use aes_gcm::{
    Aes256Gcm, Nonce,
    aead::{Aead, KeyInit, Payload},
};
use base64::{Engine as _, engine::general_purpose::STANDARD as BASE64_STD};
use hkdf::Hkdf;
type HkdfSha256 = sha2::Sha256;
use sha2::{Digest, Sha256 as HashSha256};
use x448::{PublicKey, Secret};

#[derive(Debug)]
#[allow(dead_code)]
pub enum SecurePayloadError {
    InvalidBase64,
    InvalidHex,
    EncryptionError,
    DecryptionError,
    InvalidKeyLength,
}

#[derive(Clone, Copy, Debug)]
#[allow(dead_code)]
pub enum DataFormat {
    Raw,
    Base64,
    Hex,
}

pub struct SecurePayload {
    inner_data: Vec<u8>,
    private_key: Secret,
}

impl Clone for SecurePayload {
    fn clone(&self) -> Self {
        Self {
            inner_data: self.inner_data.clone(),
            private_key: Secret::from_bytes(self.private_key.as_bytes()).unwrap(),
        }
    }
}

#[allow(dead_code)]
impl SecurePayload {
    pub fn new<S, T: AsRef<[u8]>>(
        data: T,
        format: DataFormat,
        private_key: S,
    ) -> Result<Self, SecurePayloadError>
    where
        S: Into<Secret>,
    {
        let raw_data = match format {
            DataFormat::Raw => data.as_ref().to_vec(),
            DataFormat::Base64 => BASE64_STD
                .decode(data.as_ref())
                .map_err(|_| SecurePayloadError::InvalidBase64)?,
            DataFormat::Hex => {
                hex::decode(data.as_ref()).map_err(|_| SecurePayloadError::InvalidHex)?
            }
        };

        Ok(Self {
            inner_data: raw_data,
            private_key: private_key.into(),
        })
    }

    pub fn get_public_key(&self) -> [u8; 56] {
        *PublicKey::from(&self.private_key).as_bytes()
    }

    pub fn export(&self, format: DataFormat) -> String {
        match format.into() {
            DataFormat::Raw => String::from_utf8_lossy(&self.inner_data).to_string(),
            DataFormat::Base64 => BASE64_STD.encode(&self.inner_data),
            DataFormat::Hex => hex::encode(&self.inner_data),
        }
    }

    pub fn get_bytes(&self) -> &[u8] {
        &self.inner_data
    }

    pub fn get_hash(&self, format: DataFormat) -> String {
        let mut hasher = HashSha256::new();
        hasher.update(&self.inner_data);
        let result = hasher.finalize();

        match format {
            DataFormat::Raw => String::from_utf8_lossy(&result).to_string(),
            DataFormat::Base64 => BASE64_STD.encode(result),
            DataFormat::Hex => hex::encode(result),
        }
    }

    pub fn encrypt_x448<S>(&self, public_key: S) -> Result<SecurePayload, SecurePayloadError>
    where
        S: Into<PublicKey>,
    {
        let peer_pub = public_key.into();
        let shared_secret = self.private_key.as_diffie_hellman(&peer_pub).unwrap();

        let hkdf = Hkdf::<HkdfSha256>::new(None, shared_secret.as_bytes());
        let mut okm = [0u8; 44];

        hkdf.expand(b"x448-aes-gcm-no-overhead", &mut okm)
            .map_err(|_| SecurePayloadError::EncryptionError)?;

        let key = &okm[..32];
        let nonce_bytes = &okm[32..];

        let cipher = Aes256Gcm::new(key.into());
        let nonce = Nonce::from_slice(nonce_bytes);

        let ciphertext = cipher
            .encrypt(
                nonce,
                Payload {
                    msg: &self.inner_data,
                    aad: &[],
                },
            )
            .map_err(|_| SecurePayloadError::EncryptionError)?;

        Ok(SecurePayload {
            inner_data: ciphertext,
            private_key: Secret::from_bytes(self.private_key.as_bytes()).unwrap(),
        })
    }

    pub fn decrypt_to_format(
        &self,
        peer_public_key_bytes: &[u8; 56],
        output_format: DataFormat,
    ) -> Result<String, SecurePayloadError> {
        let decrypted_instance =
            self.decrypt_x448(PublicKey::from_bytes(peer_public_key_bytes).unwrap())?;
        Ok(decrypted_instance.export(output_format))
    }

    pub fn decrypt_x448<S>(
        &self,
        peer_public_key_bytes: S,
    ) -> Result<SecurePayload, SecurePayloadError>
    where
        S: Into<PublicKey>,
    {
        let peer_pub = peer_public_key_bytes.into();
        let shared_secret = self.private_key.as_diffie_hellman(&peer_pub).unwrap();

        let hkdf = Hkdf::<HkdfSha256>::new(None, shared_secret.as_bytes());
        let mut okm = [0u8; 44];
        hkdf.expand(b"x448-aes-gcm-no-overhead", &mut okm)
            .map_err(|_| SecurePayloadError::DecryptionError)?;

        let key = &okm[..32];
        let nonce_bytes = &okm[32..];

        let cipher = Aes256Gcm::new(key.into());
        let nonce = Nonce::from_slice(nonce_bytes);

        let plaintext = cipher
            .decrypt(
                nonce,
                Payload {
                    msg: &self.inner_data,
                    aad: &[],
                },
            )
            .map_err(|_| SecurePayloadError::DecryptionError)?;

        Ok(SecurePayload {
            inner_data: plaintext,
            private_key: Secret::from_bytes(self.private_key.as_bytes()).unwrap(),
        })
    }
}