//! Paths

use core::{convert::TryFrom, fmt, marker::PhantomData, ops, ptr, slice, str};

use cstr_core::CStr;
use cty::{c_char, size_t};

use crate::consts;

/// A path
///
/// Paths must be null terminated ASCII strings
///
/// This assumption is not needed for littlefs itself (it works like Linux and
/// accepts arbitrary C strings), but the assumption makes `AsRef<str>` trivial
/// to implement.
pub struct Path {
    inner: CStr,
}

impl Path {
    /// Creates a path from a byte buffer
    ///
    /// The buffer will be first interpreted as a `CStr` and then checked to be comprised only of
    /// ASCII characters.
    pub fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self> {
        let cstr = CStr::from_bytes_with_nul(bytes).map_err(|_| Error::NotCStr)?;
        Self::from_cstr(cstr)
    }

    /// Unchecked version of `from_bytes_with_nul`
    ///
    /// # Safety
    /// `bytes` must be null terminated string comprised of only ASCII characters
    pub unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &Self {
        &*(bytes as *const [u8] as *const Path)
    }

    /// Creates a path from a C string
    ///
    /// The string will be checked to be comprised only of ASCII characters
    // XXX should we reject empty paths (`""`) here?
    pub fn from_cstr(cstr: &CStr) -> Result<&Self> {
        let bytes = cstr.to_bytes();
        let n = cstr.to_bytes().len();
        if n > consts::PATH_MAX {
            Err(Error::TooLarge)
        } else if bytes.is_ascii() {
            Ok(unsafe { Self::from_cstr_unchecked(cstr) })
        } else {
            Err(Error::NotAscii)
        }
    }

    /// Unchecked version of `from_cstr`
    ///
    /// # Safety
    /// `cstr` must be comprised only of ASCII characters
    pub unsafe fn from_cstr_unchecked(cstr: &CStr) -> &Self {
        &*(cstr as *const CStr as *const Path)
    }

    /// Returns the inner pointer to this C string.
    pub(crate) fn as_ptr(&self) -> *const c_char {
        self.inner.as_ptr()
    }

    /// Creates an owned `PathBuf` with `path` adjoined to `self`.
    pub fn join(&self, path: &Path) -> PathBuf {
        let mut p = PathBuf::from(self);
        p.push(path);
        p
    }

    pub fn exists<S: crate::driver::Storage>(&self, fs: &crate::fs::Filesystem<S>) -> bool {
        fs.metadata(self).is_ok()
    }

    // helpful for debugging wither the trailing nul is indeed a trailing nul.
    pub fn as_str_ref_with_trailing_nul(&self) -> &str {
        unsafe { str::from_utf8_unchecked(self.inner.to_bytes_with_nul()) }
    }

    pub fn parent(&self) -> Option<PathBuf> {
        let rk_path_bytes = self.as_ref()[..].as_bytes();
        match rk_path_bytes.iter().rposition(|x| *x == b'/') {
            Some(slash_index) => {
                // if we have a directory that ends with `/`,
                // still need to "go up" one parent
                if slash_index + 1 == rk_path_bytes.len() {
                    PathBuf::from(&rk_path_bytes[..slash_index]).parent()
                } else {
                    Some(PathBuf::from(&rk_path_bytes[..slash_index]))
                }
            }
            None => None,
        }
    }
}

impl AsRef<str> for Path {
    fn as_ref(&self) -> &str {
        // NOTE(unsafe) ASCII is valid UTF-8
        unsafe { str::from_utf8_unchecked(self.inner.to_bytes()) }
    }
}

impl fmt::Debug for Path {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // helpful for debugging wither the trailing nul is indeed a trailing nul.
        write!(f, "p{:?}", self.as_str_ref_with_trailing_nul())
    }
}

impl fmt::Display for Path {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(self.as_ref())
    }
}

impl<'b> TryFrom<&'b [u8]> for &'b Path {
    type Error = Error;

    fn try_from(bytes: &[u8]) -> Result<&Path> {
        Path::from_bytes_with_nul(bytes)
    }
}

impl PartialEq<str> for Path {
    fn eq(&self, rhs: &str) -> bool {
        self.as_ref() == rhs
    }
}

// without this you need to slice byte string literals (`b"foo\0"[..].try_into()`)
macro_rules! array_impls {
    ($($N:expr),+) => {
        $(
            impl<'b> TryFrom<&'b [u8; $N]> for &'b Path {
                type Error = Error;

                fn try_from(bytes: &[u8; $N]) -> Result<&Path> {
                    Path::from_bytes_with_nul(&bytes[..])
                }
            }

            impl From<&[u8; $N]> for PathBuf {
                fn from(bytes: &[u8; $N]) -> Self {
                    Self::from(&bytes[..])
                }
            }

            impl PartialEq<[u8; $N]> for Path {
                fn eq(&self, rhs: &[u8; $N]) -> bool {
                    self.as_ref().as_bytes() == &rhs[..]
                }
            }

        )+
    }
}

array_impls!(
    1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
    28, 29, 30, 31, 32
);

/// An owned, mutable path
#[derive(Clone)]
pub struct PathBuf {
    buf: [c_char; consts::PATH_MAX_PLUS_ONE],
    // NOTE `len` DOES include the final null byte
    len: usize,
}

/// # Safety
/// `s` must point to valid memory; `s` will be treated as a null terminated string
unsafe fn strlen(mut s: *const c_char) -> size_t {
    let mut n = 0;
    while *s != 0 {
        s = s.add(1);
        n += 1;
    }
    n
}

impl PathBuf {
    pub fn new() -> Self {
        Self { buf: [0; consts::PATH_MAX_PLUS_ONE], len: 1 }
    }

    pub fn clear(&mut self) {
        self.buf = [0; consts::PATH_MAX_PLUS_ONE];
        self.len = 1;
    }

    pub(crate) unsafe fn from_buffer(buf: [c_char; consts::PATH_MAX_PLUS_ONE]) -> Self {
        let len = strlen(buf.as_ptr()) + 1 /* null byte */;
        PathBuf { buf, len }
    }

    /// Extends `self` with `path`
    pub fn push(&mut self, path: &Path) {
        match path.as_ref() {
            // no-operation
            "" => return,

            // `self` becomes `/` (root), to match `std::Path` implementation
            // NOTE(allow) cast is necessary on some architectures (e.g. x86)
            #[allow(clippy::unnecessary_cast)]
            "/" => {
                self.buf[0] = b'/' as c_char;
                self.buf[1] = 0;
                self.len = 2;
                return;
            }
            _ => {}
        }

        let src = path.as_ref().as_bytes();
        let needs_separator = self
            .as_ref()
            .as_bytes()
            .last()
            .map(|byte| *byte != b'/')
            .unwrap_or(false);
        let slen = src.len();
        #[cfg(test)]
        println!("{}, {}, {}", self.len, slen, consts::PATH_MAX_PLUS_ONE);
        // hprintln!("{}, {}, {}", self.len, slen, consts::PATH_MAX_PLUS_ONE);
        assert!(
            self.len
                + slen
                + if needs_separator {
                    // b'/'
                    1
                } else {
                    0
                }
                <= consts::PATH_MAX_PLUS_ONE
        );

        let len = self.len;
        unsafe {
            let mut p = self.buf.as_mut_ptr().cast::<u8>().add(len - 1);
            if needs_separator {
                p.write(b'/');
                p = p.add(1);
                self.len += 1;
            }
            ptr::copy_nonoverlapping(src.as_ptr(), p, slen);
            p.add(slen).write(0); // null byte
            self.len += slen;
        }
    }
}

impl From<&Path> for PathBuf {
    fn from(path: &Path) -> Self {
        let bytes = path.as_ref().as_bytes();

        let mut buf = [0; consts::PATH_MAX_PLUS_ONE];
        let len = bytes.len();
        assert!(len <= consts::PATH_MAX);
        unsafe { ptr::copy_nonoverlapping(bytes.as_ptr(), buf.as_mut_ptr().cast(), len + 1) }
        Self {
            buf,
            len: len + 1,
        }
    }
}

impl From<&[u8]> for PathBuf {
    /// Accepts byte string, with or without trailing nul.
    ///
    /// PANICS: when there are embedded nuls
    fn from(bytes: &[u8]) -> Self {
        // NB: This needs to set the final NUL byte, unless it already has one
        // It also checks that there are no inner NUL bytes
        let bytes = if !bytes.is_empty() && bytes[bytes.len() - 1] == b'\0' {
            &bytes[..bytes.len() - 1]
        } else {
            bytes
        };
        let has_no_embedded_nul = bytes.iter().find(|&&byte| byte == b'\0').is_none();
        assert!(has_no_embedded_nul);

        let mut buf = [0; consts::PATH_MAX_PLUS_ONE];
        let len = bytes.len();
        assert!(len <= consts::PATH_MAX);
        assert!(bytes.is_ascii());
        unsafe { ptr::copy_nonoverlapping(bytes.as_ptr(), buf.as_mut_ptr().cast(), len) }
        Self {
            buf,
            len: len + 1,
        }
    }
}

impl From<&str> for PathBuf {
    fn from(s: &str) -> Self {
        PathBuf::from(s.as_bytes())
    }
}

impl ops::Deref for PathBuf {
    type Target = Path;

    fn deref(&self) -> &Path {
        unsafe {
            Path::from_bytes_with_nul_unchecked(slice::from_raw_parts(
                self.buf.as_ptr().cast(),
                self.len,
            ))
        }
    }
}


impl serde::Serialize for PathBuf {
    fn serialize<S>(&self, serializer: S) -> core::result::Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        serializer.serialize_bytes(self.as_ref().as_bytes())
    }
}

impl<'de> serde::Deserialize<'de> for PathBuf
{
    fn deserialize<D>(deserializer: D) -> core::result::Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        struct ValueVisitor<'de>(PhantomData<&'de ()>);

        impl<'de> serde::de::Visitor<'de> for ValueVisitor<'de>
        {
            type Value = PathBuf;

            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
                formatter.write_str("a path buffer")
            }

            fn visit_bytes<E>(self, v: &[u8]) -> core::result::Result<Self::Value, E>
            where
                E: serde::de::Error,
            {
                if v.len() > consts::PATH_MAX {
                    return Err(E::invalid_length(v.len(), &self));
                }
                Ok(PathBuf::from(v))
            }
        }

        deserializer.deserialize_bytes(ValueVisitor(PhantomData))
    }
}

impl fmt::Debug for PathBuf {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        <Path as fmt::Debug>::fmt(self, f)
    }
}

impl fmt::Display for PathBuf {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        <Path as fmt::Display>::fmt(self, f)
    }
}

impl core::cmp::PartialEq for PathBuf {
    fn eq(&self, other: &Self) -> bool {
        // from cstr_core
        self.as_ref() == other.as_ref()

        // // use cortex_m_semihosting::hprintln;
        // // hprintln!("inside PathBuf PartialEq");
        // // hprintln!("self.len {}, other.len {}", self.len, other.len).ok();
        // // hprintln!("self..len {:?}, other..len {:?}", &self.buf[..self.len], &other.buf[..other.len]).ok();
        // self.len == other.len && self.buf[..self.len - 1] == other.buf[..other.len - 1]
    }
}

impl core::cmp::Eq for PathBuf {}

// use core::cmp::Ordering;

// impl Ord for PathBuf {
//     fn cmp(&self, other: &Self) -> Ordering {
//         self.len.cmp(&other.len)
//     }
// }

// impl PartialOrd for PathBuf {
//     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
//         Some(self.cmp(other))
//     }
// }

/// Errors that arise from converting byte buffers into paths
#[derive(Clone, Copy, Debug)]
pub enum Error {
    /// Byte buffer contains non-ASCII characters
    NotAscii,
    /// Byte buffer is not a C string
    NotCStr,
    /// Byte buffer is too long (longer than `consts::PATH_MAX_PLUS_ONE`)
    TooLarge,
}

/// Result type that has its Error variant set to `path::Error`
pub type Result<T> = core::result::Result<T, Error>;

#[cfg(test)]
mod tests {
    use super::{Path, PathBuf};

    #[test]
    fn join() {
        let empty = Path::from_bytes_with_nul(b"\0").unwrap();
        let slash = Path::from_bytes_with_nul(b"/\0").unwrap();
        let a = Path::from_bytes_with_nul(b"a\0").unwrap();
        let b = Path::from_bytes_with_nul(b"b\0").unwrap();

        assert_eq!(empty.join(empty).as_ref(), "");
        assert_eq!(empty.join(slash).as_ref(), "/");
        assert_eq!(empty.join(a).as_ref(), "a");
        assert_eq!(empty.join(b).as_ref(), "b");

        assert_eq!(slash.join(empty).as_ref(), "/");
        assert_eq!(slash.join(slash).as_ref(), "/");
        assert_eq!(slash.join(a).as_ref(), "/a");
        assert_eq!(slash.join(b).as_ref(), "/b");

        assert_eq!(a.join(empty).as_ref(), "a");
        assert_eq!(a.join(slash).as_ref(), "/");
        assert_eq!(a.join(a).as_ref(), "a/a");
        assert_eq!(a.join(b).as_ref(), "a/b");

        assert_eq!(b.join(empty).as_ref(), "b");
        assert_eq!(b.join(slash).as_ref(), "/");
        assert_eq!(b.join(a).as_ref(), "b/a");
        assert_eq!(b.join(b).as_ref(), "b/b");
    }

    #[test]
    fn nulls() {
        assert!(Path::from_bytes_with_nul(b"abc\0def").is_err());
    }

    #[test]
    fn trailing_nuls() {
        assert_eq!(PathBuf::from("abc"), PathBuf::from("abc\0"));
    }
}