use aes_gcm::{                                                                                                                                                                                  
    aead::{Aead, AeadCore, KeyInit, OsRng},
    Aes256Gcm, Key, Nonce
};

use std::io;


static PASSWORD_TEST: &str = "MyPasswordStorage"; // will be added with nonce for storing each time


pub struct Encoder {
    // will be stored with padding 32 bytes
    passphrase: String
}

impl Encoder {
    pub fn from(passphrase: &String) -> Encoder {
        // TODO: throw error if password longer that 32 bytes
        let padded_passphrase = Encoder::get_passhrase_with_padding(passphrase);
        Encoder { passphrase: padded_passphrase }
    }

    fn get_passhrase_with_padding(passphrase: &String) -> String {
        let mut result = passphrase.clone();
        while result.len() < 32 {
            // use '-' for padding, can be anything else
            result.push('-');
        }
        result
    }
    
    // TODO: error type
    pub fn encrypt(&self, plain_text: &String) -> io::Result<String> {
        let key = Key::<Aes256Gcm>::from_slice(self.passphrase.as_bytes());                                                                                                                                 
        let nonce = Aes256Gcm::generate_nonce(&mut OsRng);

        let cipher = Aes256Gcm::new(key);
        
        // TODO: mar error inted of expect
        let ciphered_data = cipher.encrypt(&nonce, plain_text.as_bytes())
            .map_err(|_| io::Error::new(
                io::ErrorKind::Other,
                "Failed to encrypt"
            ))?;

        // combining nonce and encrypted data together
        // for storage purpose
        let mut encrypted_data: Vec<u8> = nonce.to_vec();
        encrypted_data.extend_from_slice(&ciphered_data);

        Ok(hex::encode(encrypted_data))

    }

    // TODO: review error type
    pub fn decrypt(&self, encrypted_data: String) -> io::Result<String> {
        let encrypted_data = hex::decode(encrypted_data)
            .map_err(|_| io::Error::new(
                io::ErrorKind::Other,
                "failed to decode hex string into vec"
            ))?;

        let key = Key::<Aes256Gcm>::from_slice(self.passphrase.as_bytes());
        let (nonce_arr, ciphered_data) = encrypted_data.split_at(12);
        let nonce = Nonce::from_slice(nonce_arr);
        let cipher = Aes256Gcm::new(key);
        let plaintext = cipher.decrypt(nonce, ciphered_data)
             .map_err(|_| io::Error::new(
                io::ErrorKind::InvalidData,
                "failed to decrypt data"
            ))?;

        let result = String::from_utf8(plaintext)
             .map_err(|_| io::Error::new(
                io::ErrorKind::InvalidData,
                "failed to convert vector of bytes to string"
            ))?;
        Ok(result)
    }

    pub fn test_encoded_passphrase(&self, passphrase_encrypted: String) -> io::Result<bool> {
        // TODO: better way to check error
        let decrypted = match self.decrypt(passphrase_encrypted) {
            Ok(decrypted) => decrypted,
            Err(_) => return Ok(false)
        };
        Ok(PASSWORD_TEST == decrypted)
    }

    pub fn get_encoded_test_passphrase(&self) -> io::Result<String> {
        self.encrypt(&PASSWORD_TEST.to_string())
    }

}