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General validation helpers

--
validateLength :: (Foldable t, Monoid e, MonadIO m) => Text -> (Int, Int) -> Getting (t a) s (t a) -> s -> m e

-- NOTE: The type signature is probably incomplete. Please refer to the usage
-- sample to figure out what the actual type signature needs to be.
validateFormat :: (MonadIO m, Monoid e) => m RE -> Lens' s a -> s -> m e

-- Strips the field of all leading and trailing whitespace and then ensures
-- that is not a blank string. TODO: Should the whitespace-stripped string be
-- stored in the DB? How do we ensure that?
validatePresence :: (Monoid e, MonadIO m) => Text -> Getting Text s Text -> s -> m e

-- Ensures that a field is either Nothing OR a blank string (ignoring all
-- leading and trailing whitespace). TODO: How do we ensure that a blank-string
-- is actually treated as a Nothing when storing into the DB? Also, is there a
-- use-case for having a non-Maybe (i.e. NOT NULL) field, which is validated to
-- be a blank string?
validateAbsence :: (Monoid e, MonadIO m) => Text -> Getting (Maybe Text) s (Maybe Text) -> s -> m e

-- This will end up making a DB call, because of which, more class -
-- constraints will get added. Like `Default Constant a1 (Column a1)`. Also,
-- please NOTE - you have to be careful while querying the DB for rows with the
-- same fields to NOT match the record which is being validated. This can be
-- ensured by passing another condition to `filterN` -
-- (id, pgNotEq, record ^.id)
validateUnique1 :: (Monoid e, HasDatabase m) => Text -> (Getting a1 s a1) -> s -> m e
validateUnique2 :: (Monoid e, HasDatabase m) => Text -> (Getting a1 s a1, Getting a2 s a2) -> s -> m e
validateUnique3 :: (Monoid e, HasDatabase m) => Text -> (Getting a1 s a1, Getting a2 s a2, Getting a3 s a3) -> s -> m e
-- and so on... til validateUnique5

--
validateIn :: (Monoid e, MonadIO m) => Text -> [a] -> Getting [a] s [a] -> s -> m e

Strict model validations

module Models.User
  (
    module Models.User
  , module Models.User.Types
  , module Autogenerated.Models.User
  ) where

instance DbModel User where
  strictValidations :: (MonadIO m) => User -> m [Error]
  strictValidations user =
    (validateUnique "Email must be unique" email)
    <> (validateLength "Name must be between 5 and 100 chars" (5, 100) name)
    <> (validateFormat "Doesn't seem like a valid email." (compiledRegex "(.*)@(.*)\.(.*)") email)
    <> (validatePresence "Name should be present" name) -- strips the field of whitespace
    <> (validateIn "Should be one of black or gray" ["black", "gray"] colourCode)
    <> (if (present $ user ^. firstName)
        then (validatePresence "Last name should be present if first name is given" lastName)
        else [])