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use std::{borrow::Cow, convert::TryInto};

use git_object::bstr::{BStr, BString, ByteSlice};

use crate::{store::packed, PartialNameRef};

/// packed-refs specific functionality
impl packed::Buffer {
    /// Find a reference with the given `name` and return it.
    pub fn try_find<'a, Name, E>(&self, name: Name) -> Result<Option<packed::Reference<'_>>, Error>
    where
        Name: TryInto<PartialNameRef<'a>, Error = E>,
        Error: From<E>,
    {
        let name = name.try_into()?;
        for inbetween in &["", "tags", "heads", "remotes"] {
            let (name, was_absolute) = if name.0.starts_with_str(b"refs/") {
                (Cow::Borrowed(name.0), true)
            } else {
                let mut full_name: BString = format!(
                    "refs/{}",
                    if inbetween.is_empty() {
                        "".to_string()
                    } else {
                        format!("{}/", inbetween)
                    }
                )
                .into();
                full_name.extend_from_slice(name.0);
                (Cow::Owned(full_name), false)
            };
            match self.binary_search_by(name.as_ref()) {
                Ok(line_start) => {
                    return Ok(Some(
                        packed::decode::reference::<()>(&self.as_ref()[line_start..])
                            .map_err(|_| Error::Parse)?
                            .1,
                    ))
                }
                Err((parse_failure, _)) => {
                    if parse_failure {
                        return Err(Error::Parse);
                    } else if was_absolute {
                        return Ok(None);
                    } else {
                        continue;
                    }
                }
            }
        }
        Ok(None)
    }

    /// Find a reference with the given `name` and return it.
    pub fn find<'a, Name, E>(&self, name: Name) -> Result<packed::Reference<'_>, existing::Error>
    where
        Name: TryInto<PartialNameRef<'a>, Error = E>,
        Error: From<E>,
    {
        match self.try_find(name) {
            Ok(Some(r)) => Ok(r),
            Ok(None) => Err(existing::Error::NotFound),
            Err(err) => Err(existing::Error::Find(err)),
        }
    }

    /// Perform a binary search where `Ok(pos)` is the beginning of the line that matches `name` perfectly and `Err(pos)`
    /// is the beginning of the line at which `name` could be inserted to still be in sort order.
    pub(in crate::store::packed) fn binary_search_by(&self, full_name: &BStr) -> Result<usize, (bool, usize)> {
        let a = self.as_ref();
        let search_start_of_record = |ofs: usize| {
            a[..ofs]
                .rfind(b"\n")
                .and_then(|pos| {
                    let candidate = pos + 1;
                    a.get(candidate).and_then(|b| {
                        if *b == b'^' {
                            a[..pos].rfind(b"\n").map(|pos| pos + 1)
                        } else {
                            Some(candidate)
                        }
                    })
                })
                .unwrap_or(0)
        };
        let mut encountered_parse_failure = false;
        a.binary_search_by_key(&full_name.as_ref(), |b: &u8| {
            let ofs = b as *const u8 as usize - a.as_ptr() as usize;
            let line = &a[search_start_of_record(ofs)..];
            packed::decode::reference::<()>(line)
                .map(|(_rest, r)| r.name.as_bstr().as_ref())
                .map_err(|err| {
                    encountered_parse_failure = true;
                    err
                })
                .unwrap_or(&[])
        })
        .map(search_start_of_record)
        .map_err(|pos| (encountered_parse_failure, search_start_of_record(pos)))
    }
}

mod error {
    use std::convert::Infallible;

    use quick_error::quick_error;

    quick_error! {
        /// The error returned by [`find()`][super::packed::Buffer::find()]
        #[derive(Debug)]
        #[allow(missing_docs)]
        pub enum Error {
            RefnameValidation(err: crate::name::Error) {
                display("The ref name or path is not a valid ref name")
                from()
                source(err)
            }
            Parse {
                display("The reference could not be parsed")
            }
        }
    }

    impl From<Infallible> for Error {
        fn from(_: Infallible) -> Self {
            unreachable!("this impl is needed to allow passing a known valid partial path as parameter")
        }
    }
}
pub use error::Error;

///
pub mod existing {
    use quick_error::quick_error;

    quick_error! {
        /// The error returned by [`find_existing()`][super::packed::Buffer::find_existing()]
        #[derive(Debug)]
        #[allow(missing_docs)]
        pub enum Error {
            Find(err: super::Error) {
                display("The find operation failed")
                from()
                source(err)
            }
            NotFound {
                display("The reference did not exist even though that was expected")
            }
        }
    }
}