{-# LANGUAGE OverloadedStrings #-}
module ER
  ( ER(..)
  , Entity(..)
  , Attribute(..)
  , Options, mergeOpts, optionsTo
  , Option(..), optionByName, optToFont, optToHtml, optToLabel
  , Relation(..) , Cardinality(..), cardByName
  , defaultTitleOpts, defaultEntityOpts, defaultHeaderOpts, defaultRelOpts
  )
where

import qualified Data.Map as M
import Data.Maybe (mapMaybe)
import Data.Text.Lazy
import Data.Word (Word8)
import Text.Printf (printf)

import Data.GraphViz.Parsing (ParseDot, parse, runParser)
import qualified Data.GraphViz.Attributes.HTML as H
import Data.GraphViz.Attributes.Colors (Color)

-- | Represents a single schema.
data ER = ER { entities :: [Entity]
             , rels :: [Relation]
             , title :: Options
             }
          deriving Show

-- | Represents a single entity in a schema.
data Entity = Entity { name :: Text
                     , attribs :: [Attribute]
                     , hoptions :: Options
                     , eoptions :: Options
                     }
              deriving Show

instance Eq Entity where
  e1 == e2 = name e1 == name e2

instance Ord Entity where
  e1 `compare` e2 = name e1 `compare` name e2

-- | Represents a single attribute in a particular entity.
data Attribute = Attribute { field :: Text
                           , pk :: Bool
                           , fk :: Bool
                           , aoptions :: Options
                           }
                 deriving Show

instance Eq Attribute where
  a1 == a2 = field a1 == field a2

instance Ord Attribute where
  a1 `compare` a2 = field a1 `compare` field a2

-- | Represents any number of options for an item in an ER diagram.
-- An item may be the graph title, an entity, an entity header or a
-- relationship between entities. Keys are options as specified in ER files.
--
-- Note that a set of options may include a label for any item.
type Options = M.Map String Option

-- | Given two sets of options, merge the second into first, where elements
-- in the first take precedence.
mergeOpts :: Options -> Options -> Options
mergeOpts opts1 opts2 = opts1 `M.union` opts2

-- | Given a set of options and a selector function, return the list of
-- only those options which matched. Examples of the selector function are
-- `optToFont`, `optToHtml` and `optToLabel`.
optionsTo :: (Option -> Maybe a) -> Options -> [a]
optionsTo f = mapMaybe f . M.elems

-- | A restricted subset of options in GraphViz that can be configured in
-- an ER file.
data Option = Label String
            | BgColor Color
            | Color Color
            | FontFace Text
            | FontSize Double
            | Border Word8
            | BorderColor Color
            | CellSpacing Word8
            | CellBorder Word8
            | CellPadding Word8
            deriving Show

-- | Given an option name and a string representation of its value,
-- `optionByName` will attempt to parse the string as a value corresponding
-- to the option. If the option doesn't exist or there was a problem parsing
-- the value, an error is returned.
optionByName :: String -> String -> Either String Option
optionByName "label" = Right . Label
optionByName "color" = optionParse Color
optionByName "bgcolor" = optionParse BgColor
optionByName "size" = optionParse FontSize
optionByName "font" = optionParse FontFace
optionByName "border" = optionParse Border
optionByName "border-color" = optionParse BorderColor
optionByName "cellspacing" = optionParse CellSpacing
optionByName "cellborder" = optionParse CellBorder
optionByName "cellpadding" = optionParse CellPadding
optionByName unk = const (Left $ printf "Option '%s' does not exist." unk)

-- | A wrapper around the GraphViz's parser for any particular option.
optionParse :: ParseDot a => (a -> Option) -> String -> Either String Option
optionParse con s =
  case fst $ runParser parse quoted of
    Left err -> Left (printf "%s (bad value '%s')" err s)
    Right a -> Right (con a)
  where quoted = "\"" `append` pack s `append` "\""

-- | Selects an option if and only if it corresponds to a font attribute.
optToFont :: Option -> Maybe H.Attribute
optToFont (Color c) = Just $ H.Color c
optToFont (FontFace s) = Just $ H.Face s
optToFont (FontSize d) = Just $ H.PointSize d
optToFont _ = Nothing

-- | Selects an option if and only if it corresponds to an HTML attribute.
-- In particular, for tables or table cells.
optToHtml :: Option -> Maybe H.Attribute
optToHtml (BgColor c) = Just $ H.BGColor c
optToHtml (Border w) = Just $ H.Border w
optToHtml (BorderColor c) = Just $ H.Color c
optToHtml (CellSpacing w) = Just $ H.CellSpacing w
optToHtml (CellBorder w) = Just $ H.CellBorder w
optToHtml (CellPadding w) = Just $ H.CellPadding w
optToHtml _ = Nothing

-- | Selects an option if and only if it corresponds to a label.
optToLabel :: Option -> Maybe Text
optToLabel (Label s) = Just $ pack s
optToLabel _ = Nothing

-- | Represents a relationship between exactly two entities. After parsing,
-- each `rel` is guaranteed to correspond to an entity defined in the same
-- ER file.
--
-- Each relationship has one of four cardinalities specified for both entities.
-- Those cardinalities are: 0 or 1, exactly 1, 0 or more and 1 or more.
data Relation = Relation { entity1, entity2 :: Text
                         , card1,   card2   :: Cardinality
                         , roptions :: Options
                         }
                deriving Show

data Cardinality = ZeroOne
                 | One
                 | ZeroPlus
                 | OnePlus

instance Show Cardinality where
  show ZeroOne = "{0,1}"
  show One = "1"
  show ZeroPlus = "0..N"
  show OnePlus ="1..N"

-- | Maps a string representation to a particular relationship cardinality.
cardByName :: Char -> Maybe Cardinality
cardByName '?' = Just ZeroOne
cardByName '1' = Just One
cardByName '*' = Just ZeroPlus
cardByName '+' = Just OnePlus
cardByName _ = Nothing

-- | Hard-coded default options for all graph titles.
defaultTitleOpts :: Options
defaultTitleOpts = M.fromList
  [ ("size", FontSize 30)
  ]

-- | Hard-coded default options for all entity headers.
defaultHeaderOpts :: Options
defaultHeaderOpts = M.fromList
  [ ("size", ER.FontSize 16)
  ]

-- | Hard-coded default options for all entities.
defaultEntityOpts :: Options
defaultEntityOpts = M.fromList
  [ ("border", Border 0)
  , ("cellborder", CellBorder 1)
  , ("cellspacing", CellSpacing 0)
  , ("cellpadding", CellPadding 4)
  , ("font", FontFace "Helvetica")
  ]

-- | Hard-coded default options for all relationships.
defaultRelOpts :: Options
defaultRelOpts = M.empty