//! # Filter
//!
//! Commony types for filtering paths to visit.
//!
//! ## Note
//! There is a branch (`unstable/fn-traits`) that adds support for rust
//! [`unboxed_closures`](https://doc.rust-lang.org/beta/unstable-book/language-features/unboxed-closures.html)
//! and [`fn_traits`](https://doc.rust-lang.org/beta/unstable-book/library-features/fn-traits.html)
//! which will solve the need for those separated types.
//!

use std::num::NonZeroUsize;
use std::path::Path;

/// Accepts all directories.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct Accept;

/// Accepts all directories which are not symlinks.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct NoSymlink;

/// Accepts directories up to a certain depth.
///
/// The depth 1 means that only the base directory is visited.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct MaxDepth(pub(crate) NonZeroUsize);

impl MaxDepth {
    const SINGLE_DEPTH: NonZeroUsize = unsafe { NonZeroUsize::new_unchecked(1) };

    /// Creates a max depth filter.
    ///
    /// This filter is dependant on the starting `dir`, it first retrieves
    /// the depth of the `dir` (right from the root ancestor) and then
    /// ensures that visited directories does not exceed the given depth
    /// (`path to visit ancestor count - dir ancestor count`).
    ///
    /// You can also use [`Path::canonicalize`] to get the absolute path, which will also
    /// produce a higher depth (if it is not already canonical), however, ensure to only pass
    /// the canonicalized version to the visitor, otherwise, their depths will never match.
    pub fn new(max_depth: NonZeroUsize) -> Self {
        Self(max_depth)
    }

    /// Creates a single depth filter (i.e, only visits files of provided directory).
    ///
    /// This filter is dependant on the starting `dir`, it first retrieves
    /// the depth of the `dir` (right from the root ancestor) and then
    /// ensures that visited directories does not exceed the given depth
    /// (`path to visit ancestor count - dir ancestor count`).
    ///
    /// You can also use [`Path::canonicalize`] to get the absolute path, which will also
    /// produce a higher depth (if it is not already canonical), however, ensure to only pass
    /// the canonicalized version to the visitor, otherwise, their depths will never match.
    pub fn single_depth() -> Self {
        Self(Self::SINGLE_DEPTH)
    }
}

/// Closure based predicate.
///
/// ## Create
///
/// This type can be created through [`From`] and [`Into`] traits for any type,
/// however, it only implements [`Filter`] when `F: Fn(&Path) -> bool`
///
/// You can also use [`Closure::new`] to create a closure for filter composition, or [`Closure::from_fn`]
/// to avoid the need to introduce explicit types.
#[derive(Debug, Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash)]
pub struct Closure<F> {
    closure: F,
}

pub trait Filter {
    /// Checks whether `path_to_visit` should be visited or not. The `base_path` is
    /// the initial directory provided to the visitor.
    ///
    /// This filter is called only for directories, if it returns `true`
    /// it means that the directory should be visited, otherwise, it will
    /// be skipped.
    ///
    /// The directory will be emitted by the iterator regardless of the
    /// return value of this function.
    fn filter(&self, base_path: &Path, path_to_visit: &Path) -> bool;

    /// Creates a filter that only accepts both this and the `other` condition.
    fn and<B>(self, other: B) -> And<Self, B>
    where
        Self: Sized,
        B: Filter,
    {
        And { a: self, b: other }
    }

    /// Creates a filter that accepts this or the `other` condition.
    fn or<B>(self, other: B) -> Or<Self, B>
    where
        Self: Sized,
        B: Filter,
    {
        Or { a: self, b: other }
    }

    /// Creates a filter that negates when this filter accepts.
    fn not(self) -> Not<Self>
    where
        Self: Sized,
    {
        Not { a: self }
    }
}

impl Filter for Accept {
    fn filter(&self, _: &Path, _: &Path) -> bool {
        true
    }
}

impl Filter for NoSymlink {
    fn filter(&self, _: &Path, p: &Path) -> bool {
        return !p.is_dir() || !p.is_symlink();
    }
}

impl Filter for MaxDepth {
    fn filter(&self, base_path: &Path, p: &Path) -> bool {
        let depth = base_path.ancestors().count();
        let MaxDepth(max_depth) = *self;
        let ancestors = p.ancestors().count();
        return if ancestors >= depth {
            ancestors - depth <= max_depth.get() - 1
        } else {
            false
        };
    }
}

impl<F> Closure<F> {
    pub fn new(closure: F) -> Self {
        Self { closure }
    }

    pub fn from_fn(closure: F) -> Self
    where
        F: Fn(&Path) -> bool,
    {
        Self { closure }
    }
}

impl<F> From<F> for Closure<F> {
    fn from(f: F) -> Self {
        Self { closure: f }
    }
}

impl<F> Filter for Closure<F>
where
    F: Fn(&Path, &Path) -> bool,
{
    fn filter(&self, base_dir: &Path, directory: &Path) -> bool {
        (self.closure)(base_dir, directory)
    }
}

#[derive(Debug, Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash)]
pub struct And<A, B> {
    a: A,
    b: B,
}

#[derive(Debug, Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash)]
pub struct Or<A, B> {
    a: A,
    b: B,
}

#[derive(Debug, Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash)]
pub struct Not<A> {
    a: A,
}

#[derive(Debug, Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash)]
pub struct This<A> {
    a: A,
}

impl<A> This<A> {
    pub fn new(a: A) -> Self {
        Self { a }
    }
}

impl<A, B> Filter for And<A, B>
where
    A: Filter,
    B: Filter,
{
    fn filter(&self, base_path: &Path, directory: &Path) -> bool {
        self.a.filter(base_path, directory) && self.b.filter(base_path, directory)
    }
}

impl<A, B> Filter for Or<A, B>
where
    A: Filter,
    B: Filter,
{
    fn filter(&self, base_path: &Path, directory: &Path) -> bool {
        self.a.filter(base_path, directory) || self.b.filter(base_path, directory)
    }
}

impl<A> Filter for Not<A>
where
    A: Filter,
{
    fn filter(&self, base_path: &Path, directory: &Path) -> bool {
        !self.a.filter(base_path, directory)
    }
}

impl<A> Filter for This<A>
where
    A: Filter,
{
    fn filter(&self, base_path: &Path, directory: &Path) -> bool {
        self.a.filter(base_path, directory)
    }
}