//! bitcoin's base58 encoding format

pub const ALPHABET: &str = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";

#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Copy, Clone)]
pub enum Error {
    /// error when a given character is not part of the supported
    /// base58 `ALPHABET`. Contains the index of the faulty byte.
    UnknownSymbol(usize),
}
impl ::std::fmt::Display for Error {
    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
        match self {
            Error::UnknownSymbol(idx) => write!(f, "Unknown symbol at byte index {}", idx),
        }
    }
}
impl ::std::error::Error for Error {}

pub type Result<T> = ::std::result::Result<T, Error>;

/// encode in base58 the given input
pub fn encode(input: &[u8]) -> String {
    // unsafe to unwrap the result of `String::from_utf8` as the given
    // returned bytes are valid within the base58 alphabet (they are all ASCII7)
    String::from_utf8(base_encode(ALPHABET, input)).unwrap()
}

/// decode from base58 the given input
pub fn decode(input: &str) -> Result<Vec<u8>> {
    base_decode(ALPHABET, input.as_bytes())
}

/// decode from base58 the given input
//pub fn decode_bytes(input: &[u8]) -> Result<Vec<u8>> {
//    base_decode(ALPHABET, input)
//}

#[cfg(test)]
mod tests {
    fn encode(input: &[u8], expected: &str) {
        let encoded = super::encode(input);
        assert_eq!(encoded, expected);
    }
    fn decode(expected: &[u8], input: &str) {
        let decoded = super::decode(input).unwrap();
        assert_eq!(decoded.as_slice(), expected);
    }

    #[test]
    fn test_vector_1() {
        encode(b"\0\0\0\0", "11111");
        decode(b"\0\0\0\0", "11111");
    }

    #[test]
    fn test_vector_2() {
        encode(b"This is awesome!", "BRY7dK2V98Sgi7CFWiZbap");
        decode(b"This is awesome!", "BRY7dK2V98Sgi7CFWiZbap");
    }

    #[test]
    fn test_vector_3() {
        encode(b"Hello World...", "TcgsE5dzphUWfjcb9i5");
        decode(b"Hello World...", "TcgsE5dzphUWfjcb9i5");
    }

    #[test]
    fn test_vector_4() {
        encode(b"\0abc", "1ZiCa");
        decode(b"\0abc", "1ZiCa");
    }

    #[test]
    fn test_vector_5() {
        encode(b"\0\0abc", "11ZiCa");
        decode(b"\0\0abc", "11ZiCa");
    }

    #[test]
    fn test_vector_6() {
        encode(b"\0\0\0abc", "111ZiCa");
        decode(b"\0\0\0abc", "111ZiCa");
    }

    #[test]
    fn test_vector_7() {
        encode(b"\0\0\0\0abc", "1111ZiCa");
        decode(b"\0\0\0\0abc", "1111ZiCa");
    }

    #[test]
    fn test_vector_8() {
        encode(
            b"abcdefghijklmnopqrstuvwxyz",
            "3yxU3u1igY8WkgtjK92fbJQCd4BZiiT1v25f",
        );
        decode(
            b"abcdefghijklmnopqrstuvwxyz",
            "3yxU3u1igY8WkgtjK92fbJQCd4BZiiT1v25f",
        );
    }
}

fn base_encode(alphabet_s: &str, input: &[u8]) -> Vec<u8> {
    let alphabet = alphabet_s.as_bytes();
    let base = alphabet.len() as u32;

    let mut digits = vec![0u8];
    for input in input.iter() {
        let mut carry = *input as u32;
        for digit in digits.iter_mut() {
            carry += (*digit as u32) << 8;
            *digit = (carry % base) as u8;
            carry /= base;
        }

        while carry > 0 {
            digits.push((carry % base) as u8);
            carry /= base;
        }
    }

    let mut string = vec![];

    let mut k = 0;
    while (k < input.len()) && (input[k] == 0) {
        string.push(alphabet[0]);
        k += 1;
    }
    for digit in digits.iter().rev() {
        string.push(alphabet[*digit as usize]);
    }

    string
}

fn base_decode(alphabet_s: &str, input: &[u8]) -> Result<Vec<u8>> {
    let alphabet = alphabet_s.as_bytes();
    let base = alphabet.len() as u32;

    let mut bytes: Vec<u8> = vec![0];
    let zcount = input.iter().take_while(|x| **x == alphabet[0]).count();

    for (i, input) in input[zcount..].iter().enumerate() {
        let value = match alphabet.iter().position(|&x| x == *input) {
            Some(idx) => idx,
            None => return Err(Error::UnknownSymbol(i)),
        };
        let mut carry = value as u32;
        for byte in bytes.iter_mut() {
            carry += (*byte as u32) * base;
            *byte = carry as u8;
            carry >>= 8;
        }

        while carry > 0 {
            bytes.push(carry as u8);
            carry >>= 8;
        }
    }
    let leading_zeros = bytes.iter().rev().take_while(|x| **x == 0).count();
    if zcount > leading_zeros {
        let unpad = if leading_zeros > 0 {
            leading_zeros + 1
        } else {
            0
        };
        bytes.resize(bytes.len() + zcount - unpad, 0);
    }
    bytes.reverse();
    Ok(bytes)
}