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use std::fmt;

/// Hex is a simple wrapper type that you can use to wrap your type so that it
/// prints in lower hexadecimal format when use as a formatting argument.
///
/// # Examples
///
/// ```
/// use substreams::Hex;
///
/// println!("Got an hex value {}", Hex(&[0xabu8, 0xcdu8, 0xefu8]));
/// ```
///
/// It can also be used directly to encode your type as a lower hexadecimal
/// `String`:
///
/// # Examples
///
/// ```
/// use substreams::Hex;
///
/// let encode = Hex::encode(&[0xabu8, 0xcdu8, 0xefu8]);
/// ```
pub struct Hex<T>(pub T);

impl<T: AsRef<[u8]>> Hex<T> {
    pub fn decode(data: T) -> Result<Vec<u8>, hex::FromHexError> {
        ::hex::decode(data)
    }

    pub fn encode(input: T) -> String {
        encode_lower_hex(input.as_ref())
    }

    pub fn to_string(&self) -> String {
        encode_lower_hex(self.0.as_ref())
    }
}

impl<T: AsRef<[u8]>> fmt::Debug for Hex<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write_lower_hex(self.0.as_ref(), f)
    }
}

impl<T: AsRef<[u8]>> fmt::Display for Hex<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write_lower_hex(self.0.as_ref(), f)
    }
}

impl<T: AsRef<[u8]>> fmt::LowerHex for Hex<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write_lower_hex(self.0.as_ref(), f)
    }
}

const LOWER_HEX_BYTES: [&str; 256] = [
    "00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "0a", "0b", "0c", "0d", "0e", "0f",
    "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "1a", "1b", "1c", "1d", "1e", "1f",
    "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "2a", "2b", "2c", "2d", "2e", "2f",
    "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "3a", "3b", "3c", "3d", "3e", "3f",
    "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "4a", "4b", "4c", "4d", "4e", "4f",
    "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "5a", "5b", "5c", "5d", "5e", "5f",
    "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "6a", "6b", "6c", "6d", "6e", "6f",
    "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "7a", "7b", "7c", "7d", "7e", "7f",
    "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "8a", "8b", "8c", "8d", "8e", "8f",
    "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "9a", "9b", "9c", "9d", "9e", "9f",
    "a0", "a1", "a2", "a3", "a4", "a5", "a6", "a7", "a8", "a9", "aa", "ab", "ac", "ad", "ae", "af",
    "b0", "b1", "b2", "b3", "b4", "b5", "b6", "b7", "b8", "b9", "ba", "bb", "bc", "bd", "be", "bf",
    "c0", "c1", "c2", "c3", "c4", "c5", "c6", "c7", "c8", "c9", "ca", "cb", "cc", "cd", "ce", "cf",
    "d0", "d1", "d2", "d3", "d4", "d5", "d6", "d7", "d8", "d9", "da", "db", "dc", "dd", "de", "df",
    "e0", "e1", "e2", "e3", "e4", "e5", "e6", "e7", "e8", "e9", "ea", "eb", "ec", "ed", "ee", "ef",
    "f0", "f1", "f2", "f3", "f4", "f5", "f6", "f7", "f8", "f9", "fa", "fb", "fc", "fd", "fe", "ff",
];

fn write_lower_hex(input: &[u8], mut w: impl std::fmt::Write) -> fmt::Result {
    for byte in input {
        w.write_str(LOWER_HEX_BYTES[*byte as usize])?;
    }

    return Ok(());
}

fn encode_lower_hex<T: AsRef<[u8]>>(input: T) -> String {
    let bytes = input.as_ref();

    if bytes.len() == 0 {
        return String::new();
    }

    let mut buffer = String::with_capacity(bytes.len());
    write_lower_hex(bytes, &mut buffer).expect("non-faillible pre-allocated buffer");
    buffer
}

#[cfg(test)]
mod tests {
    use crate::hex::encode_lower_hex;

    #[test]
    fn it_encode_lower_hex_correctly() {
        assert_eq!(encode_lower_hex(&[] as &[u8; 0]), "");
        assert_eq!(encode_lower_hex(&[0x01u8]), "01");
        assert_eq!(encode_lower_hex(&[0xa1u8, 0xc3u8]), "a1c3");
    }
}