{-|
  Copyright  :  (C) 2026, QBayLogic B.V.
  License    :  BSD2 (see the file LICENSE)
  Maintainer :  QBayLogic B.V. <devops@qbaylogic.com>

  Stub transformations, test terms, and strategy fragments for
  "Clash.Tests.Rewrite.StrategyDSL". They live in their own module because
  Template Haskell splices can only evaluate imported values: the test module
  splices 'Clash.Rewrite.StrategyDSL.TH.compileStrategy' over the 'Step's and
  helpers defined here.
-}

{-# LANGUAGE DisambiguateRecordFields #-}
{-# LANGUAGE DuplicateRecordFields #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE NoFieldSelectors #-}
{-# LANGUAGE OverloadedRecordDot #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskellQuotes #-}

module Clash.Tests.Rewrite.StrategyDSL.Stubs where

import Language.Haskell.TH (Exp, Name, Q, listE, stringE)

import Clash.Core.Literal (Literal (..))
import Clash.Core.Name (mkUnsafeSystemName)
import Clash.Core.Term
  (Bind (..), IsMultiPrim (..), Pat (..), PrimInfo (..), PrimUnfolding (..),
   Term (..), TickInfo (..), WorkInfo (..))
import Clash.Core.Type (ConstTy (..), Type (..))
import Clash.Core.Var (Id, mkLocalId, mkTyVar)
import Clash.Rewrite.StrategyDSL
import Clash.Rewrite.StrategyDSL.TH (compileStrategy, compileStrategyReference)
import Clash.Rewrite.Types (Rewrite, RewriteMonad, TransformContext (..))
import Clash.Rewrite.Util (changed)
import Clash.Unique (Unique)

-- * Term construction helpers

someType :: Type
someType = ConstTy (TyCon (mkUnsafeSystemName "T" 0))

someId :: Unique -> Id
someId unique = mkLocalId someType (mkUnsafeSystemName "x" unique)

somePrim :: PrimInfo
somePrim = PrimInfo
  { primName = "somePrim"
  , primType = someType
  , primWorkInfo = WorkConstant
  , primMultiResult = SingleResult
  , primUnfolding = NoUnfolding
  }

integer :: Integer -> Term
integer = Literal . IntLiteral

-- * Stub transformations
--
-- Each stub is a worker plus its 'Transformation'; some also come with a
-- hand-written 'Rewrite' doing its own constructor match, to compare the
-- compiled dispatch against.

-- | @f 3@ becomes @3@: fires on an application whose argument is an integer
-- literal, changing the node's constructor.
collapseApplicationWorker
  :: TransformContext -> Term -> Term -> Term -> RewriteMonad () Term
collapseApplicationWorker _ctx _node _function argument@(Literal IntLiteral{}) =
  changed argument
collapseApplicationWorker _ctx node _function _argument = pure node

collapseApplication :: Transformation
collapseApplication =
  toTransformation "collapseApplication" (onApp 'collapseApplicationWorker)

collapseApplicationRewrite :: Rewrite ()
collapseApplicationRewrite _ctx (App _function argument@(Literal IntLiteral{})) =
  changed argument
collapseApplicationRewrite _ctx term = pure term

-- | Like 'collapseApplication', but as a node-receiving worker registered at
-- 'App', the way spine transformations are registered.
collapseSpineWorker :: Rewrite ()
collapseSpineWorker _ctx (App _function argument@(Literal IntLiteral{})) =
  changed argument
collapseSpineWorker _ctx term = pure term

collapseSpine :: Transformation
collapseSpine =
  toTransformation "collapseSpine" (onAppNode 'collapseSpineWorker)

-- | Increments odd integer literals (even results keep repeated traversals
-- terminating).
incrementOddWorker
  :: TransformContext -> Term -> Literal -> RewriteMonad () Term
incrementOddWorker _ctx _node (IntLiteral i) | odd i = changed (integer (i + 1))
incrementOddWorker _ctx node _literal = pure node

incrementOdd :: Transformation
incrementOdd = toTransformation "incrementOdd" (onLiteral 'incrementOddWorker)

-- | Like 'incrementOdd', but constructor-agnostic: a plain rewrite offered at
-- every node, with its own match.
incrementOddAnyWorker :: Rewrite ()
incrementOddAnyWorker _ctx (Literal (IntLiteral i))
  | odd i = changed (integer (i + 1))
incrementOddAnyWorker _ctx term = pure term

incrementOddAny :: Transformation
incrementOddAny = anyConstructor "incrementOddAny" 'incrementOddAnyWorker

-- | Multi-constructor: increments an odd integer literal, either as the
-- argument of an application or bare. Registered for App and Literal, to
-- observe the guarded suffix.
incrementBothAppWorker
  :: TransformContext -> Term -> Term -> Term -> RewriteMonad () Term
incrementBothAppWorker _ctx _node function (Literal (IntLiteral i))
  | odd i = changed (App function (integer (i + 1)))
incrementBothAppWorker _ctx node _function _argument = pure node

incrementBothLiteralWorker
  :: TransformContext -> Term -> Literal -> RewriteMonad () Term
incrementBothLiteralWorker _ctx _node (IntLiteral i)
  | odd i = changed (integer (i + 1))
incrementBothLiteralWorker _ctx node _literal = pure node

incrementBoth :: Transformation
incrementBoth = toTransformation "incrementBoth"
  (onApp 'incrementBothAppWorker <> onLiteral 'incrementBothLiteralWorker)

incrementBothRewrite :: Rewrite ()
incrementBothRewrite _ctx (App function (Literal (IntLiteral i)))
  | odd i = changed (App function (integer (i + 1)))
incrementBothRewrite _ctx (Literal (IntLiteral i))
  | odd i = changed (integer (i + 1))
incrementBothRewrite _ctx term = pure term

-- | Inlines a let binder into its body when the body is exactly that
-- variable: @let x = e in x@ becomes @e@. Fires on 'Let'.
inlineTrivialLetWorker
  :: TransformContext -> Term -> Bind Term -> Term -> RewriteMonad () Term
inlineTrivialLetWorker _ctx node bind body = case (bind, body) of
  (NonRec i boundTerm, Var v) | v == i -> changed boundTerm
  (Rec [(i, boundTerm)], Var v) | v == i -> changed boundTerm
  _ -> pure node

inlineTrivialLet :: Transformation
inlineTrivialLet =
  toTransformation "inlineTrivialLet" (onLet 'inlineTrivialLetWorker)

inlineTrivialLetRewrite :: Rewrite ()
inlineTrivialLetRewrite _ctx node@(Let bind body) = case (bind, body) of
  (NonRec i boundTerm, Var v) | v == i -> changed boundTerm
  (Rec [(i, boundTerm)], Var v) | v == i -> changed boundTerm
  _ -> pure node
inlineTrivialLetRewrite _ctx term = pure term

-- | Replaces variable references with a string literal spelling out the full
-- 'Clash.Core.Term.CoreContext' path, exposing every context push of the
-- descent arms to the equivalence tests.
reifyContextWorker
  :: TransformContext -> Term -> Id -> RewriteMonad () Term
reifyContextWorker ctx _node _i =
  changed (Literal (StringLiteral (show (tfContext ctx))))

reifyContext :: Transformation
reifyContext = toTransformation "reifyContext" (onVar 'reifyContextWorker)

-- | Rewrites references to one specific variable to a primitive, so the
-- 'Clash.Core.Term.AppArg' context a sibling argument sees is computed from
-- an already rewritten function.
functionToPrimWorker
  :: TransformContext -> Term -> Id -> RewriteMonad () Term
functionToPrimWorker _ctx node i
  | i == someId 2 = changed (Prim somePrim)
  | otherwise = pure node

functionToPrim :: Transformation
functionToPrim = toTransformation "functionToPrim" (onVar 'functionToPrimWorker)

-- * Test terms

-- | @(let x = f 3 in x) (let y = 5 in y)@: exercises App, Let (both binder
-- and body positions), and literals at several depths.
nestedTerm :: Term
nestedTerm =
  App
    (Let (NonRec x (App (Var f) (integer 3))) (Var x))
    (Let (Rec [(y, integer 5)]) (Var y))
 where
  x = someId 0
  y = someId 1
  f = someId 2

-- | A term covering every recursive constructor: Lam, TyLam, App, TyApp,
-- Let, Case (subject and alternatives), Cast, and Tick.
allConstructorsTerm :: Term
allConstructorsTerm =
  Lam lamBinder
    (TyLam tyVariable
      (Tick DeDup
        (Case
          (Cast (App (Var lamBinder) subject) someType someType)
          someType
          [ (DefaultPat, integer 3)
          , (LitPat (IntLiteral 0), TyApp (Var lamBinder) someType)
          ])))
 where
  lamBinder = someId 3
  tyVariable = mkTyVar someType (mkUnsafeSystemName "a" 100)
  subject = Let (NonRec (someId 5) (integer 7)) (Var (someId 5))

simpleApplication :: Term
simpleApplication = App (Var (someId 6)) (integer 3)

-- | The function position rewrites to a primitive; the argument's probed
-- context must show the 'Clash.Core.Term.AppArg' of that primitive.
appArgProbeTerm :: Term
appArgProbeTerm = App (Var (someId 2)) (Var (someId 7))

-- * Strategy fragments compared across all traversals

constructorChangingStep :: Step
constructorChangingStep =
  chain [collapseApplication, incrementBoth, inlineTrivialLet]

literalStep :: Step
literalStep = chain [incrementOdd]

contextProbeStep :: Step
contextProbeStep = chain [reifyContext]

appArgProbeStep :: Step
appArgProbeStep = chain [functionToPrim, reifyContext]

noOpStep :: Step
noOpStep = chain [inlineTrivialLet]

anyWorkerStep :: Step
anyWorkerStep = chain [collapseApplication, incrementOddAny]

nodeWorkerStep :: Step
nodeWorkerStep = chain [collapseSpine, incrementBoth]

-- | A cross-constructor conditional between chain segments inside one
-- traversal, the @flatten@ strategy's structure.
conditionalStep :: Step
conditionalStep =
  (one collapseApplication !-> one incrementOdd) >-> chain [inlineTrivialLet]

-- | A whole nested traversal embedded as one node action, the @conSpec@
-- strategy's structure.
nestedTraversalStep :: Step
nestedTraversalStep =
  (one collapseApplication !-> nested (bottomup incrementOdd))
  >-! one incrementBoth

-- | A strategy calling another compiled strategy, parameterized over the
-- callee so the test module can point it at either compilation of it.
callStrategyStrat :: Name -> Strat
callStrategyStrat callee = callStrategy callee >-> topdown collapseApplication

-- | Every fused traversal of a 'Step' next to its unfused reference:
-- @[(name, fast, reference)]@. Spliced by the test module.
allTraversals :: Step -> Q Exp
allTraversals step = listE
  [ [| ($(stringE name), $(compileStrategy strat), $(compileStrategyReference strat)) |]
  | (name, strat) <-
      [ ("topdown", topdown step)
      , ("bottomup", bottomup step)
      , ("topdownFix", topdownFix step)
      , ("topdownSuc", topdownSuc step)
      , ("innerMost", innerMost step)
      ]
  ]