use alloc::{collections::VecDeque, vec::Vec};

const SEPERATOR: u8 = b'/';

pub trait Path: AsRef<[u8]> {
    fn is_absolute(&self) -> bool {
        self.as_ref().get(0) == Some(&SEPERATOR)
    }

    fn is_relative(&self) -> bool {
        !self.is_absolute()
    }

    fn path_segment_iter<'a>(&'a self) -> PathIterator<'a> {
        let bytes = if self.is_absolute() {
            &self.as_ref()[1..]
        } else {
            self.as_ref()
        };
        PathIterator { bytes }
    }

    fn segment_iter<'a>(&'a self) -> PathSegmentIter<'a> {
        PathSegmentIter {
            bytes: self.as_ref(),
            offset: 0,
        }
    }

    fn normalize(&self) -> NormalizedPath<'_> {
        let iter = self.segment_iter();

        let mut segments =
            VecDeque::with_capacity(self.as_ref().iter().filter(|&b| b == &SEPERATOR).count());

        for segment in iter {
            match segment {
                Segment::NoOp | Segment::CurrentDir => {}
                Segment::Root | Segment::File(_) => segments.push_back(segment),
                Segment::ParentDir => {
                    if segments.back() != Some(&Segment::Root) {
                        segments.pop_back();
                    }
                }
            }
        }

        NormalizedPath { segments }
    }
}

#[derive(Debug, PartialEq, Eq)]
pub enum Segment<'a> {
    Root,
    NoOp,
    CurrentDir,
    ParentDir,
    File(&'a [u8]),
}

impl<T> Path for T where T: AsRef<[u8]> {}

pub struct NormalizedPath<'a> {
    segments: VecDeque<Segment<'a>>,
}

impl<'a> NormalizedPath<'a> {
    pub fn into_iter(self) -> alloc::collections::vec_deque::IntoIter<Segment<'a>> {
        self.segments.into_iter()
    }
    pub fn iter(&self) -> alloc::collections::vec_deque::Iter<Segment> {
        self.segments.iter()
    }

    pub fn pop_segment(&mut self) -> Option<Segment<'a>> {
        self.segments.pop_front()
    }
}

pub struct PathSegmentIter<'a> {
    bytes: &'a [u8],
    offset: usize,
}

impl<'a> Iterator for PathSegmentIter<'a> {
    type Item = Segment<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        let bytes = &self.bytes[self.offset..];
        if !bytes.is_empty() {
            let next = bytes
                .iter()
                .position(|c| c == &SEPERATOR)
                .unwrap_or(bytes.len());

            // bytes of segment
            let segment = &bytes[..next];
            log::info!("{}", alloc::string::String::from_utf8_lossy(segment));

            let segment = if segment.is_empty() {
                if self.offset == 0 {
                    // handle root segment
                    Some(Segment::Root)
                } else if bytes.is_empty() {
                    // trailign seperator
                    None
                } else {
                    // noop
                    Some(Segment::NoOp)
                }
            } else if segment == &b"."[..] {
                Some(Segment::CurrentDir)
            } else if segment == &b".."[..] {
                Some(Segment::ParentDir)
            } else {
                Some(Segment::File(segment))
            };
            self.offset += bytes.len().min(next + 1);

            segment
        } else {
            None
        }
    }
}

/// iterator that returns path segments
pub struct PathIterator<'a> {
    bytes: &'a [u8],
}

impl<'a> PathIterator<'a> {}

impl<'a> Iterator for PathIterator<'a> {
    type Item = &'a [u8];

    fn next(&mut self) -> Option<Self::Item> {
        if !self.bytes.is_empty() {
            let next = self
                .bytes
                .iter()
                .position(|c| c == &SEPERATOR)
                .unwrap_or(self.bytes.len());
            let segment = &self.bytes[..next];
            self.bytes = &self.bytes[self.bytes.len().min(next + 1)..];
            Some(segment)
        } else {
            None
        }
    }
}

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

    #[test]
    fn test_iter() {
        let mut iter = b"/this/is/a//path/to/some.file".path_segment_iter();

        assert_eq!(iter.next(), Some(&b"this"[..]));
        assert_eq!(iter.next(), Some(&b"is"[..]));
        assert_eq!(iter.next(), Some(&b"a"[..]));
        assert_eq!(iter.next(), Some(&b""[..]));
        assert_eq!(iter.next(), Some(&b"path"[..]));
        assert_eq!(iter.next(), Some(&b"to"[..]));
        assert_eq!(iter.next(), Some(&b"some.file"[..]));
        assert_eq!(iter.next(), None);
    }
}

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

    #[test]
    fn test_noop() {
        let mut iter = b"this//a//path//some.file".segment_iter();

        assert_eq!(iter.next(), Some(Segment::File(&b"this"[..])));
        assert_eq!(iter.next(), Some(Segment::NoOp));
        assert_eq!(iter.next(), Some(Segment::File(&b"a"[..])));
        assert_eq!(iter.next(), Some(Segment::NoOp));
        assert_eq!(iter.next(), Some(Segment::File(&b"path"[..])));
        assert_eq!(iter.next(), Some(Segment::NoOp));
        assert_eq!(iter.next(), Some(Segment::File(&b"some.file"[..])));
        assert_eq!(iter.next(), None);
    }

    #[test]
    fn test_root() {
        let path = b"/absolute/path";
        let path2 = b"relative/path";
        let path3 = b"../relative/path";
        let path4 = b"./relative/path";
        let path5 = b".//relative/path";
        let relative_paths = [&path2[..], &path3[..], &path4[..], &path5[..]];
        assert!(path.is_absolute());
        let mut iter = path.segment_iter();
        assert_eq!(iter.next(), Some(Segment::Root));

        for path in relative_paths {
            assert!(path.is_relative());
            let mut iter = path.segment_iter();
            assert_ne!(iter.next(), Some(Segment::Root));
        }
    }

    #[test]
    fn test_trailing_seperator() {
        let mut iter = b"/this//".segment_iter();

        assert_eq!(iter.next(), Some(Segment::Root));
        assert_eq!(iter.next(), Some(Segment::File(&b"this"[..])));
        assert_eq!(iter.next(), Some(Segment::NoOp));
        assert_eq!(iter.next(), None);

        let mut iter = b"this//".segment_iter();

        assert_eq!(iter.next(), Some(Segment::File(&b"this"[..])));
        assert_eq!(iter.next(), Some(Segment::NoOp));
        assert_eq!(iter.next(), None);

        let mut iter = b"/this////".segment_iter();

        assert_eq!(iter.next(), Some(Segment::Root));
        assert_eq!(iter.next(), Some(Segment::File(&b"this"[..])));
        assert_eq!(iter.next(), Some(Segment::NoOp));
        assert_eq!(iter.next(), Some(Segment::NoOp));
        assert_eq!(iter.next(), Some(Segment::NoOp));
        assert_eq!(iter.next(), None);

        let mut iter = b"/this////".normalize().into_iter();

        assert_eq!(iter.next(), Some(Segment::Root));
        assert_eq!(iter.next(), Some(Segment::File(&b"this"[..])));
        assert_eq!(iter.next(), None);

        let mut iter = b"/this/".normalize().into_iter();

        assert_eq!(iter.next(), Some(Segment::Root));
        assert_eq!(iter.next(), Some(Segment::File(&b"this"[..])));
        assert_eq!(iter.next(), None);

        let mut iter = b"/this".normalize().into_iter();

        assert_eq!(iter.next(), Some(Segment::Root));
        assert_eq!(iter.next(), Some(Segment::File(&b"this"[..])));
        assert_eq!(iter.next(), None);
    }

    #[test]
    fn test_iter() {
        let mut iter = b"/this/is/a//path/to/some.file".segment_iter();

        assert_eq!(iter.next(), Some(Segment::Root));
        assert_eq!(iter.next(), Some(Segment::File(&b"this"[..])));
        assert_eq!(iter.next(), Some(Segment::File(&b"is"[..])));
        assert_eq!(iter.next(), Some(Segment::File(&b"a"[..])));
        assert_eq!(iter.next(), Some(Segment::NoOp));
        assert_eq!(iter.next(), Some(Segment::File(&b"path"[..])));
        assert_eq!(iter.next(), Some(Segment::File(&b"to"[..])));
        assert_eq!(iter.next(), Some(Segment::File(&b"some.file"[..])));
        assert_eq!(iter.next(), None);
    }
}