//!
//! Structs and information to create/parse the _fenrir DNSSEC record
//!
//! Encoding and decoding in base85, RFC1924
//!
//!
//! Basic encoding idea:
//! * 1 byte: half-bytes
//!   * half: num of addresses
//!   * half: num of pubkeys
//! [ # list of addresses
//!   * 1 byte: bitfield
//!     * 0..1 ipv4/ipv6
//!     * 2..4 priority (for failover)
//!     * 5..7 weight between priority
//!   * 1 byte: public key id
//!   * 2 bytes: UDP port
//!   * X bytes: IP
//! ]
//! [ # list of pubkeys
//!   * 1 byte: pubkey type
//!   * 1 byte: pubkey id
//!   * Y bytes: pubkey
//! ]

use ::core::num::NonZeroU16;
use ::num_traits::FromPrimitive;
use ::std::{net::IpAddr, vec::Vec};

/*
 * Public key data
 */

/// Public Key ID
#[derive(Debug, Copy, Clone)]
pub struct PublicKeyId(u8);

/// Public Key Type
#[derive(::num_derive::FromPrimitive, Debug, Copy, Clone)]
// public enum: use non_exhaustive to force users to add a default case
// so in the future we can expand this easily
#[non_exhaustive]
#[repr(u8)]
pub enum PublicKeyType {
    /// ed25519 asymmetric key
    Ed25519 = 0,
}

impl PublicKeyType {
    /// Get the size of a public key of this kind
    pub fn key_len(&self) -> usize {
        match &self {
            PublicKeyType::Ed25519 => 42,
        }
    }
}

/// Public Key, with its type and id
#[derive(Debug, Clone)]
pub struct PublicKey {
    /// public key raw data
    raw: Vec<u8>,
    /// type of public key
    kind: PublicKeyType,
    /// id of public key
    id: PublicKeyId,
}

impl PublicKey {
    fn raw_len(&self) -> usize {
        let size = 2; // Public Key Type + ID
        size + self.raw.len()
    }
    fn encode_into(&self, raw: &mut Vec<u8>) {
        raw.push(self.kind as u8);
        raw.push(self.id.0);
        raw.extend_from_slice(&self.raw);
    }
    fn decode_raw(raw: &[u8]) -> Result<(Self, usize), Error> {
        if raw.len() < 4 {
            return Err(Error::NotEnoughData(0));
        }

        let kind = PublicKeyType::from_u8(raw[0]).unwrap();
        let id = PublicKeyId(raw[1]);
        if raw.len() < 2 + kind.key_len() {
            return Err(Error::NotEnoughData(2));
        }

        let mut raw_key = Vec::with_capacity(kind.key_len());
        raw_key.extend_from_slice(&raw[2..(2 + kind.key_len())]);

        let total_length = 2 + kind.key_len();

        Ok((
            Self {
                raw: raw_key,
                kind,
                id,
            },
            total_length,
        ))
    }
}

/*
 * Address data
 */

/// Priority of each group of addresses
#[derive(::num_derive::FromPrimitive, Debug, Copy, Clone)]
// public enum: use non_exhaustive to force users to add a default case
// so in the future we can expand this easily
#[non_exhaustive]
#[repr(u8)]
pub enum AddressPriority {
    /// Initially contact addresses in this priority
    P0 = 0,
    /// First failover
    P1,
    /// Second failover
    P2,
    /// Third failover
    P3,
    /// Fourth failover
    P4,
    /// Fifth failover
    P5,
    /// Sisth failover
    P6,
    /// Seventh failover
    P7,
}

/// Inside of each group, weight of the address
/// This helps in distributing the traffic to multiple authentication servers:
/// * client sums all weights in a group
/// * generate a random number [0..sum_of_weights]
/// * the number indicates which server will take the connection
/// So to equally distribute all connections you just have to use the same
/// weight in the same group
#[derive(::num_derive::FromPrimitive, Debug, Copy, Clone)]
// public enum: use non_exhaustive to force users to add a default case
// so in the future we can expand this easily
#[non_exhaustive]
#[repr(u8)]
pub enum AddressWeight {
    /// Minimum weigth: 1
    W1 = 0,
    /// little weigth: 2
    W2,
    /// little weigth: 3
    W3,
    /// medium weigth: 4
    W4,
    /// medium weigth: 5
    W5,
    /// heavy weigth: 6
    W6,
    /// heavy weigth: 7
    W7,
    /// Maximum weigth: 8
    W8,
}

/// Authentication server address information:
/// * ip
/// * udp port
/// * priority
/// * weight within priority
#[derive(Debug, Clone, Copy)]
pub struct Address {
    /// Ip address of server, v4 or v6
    pub ip: IpAddr,
    /// udp port. None means that this address is reachable only
    /// with Fenrir over IP
    pub port: Option<NonZeroU16>,
    /// Priority group of this address
    pub priority: AddressPriority,
    /// Weight of this address in the priority group
    pub weight: AddressWeight,
    /// Public key ID used by this address
    pub public_key_id: PublicKeyId,
}

impl Address {
    fn raw_len(&self) -> usize {
        let size = 4; // UDP port + Priority + Weight
        match self.ip {
            IpAddr::V4(_) => size + 4,
            IpAddr::V6(_) => size + 16,
        }
    }
    fn encode_into(&self, raw: &mut Vec<u8>) {
        let mut bitfield: u8 = match self.ip {
            IpAddr::V4(_) => 0,
            IpAddr::V6(_) => 1,
        };
        bitfield <<= 3;
        bitfield |= self.priority as u8;
        bitfield <<= 3;
        bitfield |= self.weight as u8;

        raw.push(bitfield);

        raw.push(self.public_key_id.0);
        raw.extend_from_slice(
            &(match self.port {
                Some(port) => port.get().to_le_bytes(),
                None => [0, 0], // oh noez, which zero goes first?
            }),
        );

        match self.ip {
            IpAddr::V4(ip) => {
                let raw_ip = ip.octets();
                raw.extend_from_slice(&raw_ip);
            }
            IpAddr::V6(ip) => {
                let raw_ip = ip.octets();
                raw.extend_from_slice(&raw_ip);
            }
        };
    }
    fn decode_raw(raw: &[u8]) -> Result<(Self, usize), Error> {
        if raw.len() < 8 {
            return Err(Error::NotEnoughData(0));
        }
        let ip_type = raw[0] >> 6;
        let is_ipv6: bool;
        let total_length: usize;
        match ip_type {
            0 => {
                is_ipv6 = false;
                total_length = 8;
            }
            1 => {
                total_length = 20;
                if raw.len() < total_length {
                    return Err(Error::NotEnoughData(1));
                }
                is_ipv6 = true
            }
            _ => return Err(Error::UnsupportedData(0)),
        }
        let raw_priority = (raw[0] << 2) >> 5;
        let raw_weight = (raw[0] << 5) >> 5;
        let priority = AddressPriority::from_u8(raw_priority).unwrap();
        let weight = AddressWeight::from_u8(raw_weight).unwrap();

        let public_key_id = PublicKeyId(raw[1]);

        let raw_port = u16::from_le_bytes(raw[2..3].try_into().unwrap());
        let port = if raw_port == 0 {
            None
        } else {
            Some(NonZeroU16::new(raw_port).unwrap())
        };
        let ip = if is_ipv6 {
            let raw_ip: [u8; 16] = raw[4..20].try_into().unwrap();
            IpAddr::from(raw_ip)
        } else {
            let raw_ip: [u8; 4] = raw[4..8].try_into().unwrap();
            IpAddr::from(raw_ip)
        };

        Ok((
            Self {
                ip,
                port,
                priority,
                weight,
                public_key_id,
            },
            total_length,
        ))
    }
}

/*
 * Actual record puuting it all toghether
 */

/// All informations found in the DNSSEC record
#[derive(Debug, Clone)]
pub struct Record {
    /// Public keys used by any authentication server
    public_keys: Vec<PublicKey>,
    /// List of all authentication servers' addresses.
    /// Multiple ones can point to the same authentication server
    addresses: Vec<Address>,
}

impl Record {
    /// Simply encode all the record in base85
    pub fn encode(&self) -> Result<String, Error> {
        // check possible failure scenarios
        if self.public_keys.len() == 0 {
            return Err(Error::NoPublicKeyFound);
        }
        if self.public_keys.len() > 16 {
            return Err(Error::Max16PublicKeys);
        }
        if self.addresses.len() == 0 {
            return Err(Error::NoAddressFound);
        }
        if self.addresses.len() > 16 {
            return Err(Error::Max16Addresses);
        }
        // everything else is all good

        let total_size: usize = 1
            + self.addresses.iter().map(|a| a.raw_len()).sum::<usize>()
            + self.public_keys.iter().map(|a| a.raw_len()).sum::<usize>();

        let mut raw = Vec::with_capacity(total_size);

        // amount of data. addresses, then pubkeys. 4 bits each
        let len_combined: u8 = self.addresses.len() as u8;
        let len_combined = len_combined << 4;
        let len_combined = len_combined | self.public_keys.len() as u8;

        raw.push(len_combined);

        for address in self.addresses.iter() {
            address.encode_into(&mut raw);
        }
        for public_key in self.public_keys.iter() {
            public_key.encode_into(&mut raw);
        }

        Ok(::base85::encode(&raw))
    }
    /// Decode from base85 to the actual object
    pub fn decode(raw: &[u8]) -> Result<Self, Error> {
        // bare minimum for 1 address and key
        const MIN_RAW_LENGTH: usize = 1 + 8 + 8;
        if raw.len() <= MIN_RAW_LENGTH {
            return Err(Error::NotEnoughData(0));
        }
        let mut num_addresses = (raw[0] >> 4) as usize;
        let mut num_public_keys = (raw[0] & 0x0F) as usize;
        let mut bytes_parsed = 1;

        let mut result = Self {
            addresses: Vec::with_capacity(num_addresses),
            public_keys: Vec::with_capacity(num_public_keys),
        };

        while num_addresses > 0 {
            let (address, bytes) =
                match Address::decode_raw(&raw[bytes_parsed..]) {
                    Ok(address) => address,
                    Err(Error::UnsupportedData(b)) => {
                        return Err(Error::UnsupportedData(bytes_parsed + b))
                    }
                    Err(Error::NotEnoughData(b)) => {
                        return Err(Error::NotEnoughData(bytes_parsed + b))
                    }
                    Err(e) => return Err(e),
                };
            bytes_parsed = bytes_parsed + bytes;
            result.addresses.push(address);
            num_addresses = num_addresses - 1;
        }
        while num_public_keys > 0 {
            let (public_key, bytes) =
                match PublicKey::decode_raw(&raw[bytes_parsed..]) {
                    Ok(public_key) => public_key,
                    Err(Error::UnsupportedData(b)) => {
                        return Err(Error::UnsupportedData(bytes_parsed + b))
                    }
                    Err(Error::NotEnoughData(b)) => {
                        return Err(Error::NotEnoughData(bytes_parsed + b))
                    }
                    Err(e) => return Err(e),
                };
            bytes_parsed = bytes_parsed + bytes;
            result.public_keys.push(public_key);
            num_public_keys = num_public_keys - 1;
        }
        if bytes_parsed != raw.len() {
            Err(Error::UnknownData(bytes_parsed))
        } else {
            Ok(result)
        }
    }
}

/// Possible errors in encoding or decoding the DNSSEC record
#[derive(::thiserror::Error, Debug)]
pub enum Error {
    /// General IO error
    #[error("IO error: {0:?}")]
    IO(#[from] ::std::io::Error),
    /// We need at least one address
    #[error("no addresses found")]
    NoAddressFound,
    /// Too many addresses (max 16)
    #[error("can't encode more than 16 addresses")]
    Max16Addresses,
    /// We need at least one public key
    #[error("no public keys found")]
    NoPublicKeyFound,
    /// Maximum 16 public keys supported
    #[error("can't encode more than 16 public keys")]
    Max16PublicKeys,
    /// Not enough data to decode something meaningful
    #[error("not enough data. Parsed {0} bytes")]
    NotEnoughData(usize),
    /// Unsupported Data: can't parse
    #[error("Unsupported data. Parsed {0} bytes")]
    UnsupportedData(usize),
    /// Unknown data at the end
    #[error("Unknown data after {0} bytes")]
    UnknownData(usize),
}