use std::fmt::{Debug, Display, Formatter, Pointer};
use std::ops::Deref;
use crypto::digest::Digest;
use crypto::sha1::Sha1;
use serde::{Deserialize, Deserializer};
use serde::de::{Error, Visitor};
use hex::{FromHex, ToHex};

// sha1 digests are 20 bytes long
pub const SHA1_DIGEST_BYTES: usize = 20;
pub type Sha1DigestBytes = [u8; SHA1_DIGEST_BYTES];

#[derive(PartialEq, Eq, PartialOrd, Ord, Clone)]
pub struct Sha1Digest(pub Sha1DigestBytes);

impl Debug for Sha1Digest {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        write!(f, "Sha1Digest {{{}}}", self.0.encode_hex::<String>())
    }
}

impl Display for Sha1Digest {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        f.write_str(&self.0.encode_hex::<String>())
    }
}

impl Sha1Digest {
    pub fn verify(&self, s: &str) -> Result<(), Sha1Digest> {
        let mut st = Sha1::new();
        let mut dig = [0u8; SHA1_DIGEST_BYTES];

        st.input_str(s);
        st.result(&mut dig);

        if self.0 == dig {
            return Ok(());
        }

        Err(Sha1Digest(dig))
    }
}

struct Sha1DigestVisitor;

impl <'a> Visitor<'a> for Sha1DigestVisitor {
    type Value = Sha1Digest;

    fn expecting(&self, formatter: &mut Formatter) -> std::fmt::Result {
        write!(formatter, "a valid SHA-1 digest (40-character hex string)")
    }

    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
    where
        E: Error,
    {
        Sha1DigestBytes::from_hex(v).map_err(|e| E::custom(e)).map(Sha1Digest)
    }
}

impl<'a> Deserialize<'a> for Sha1Digest {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'a>,
    {
        deserializer.deserialize_any(Sha1DigestVisitor)
    }
}