# OPTIONS_GHC -Wall #
{-# LANGUAGE OverloadedStrings #-}
module Optimize.Expression
  ( optimize
  , destructArgs
  , optimizePotentialTailCall
  )
  where


import Prelude hiding (cycle)
import Control.Monad (foldM)
import qualified Data.Map as Map
import qualified Data.Name as Name
import qualified Data.Set as Set

import qualified AST.Canonical as Can
import qualified AST.Optimized as Opt
import qualified AST.Utils.Shader as Shader
import qualified Data.Index as Index
import qualified Elm.ModuleName as ModuleName
import qualified Optimize.Case as Case
import qualified Optimize.Names as Names
import qualified Reporting.Annotation as A



-- OPTIMIZE


type Cycle =
  Set.Set Name.Name


optimize :: Cycle -> Can.Expr -> Names.Tracker Opt.Expr
optimize cycle (A.At region expression) =
  case expression of
    Can.VarLocal name ->
      pure (Opt.VarLocal name)

    Can.VarTopLevel home name ->
      if Set.member name cycle then
        pure (Opt.VarCycle home name)
      else
        Names.registerGlobal home name

    Can.VarKernel home name ->
      Names.registerKernel home (Opt.VarKernel home name)

    Can.VarForeign home name _ ->
      Names.registerGlobal home name

    Can.VarCtor opts home name index _ ->
      Names.registerCtor home name index opts

    Can.VarDebug home name _ ->
      Names.registerDebug name home region

    Can.VarOperator _ home name _ ->
      Names.registerGlobal home name

    Can.Chr chr ->
      Names.registerKernel Name.utils (Opt.Chr chr)

    Can.Str str ->
      pure (Opt.Str str)

    Can.Int int ->
      pure (Opt.Int int)

    Can.Float float ->
      pure (Opt.Float float)

    Can.List entries ->
      Names.registerKernel Name.list Opt.List
        <*> traverse (optimize cycle) entries

    Can.Negate expr ->
      do  func <- Names.registerGlobal ModuleName.basics Name.negate
          arg <- optimize cycle expr
          pure $ Opt.Call func [arg]

    Can.Binop _ home name _ left right ->
      do  optFunc <- Names.registerGlobal home name
          optLeft <- optimize cycle left
          optRight <- optimize cycle right
          return (Opt.Call optFunc [optLeft, optRight])

    Can.Lambda args body ->
      do  (argNames, destructors) <- destructArgs args
          obody <- optimize cycle body
          pure $ Opt.Function argNames (foldr Opt.Destruct obody destructors)

    Can.Call func args ->
      Opt.Call
        <$> optimize cycle func
        <*> traverse (optimize cycle) args

    Can.If branches finally ->
      let
        optimizeBranch (condition, branch) =
          (,)
            <$> optimize cycle condition
            <*> optimize cycle branch
      in
      Opt.If
        <$> traverse optimizeBranch branches
        <*> optimize cycle finally

    Can.Let def body ->
      optimizeDef cycle def =<< optimize cycle body

    Can.LetRec defs body ->
      case defs of
        [def] ->
          Opt.Let
            <$> optimizePotentialTailCallDef cycle def
            <*> optimize cycle body

        _ ->
          do  obody <- optimize cycle body
              foldM (\bod def -> optimizeDef cycle def bod) obody defs

    Can.LetDestruct pattern expr body ->
      do  (name, destructs) <- destruct pattern
          oexpr <- optimize cycle expr
          obody <- optimize cycle body
          pure $
            Opt.Let (Opt.Def name oexpr) (foldr Opt.Destruct obody destructs)

    Can.Case expr branches ->
      let
        optimizeBranch root (Can.CaseBranch pattern branch) =
          do  destructors <- destructCase root pattern
              obranch <- optimize cycle branch
              pure (pattern, foldr Opt.Destruct obranch destructors)
      in
      do  temp <- Names.generate
          oexpr <- optimize cycle expr
          case oexpr of
            Opt.VarLocal root ->
              Case.optimize temp root <$> traverse (optimizeBranch root) branches

            _ ->
              do  obranches <- traverse (optimizeBranch temp) branches
                  return $ Opt.Let (Opt.Def temp oexpr) (Case.optimize temp temp obranches)

    Can.Accessor field ->
      Names.registerField field (Opt.Accessor field)

    Can.Access record (A.At _ field) ->
      do  optRecord <- optimize cycle record
          Names.registerField field (Opt.Access optRecord field)

    Can.Update _ record updates ->
      Names.registerFieldDict updates Opt.Update
        <*> optimize cycle record
        <*> traverse (optimizeUpdate cycle) updates

    Can.Record fields ->
      Names.registerFieldDict fields Opt.Record
        <*> traverse (optimize cycle) fields

    Can.Unit ->
      Names.registerKernel Name.utils Opt.Unit

    Can.Tuple a b maybeC ->
      Names.registerKernel Name.utils Opt.Tuple
        <*> optimize cycle a
        <*> optimize cycle b
        <*> traverse (optimize cycle) maybeC

    Can.Shader src (Shader.Types attributes uniforms _varyings) ->
      pure (Opt.Shader src (Map.keysSet attributes) (Map.keysSet uniforms))



-- UPDATE


optimizeUpdate :: Cycle -> Can.FieldUpdate -> Names.Tracker Opt.Expr
optimizeUpdate cycle (Can.FieldUpdate _ expr) =
  optimize cycle expr



-- DEFINITION


optimizeDef :: Cycle -> Can.Def -> Opt.Expr -> Names.Tracker Opt.Expr
optimizeDef cycle def body =
  case def of
    Can.Def (A.At _ name) args expr ->
      optimizeDefHelp cycle name args expr body

    Can.TypedDef (A.At _ name) _ typedArgs expr _ ->
      optimizeDefHelp cycle name (map fst typedArgs) expr body


optimizeDefHelp :: Cycle -> Name.Name -> [Can.Pattern] -> Can.Expr -> Opt.Expr -> Names.Tracker Opt.Expr
optimizeDefHelp cycle name args expr body =
  do  oexpr <- optimize cycle expr
      case args of
        [] ->
          pure $ Opt.Let (Opt.Def name oexpr) body

        _ ->
          do  (argNames, destructors) <- destructArgs args
              let ofunc = Opt.Function argNames (foldr Opt.Destruct oexpr destructors)
              pure $ Opt.Let (Opt.Def name ofunc) body



-- DESTRUCTURING


destructArgs :: [Can.Pattern] -> Names.Tracker ([Name.Name], [Opt.Destructor])
destructArgs args =
  do  (argNames, destructorLists) <- unzip <$> traverse destruct args
      return (argNames, concat destructorLists)


destructCase :: Name.Name -> Can.Pattern -> Names.Tracker [Opt.Destructor]
destructCase rootName pattern =
  reverse <$> destructHelp (Opt.Root rootName) pattern []


destruct :: Can.Pattern -> Names.Tracker (Name.Name, [Opt.Destructor])
destruct pattern@(A.At _ ptrn) =
  case ptrn of
    Can.PVar name ->
      pure (name, [])

    Can.PAlias subPattern name ->
      do  revDs <- destructHelp (Opt.Root name) subPattern []
          pure (name, reverse revDs)

    _ ->
      do  name <- Names.generate
          revDs <- destructHelp (Opt.Root name) pattern []
          pure (name, reverse revDs)


destructHelp :: Opt.Path -> Can.Pattern -> [Opt.Destructor] -> Names.Tracker [Opt.Destructor]
destructHelp path (A.At region pattern) revDs =
  case pattern of
    Can.PAnything ->
      pure revDs

    Can.PVar name ->
      pure (Opt.Destructor name path : revDs)

    Can.PRecord fields ->
      let
        toDestruct name =
          Opt.Destructor name (Opt.Field name path)
      in
      Names.registerFieldList fields (map toDestruct fields ++ revDs)

    Can.PAlias subPattern name ->
      destructHelp (Opt.Root name) subPattern $
        Opt.Destructor name path : revDs

    Can.PUnit ->
      pure revDs

    Can.PTuple a b Nothing ->
      destructTwo path a b revDs

    Can.PTuple a b (Just c) ->
      case path of
        Opt.Root _ ->
          destructHelp (Opt.Index Index.third path) c =<<
            destructHelp (Opt.Index Index.second path) b =<<
              destructHelp (Opt.Index Index.first path) a revDs

        _ ->
          do  name <- Names.generate
              let newRoot = Opt.Root name
              destructHelp (Opt.Index Index.third newRoot) c =<<
                destructHelp (Opt.Index Index.second newRoot) b =<<
                  destructHelp (Opt.Index Index.first newRoot) a (Opt.Destructor name path : revDs)

    Can.PList [] ->
      pure revDs

    Can.PList (hd:tl) ->
      destructTwo path hd (A.At region (Can.PList tl)) revDs

    Can.PCons hd tl ->
      destructTwo path hd tl revDs

    Can.PChr _ ->
      pure revDs

    Can.PStr _ ->
      pure revDs

    Can.PInt _ ->
      pure revDs

    Can.PBool _ _ ->
      pure revDs

    Can.PCtor _ _ (Can.Union _ _ _ opts) _ _ args ->
      case args of
        [Can.PatternCtorArg _ _ arg] ->
          case opts of
            Can.Normal -> destructHelp (Opt.Index Index.first path) arg revDs
            Can.Unbox  -> destructHelp (Opt.Unbox path) arg revDs
            Can.Enum   -> destructHelp (Opt.Index Index.first path) arg revDs

        _ ->
          case path of
            Opt.Root _ ->
              foldM (destructCtorArg path) revDs args

            _ ->
              do  name <- Names.generate
                  foldM (destructCtorArg (Opt.Root name)) (Opt.Destructor name path : revDs) args


destructTwo :: Opt.Path -> Can.Pattern -> Can.Pattern -> [Opt.Destructor] -> Names.Tracker [Opt.Destructor]
destructTwo path a b revDs =
  case path of
    Opt.Root _ ->
      destructHelp (Opt.Index Index.second path) b =<<
        destructHelp (Opt.Index Index.first path) a revDs

    _ ->
      do  name <- Names.generate
          let newRoot = Opt.Root name
          destructHelp (Opt.Index Index.second newRoot) b =<<
            destructHelp (Opt.Index Index.first newRoot) a (Opt.Destructor name path : revDs)


destructCtorArg :: Opt.Path -> [Opt.Destructor] -> Can.PatternCtorArg -> Names.Tracker [Opt.Destructor]
destructCtorArg path revDs (Can.PatternCtorArg index _ arg) =
  destructHelp (Opt.Index index path) arg revDs



-- TAIL CALL


optimizePotentialTailCallDef :: Cycle -> Can.Def -> Names.Tracker Opt.Def
optimizePotentialTailCallDef cycle def =
  case def of
    Can.Def (A.At _ name) args expr ->
      optimizePotentialTailCall cycle name args expr

    Can.TypedDef (A.At _ name) _ typedArgs expr _ ->
      optimizePotentialTailCall cycle name (map fst typedArgs) expr


optimizePotentialTailCall :: Cycle -> Name.Name -> [Can.Pattern] -> Can.Expr -> Names.Tracker Opt.Def
optimizePotentialTailCall cycle name args expr =
  do  (argNames, destructors) <- destructArgs args
      toTailDef name argNames destructors <$>
        optimizeTail cycle name argNames expr


optimizeTail :: Cycle -> Name.Name -> [Name.Name] -> Can.Expr -> Names.Tracker Opt.Expr
optimizeTail cycle rootName argNames locExpr@(A.At _ expression) =
  case expression of
    Can.Call func args ->
      do  oargs <- traverse (optimize cycle) args

          let isMatchingName =
                case A.toValue func of
                  Can.VarLocal      name -> rootName == name
                  Can.VarTopLevel _ name -> rootName == name
                  _                      -> False

          if isMatchingName
            then
              case Index.indexedZipWith (\_ a b -> (a,b)) argNames oargs of
                Index.LengthMatch pairs ->
                  pure $ Opt.TailCall rootName pairs

                Index.LengthMismatch _ _ ->
                  do  ofunc <- optimize cycle func
                      pure $ Opt.Call ofunc oargs
            else
              do  ofunc <- optimize cycle func
                  pure $ Opt.Call ofunc oargs

    Can.If branches finally ->
      let
        optimizeBranch (condition, branch) =
          (,)
            <$> optimize cycle condition
            <*> optimizeTail cycle rootName argNames branch
      in
      Opt.If
        <$> traverse optimizeBranch branches
        <*> optimizeTail cycle rootName argNames finally

    Can.Let def body ->
      optimizeDef cycle def =<< optimizeTail cycle rootName argNames body

    Can.LetRec defs body ->
      case defs of
        [def] ->
          Opt.Let
            <$> optimizePotentialTailCallDef cycle def
            <*> optimizeTail cycle rootName argNames body

        _ ->
          do  obody <- optimizeTail cycle rootName argNames body
              foldM (\bod def -> optimizeDef cycle def bod) obody defs

    Can.LetDestruct pattern expr body ->
      do  (dname, destructors) <- destruct pattern
          oexpr <- optimize cycle expr
          obody <- optimizeTail cycle rootName argNames body
          pure $
            Opt.Let (Opt.Def dname oexpr) (foldr Opt.Destruct obody destructors)

    Can.Case expr branches ->
      let
        optimizeBranch root (Can.CaseBranch pattern branch) =
          do  destructors <- destructCase root pattern
              obranch <- optimizeTail cycle rootName argNames branch
              pure (pattern, foldr Opt.Destruct obranch destructors)
      in
      do  temp <- Names.generate
          oexpr <- optimize cycle expr
          case oexpr of
            Opt.VarLocal root ->
              Case.optimize temp root <$> traverse (optimizeBranch root) branches

            _ ->
              do  obranches <- traverse (optimizeBranch temp) branches
                  return $ Opt.Let (Opt.Def temp oexpr) (Case.optimize temp temp obranches)

    _ ->
      optimize cycle locExpr



-- DETECT TAIL CALLS


toTailDef :: Name.Name -> [Name.Name] -> [Opt.Destructor] -> Opt.Expr -> Opt.Def
toTailDef name argNames destructors body =
  if hasTailCall body then
    Opt.TailDef name argNames (foldr Opt.Destruct body destructors)
  else
    Opt.Def name (Opt.Function argNames (foldr Opt.Destruct body destructors))


hasTailCall :: Opt.Expr -> Bool
hasTailCall expression =
  case expression of
    Opt.TailCall _ _ ->
      True

    Opt.If branches finally ->
      hasTailCall finally || any (hasTailCall . snd) branches

    Opt.Let _ body ->
      hasTailCall body

    Opt.Destruct _ body ->
      hasTailCall body

    Opt.Case _ _ decider jumps ->
      decidecHasTailCall decider || any (hasTailCall . snd) jumps

    _ ->
      False


decidecHasTailCall :: Opt.Decider Opt.Choice -> Bool
decidecHasTailCall decider =
  case decider of
    Opt.Leaf choice ->
      case choice of
        Opt.Inline expr ->
          hasTailCall expr

        Opt.Jump _ ->
          False

    Opt.Chain _ success failure ->
      decidecHasTailCall success || decidecHasTailCall failure

    Opt.FanOut _ tests fallback ->
      decidecHasTailCall fallback || any (decidecHasTailCall . snd) tests

# LANGUAGE OverloadedStrings #
 OPTIMIZE
 UPDATE
 DEFINITION
 DESTRUCTURING
 TAIL CALL
 DETECT TAIL CALLS
# OPTIONS_GHC -Wall #
module Optimize.Expression
  ( optimize
  , destructArgs
  , optimizePotentialTailCall
  )
  where


import Prelude hiding (cycle)
import Control.Monad (foldM)
import qualified Data.Map as Map
import qualified Data.Name as Name
import qualified Data.Set as Set

import qualified AST.Canonical as Can
import qualified AST.Optimized as Opt
import qualified AST.Utils.Shader as Shader
import qualified Data.Index as Index
import qualified Elm.ModuleName as ModuleName
import qualified Optimize.Case as Case
import qualified Optimize.Names as Names
import qualified Reporting.Annotation as A





type Cycle =
  Set.Set Name.Name


optimize :: Cycle -> Can.Expr -> Names.Tracker Opt.Expr
optimize cycle (A.At region expression) =
  case expression of
    Can.VarLocal name ->
      pure (Opt.VarLocal name)

    Can.VarTopLevel home name ->
      if Set.member name cycle then
        pure (Opt.VarCycle home name)
      else
        Names.registerGlobal home name

    Can.VarKernel home name ->
      Names.registerKernel home (Opt.VarKernel home name)

    Can.VarForeign home name _ ->
      Names.registerGlobal home name

    Can.VarCtor opts home name index _ ->
      Names.registerCtor home name index opts

    Can.VarDebug home name _ ->
      Names.registerDebug name home region

    Can.VarOperator _ home name _ ->
      Names.registerGlobal home name

    Can.Chr chr ->
      Names.registerKernel Name.utils (Opt.Chr chr)

    Can.Str str ->
      pure (Opt.Str str)

    Can.Int int ->
      pure (Opt.Int int)

    Can.Float float ->
      pure (Opt.Float float)

    Can.List entries ->
      Names.registerKernel Name.list Opt.List
        <*> traverse (optimize cycle) entries

    Can.Negate expr ->
      do  func <- Names.registerGlobal ModuleName.basics Name.negate
          arg <- optimize cycle expr
          pure $ Opt.Call func [arg]

    Can.Binop _ home name _ left right ->
      do  optFunc <- Names.registerGlobal home name
          optLeft <- optimize cycle left
          optRight <- optimize cycle right
          return (Opt.Call optFunc [optLeft, optRight])

    Can.Lambda args body ->
      do  (argNames, destructors) <- destructArgs args
          obody <- optimize cycle body
          pure $ Opt.Function argNames (foldr Opt.Destruct obody destructors)

    Can.Call func args ->
      Opt.Call
        <$> optimize cycle func
        <*> traverse (optimize cycle) args

    Can.If branches finally ->
      let
        optimizeBranch (condition, branch) =
          (,)
            <$> optimize cycle condition
            <*> optimize cycle branch
      in
      Opt.If
        <$> traverse optimizeBranch branches
        <*> optimize cycle finally

    Can.Let def body ->
      optimizeDef cycle def =<< optimize cycle body

    Can.LetRec defs body ->
      case defs of
        [def] ->
          Opt.Let
            <$> optimizePotentialTailCallDef cycle def
            <*> optimize cycle body

        _ ->
          do  obody <- optimize cycle body
              foldM (\bod def -> optimizeDef cycle def bod) obody defs

    Can.LetDestruct pattern expr body ->
      do  (name, destructs) <- destruct pattern
          oexpr <- optimize cycle expr
          obody <- optimize cycle body
          pure $
            Opt.Let (Opt.Def name oexpr) (foldr Opt.Destruct obody destructs)

    Can.Case expr branches ->
      let
        optimizeBranch root (Can.CaseBranch pattern branch) =
          do  destructors <- destructCase root pattern
              obranch <- optimize cycle branch
              pure (pattern, foldr Opt.Destruct obranch destructors)
      in
      do  temp <- Names.generate
          oexpr <- optimize cycle expr
          case oexpr of
            Opt.VarLocal root ->
              Case.optimize temp root <$> traverse (optimizeBranch root) branches

            _ ->
              do  obranches <- traverse (optimizeBranch temp) branches
                  return $ Opt.Let (Opt.Def temp oexpr) (Case.optimize temp temp obranches)

    Can.Accessor field ->
      Names.registerField field (Opt.Accessor field)

    Can.Access record (A.At _ field) ->
      do  optRecord <- optimize cycle record
          Names.registerField field (Opt.Access optRecord field)

    Can.Update _ record updates ->
      Names.registerFieldDict updates Opt.Update
        <*> optimize cycle record
        <*> traverse (optimizeUpdate cycle) updates

    Can.Record fields ->
      Names.registerFieldDict fields Opt.Record
        <*> traverse (optimize cycle) fields

    Can.Unit ->
      Names.registerKernel Name.utils Opt.Unit

    Can.Tuple a b maybeC ->
      Names.registerKernel Name.utils Opt.Tuple
        <*> optimize cycle a
        <*> optimize cycle b
        <*> traverse (optimize cycle) maybeC

    Can.Shader src (Shader.Types attributes uniforms _varyings) ->
      pure (Opt.Shader src (Map.keysSet attributes) (Map.keysSet uniforms))





optimizeUpdate :: Cycle -> Can.FieldUpdate -> Names.Tracker Opt.Expr
optimizeUpdate cycle (Can.FieldUpdate _ expr) =
  optimize cycle expr





optimizeDef :: Cycle -> Can.Def -> Opt.Expr -> Names.Tracker Opt.Expr
optimizeDef cycle def body =
  case def of
    Can.Def (A.At _ name) args expr ->
      optimizeDefHelp cycle name args expr body

    Can.TypedDef (A.At _ name) _ typedArgs expr _ ->
      optimizeDefHelp cycle name (map fst typedArgs) expr body


optimizeDefHelp :: Cycle -> Name.Name -> [Can.Pattern] -> Can.Expr -> Opt.Expr -> Names.Tracker Opt.Expr
optimizeDefHelp cycle name args expr body =
  do  oexpr <- optimize cycle expr
      case args of
        [] ->
          pure $ Opt.Let (Opt.Def name oexpr) body

        _ ->
          do  (argNames, destructors) <- destructArgs args
              let ofunc = Opt.Function argNames (foldr Opt.Destruct oexpr destructors)
              pure $ Opt.Let (Opt.Def name ofunc) body





destructArgs :: [Can.Pattern] -> Names.Tracker ([Name.Name], [Opt.Destructor])
destructArgs args =
  do  (argNames, destructorLists) <- unzip <$> traverse destruct args
      return (argNames, concat destructorLists)


destructCase :: Name.Name -> Can.Pattern -> Names.Tracker [Opt.Destructor]
destructCase rootName pattern =
  reverse <$> destructHelp (Opt.Root rootName) pattern []


destruct :: Can.Pattern -> Names.Tracker (Name.Name, [Opt.Destructor])
destruct pattern@(A.At _ ptrn) =
  case ptrn of
    Can.PVar name ->
      pure (name, [])

    Can.PAlias subPattern name ->
      do  revDs <- destructHelp (Opt.Root name) subPattern []
          pure (name, reverse revDs)

    _ ->
      do  name <- Names.generate
          revDs <- destructHelp (Opt.Root name) pattern []
          pure (name, reverse revDs)


destructHelp :: Opt.Path -> Can.Pattern -> [Opt.Destructor] -> Names.Tracker [Opt.Destructor]
destructHelp path (A.At region pattern) revDs =
  case pattern of
    Can.PAnything ->
      pure revDs

    Can.PVar name ->
      pure (Opt.Destructor name path : revDs)

    Can.PRecord fields ->
      let
        toDestruct name =
          Opt.Destructor name (Opt.Field name path)
      in
      Names.registerFieldList fields (map toDestruct fields ++ revDs)

    Can.PAlias subPattern name ->
      destructHelp (Opt.Root name) subPattern $
        Opt.Destructor name path : revDs

    Can.PUnit ->
      pure revDs

    Can.PTuple a b Nothing ->
      destructTwo path a b revDs

    Can.PTuple a b (Just c) ->
      case path of
        Opt.Root _ ->
          destructHelp (Opt.Index Index.third path) c =<<
            destructHelp (Opt.Index Index.second path) b =<<
              destructHelp (Opt.Index Index.first path) a revDs

        _ ->
          do  name <- Names.generate
              let newRoot = Opt.Root name
              destructHelp (Opt.Index Index.third newRoot) c =<<
                destructHelp (Opt.Index Index.second newRoot) b =<<
                  destructHelp (Opt.Index Index.first newRoot) a (Opt.Destructor name path : revDs)

    Can.PList [] ->
      pure revDs

    Can.PList (hd:tl) ->
      destructTwo path hd (A.At region (Can.PList tl)) revDs

    Can.PCons hd tl ->
      destructTwo path hd tl revDs

    Can.PChr _ ->
      pure revDs

    Can.PStr _ ->
      pure revDs

    Can.PInt _ ->
      pure revDs

    Can.PBool _ _ ->
      pure revDs

    Can.PCtor _ _ (Can.Union _ _ _ opts) _ _ args ->
      case args of
        [Can.PatternCtorArg _ _ arg] ->
          case opts of
            Can.Normal -> destructHelp (Opt.Index Index.first path) arg revDs
            Can.Unbox  -> destructHelp (Opt.Unbox path) arg revDs
            Can.Enum   -> destructHelp (Opt.Index Index.first path) arg revDs

        _ ->
          case path of
            Opt.Root _ ->
              foldM (destructCtorArg path) revDs args

            _ ->
              do  name <- Names.generate
                  foldM (destructCtorArg (Opt.Root name)) (Opt.Destructor name path : revDs) args


destructTwo :: Opt.Path -> Can.Pattern -> Can.Pattern -> [Opt.Destructor] -> Names.Tracker [Opt.Destructor]
destructTwo path a b revDs =
  case path of
    Opt.Root _ ->
      destructHelp (Opt.Index Index.second path) b =<<
        destructHelp (Opt.Index Index.first path) a revDs

    _ ->
      do  name <- Names.generate
          let newRoot = Opt.Root name
          destructHelp (Opt.Index Index.second newRoot) b =<<
            destructHelp (Opt.Index Index.first newRoot) a (Opt.Destructor name path : revDs)


destructCtorArg :: Opt.Path -> [Opt.Destructor] -> Can.PatternCtorArg -> Names.Tracker [Opt.Destructor]
destructCtorArg path revDs (Can.PatternCtorArg index _ arg) =
  destructHelp (Opt.Index index path) arg revDs





optimizePotentialTailCallDef :: Cycle -> Can.Def -> Names.Tracker Opt.Def
optimizePotentialTailCallDef cycle def =
  case def of
    Can.Def (A.At _ name) args expr ->
      optimizePotentialTailCall cycle name args expr

    Can.TypedDef (A.At _ name) _ typedArgs expr _ ->
      optimizePotentialTailCall cycle name (map fst typedArgs) expr


optimizePotentialTailCall :: Cycle -> Name.Name -> [Can.Pattern] -> Can.Expr -> Names.Tracker Opt.Def
optimizePotentialTailCall cycle name args expr =
  do  (argNames, destructors) <- destructArgs args
      toTailDef name argNames destructors <$>
        optimizeTail cycle name argNames expr


optimizeTail :: Cycle -> Name.Name -> [Name.Name] -> Can.Expr -> Names.Tracker Opt.Expr
optimizeTail cycle rootName argNames locExpr@(A.At _ expression) =
  case expression of
    Can.Call func args ->
      do  oargs <- traverse (optimize cycle) args

          let isMatchingName =
                case A.toValue func of
                  Can.VarLocal      name -> rootName == name
                  Can.VarTopLevel _ name -> rootName == name
                  _                      -> False

          if isMatchingName
            then
              case Index.indexedZipWith (\_ a b -> (a,b)) argNames oargs of
                Index.LengthMatch pairs ->
                  pure $ Opt.TailCall rootName pairs

                Index.LengthMismatch _ _ ->
                  do  ofunc <- optimize cycle func
                      pure $ Opt.Call ofunc oargs
            else
              do  ofunc <- optimize cycle func
                  pure $ Opt.Call ofunc oargs

    Can.If branches finally ->
      let
        optimizeBranch (condition, branch) =
          (,)
            <$> optimize cycle condition
            <*> optimizeTail cycle rootName argNames branch
      in
      Opt.If
        <$> traverse optimizeBranch branches
        <*> optimizeTail cycle rootName argNames finally

    Can.Let def body ->
      optimizeDef cycle def =<< optimizeTail cycle rootName argNames body

    Can.LetRec defs body ->
      case defs of
        [def] ->
          Opt.Let
            <$> optimizePotentialTailCallDef cycle def
            <*> optimizeTail cycle rootName argNames body

        _ ->
          do  obody <- optimizeTail cycle rootName argNames body
              foldM (\bod def -> optimizeDef cycle def bod) obody defs

    Can.LetDestruct pattern expr body ->
      do  (dname, destructors) <- destruct pattern
          oexpr <- optimize cycle expr
          obody <- optimizeTail cycle rootName argNames body
          pure $
            Opt.Let (Opt.Def dname oexpr) (foldr Opt.Destruct obody destructors)

    Can.Case expr branches ->
      let
        optimizeBranch root (Can.CaseBranch pattern branch) =
          do  destructors <- destructCase root pattern
              obranch <- optimizeTail cycle rootName argNames branch
              pure (pattern, foldr Opt.Destruct obranch destructors)
      in
      do  temp <- Names.generate
          oexpr <- optimize cycle expr
          case oexpr of
            Opt.VarLocal root ->
              Case.optimize temp root <$> traverse (optimizeBranch root) branches

            _ ->
              do  obranches <- traverse (optimizeBranch temp) branches
                  return $ Opt.Let (Opt.Def temp oexpr) (Case.optimize temp temp obranches)

    _ ->
      optimize cycle locExpr





toTailDef :: Name.Name -> [Name.Name] -> [Opt.Destructor] -> Opt.Expr -> Opt.Def
toTailDef name argNames destructors body =
  if hasTailCall body then
    Opt.TailDef name argNames (foldr Opt.Destruct body destructors)
  else
    Opt.Def name (Opt.Function argNames (foldr Opt.Destruct body destructors))


hasTailCall :: Opt.Expr -> Bool
hasTailCall expression =
  case expression of
    Opt.TailCall _ _ ->
      True

    Opt.If branches finally ->
      hasTailCall finally || any (hasTailCall . snd) branches

    Opt.Let _ body ->
      hasTailCall body

    Opt.Destruct _ body ->
      hasTailCall body

    Opt.Case _ _ decider jumps ->
      decidecHasTailCall decider || any (hasTailCall . snd) jumps

    _ ->
      False


decidecHasTailCall :: Opt.Decider Opt.Choice -> Bool
decidecHasTailCall decider =
  case decider of
    Opt.Leaf choice ->
      case choice of
        Opt.Inline expr ->
          hasTailCall expr

        Opt.Jump _ ->
          False

    Opt.Chain _ success failure ->
      decidecHasTailCall success || decidecHasTailCall failure

    Opt.FanOut _ tests fallback ->
      decidecHasTailCall fallback || any (decidecHasTailCall . snd) tests
