use std::fmt;

#[cfg(any(test, feature = "quickcheck"))]
use quickcheck::{Arbitrary, Gen};

use crate::Error;
use crate::Fingerprint;
use crate::Result;

/// A short identifier for certificates and keys.
///
/// A KeyID is a fingerprint fragment.  It identifies a public key,
/// but is easy to forge.  For more details about how a KeyID is
/// generated, see [Section 12.2 of RFC 4880].
///
///   [Section 12.2 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-12.2
///
/// Note: This enum cannot be exhaustively matched to allow future
/// extensions.
#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
pub enum KeyID {
    /// Lower 8 byte SHA-1 hash.
    V4([u8;8]),
    /// Used for holding keyids that we don't understand.  For
    /// instance, we don't grok v3 keyids.  And, it is possible that
    /// the Issuer subpacket contains the wrong number of bytes.
    Invalid(Box<[u8]>),

    /// This marks this enum as non-exhaustive.  Do not use this
    /// variant.
    #[doc(hidden)] __Nonexhaustive,
}

impl fmt::Display for KeyID {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.convert_to_string(true))
    }
}

impl fmt::Debug for KeyID {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_tuple("KeyID")
            .field(&self.to_string())
            .finish()
    }
}

impl fmt::UpperHex for KeyID {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.write_str(&self.convert_to_string(false))
    }
}

impl fmt::LowerHex for KeyID {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let mut hex = self.convert_to_string(false);
        hex.make_ascii_lowercase();
        f.write_str(&hex)
    }
}

impl std::str::FromStr for KeyID {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
        let bytes = crate::fmt::hex::decode_pretty(s)?;

        // A KeyID is exactly 8 bytes long.
        if bytes.len() == 8 {
            Ok(KeyID::from_bytes(&bytes[..]))
        } else {
            // Maybe a fingerprint was given.  Try to parse it and
            // convert it to a KeyID.
            Ok(s.parse::<Fingerprint>()?.into())
        }
    }
}

impl From<KeyID> for Vec<u8> {
    fn from(id: KeyID) -> Self {
        let mut r = Vec::with_capacity(8);
        match id {
            KeyID::V4(ref b) => r.extend_from_slice(b),
            KeyID::Invalid(ref b) => r.extend_from_slice(b),
            KeyID::__Nonexhaustive => unreachable!(),
        }
        r
    }
}

impl From<u64> for KeyID {
    fn from(id: u64) -> Self {
        Self::new(id)
    }
}

impl From<[u8; 8]> for KeyID {
    fn from(id: [u8; 8]) -> Self {
        KeyID::from_bytes(&id[..])
    }
}

impl From<&Fingerprint> for KeyID {
    fn from(fp: &Fingerprint) -> Self {
        match fp {
            Fingerprint::V4(fp) =>
                KeyID::from_bytes(&fp[fp.len() - 8..]),
            Fingerprint::Invalid(fp) => {
                KeyID::Invalid(fp.clone())
            }
            Fingerprint::__Nonexhaustive => unreachable!(),
        }
    }
}

impl From<Fingerprint> for KeyID {
    fn from(fp: Fingerprint) -> Self {
        match fp {
            Fingerprint::V4(fp) =>
                KeyID::from_bytes(&fp[fp.len() - 8..]),
            Fingerprint::Invalid(fp) => {
                KeyID::Invalid(fp)
            }
            Fingerprint::__Nonexhaustive => unreachable!(),
        }
    }
}

impl KeyID {
    /// Converts a u64 to a KeyID.
    pub fn new(data: u64) -> KeyID {
        let bytes = data.to_be_bytes();
        Self::from_bytes(&bytes[..])
    }

    /// Converts the KeyID to a u64 if possible.
    pub fn as_u64(&self) -> Result<u64> {
        match &self {
            KeyID::V4(ref b) =>
                Ok(u64::from_be_bytes(*b)),
            KeyID::Invalid(_) =>
                Err(Error::InvalidArgument("Invalid KeyID".into()).into()),
            KeyID::__Nonexhaustive => unreachable!(),
        }
    }

    /// Reads a binary key ID.
    pub fn from_bytes(raw: &[u8]) -> KeyID {
        if raw.len() == 8 {
            let mut keyid : [u8; 8] = Default::default();
            keyid.copy_from_slice(raw);
            KeyID::V4(keyid)
        } else {
            KeyID::Invalid(raw.to_vec().into_boxed_slice())
        }
    }

    /// Returns a reference to the raw KeyID.
    pub fn as_bytes(&self) -> &[u8] {
        match self {
            &KeyID::V4(ref id) => id,
            &KeyID::Invalid(ref id) => id,
            KeyID::__Nonexhaustive => unreachable!(),
        }
    }

    /// Returns the wildcard KeyID.
    pub fn wildcard() -> Self {
        Self::from_bytes(&[0u8; 8][..])
    }

    /// Returns true if this is a wild card ID.
    pub fn is_wildcard(&self) -> bool {
        self.as_bytes().iter().all(|b| *b == 0)
    }

    /// Converts this key ID to its canonical hexadecimal representation.
    ///
    /// This representation is always uppercase and without spaces and is
    /// suitable for stable key identifiers.
    ///
    /// The output of this function is exactly the same as formatting this
    /// object with the `:X` format specifier.
    ///
    /// ```rust
    /// # extern crate sequoia_openpgp as openpgp;
    /// use openpgp::KeyID;
    ///
    /// let keyid = "fb3751f1587daef1".parse::<KeyID>().unwrap();
    ///
    /// assert_eq!("FB3751F1587DAEF1", keyid.to_hex());
    /// assert_eq!(format!("{:X}", keyid), keyid.to_hex());
    /// ```
    pub fn to_hex(&self) -> String {
        format!("{:X}", self)
    }

    /// Parses the hexadecimal representation of an OpenPGP key ID.
    ///
    /// This function is the reverse of `to_hex`. It also accepts other variants
    /// of the key ID notation including lower-case letters, spaces and optional
    /// leading `0x`.
    ///
    /// ```rust
    /// # extern crate sequoia_openpgp as openpgp;
    /// use openpgp::KeyID;
    ///
    /// let keyid = KeyID::from_hex("0xfb3751f1587daef1").unwrap();
    ///
    /// assert_eq!("FB3751F1587DAEF1", keyid.to_hex());
    /// ```
    pub fn from_hex(s: &str) -> std::result::Result<Self, anyhow::Error> {
        std::str::FromStr::from_str(s)
    }

    /// Common code for the above functions.
    fn convert_to_string(&self, pretty: bool) -> String {
        let raw = match self {
            &KeyID::V4(ref fp) => &fp[..],
            &KeyID::Invalid(ref fp) => &fp[..],
            KeyID::__Nonexhaustive => unreachable!(),
        };

        // We currently only handle V4 key IDs, which look like:
        //
        //   AACB 3243 6300 52D9
        //
        // Since we have no idea how to format an invalid key ID, just
        // format it like a V4 fingerprint and hope for the best.

        let mut output = Vec::with_capacity(
            // Each byte results in to hex characters.
            raw.len() * 2
            + if pretty {
                // Every 2 bytes of output, we insert a space.
                raw.len() / 2
            } else { 0 });

        for (i, b) in raw.iter().enumerate() {
            if pretty && i > 0 && i % 2 == 0 {
                output.push(' ' as u8);
            }

            let top = b >> 4;
            let bottom = b & 0xFu8;

            if top < 10u8 {
                output.push('0' as u8 + top)
            } else {
                output.push('A' as u8 + (top - 10u8))
            }

            if bottom < 10u8 {
                output.push('0' as u8 + bottom)
            } else {
                output.push('A' as u8 + (bottom - 10u8))
            }
        }

        // We know the content is valid UTF-8.
        String::from_utf8(output).unwrap()
    }
}

#[cfg(any(test, feature = "quickcheck"))]
impl Arbitrary for KeyID {
    fn arbitrary<G: Gen>(g: &mut G) -> Self {
        KeyID::new(u64::arbitrary(g))
    }
}

#[cfg(test)]
mod test {
    use super::*;
    quickcheck! {
        fn u64_roundtrip(id: u64) -> bool {
            KeyID::new(id).as_u64().unwrap() == id
        }
    }

    #[test]
    fn from_hex() {
        "FB3751F1587DAEF1".parse::<KeyID>().unwrap();
        "39D100AB67D5BD8C04010205FB3751F1587DAEF1".parse::<KeyID>()
            .unwrap();
        "0xFB3751F1587DAEF1".parse::<KeyID>().unwrap();
        "0x39D100AB67D5BD8C04010205FB3751F1587DAEF1".parse::<KeyID>()
            .unwrap();
        "FB37 51F1 587D AEF1".parse::<KeyID>().unwrap();
        "39D1 00AB 67D5 BD8C 0401  0205 FB37 51F1 587D AEF1".parse::<KeyID>()
            .unwrap();
        "GB3751F1587DAEF1".parse::<KeyID>().unwrap_err();
        "EFB3751F1587DAEF1".parse::<KeyID>().unwrap_err();
        "%FB3751F1587DAEF1".parse::<KeyID>().unwrap_err();
        assert_match!(KeyID::Invalid(_) = "587DAEF1".parse().unwrap());
        assert_match!(KeyID::Invalid(_) = "0x587DAEF1".parse().unwrap());
    }

    #[test]
    fn hex_formatting() {
        let keyid = "FB3751F1587DAEF1".parse::<KeyID>().unwrap();
        assert_eq!(format!("{:X}", keyid), "FB3751F1587DAEF1");
        assert_eq!(format!("{:x}", keyid), "fb3751f1587daef1");
    }

    #[test]
    fn keyid_is_send_and_sync() {
        fn f<T: Send + Sync>(_: T) {}
        f("89AB CDEF 0123 4567".parse::<KeyID>().unwrap());
    }
}