{- sv2v
 - Author: Zachary Snow <zach@zachjs.com>
 -
 - Verilog-2005 requires that for loops have have exactly one assignment in the
 - initialization section. For generate for loops, we move any genvar
 - declarations to a wrapping generate block. For procedural for loops, we pull
 - the declarations out to a wrapping block, and convert all but one assignment
 - to a preceding statement. If a for loop has no assignments or declarations, a
 - dummy declaration is generated.
 -}

module Convert.ForDecl (convert) where

import Data.Either (isLeft, isRight, lefts, rights)

import Convert.Traverse
import Language.SystemVerilog.AST

convert :: [AST] -> [AST]
convert =
    map $ traverseDescriptions $ traverseModuleItems $
    ( traverseStmts    convertStmt
    . traverseGenItems convertGenItem
    )

convertGenItem :: GenItem -> GenItem
convertGenItem (GenFor (True, x, e) a b mx c) =
    GenBlock (fmap (++ "_for_decl") mx)
    [ GenModuleItem $ Genvar x
    , GenFor (False, x, e) a b mx c
    ]
convertGenItem other = other

convertStmt :: Stmt -> Stmt
convertStmt (For [] cc asgns stmt) =
    convertStmt $ For inits cc asgns stmt
    where inits = [Left $ dummyDecl (Just $ Number "0")]
convertStmt (orig @ (For [Right _] _ _ _)) = orig

convertStmt (orig @ (For (inits @ (Left _: _)) cc asgns stmt)) =
    if not $ all isLeft inits
    then error $ "for loop has mix of decls and asgns: " ++ show orig
    else Block
            Nothing
            decls
            (initAsgns ++ [For [Right (lhs, expr)] cc asgns stmt])
    where
        splitDecls = map splitDecl $ lefts inits
        decls = map fst splitDecls
        initAsgns = map asgnStmt $ init $ map snd splitDecls
        (lhs, expr) = snd $ last splitDecls

convertStmt (orig @ (For inits cc asgns stmt)) =
    if not $ all isRight inits
    then error $ "for loop has mix of decls and asgns: " ++ show orig
    else Block
            Nothing
            []
            (initAsgns ++ [For [Right (lhs, expr)] cc asgns stmt])
    where
        origPairs = rights inits
        (lhs, expr) = last origPairs
        initAsgns = map asgnStmt $ init origPairs

convertStmt other = other

splitDecl :: Decl -> (Decl, (LHS, Expr))
splitDecl (Variable d t ident a (Just e)) =
    (Variable d t ident a Nothing, (LHSIdent ident, e))
splitDecl other =
    error $ "invalid for loop decl: " ++ show other

asgnStmt :: (LHS, Expr) -> Stmt
asgnStmt = uncurry $ AsgnBlk AsgnOpEq

dummyDecl :: Maybe Expr -> Decl
dummyDecl = Variable Local (IntegerAtom TInteger Unspecified) "_sv2v_dummy" []