{- Copyright (C) 2013-2015 Dr. Alistair Ward This file is part of WeekDaze. WeekDaze is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. WeekDaze is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with WeekDaze. If not, see <http://www.gnu.org/licenses/>. -} {- | [@AUTHOR@] Dr. Alistair Ward [@DESCRIPTION@] Describes the interface to an abstract user of /resource/s. -} module WeekDaze.Model.ResourceUser( -- * Type-classes ResourceUser(..), -- * Functions -- ** Predicates areMergeableWith, areMutuallyMergeable ) where import Control.Arrow((&&&)) import qualified Data.Foldable import qualified Data.Set import qualified WeekDaze.Model.Lesson as Model.Lesson -- | An interface to which users of /resource/s can conform. class ResourceUser resourceUser where areIndependent :: resourceUser -> resourceUser -> Bool -- ^ Whether the /resource/s used by the first instance, are independent of those used by the second. instance Ord resource => ResourceUser (Data.Set.Set resource) where areIndependent s = Data.Set.null . Data.Set.intersection s -- To support student-classes. {- | * Check whether the specified /lesson/ is compatible with the incumbent collection of synchronous /lesson/s. * Each of the incumbent /lesson/s must either be identical to the proposed /lesson/, or use completely different /resource/s. * This property allows the specified /lesson/ to be booked into a /timetable/ at the same /time/. * CAVEAT: performance-hotspot. -} areMergeableWith :: ( Data.Foldable.Foldable foldable, Eq resourceIds, Eq level, ResourceUser resourceIds ) => Model.Lesson.Lesson resourceIds level -- ^ The proposed /lesson/. -> foldable (Model.Lesson.Lesson resourceIds level) -- ^ The /lesson/s already booked in the /timetable/, at the proposed /time/. -> Bool areMergeableWith lesson = Data.Foldable.all ( uncurry (||) . ( (== lesson) &&& areIndependent (Model.Lesson.getResourceIds lesson) . Model.Lesson.getResourceIds ) ) {- | * 'True' if all the listed /lesson/s are identical, or none of their /resource-Id/s are common. * This property allows them to co-exist, when booked into the weekly /timetable/s of distinct /observer/s, but at the same /time/. * CAVEAT: is pretty inefficient; all we're really want to do is 'nub' the list of /lesson/s, then check that neither of the two /resource/s per /lesson/, is used more than once, it's just that we can't access the two /resource/s, because they're behind the class-interface. -} areMutuallyMergeable :: ( Eq resourceIds, Eq level, ResourceUser resourceIds ) => [Model.Lesson.Lesson resourceIds level] -> Bool areMutuallyMergeable [] = True areMutuallyMergeable (x : xs) = areMergeableWith x xs && areMutuallyMergeable xs {-recurse-}