use serde::{Deserialize, Deserializer, Serialize, Serializer};

#[derive(Clone, Debug, Deserialize, Serialize, Eq, Hash, PartialEq)]
pub struct Sha256(#[serde(serialize_with = "as_hex", deserialize_with = "from_hex")] pub [u8; 32]);

fn hash_to_hex_string(hash: &[u8; 32]) -> String {
    use std::fmt::*;

    let mut hex_string = String::with_capacity(64);
    for digit in hash.iter() {
        write!(hex_string, "{:02X}", digit).unwrap();
    }
    hex_string
}

impl Sha256 {
    pub fn as_hex_string(&self) -> String {
        hash_to_hex_string(&self.0)
    }

    pub fn from_data(data: &[u8]) -> Self {
        use sha2::Digest;

        let mut hasher = sha2::Sha256::new();
        hasher.input(data);

        let hash_result = hasher.result();

        let mut hash_arr = [0u8; 32];
        for i in 0..32 {
            hash_arr[i] = hash_result[i];
        }

        Sha256(hash_arr)
    }
}

fn as_hex<S>(hash: &[u8; 32], serializer: S) -> Result<S::Ok, S::Error>
where
    S: Serializer,
{
    serializer.serialize_str(&hash_to_hex_string(hash))
}

fn from_hex<'de, D>(deserializer: D) -> Result<[u8; 32], D::Error>
where
    D: Deserializer<'de>,
{
    use serde::de::Error;

    fn hex2bytes(s: &str) -> Option<[u8; 32]> {
        if s.len() != 32 * 2 {
            return None; // String has wrong length
        }

        let mut out = [0u8; 32];
        for (i, byte) in out.iter_mut().enumerate() {
            let string_index = i * 2;
            *byte = u8::from_str_radix(&s[string_index..=string_index + 1], 16).ok()?;
        }

        return Some(out);
    }

    String::deserialize(deserializer).and_then(|string| {
        hex2bytes(&string).ok_or_else(|| Error::custom("Invalid HEX String!".to_string()))
    })
}

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

    const HASH_BYTES: [u8; 32] = [
        0, 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,
    ];

    const HASH_STRING: &'static str =
        r#""000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F""#;

    #[test]
    fn serialize() {
        let hash = serde_json::to_string_pretty(&Sha256(HASH_BYTES)).unwrap();
        assert_eq!(&hash, HASH_STRING);
    }

    #[test]
    fn deserialize() {
        let hash: Sha256 = serde_json::from_str(HASH_STRING).unwrap();
        assert_eq!(hash, Sha256(HASH_BYTES))
    }

    #[test]
    fn fail_deserialize() {
        // too short.
        assert_eq!(
            serde_json::from_str::<'_, Sha256>(r#""0102013""#).is_err(),
            true
        );
        // wrong radix
        assert_eq!(
            serde_json::from_str::<'_, Sha256>(r#""Hallo Welt""#).is_err(),
            true
        );
        // too long.
        assert_eq!(
            serde_json::from_str::<'_, Sha256>( r#""000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F""#).is_err(),
            true
        );
    }
}