-- | A simple implementation of /incremental build rules/, which can be used to avoid unnecessary
-- recomputation on incrementally-changing input. See 'Rule' for more details.
module Hasura.Incremental
  ( -- * The @Rule@ datatype
    Rule,
    Result,
    build,
    rebuild,
    rebuildRule,
    result,

    -- * Abstract interface
    ArrowDistribute (..),
    ArrowCache (..),
    MonadDepend (..),
    DependT,

    -- * Fine-grained dependencies
    Dependency,
    Select (Selector),
    selectD,
    selectKeyD,
    selectMaybeD,
    Cacheable (..),
    Accesses,

    -- * Cache invalidation
    InvalidationKey,
    initialInvalidationKey,
    invalidate,
  )
where

import Hasura.Incremental.Internal.Cache
import Hasura.Incremental.Internal.Dependency
import Hasura.Incremental.Internal.Rule
import Hasura.Incremental.Select
import Hasura.Prelude

-- | A simple helper type that can be used to implement explicit cache invalidation. Internally,
-- each 'InvalidationKey' is a counter; 'initialInvalidationKey' starts the counter at 0 and
-- 'invalidate' increments it by 1. Two 'InvalidationKey's are equal iff they have the same internal
-- count, so depending on an 'InvalidationKey' provides a mechanism to force portions of the build
-- process to be reexecuted by calling 'invalidate' before running the build.
newtype InvalidationKey = InvalidationKey Int
  deriving (Show, Eq, Ord, Cacheable)

initialInvalidationKey :: InvalidationKey
initialInvalidationKey = InvalidationKey 0

invalidate :: InvalidationKey -> InvalidationKey
invalidate (InvalidationKey n) = InvalidationKey (n + 1)