-- | The shapes the rest of the app talks in.
module Todo.Model
  ( ListId (..)
  , TodoId (..)
  , Todo (..)
  , Filter (..)
  , parseFilter
  , filterName
  , filterPath
  , visible
  , parseTodoId
  , todoIdText
  ) where

import Data.Int (Int64)
import Data.Text (Text)
import Data.Text qualified as T
import Data.Text.Read qualified as T

-- | One visitor's list. Every query about todos is scoped by one.
newtype ListId = ListId Int64
  deriving (Eq, Show)

newtype TodoId = TodoId Int64
  deriving (Eq, Show)

data Todo = Todo
  { todoId :: !TodoId
  , todoTitle :: !Text
  , todoCompleted :: !Bool
  }
  deriving (Eq, Show)

data Filter = All | Active | Completed
  deriving (Eq, Show, Enum, Bounded)

-- | The @filter@ form field. Anything missing or unknown means 'All'.
parseFilter :: Maybe Text -> Filter
parseFilter = \case
  Just "active" -> Active
  Just "completed" -> Completed
  _ -> All

filterName :: Filter -> Text
filterName = \case
  All -> "all"
  Active -> "active"
  Completed -> "completed"

filterPath :: Filter -> Text
filterPath = \case
  All -> "/"
  Active -> "/active"
  Completed -> "/completed"

visible :: Filter -> Todo -> Bool
visible = \case
  All -> const True
  Active -> not . todoCompleted
  Completed -> todoCompleted

-- | A todo id as it appears in a path or a query: plain decimal digits,
-- short enough to fit an 'Int64'.
parseTodoId :: Text -> Maybe TodoId
parseTodoId t
  | T.null t || T.length t > 18 || not (T.all (\c -> c >= '0' && c <= '9') t) = Nothing
  | otherwise = case T.decimal t of
      Right (n, rest) | T.null rest -> Just (TodoId n)
      _ -> Nothing

todoIdText :: TodoId -> Text
todoIdText (TodoId n) = T.pack (show n)