{-# LANGUAGE DeriveDataTypeable #-}

module Network.DNS.Internal where

import Control.Exception (Exception)
import Data.ByteString (ByteString)
import qualified Data.ByteString.Char8 as BS
import Data.IP (IP, IPv4, IPv6)
import Data.Maybe (fromMaybe)
import Data.Typeable (Typeable)

----------------------------------------------------------------

-- | Type for domain.
type Domain = ByteString

----------------------------------------------------------------

-- | Types for resource records.
data TYPE = A
          | AAAA
          | NS
          | TXT
          | MX
          | CNAME
          | SOA
          | PTR
          | SRV
          | DNAME
          | OPT
          | UNKNOWN Int deriving (Eq, Show, Read)

rrDB :: [(TYPE, Int)]
rrDB = [
    (A,      1)
  , (NS,     2)
  , (CNAME,  5)
  , (SOA,    6)
  , (PTR,   12)
  , (MX,    15)
  , (TXT,   16)
  , (AAAA,  28)
  , (SRV,   33)
  , (DNAME, 39) -- RFC 2672
  , (OPT,   41) -- RFC 6891
  ]

data OPTTYPE = ClientSubnet
             | OUNKNOWN Int
    deriving (Eq)

orDB :: [(OPTTYPE, Int)]
orDB = [
        (ClientSubnet, 8)
       ]

rookup                  :: (Eq b) => b -> [(a,b)] -> Maybe a
rookup _    []          =  Nothing
rookup  key ((x,y):xys)
  | key == y          =  Just x
  | otherwise         =  rookup key xys

intToType :: Int -> TYPE
intToType n = fromMaybe (UNKNOWN n) $ rookup n rrDB
typeToInt :: TYPE -> Int
typeToInt (UNKNOWN x)  = x
typeToInt t = fromMaybe (error "typeToInt") $ lookup t rrDB

intToOptType :: Int -> OPTTYPE
intToOptType n = fromMaybe (OUNKNOWN n) $ rookup n orDB
optTypeToInt :: OPTTYPE -> Int
optTypeToInt (OUNKNOWN x)  = x
optTypeToInt t = fromMaybe (error "optTypeToInt") $ lookup t orDB

----------------------------------------------------------------

-- | An enumeration of all possible DNS errors that can occur.
data DNSError =
    -- | The sequence number of the answer doesn't match our query. This
    --   could indicate foul play.
    SequenceNumberMismatch
    -- | The request simply timed out.
  | TimeoutExpired
    -- | The answer has the correct sequence number, but returned an
    --   unexpected RDATA format.
  | UnexpectedRDATA
    -- | The domain for query is illegal.
  | IllegalDomain
    -- | The name server was unable to interpret the query.
  | FormatError
    -- | The name server was unable to process this query due to a
    --   problem with the name server.
  | ServerFailure
    -- | Meaningful only for responses from an authoritative name
    -- server, this code signifies that the
    -- domain name referenced in the query does not exist.
  | NameError
    -- | The name server does not support the requested kind of query.
  | NotImplemented
    -- | The name server refuses to perform the specified operation for
    --   policy reasons.  For example, a name
    --   server may not wish to provide the
    --   information to the particular requester,
    --   or a name server may not wish to perform
    --   a particular operation (e.g., zone transfer) for particular data.
  | OperationRefused
    -- | The server detected a malformed OPT RR.
  | BadOptRecord
  deriving (Eq, Show, Typeable)

instance Exception DNSError

-- | Raw data format for DNS Query and Response.
data DNSMessage = DNSMessage {
    header     :: DNSHeader
  , question   :: [Question]
  , answer     :: [ResourceRecord]
  , authority  :: [ResourceRecord]
  , additional :: [ResourceRecord]
  } deriving (Eq, Show)

-- | For backward compatibility.
type DNSFormat = DNSMessage

-- | Raw data format for the header of DNS Query and Response.
data DNSHeader = DNSHeader {
    identifier :: Int
  , flags      :: DNSFlags
  } deriving (Eq, Show)

-- | Raw data format for the flags of DNS Query and Response.
data DNSFlags = DNSFlags {
    qOrR         :: QorR
  , opcode       :: OPCODE
  , authAnswer   :: Bool
  , trunCation   :: Bool
  , recDesired   :: Bool
  , recAvailable :: Bool
  , rcode        :: RCODE
  } deriving (Eq, Show)

----------------------------------------------------------------

data QorR = QR_Query | QR_Response deriving (Eq, Show)

data OPCODE = OP_STD | OP_INV | OP_SSR deriving (Eq, Show, Enum)

data RCODE = NoErr | FormatErr | ServFail | NameErr | NotImpl | Refused | BadOpt deriving (Eq, Show, Enum)

----------------------------------------------------------------

-- | Raw data format for DNS questions.
data Question = Question {
    qname  :: Domain
  , qtype  :: TYPE
  } deriving (Eq, Show)

-- | Making "Question".
makeQuestion :: Domain -> TYPE -> Question
makeQuestion = Question

----------------------------------------------------------------

-- | Raw data format for resource records.
data ResourceRecord = ResourceRecord {
                            rrname :: Domain
                          , rrtype :: TYPE
                          , rrttl  :: Int
                          , rdata  :: RData
                          }
                    | OptRecord {
                            orudpsize   :: Int
                          , ordnssecok  :: Bool
                          , orversion   :: Int
                          , rdata       :: RData
                          }
                    deriving (Eq,Show)

-- | Raw data format for each type.
data RData = RD_NS Domain
           | RD_CNAME Domain
           | RD_DNAME Domain
           | RD_MX Int Domain
           | RD_PTR Domain
           | RD_SOA Domain Domain Int Int Int Int Int
           | RD_A IPv4
           | RD_AAAA IPv6
           | RD_TXT ByteString
           | RD_SRV Int Int Int Domain
           | RD_OPT [OData]
           | RD_OTH ByteString
    deriving (Eq)

instance Show RData where
  show (RD_NS dom) = BS.unpack dom
  show (RD_MX prf dom) = BS.unpack dom ++ " " ++ show prf
  show (RD_CNAME dom) = BS.unpack dom
  show (RD_DNAME dom) = BS.unpack dom
  show (RD_A a) = show a
  show (RD_AAAA aaaa) = show aaaa
  show (RD_TXT txt) = BS.unpack txt
  show (RD_SOA mn _ _ _ _ _ mi) = BS.unpack mn ++ " " ++ show mi
  show (RD_PTR dom) = BS.unpack dom
  show (RD_SRV pri wei prt dom) = show pri ++ " " ++ show wei ++ " " ++ show prt ++ BS.unpack dom
  show (RD_OPT od) = show od
  show (RD_OTH is) = show is


data OData = OD_ClientSubnet Int Int IP
           | OD_Unknown Int ByteString
    deriving (Eq,Show)

----------------------------------------------------------------

defaultQuery :: DNSMessage
defaultQuery = DNSMessage {
    header = DNSHeader {
       identifier = 0
     , flags = DNSFlags {
           qOrR         = QR_Query
         , opcode       = OP_STD
         , authAnswer   = False
         , trunCation   = False
         , recDesired   = True
         , recAvailable = False
         , rcode        = NoErr
         }
     }
  , question   = []
  , answer     = []
  , authority  = []
  , additional = []
  }

defaultResponse :: DNSMessage
defaultResponse =
  let hd = header defaultQuery
      flg = flags hd
  in  defaultQuery {
        header = hd {
          flags = flg {
              qOrR = QR_Response
            , authAnswer = True
            , recAvailable = True
            }
        }
      }

responseA :: Int -> Question -> [IPv4] -> DNSMessage
responseA ident q ips =
  let hd = header defaultResponse
      dom = qname q
      an = fmap (ResourceRecord dom A 300 . RD_A) ips
  in  defaultResponse {
          header = hd { identifier=ident }
        , question = [q]
        , answer = an
      }

responseAAAA :: Int -> Question -> [IPv6] -> DNSMessage
responseAAAA ident q ips =
  let hd = header defaultResponse
      dom = qname q
      an = fmap (ResourceRecord dom AAAA 300 . RD_AAAA) ips
  in  defaultResponse {
          header = hd { identifier=ident }
        , question = [q]
        , answer = an
      }
