" is intended to be a globally shared, hence locked, resource
    /// in Cargo.
    ///
    /// The `Path` of a filesystem cannot be learned unless it's done in a locked
    /// fashion, and otherwise functions on this structure are prepared to handle
    /// concurrent invocations across multiple instances of Cargo.
    ///
    /// The methods on `Filesystem` that open files return a [`FileLock`] which
    /// holds the lock, and that type provides methods for accessing the
    /// underlying file.
    ///
    /// If the blocking methods (like [`Filesystem::open_ro_shared`]) detect that
    /// they will block, then they will display a message to the user letting them
    /// know it is blocked. There are non-blocking variants starting with the
    /// `try_` prefix like [`Filesystem::try_open_ro_shared_create`].
    ///
    /// The behavior of locks acquired by the `Filesystem` depend on the operating
    /// system. On unix-like system, they are advisory using [`flock`], and thus
    /// not enforced against processes which do not try to acquire the lock. On
    /// Windows, they are mandatory using [`LockFileEx`], enforced against all
    /// processes.
    ///
    /// This **does not** guarantee that a lock is acquired. In some cases, for
    /// example on filesystems that don't support locking, it will return a
    /// [`FileLock`] even though the filesystem lock was not acquired. This is
    /// intended to provide a graceful fallback instead of refusing to work.
    /// Usually there aren't multiple processes accessing the same resource. In
    /// that case, it is the user's responsibility to not run concurrent
    /// processes.
    ///
    /// [`flock`]: https://linux.die.net/man/2/flock
    /// [`LockFileEx`]: https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-lockfileex
    #[derive(Clone, Debug)]
    pub struct Filesystem {
        root: PathBuf,
    }

    impl Filesystem {
        /// Creates a new filesystem to be rooted at the given path.
        pub fn new(path: PathBuf) -> Filesystem {
            Filesystem { root: path }
        }

        /// Like `Path::join`, creates a new filesystem rooted at this filesystem
        /// joined with the given path.
        pub fn join<T: AsRef<Path>>(&self, other: T) -> Filesystem {
            Filesystem::new(self.root.join(other))
        }

        /// Like `Path::push`, pushes a new path component onto this filesystem.
        pub fn push<T: AsRef<Path>>(&mut self, other: T) {
            self.root.push(other);
        }

        /// Consumes this filesystem and returns the underlying `PathBuf`.
        ///
        /// Note that this is a relatively dangerous operation and should be used
        /// with great caution!.
        pub fn into_path_unlocked(self) -> PathBuf {
            self.root
        }

        /// Returns the underlying `Path`.
        ///
        /// Note that this is a relatively dangerous operation and should be used
        /// with great caution!.
        pub fn as_path_unlocked(&self) -> &Path {
            &self.root
        }

        /// Creates the directory pointed to by this filesystem.
        ///
        /// Handles errors where other Cargo processes are also attempting to
        /// concurrently create this directory.
        pub fn create_dir(&self) -> CargoResult<()> {
            paths::create_dir_all(&self.root)
        }

        /// Returns an adaptor that can be used to print the path of this
        /// filesystem.
        pub fn display(&self) -> Display<'_> {
            self.root.display()
        }

        /// Opens read-write exclusive access to a file, returning the locked
        /// version of a file.
        ///
        /// This function will create a file at `path` if it doesn't already exist
        /// (including intermediate directories), and then it will acquire an
        /// exclusive lock on `path`. If the process must block waiting for the
        /// lock, the `msg` is printed to [`GlobalContext`].
        ///
        /// The returned file can be accessed to look at the path and also has
        /// read/write access to the underlying file.
        pub fn open_rw_exclusive_create<P>(
            &self,
            path: P,
            gctx: &GlobalContext,
            msg: &str,
        ) -> CargoResult<FileLock>
        where
            P: AsRef<Path>,
        {
            let mut opts = OpenOptions::new();
            opts.read(true).write(true).create(true);
            let (path, f) = self.open(path.as_ref(), &opts, true)?;
            acquire(gctx, msg, &path, &|| try_lock_exclusive(&f), &|| {
                lock_exclusive(&f)
            })?;
            Ok(FileLock { f: Some(f), path })
        }

        /// A non-blocking version of [`Filesystem::open_rw_exclusive_create`].
        ///
        /// Returns `None` if the operation would block due to another process
        /// holding the lock.
        pub fn try_open_rw_exclusive_create<P: AsRef<Path>>(
            &self,
            path: P,
        ) -> CargoResult<Option<FileLock>> {
            let mut opts = OpenOptions::new();
            opts.read(true).write(true).create(true);
            let (path, f) = self.open(path.as_ref(), &opts, true)?;
            if try_acquire(&path, &|| try_lock_exclusive(&f))? {
                Ok(Some(FileLock { f: Some(f), path }))
            } else {
                Ok(None)
            }
        }

        /// Opens read-only shared access to a file, returning the locked version of a file.
        ///
        /// This function will fail if `path` doesn't already exist, but if it does
        /// then it will acquire a shared lock on `path`. If the process must block
        /// waiting for the lock, the `msg` is printed to [`GlobalContext`].
        ///
        /// The returned file can be accessed to look at the path and also has read
        /// access to the underlying file. Any writes to the file will return an
        /// error.
        pub fn open_ro_shared<P>(
            &self,
            path: P,
            gctx: &GlobalContext,
            msg: &str,
        ) -> CargoResult<FileLock>
        where
            P: AsRef<Path>,
        {
            let (path, f) = self.open(path.as_ref(), &OpenOptions::new().read(true), false)?;
            acquire(gctx, msg, &path, &|| try_lock_shared(&f), &|| {
                lock_shared(&f)
            })?;
            Ok(FileLock { f: Some(f), path })
        }

        /// Opens read-only shared access to a file, returning the locked version of a file.
        ///
        /// Compared to [`Filesystem::open_ro_shared`], this will create the file
        /// (and any directories in the parent) if the file does not already
        /// exist.
        pub fn open_ro_shared_create<P: AsRef<Path>>(
            &self,
            path: P,
            gctx: &GlobalContext,
            msg: &str,
        ) -> CargoResult<FileLock> {
            let mut opts = OpenOptions::new();
            opts.read(true).write(true).create(true);
            let (path, f) = self.open(path.as_ref(), &opts, true)?;
            acquire(gctx, msg, &path, &|| try_lock_shared(&f), &|| {
                lock_shared(&f)
            })?;
            Ok(FileLock { f: Some(f), path })
        }

        /// A non-blocking version of [`Filesystem::open_ro_shared_create`].
        ///
        /// Returns `None` if the operation would block due to another process
        /// holding the lock.
        pub fn try_open_ro_shared_create<P: AsRef<Path>>(
            &self,
            path: P,
        ) -> CargoResult<Option<FileLock>> {
            let mut opts = OpenOptions::new();
            opts.read(true).write(true).create(true);
            let (path, f) = self.open(path.as_ref(), &opts, true)?;
            if try_acquire(&path, &|| try_lock_shared(&f))? {
                Ok(Some(FileLock { f: Some(f), path }))
            } else {
                Ok(None)
            }
        }

        fn open(&self, path: &Path, opts: &OpenOptions, create: bool) -> CargoResult<(PathBuf, File)> {
            let path = self.root.join(path);
            let f = opts
                .open(&path)
                .or_else(|e| {
                    // If we were requested to create this file, and there was a
                    // NotFound error, then that was likely due to missing
                    // intermediate directories. Try creating them and try again.
                    if e.kind() == io::ErrorKind::NotFound && create {
                        paths::create_dir_all(path.parent().unwrap())?;
                        Ok(opts.open(&path)?)
                    } else {
                        Err(anyhow::Error::from(e))
                    }
                })
                .with_context(|| format!("failed to open: {}", path.display()))?;
            Ok((path, f))
        }
    }

    impl PartialEq<Path> for Filesystem {
        fn eq(&self, other: &Path) -> bool {
            self.root == other
        }
    }

    impl PartialEq<Filesystem> for Path {
        fn eq(&self, other: &Filesystem) -> bool {
            self == other.root
        }
    }

    fn try_acquire(path: &Path, lock_try: &dyn Fn() -> io::Result<()>) -> CargoResult<bool> {
        // File locking on Unix is currently implemented via `flock`, which is known
        // to be broken on NFS. We could in theory just ignore errors that happen on
        // NFS, but apparently the failure mode [1] for `flock` on NFS is **blocking
        // forever**, even if the "non-blocking" flag is passed!
        //
        // As a result, we just skip all file locks entirely on NFS mounts. That
        // should avoid calling any `flock` functions at all, and it wouldn't work
        // there anyway.
        //
        // [1]: https://github.com/rust-lang/cargo/issues/2615
        if is_on_nfs_mount(path) {
            tracing::debug!("{path:?} appears to be an NFS mount, not trying to lock");
            return Ok(true);
        }

        match lock_try() {
            Ok(()) => return Ok(true),

            // In addition to ignoring NFS which is commonly not working we also
            // just ignore locking on filesystems that look like they don't
            // implement file locking.
            Err(e) if error_unsupported(&e) => return Ok(true),

            Err(e) => {
                if !error_contended(&e) {
                    let e = anyhow::Error::from(e);
                    let cx = format!("failed to lock file: {}", path.display());
                    return Err(e.context(cx));
                }
            }
        }
        Ok(false)
    }

    /// Acquires a lock on a file in a "nice" manner.
    ///
    /// Almost all long-running blocking actions in Cargo have a status message
    /// associated with them as we're not sure how long they'll take. Whenever a
    /// conflicted file lock happens, this is the case (we're not sure when the lock
    /// will be released).
    ///
    /// This function will acquire the lock on a `path`, printing out a nice message
    /// to the console if we have to wait for it. It will first attempt to use `try`
    /// to acquire a lock on the crate, and in the case of contention it will emit a
    /// status message based on `msg` to [`GlobalContext`]'s shell, and then use `block` to
    /// block waiting to acquire a lock.
    ///
    /// Returns an error if the lock could not be acquired or if any error other
    /// than a contention error happens.
    fn acquire(
        gctx: &GlobalContext,
        msg: &str,
        path: &Path,
        lock_try: &dyn Fn() -> io::Result<()>,
        lock_block: &dyn Fn() -> io::Result<()>,
    ) -> CargoResult<()> {
        if try_acquire(path, lock_try)? {
            return Ok(());
        }
        let msg = format!("waiting for file lock on {}", msg);
        gctx.shell()
            .status_with_color("Blocking", &msg, &style::NOTE)?;

        lock_block().with_context(|| format!("failed to lock file: {}", path.display()))?;
        Ok(())
    }

    #[cfg(all(target_os = "linux", not(target_env = "musl")))]
    fn is_on_nfs_mount(path: &Path) -> bool {
        use std::ffi::CString;
        use std::mem;
        use std::os::unix::prelude::*;

        let Ok(path) = CString::new(path.as_os_str().as_bytes()) else {
            return false;
        };

        unsafe {
            let mut buf: libc::statfs = mem::zeroed();
            let r = libc::statfs(path.as_ptr(), &mut buf);

            r == 0 && buf.f_type as u32 == libc::NFS_SUPER_MAGIC as u32
        }
    }

    #[cfg(any(not(target_os = "linux"), target_env = "musl"))]
    fn is_on_nfs_mount(_path: &Path) -> bool {
        false
    }

    #[cfg(unix)]
    mod sys {
        use std::fs::File;
        use std::io::{Error, Result};
        use std::os::unix::io::AsRawFd;

        pub(super) fn lock_shared(file: &File) -> Result<()> {
            flock(file, libc::LOCK_SH)
        }

        pub(super) fn lock_exclusive(file: &File) -> Result<()> {
            flock(file, libc::LOCK_EX)
        }

        pub(super) fn try_lock_shared(file: &File) -> Result<()> {
            flock(file, libc::LOCK_SH | libc::LOCK_NB)
        }

        pub(super) fn try_lock_exclusive(file: &File) -> Result<()> {
            flock(file, libc::LOCK_EX | libc::LOCK_NB)
        }

        pub(super) fn unlock(file: &File) -> Result<()> {
            flock(file, libc::LOCK_UN)
        }

        pub(super) fn error_contended(err: &Error) -> bool {
            err.raw_os_error().map_or(false, |x| x == libc::EWOULDBLOCK)
        }

        pub(super) fn error_unsupported(err: &Error) -> bool {
            match err.raw_os_error() {
                // Unfortunately, depending on the target, these may or may not be the same.
                // For targets in which they are the same, the duplicate pattern causes a warning.
                #[allow(unreachable_patterns)]
                Some(libc::ENOTSUP | libc::EOPNOTSUPP) => true,
                Some(libc::ENOSYS) => true,
                _ => false,
            }
        }

        #[cfg(not(target_os = "solaris"))]
        fn flock(file: &File, flag: libc::c_int) -> Result<()> {
            let ret = unsafe { libc::flock(file.as_raw_fd(), flag) };
            if ret < 0 {
                Err(Error::last_os_error())
            } else {
                Ok(())
            }
        }

        #[cfg(target_os = "solaris")]
        fn flock(file: &File, flag: libc::c_int) -> Result<()> {
            // Solaris lacks flock(), so try to emulate using fcntl()
            let mut flock = libc::flock {
                l_type: 0,
                l_whence: 0,
                l_start: 0,
                l_len: 0,
                l_sysid: 0,
                l_pid: 0,
                l_pad: [0, 0, 0, 0],
            };
            flock.l_type = if flag & libc::LOCK_UN != 0 {
                libc::F_UNLCK
            } else if flag & libc::LOCK_EX != 0 {
                libc::F_WRLCK
            } else if flag & libc::LOCK_SH != 0 {
                libc::F_RDLCK
            } else {
                panic!("unexpected flock() operation")
            };

            let mut cmd = libc::F_SETLKW;
            if (flag & libc::LOCK_NB) != 0 {
                cmd = libc::F_SETLK;
            }

            let ret = unsafe { libc::fcntl(file.as_raw_fd(), cmd, &flock) };

            if ret < 0 {
                Err(Error::last_os_error())
            } else {
                Ok(())
            }
        }
    }

    #[cfg(windows)]
    mod sys {
        use std::fs::File;
        use std::io::{Error, Result};
        use std::mem;
        use std::os::windows::io::AsRawHandle;

        use windows_sys::Win32::Foundation::HANDLE;
        use windows_sys::Win32::Foundation::{ERROR_INVALID_FUNCTION, ERROR_LOCK_VIOLATION};
        use windows_sys::Win32::Storage::FileSystem::{
            LockFileEx, UnlockFile, LOCKFILE_EXCLUSIVE_LOCK, LOCKFILE_FAIL_IMMEDIATELY,
        };

        pub(super) fn lock_shared(file: &File) -> Result<()> {
            lock_file(file, 0)
        }

        pub(super) fn lock_exclusive(file: &File) -> Result<()> {
            lock_file(file, LOCKFILE_EXCLUSIVE_LOCK)
        }

        pub(super) fn try_lock_shared(file: &File) -> Result<()> {
            lock_file(file, LOCKFILE_FAIL_IMMEDIATELY)
        }

        pub(super) fn try_lock_exclusive(file: &File) -> Result<()> {
            lock_file(file, LOCKFILE_EXCLUSIVE_LOCK | LOCKFILE_FAIL_IMMEDIATELY)
        }

        pub(super) fn error_contended(err: &Error) -> bool {
            err.raw_os_error()
                .map_or(false, |x| x == ERROR_LOCK_VIOLATION as i32)
        }

        pub(super) fn error_unsupported(err: &Error) -> bool {
            err.raw_os_error()
                .map_or(false, |x| x == ERROR_INVALID_FUNCTION as i32)
        }

        pub(super) fn unlock(file: &File) -> Result<()> {
            unsafe {
                let ret = UnlockFile(file.as_raw_handle() as HANDLE, 0, 0, !0, !0);
                if ret == 0 {
                    Err(Error::last_os_error())
                } else {
                    Ok(())
                }
            }
        }

        fn lock_file(file: &File, flags: u32) -> Result<()> {
            unsafe {
                let mut overlapped = mem::zeroed();
                let ret = LockFileEx(
                    file.as_raw_handle() as HANDLE,
                    flags,
                    0,
                    !0,
                    !0,
                    &mut overlapped,
                );
                if ret == 0 {
                    Err(Error::last_os_error())
                } else {
                    Ok(())
                }
            }
        }
    }