fs-more 0.8.1

use std::path::{Path, PathBuf};

use crate::{error::SourceSubPathNotUnderBaseSourceDirectory, file::CollidingFileBehaviour};


/// Rules that dictate how existing sub-directories inside the
/// directory copy or move destination are handled when they collide with the
/// ones we're trying to copy or move from the source.
///
/// See also: [`DestinationDirectoryRule`].
#[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
pub enum CollidingSubDirectoryBehaviour {
    /// An existing (colliding) destination sub-directory will cause an error.
    Abort,

    /// An existing (colliding) destination sub-directory will have no effect.
    Continue,
}


/// Specifies whether you allow the destination directory to exist
/// before copying or moving files or directories into it.
///
/// If you allow the destination directory to exist, you can also specify whether it must be empty;
/// if not, you may also specify how to behave for existing destination files and directories.
///
///
/// # Defaults
/// [`Default`] is implemented for this enum. The default value is [`DestinationDirectoryRule::AllowEmpty`].
///
///
/// # Examples
/// If you want the associated directory copying or moving function to
/// return an error if the provided destination directory already exists,
/// use [`DestinationDirectoryRule::DisallowExisting`]. This is the strictest rule,
/// requiring the destination to not exist.
///
/// <br>
///
/// If you at most want to copy into an empty destination directory, use [`DestinationDirectoryRule::AllowEmpty`].
/// This rule is slightly more relaxed than the previous one.
/// It, however, does not require the destination directory to exist - it will be created if missing.
///
/// <br>
///
/// If the destination directory is allowed to exist *and* contain existing files or sub-directories,
/// but you don't want to overwrite any of the existing files, you can use the following rule:
///
/// ```no_run
/// # use fs_more::directory::DestinationDirectoryRule;
/// # use fs_more::directory::CollidingSubDirectoryBehaviour;
/// # use fs_more::file::CollidingFileBehaviour;
/// let rules = DestinationDirectoryRule::AllowNonEmpty {
///     colliding_file_behaviour: CollidingFileBehaviour::Abort,
///     colliding_subdirectory_behaviour: CollidingSubDirectoryBehaviour::Continue,
/// };
/// ```
///
/// This will create any missing destination sub-directories and ignore the ones that already exist,
/// even if their counterparts also exist in the source directory. Also, this will still not overwrite
/// existing destination files - it will effectively be a merge without overwrites.
///
/// <br>
///
/// If you want files to be overwritten, you may set the behaviour this way:
///
/// ```no_run
/// # use fs_more::directory::DestinationDirectoryRule;
/// # use fs_more::directory::CollidingSubDirectoryBehaviour;
/// # use fs_more::file::CollidingFileBehaviour;
/// let rules = DestinationDirectoryRule::AllowNonEmpty {
///     colliding_file_behaviour: CollidingFileBehaviour::Overwrite,
///     colliding_subdirectory_behaviour: CollidingSubDirectoryBehaviour::Continue,
/// };
/// ```
///
///
/// # A word of caution
/// **Do not use [`DestinationDirectoryRule::AllowNonEmpty`] as a default
/// unless you're sure you are okay with merged directories.**
///
/// If the destination directory already has some content, this would
/// allow a copy or move that results in a destination directory
/// with *merged* source and destination directory contents.
/// Unless this is precisely what you're after, you may want to avoid this option.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum DestinationDirectoryRule {
    /// Indicates the associated directory function should return an error,
    /// if the destination directory already exists.
    DisallowExisting,

    /// Indicates the associated function should return an error,
    /// if the destination directory exists *and is not empty*.
    ///
    /// **This is the default.**
    AllowEmpty,

    /// Indicates that an existing (colliding) destination directory should
    /// not cause an error, even if non-empty.
    ///
    /// **Do not use this as a default if you're not sure what rule to choose.**
    ///
    /// If the destination directory already has some content, this would
    /// allow a copy or move that results in a destination directory
    /// with *merged* source and destination directory contents.
    /// Unless this is precisely what you're after, you may want to avoid this option.
    ///
    /// Missing destination directories will always be created,
    /// regardless of the `colliding_subdirectory_behaviour` option.
    /// Setting it to [`CollidingSubDirectoryBehaviour::Continue`] simply means that
    /// if they already exist on the destination, they will not need to be created.
    AllowNonEmpty {
        /// How to behave when encountering existing (colliding) destination files.
        ///
        /// This option has no effect on existing destination files
        /// that don't collide with the ones we're copying or moving.
        colliding_file_behaviour: CollidingFileBehaviour,

        /// How to behave when encountering existing (colliding) destination subdirectories.
        ///
        /// This option has no effect on existing destination subdirectories
        /// that don't collide with the ones we're copying or moving.
        colliding_subdirectory_behaviour: CollidingSubDirectoryBehaviour,
    },
}

impl Default for DestinationDirectoryRule {
    /// The default value for this struct is [`Self::AllowEmpty`].
    fn default() -> Self {
        Self::AllowEmpty
    }
}

impl DestinationDirectoryRule {
    pub(crate) fn allows_overwriting_existing_destination_files(&self) -> bool {
        matches!(
            self,
            Self::AllowNonEmpty {
                colliding_file_behaviour: CollidingFileBehaviour::Overwrite,
                ..
            }
        )
    }

    pub(crate) fn allows_existing_destination_subdirectories(&self) -> bool {
        matches!(
            self,
            Self::AllowNonEmpty {
                colliding_subdirectory_behaviour: CollidingSubDirectoryBehaviour::Continue,
                ..
            }
        )
    }
}



/// Computes a relative path of `source_sub_path` relative to `source_base_directory_path`,
/// and applies it onto `target_base_directory_path`.
///
/// `source_base_directory_path` is the base source directory path,
/// and `source_sub_path` *must* be a descendant of that path.
/// `target_base_directory_path` can be an arbitrary target directory path.
///
/// Returns [`SourceSubPathNotUnderBaseSourceDirectory`]
/// if `source_sub_path` is not a sub-path of `source_base_directory_path`.
///
///
/// # Example
/// ```ignore
/// # use std::path::Path;
/// # use fs_more::directory::copy::join_relative_source_path_onto_destination;
///
/// let foo = Path::new("/foo");
/// let foo_hello_world = Path::new("/foo/abc/hello-world.txt");
/// let bar = Path::new("/bar");
///
/// assert_eq!(
///     join_relative_source_path_onto_destination(
///         foo,
///         foo_hello_world,
///         bar
///     ).unwrap(),
///     Path::new("/bar/abc/hello-world.txt")
/// );
/// ```
pub(crate) fn join_relative_source_path_onto_destination(
    source_base_directory_path: &Path,
    source_sub_path: &Path,
    target_base_directory_path: &Path,
) -> Result<PathBuf, SourceSubPathNotUnderBaseSourceDirectory> {
    // Strip the base source directory path from the full source path
    // and place it on top of the target base directory path.

    if source_base_directory_path.eq(source_sub_path) {
        return Ok(target_base_directory_path.to_path_buf());
    }

    let source_sub_path_relative_to_base = source_sub_path
        .strip_prefix(source_base_directory_path)
        .map_err(|_| SourceSubPathNotUnderBaseSourceDirectory {
            path: source_base_directory_path.join(source_sub_path),
        })?;

    Ok(target_base_directory_path.join(source_sub_path_relative_to_base))
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn properly_rejoin_source_subpath_onto_target() {
        let root_a = Path::new("/hello/there");
        let foo = Path::new("/hello/there/some/content");
        let root_b = Path::new("/different/root");

        assert_eq!(
            join_relative_source_path_onto_destination(root_a, foo, root_b).unwrap(),
            Path::new("/different/root/some/content"),
            "rejoin_source_subpath_onto_target did not rejoin the path properly."
        );

        let foo = Path::new("/foo");
        let foo_hello_world = Path::new("/foo/abc/hello-world.txt");
        let bar = Path::new("/bar");

        assert_eq!(
            join_relative_source_path_onto_destination(foo, foo_hello_world, bar).unwrap(),
            Path::new("/bar/abc/hello-world.txt")
        );
    }

    #[test]
    fn error_on_subpath_not_being_under_source_root() {
        let root_a = Path::new("/hello/there");
        let foo = Path::new("/completely/different/path");
        let root_b = Path::new("/different/root");

        let rejoin_result = join_relative_source_path_onto_destination(root_a, foo, root_b);

        assert!(
            rejoin_result.is_err(),
            "rejoin_source_subpath_onto_target did not return Err when \
            the source path to rejoin wasn't under the source root path"
        );
    }
}