//! Functionality for opening files while verifying their permissions.

use std::{

    borrow::Cow,

    fs::{File, OpenOptions},

    io::{Read as _, Write},

    path::{Path, PathBuf},

};

#[cfg(unix)]

use std::os::unix::fs::OpenOptionsExt as _;

use crate::{CheckedDir, Error, Result, Verifier, dir::FullPathCheck, walk::PathType};

/// Helper object for accessing a file on disk while checking the necessary permissions.

///

/// You can use a `FileAccess` when you want to read or write a file,

/// while making sure that the file obeys the permissions rules of

/// an associated [`CheckedDir`] or [`Verifier`].

///

/// `FileAccess` is a separate type from `CheckedDir` and `Verifier`

/// so that you can set options to control the behavior of how files are opened.

///

/// Note: When we refer to a path _"obeying the constraints"_ of this `FileAccess`,

/// we mean:

/// * If the `FileAccess` wraps a `CheckedDir`, the requirement that it is a relative path

///   containing no ".." elements,

///   or other elements that would take it outside the `CheckedDir`.

/// * If the `FileAccess` wraps a `Verifier`, there are no requirements.

pub struct FileAccess<'a> {

    /// Validator object that we use for checking file permissions.

    pub(crate) inner: Inner<'a>,

    /// If set, we create files with this mode.

    #[cfg(unix)]

    create_with_mode: Option<u32>,

    /// If set, we follow final-position symlinks in provided paths.

    follow_final_links: bool,

}

/// Inner object for checking file permissions.

pub(crate) enum Inner<'a> {

    /// A CheckedDir backing this FileAccess.

    CheckedDir(&'a CheckedDir),

    /// A Verifier backing this FileAccess.

    Verifier(Verifier<'a>),

}

impl<'a> FileAccess<'a> {

    /// Create a new `FileAccess` to access files within CheckedDir,

    /// using default options.

    /// Create a new `FileAccess` to access files anywhere on the filesystem,

    /// using default options.

    /// Create a new `FileAccess` from `inner`,

    /// using default options.

    /// Check path constraints on `path` and verify its permissions

    /// (or the permissions of its parent) according to `check_type`

                };

            }

        }

    /// Return a `Verifier` to use for checking permissions.

        }

    /// Return the location of `path` relative to this verifier.

    ///

    /// Fails if `path` does not [obey the constraints](FileAccess) of this `FileAccess`,

    /// but does not do any permissions checking.

        })

    /// Configure this FileAccess: when used to create a file,

    /// that file will be created with the provided unix permissions.

    ///

    /// If this option is not set, newly created files have mode 0600.

    #[cfg_attr(not(unix), expect(unused_mut))]

    #[cfg_attr(not(unix), expect(unused_variables))]

        #[cfg(unix)]

    /// Configure this FileAccess: if the file to be accessed is a symlink,

    /// and this is set to true, we will follow that symlink when creating or reading the file.

    ///

    /// By default, this option is false.

    ///

    /// Note that if you use this option with a `CheckedDir`,

    /// it can read or write a file outside of the `CheckedDir`,

    /// which might not be what you wanted.

    ///

    /// This option does not affect the handling of links that are _not_

    /// in the final position of the path.

    ///

    /// This option does not disable the regular `fs-mistrust` checks:

    /// we still ensure that the link's target, and its location, are not

    /// modifiable by an untrusted user.

    /// Open a file relative to this `FileAccess`, using a set of [`OpenOptions`].

    ///

    /// `path` must be a path to the new file, [obeying the constraints](FileAccess) of this `FileAccess`.

    /// We check, but do not create, the file's parent directories.

    /// We check the file's permissions after opening it.

    ///

    /// If the file is created (and this is a unix-like operating system), we

    /// always create it with a mode based on [`create_with_mode()`](Self::create_with_mode),

    /// regardless of any mode set in `options`.

    /// If `create_with_mode()` wasn't called, we create the file with mode 600.

    //

    // Note: This function, and others, take ownership of `self`, to prevent people from storing and

    // reusing FileAccess objects.  We're avoiding that because we don't want people confusing

    // FileAccess objects created with CheckedDir and Verifier.

    /// As `open`, but take `self` by reference.  For internal use.

        // If we're following links, then we want to look at the whole path,

        // since the final element might be a link.  If so, we need to look at

        // where it is linking to, and validate that as well.

        } else {

        };

            // We tolerate a not-found error if we're following links:

            // - If the final element of the path is what wasn't found, then we might create it

            //   ourselves when we open it.

            // - If an earlier element of the path wasn't found, we will get a second NotFound error

            //   when we try to open the file, which is okay.

        };

        #[allow(unused_mut)]

        #[cfg(unix)]

        {

            // Don't follow symlinks out of a secure directory.

        }

        {

        } else {

        }

    /// Read the contents of the file at `path` relative to this `FileAccess`, as a

    /// String, if possible.

    ///

    /// Return an error if `path` is absent, if its permissions are incorrect,

    /// if it does not [obey the constraints](FileAccess) of this `FileAccess`,

    /// or if its contents are not UTF-8.

    /// Read the contents of the file at `path` relative to this `FileAccess`, as a

    /// vector of bytes, if possible.

    ///

    /// Return an error if `path` is absent, if its permissions are incorrect,

    /// or if it does not [obey the constraints](FileAccess) of this `FileAccess`.

    /// Store `contents` into the file located at `path` relative to this `FileAccess`.

    ///

    /// We won't write to `path` directly: instead, we'll write to a temporary

    /// file in the same directory as `path`, and then replace `path` with that

    /// temporary file if we were successful.  (This isn't truly atomic on all

    /// file systems, but it's closer than many alternatives.)

    ///

    /// # Limitations

    ///

    /// This function will clobber any existing files with the same name as

    /// `path` but with the extension `tmp`.  (That is, if you are writing to

    /// "foo.txt", it will replace "foo.tmp" in the same directory.)

    ///

    /// This function may give incorrect behavior if multiple threads or

    /// processes are writing to the same file at the same time: it is the

    /// programmer's responsibility to use appropriate locking to avoid this.

        // We remove the temporary file before opening it, if it's present: otherwise it _might_ be

        // a symlink to somewhere silly.

        // TODO: The parent directory  verification performed by "open" here is redundant with that done in

        // `verified_full_path` above.

        // Write the data.

        // Flush and close.

        // Replace the old file.

            // It's okay to use location_unverified here, since we already verified it when we

            // called `open`.

        )

}

#[cfg(test)]

mod test {

    // @@ begin test lint list maintained by maint/add_warning @@

    #![allow(clippy::bool_assert_comparison)]

    #![allow(clippy::clone_on_copy)]

    #![allow(clippy::dbg_macro)]

    #![allow(clippy::mixed_attributes_style)]

    #![allow(clippy::print_stderr)]

    #![allow(clippy::print_stdout)]

    #![allow(clippy::single_char_pattern)]

    #![allow(clippy::unwrap_used)]

    #![allow(clippy::unchecked_time_subtraction)]

    #![allow(clippy::useless_vec)]

    #![allow(clippy::needless_pass_by_value)]

    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->

    #[cfg(unix)]

    use std::fs;

    use super::*;

    use crate::{Mistrust, testing::Dir};

    #[test]

    fn create_public_in_checked_dir() {

        let d = Dir::new();

        d.dir("a");

        d.chmod("a", 0o700);

        let m = Mistrust::builder()

            .ignore_prefix(d.canonical_root())

            .build()

            .unwrap();

        let checked = m.verifier().secure_dir(d.path("a")).unwrap();

        {

            let mut f = checked

                .file_access()

                .open(

                    "private-1.txt",

                    OpenOptions::new().write(true).create_new(true),

                )

                .unwrap();

            f.write_all(b"Hello world\n").unwrap();

            checked

                .file_access()

                .write_and_replace("private-2.txt", b"Hello world 2\n")

                .unwrap();

        }

        {

            let mut f = checked

                .file_access()

                .create_with_mode(0o640)

                .open(

                    "public-1.txt",

                    OpenOptions::new().write(true).create_new(true),

                )

                .unwrap();

            f.write_all(b"Hello wider world\n").unwrap();

            checked

                .file_access()

                .create_with_mode(0o644)

                .write_and_replace("public-2.txt", b"Hello wider world 2")

                .unwrap();

        }

        #[cfg(target_family = "unix")]

        {

            use std::os::unix::fs::MetadataExt;

            assert_eq!(

                fs::metadata(d.path("a/private-1.txt")).unwrap().mode() & 0o7777,

                0o600

            );

            assert_eq!(

                fs::metadata(d.path("a/private-2.txt")).unwrap().mode() & 0o7777,

                0o600

            );

            assert_eq!(

                fs::metadata(d.path("a/public-1.txt")).unwrap().mode() & 0o7777,

                0o640

            );

            assert_eq!(

                fs::metadata(d.path("a/public-2.txt")).unwrap().mode() & 0o7777,

                0o644

            );

        }

    }

    #[test]

    #[cfg(unix)]

    fn open_symlinks() {

        use crate::testing::LinkType;

        let d = Dir::new();

        d.dir("a");

        d.dir("a/b");

        d.dir("a/c");

        d.file("a/c/file1.txt");

        d.link_rel(LinkType::File, "../c/file1.txt", "a/b/present");

        d.link_rel(LinkType::File, "../c/file2.txt", "a/b/absent");

        d.chmod("a", 0o700);

        d.chmod("a/b", 0o700);

        d.chmod("a/c", 0o700);

        d.chmod("a/c/file1.txt", 0o600);

        let m = Mistrust::builder()

            .ignore_prefix(d.canonical_root())

            .build()

            .unwrap();

        // Try reading

        let contents = m

            .file_access()

            .follow_final_links(true)

            .read(d.path("a/b/present"))

            .unwrap();

        assert_eq!(

            &contents[..],

            &b"This space is intentionally left blank"[..]

        );

        let error = m

            .file_access()

            .follow_final_links(true)

            .read(d.path("a/b/absent"))

            .unwrap_err();

        assert!(matches!(error, Error::NotFound(_)));

        // Try writing.

        {

            let mut f = m

                .file_access()

                .follow_final_links(true)

                .open(

                    d.path("a/b/present"),

                    OpenOptions::new().write(true).truncate(true),

                )

                .unwrap();

            f.write_all(b"This is extremely serious!").unwrap();

        }

        let contents = m

            .file_access()

            .follow_final_links(true)

            .read(d.path("a/b/present"))

            .unwrap();

        assert_eq!(&contents[..], &b"This is extremely serious!"[..]);

        let contents = m.file_access().read(d.path("a/c/file1.txt")).unwrap();

        assert_eq!(&contents[..], &b"This is extremely serious!"[..]);

        {

            let mut f = m

                .file_access()

                .follow_final_links(true)

                .open(

                    d.path("a/b/absent"),

                    OpenOptions::new().create(true).write(true),

                )

                .unwrap();

            f.write_all(b"This is extremely silly!").unwrap();

        }

        let contents = m.file_access().read(d.path("a/c/file2.txt")).unwrap();

        assert_eq!(&contents[..], &b"This is extremely silly!"[..]);

    }

}