use std::ffi::OsStr;
use std::fmt;
use std::iter::FusedIterator;

use crate::path::{Component, Components, Path};

/// An iterator over the [`Component`]s of a [`Path`], as [`OsStr`] slices.
///
/// This `struct` is created by the [`iter`] method on [`Path`].
/// See its documentation for more.
///
/// [`Component`]: enum.Component.html
/// [`iter`]: struct.Path.html#method.iter
/// [`OsStr`]: ../../std/ffi/struct.OsStr.html
/// [`Path`]: struct.Path.html
#[derive(Clone)]
pub struct Iter<'a> {
    pub(crate) inner: Components<'a>,
}

impl<'a> Iter<'a> {
    /// Extracts a slice corresponding to the portion of the path remaining for iteration.
    ///
    /// # Examples
    ///
    /// ```
    /// use async_std::path::Path;
    ///
    /// let mut iter = Path::new("/tmp/foo/bar.txt").iter();
    /// iter.next();
    /// iter.next();
    ///
    /// assert_eq!(Path::new("foo/bar.txt"), iter.as_path());
    /// ```
    pub fn as_path(&self) -> &'a Path {
        self.inner.as_path()
    }
}

impl<'a> Iterator for Iter<'a> {
    type Item = &'a OsStr;

    fn next(&mut self) -> Option<&'a OsStr> {
        self.inner.next().map(Component::as_os_str)
    }
}

impl fmt::Debug for Iter<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        struct DebugHelper<'a>(&'a Path);

        impl fmt::Debug for DebugHelper<'_> {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                f.debug_list().entries(self.0.iter()).finish()
            }
        }

        f.debug_tuple("Iter")
            .field(&DebugHelper(self.as_path()))
            .finish()
    }
}

impl AsRef<Path> for Iter<'_> {
    fn as_ref(&self) -> &Path {
        self.as_path()
    }
}

impl AsRef<OsStr> for Iter<'_> {
    fn as_ref(&self) -> &OsStr {
        self.as_path().as_os_str()
    }
}

impl<'a> DoubleEndedIterator for Iter<'a> {
    fn next_back(&mut self) -> Option<&'a OsStr> {
        self.inner.next_back().map(Component::as_os_str)
    }
}

impl FusedIterator for Iter<'_> {}