use crate::SIZE_OF_SHA1_DIGEST;
use bstr::ByteSlice;
use std::{
    convert::{TryFrom, TryInto},
    fmt,
};

/// A borrowed reference to a hash identifying objects.
#[derive(PartialEq, Eq, Debug, Hash, Ord, PartialOrd, Clone, Copy)]
#[cfg_attr(feature = "serde1", derive(serde::Serialize))]
pub struct Digest<'a>(&'a [u8; SIZE_OF_SHA1_DIGEST]);

/// Access
impl<'a> Digest<'a> {
    /// The kind of hash used for this Digest
    pub fn kind(&self) -> crate::Kind {
        crate::Kind::Sha1
    }
    /// The first byte of the hash, commonly used to partition a set of `Digest`s
    pub fn first_byte(&self) -> u8 {
        self.0[0]
    }
}

/// Sha1 specific methods
impl<'a> Digest<'a> {
    /// Returns an array with a hexadecimal encoded version of the Sha1 hash this `Digest` represents.
    ///
    /// **Panics** if this is not a Sha1 hash, as identifiable by [`Digest::kind()`].
    pub fn to_sha1_hex(&self) -> [u8; SIZE_OF_SHA1_DIGEST * 2] {
        let mut buf = [0u8; SIZE_OF_SHA1_DIGEST * 2];
        hex::encode_to_slice(self.0, &mut buf).expect("to count correctly");
        buf
    }

    /// Returns the bytes making up the Sha1.
    ///
    /// **Panics** if this is not a Sha1 hash, as identifiable by [`Digest::kind()`].
    pub fn sha1(&self) -> &[u8; SIZE_OF_SHA1_DIGEST] {
        self.0
    }

    /// Returns a Sha1 digest with all bytes being initialized to zero.
    pub fn null_sha1() -> Self {
        Digest(&[0u8; SIZE_OF_SHA1_DIGEST])
    }
}

impl<'a> From<&'a [u8; SIZE_OF_SHA1_DIGEST]> for Digest<'a> {
    fn from(v: &'a [u8; SIZE_OF_SHA1_DIGEST]) -> Self {
        Digest(v)
    }
}

impl<'a> TryFrom<&'a [u8]> for Digest<'a> {
    type Error = std::array::TryFromSliceError;

    fn try_from(value: &'a [u8]) -> Result<Self, Self::Error> {
        Ok(Digest(value.try_into()?))
    }
}

impl fmt::Display for Digest<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", &self.to_sha1_hex().as_bstr())
    }
}

/// Manually created from a version that uses a slice, and we forcefully try to convert it into a borrowed array of the desired size
/// Could be improved by fitting this into serde
/// Unfortunately the serde::Deserialize derive wouldn't work for borrowed arrays.
#[cfg(feature = "serde1")]
impl<'de: 'a, 'a> serde::Deserialize<'de> for Digest<'a> {
    fn deserialize<D>(deserializer: D) -> Result<Self, <D as serde::Deserializer<'de>>::Error>
    where
        D: serde::Deserializer<'de>,
    {
        struct __Visitor<'de: 'a, 'a> {
            marker: serde::export::PhantomData<Digest<'a>>,
            lifetime: serde::export::PhantomData<&'de ()>,
        }
        impl<'de: 'a, 'a> serde::de::Visitor<'de> for __Visitor<'de, 'a> {
            type Value = Digest<'a>;
            fn expecting(&self, __formatter: &mut serde::export::Formatter<'_>) -> serde::export::fmt::Result {
                serde::export::Formatter::write_str(__formatter, "tuple struct Digest")
            }
            #[inline]
            fn visit_newtype_struct<__E>(self, __e: __E) -> serde::export::Result<Self::Value, __E::Error>
            where
                __E: serde::Deserializer<'de>,
            {
                let __field0: &'a [u8] = match <&'a [u8] as serde::Deserialize>::deserialize(__e) {
                    serde::export::Ok(__val) => __val,
                    serde::export::Err(__err) => {
                        return serde::export::Err(__err);
                    }
                };
                serde::export::Ok(Digest(__field0.try_into().expect("exactly 20 bytes")))
            }
            #[inline]
            fn visit_seq<__A>(self, mut __seq: __A) -> serde::export::Result<Self::Value, __A::Error>
            where
                __A: serde::de::SeqAccess<'de>,
            {
                let __field0 = match match serde::de::SeqAccess::next_element::<&'a [u8]>(&mut __seq) {
                    serde::export::Ok(__val) => __val,
                    serde::export::Err(__err) => {
                        return serde::export::Err(__err);
                    }
                } {
                    serde::export::Some(__value) => __value,
                    serde::export::None => {
                        return serde::export::Err(serde::de::Error::invalid_length(
                            0usize,
                            &"tuple struct Digest with 1 element",
                        ));
                    }
                };
                serde::export::Ok(Digest(__field0.try_into().expect("exactly 20 bytes")))
            }
        }
        serde::Deserializer::deserialize_newtype_struct(
            deserializer,
            "Digest",
            __Visitor {
                marker: serde::export::PhantomData::<Digest<'a>>,
                lifetime: serde::export::PhantomData,
            },
        )
    }
}