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use byteorder::{ByteOrder, LittleEndian};
use base32;
use crc16::{State, XMODEM};
use error::{Result, Error};

pub type Key = Vec<u8>;

const ACCOUNT_ID_VERSION_BYTE: u8 = 6 << 3; // G
const SEED_VERSION_BYTE: u8 = 18 << 3; // S
const PRE_AUTH_TX_VERSION_BYTE: u8 = 19 << 3; // T
const SHA256_HASH_VERSION_BYTE: u8 = 23 << 3; // X

static ALPHABET: base32::Alphabet = base32::Alphabet::RFC4648 { padding: false };

#[derive(Debug, Clone)]
pub enum StrKey {
    AccountId(Key),
    Seed(Key),
    PreAuthTx(Key),
    Sha256Hash(Key),
}


impl StrKey {
    pub fn from_account_id(account_id: &str) -> Result<StrKey> {
        Self::decode(ACCOUNT_ID_VERSION_BYTE, account_id).map(StrKey::AccountId)
    }

    pub fn from_seed(seed: &str) -> Result<StrKey> {
        Self::decode(SEED_VERSION_BYTE, seed).map(StrKey::Seed)
    }

    pub fn from_pre_auth_tx(pre_auth_tx: &str) -> Result<StrKey> {
        Self::decode(PRE_AUTH_TX_VERSION_BYTE, pre_auth_tx).map(StrKey::PreAuthTx)
    }

    pub fn from_sha256_hash(hash: &str) -> Result<StrKey> {
        Self::decode(SHA256_HASH_VERSION_BYTE, hash).map(StrKey::Sha256Hash)
    }

    pub fn encode(&self) -> Result<String> {
        let version_byte = self.version_byte();
        let mut data = Vec::with_capacity(35);
        data.push(version_byte);
        match *self {
            StrKey::AccountId(ref key) => data.extend_from_slice(&key),
            StrKey::Seed(ref key) => data.extend_from_slice(&key),
            StrKey::PreAuthTx(ref key) => data.extend_from_slice(&key),
            StrKey::Sha256Hash(ref key) => data.extend_from_slice(&key),
        }
        let checksum = Self::calculate_checksum(&data);
        let data_end = data.len();
        data.resize(data_end + 2, 0);
        LittleEndian::write_u16(&mut data[data_end..], checksum);
        Ok(base32::encode(ALPHABET, &data))
    }

    fn decode(expected_version_byte: u8, encoded: &str) -> Result<Key> {
        let decoded = base32::decode(ALPHABET, &encoded).ok_or(Error::InvalidStrKey)?;
        let decoded_len = decoded.len();
        let version_byte = decoded[0];
        if version_byte != expected_version_byte {
            return Err(Error::InvalidStrKeyVersionByte);
        }

        let payload = &decoded[..decoded_len - 2];
        let data = &payload[1..];
        let checksum_bytes = &decoded[decoded_len - 2..];
        let checksum = Self::calculate_checksum(payload);

        if Self::verify_checksum(checksum, checksum_bytes) {
            let key = data.to_vec();
            Ok(key)
        } else {
            Err(Error::InvalidStrKeyChecksum)
        }
    }

    fn calculate_checksum(payload: &[u8]) -> u16 {
        State::<XMODEM>::calculate(payload)
    }

    fn verify_checksum(checksum: u16, bytes: &[u8]) -> bool {
        let expected = LittleEndian::read_u16(bytes);
        expected == checksum
    }

    fn version_byte(&self) -> u8 {
        match *self {
            StrKey::AccountId(_) => ACCOUNT_ID_VERSION_BYTE,
            StrKey::Seed(_) => SEED_VERSION_BYTE,
            StrKey::PreAuthTx(_) => PRE_AUTH_TX_VERSION_BYTE,
            StrKey::Sha256Hash(_) => SHA256_HASH_VERSION_BYTE,
        }
    }
}


#[cfg(test)]
mod tests {
    use StrKey;

    #[test]
    fn test_from_account_id() {
        let account_id = "GCLDNMHZTEY6PUYQBYOVERBBZ2W3RLMYOSZWHAMY5R4YW2N6MM4LFA72";
        let strkey = StrKey::from_account_id(&account_id).unwrap();
        let new_account_id = strkey.encode().unwrap();
        assert_eq!(account_id, new_account_id);
    }

    #[test]
    fn test_from_seed() {
        let seed = "SDAKFNYEIAORZKKCYRILFQKLLOCNPL5SWJ3YY5NM3ZH6GJSZGXHZEPQS";
        let strkey = StrKey::from_seed(&seed).unwrap();
        let new_seed = strkey.encode().unwrap();
        assert_eq!(seed, new_seed);
    }

    #[test]
    fn test_from_seed_returns_error() {
        let seed = "GDAKFNYEIAORZKKCYRILFQKLLOCNPL5SWJ3YY5NM3ZH6GJSZGXHZEPQS";
        let strkey = StrKey::from_seed(&seed);
        assert!(strkey.is_err());
    }
}