use blake3::{Hash, Hasher};

use crate::errors::ApiError;

pub trait CustomHash {
    fn updater(&self, hasher: &mut Hasher);

    fn hash(&self) -> Hash {
        let mut hasher = Hasher::new();
        Self::updater(&self, &mut hasher);
        hasher.finalize()
    }
}

pub struct IntegrityVerifier {
    mac: Hasher,
}

impl IntegrityVerifier {
    pub fn new() -> Result<Self, ApiError> {
        Ok(Self {
            mac: Hasher::new_derive_key(include_str!("./verification_secret")),
        })
    }

    pub fn sign<T>(&self, data: &T) -> Result<Hash, ApiError>
    where
        T: CustomHash,
    {
        let mut mac = self.mac.clone();

        mac.update(data.hash().as_bytes());
        let signature = mac.finalize();
        mac.reset();

        Ok(signature)
    }

    pub fn verify<T>(&self, data: &T, signature: Hash) -> Result<(), ApiError>
    where
        T: CustomHash,
    {
        let mut mac = self.mac.clone();
        mac.update(data.hash().as_bytes());
        let verify = mac.finalize();
        mac.reset();

        match verify == signature {
            true => Ok(()),
            false => Err(ApiError::AccessDenied),
        }
    }
}

#[cfg(test)]
mod test {

    use blake3::Hasher;

    use crate::api::backend::integrity_verification::{CustomHash, IntegrityVerifier};

    #[test]
    fn integrity_verification() {
        struct TestData {
            one: u32,
            two: String,
        }

        impl CustomHash for TestData {
            fn updater(&self, hasher: &mut Hasher) {
                hasher.update(&self.one.to_be_bytes());
                hasher.update(&self.two.as_bytes());
            }
        }

        let verifier = IntegrityVerifier::new().unwrap();

        let mut item = TestData {
            one: 24,
            two: "MyTesting".to_string(),
        };

        let signature = verifier.sign(&item).unwrap();
        assert!(verifier.verify(&item, signature).is_ok());

        item.two = "Wrong".to_string();
        assert!(verifier.verify(&item, signature).is_err());
    }
}