{-|
Module      : Verismith.Verilog.Preprocess
Description : Simple preprocessor for `define and comments.
Copyright   : (c) 2011-2015 Tom Hawkins, 2019 Yann Herklotz
License     : GPL-3
Maintainer  : yann [at] yannherklotz [dot] com
Stability   : experimental
Portability : POSIX

Simple preprocessor for `define and comments.

The code is from https://github.com/tomahawkins/verilog.

Edits to the original code are warning fixes and formatting changes.
-}

module Verismith.Verilog.Preprocess
    ( uncomment
    , preprocess
    )
where

-- | Remove comments from code. There is no difference between @(* *)@ and
-- @/* */@, therefore in this implementation, @*/@ could close @(*@ and vice-versa,
-- This will be fixed in an upcoming version.
uncomment :: FilePath -> String -> String
uncomment file = uncomment'
  where
    uncomment' a = case a of
        ""               -> ""
        '/' : '/' : rest -> "  " ++ removeEOL rest
        '/' : '*' : rest -> "  " ++ remove rest
        '(' : '*' : rest -> "  " ++ remove rest
        '"'       : rest -> '"' : ignoreString rest
        b         : rest -> b : uncomment' rest

    removeEOL a = case a of
        ""          -> ""
        '\n' : rest -> '\n' : uncomment' rest
        '\t' : rest -> '\t' : removeEOL rest
        _    : rest -> ' ' : removeEOL rest

    remove a = case a of
        "" -> error $ "File ended without closing comment (*/): " ++ file
        '"'       : rest -> removeString rest
        '\n'      : rest -> '\n' : remove rest
        '\t'      : rest -> '\t' : remove rest
        '*' : '/' : rest -> "  " ++ uncomment' rest
        '*' : ')' : rest -> "  " ++ uncomment' rest
        _         : rest -> " " ++ remove rest

    removeString a = case a of
        "" -> error $ "File ended without closing string: " ++ file
        '"'        : rest -> " " ++ remove rest
        '\\' : '"' : rest -> "  " ++ removeString rest
        '\n'       : rest -> '\n' : removeString rest
        '\t'       : rest -> '\t' : removeString rest
        _          : rest -> ' ' : removeString rest

    ignoreString a = case a of
        "" -> error $ "File ended without closing string: " ++ file
        '"'        : rest -> '"' : uncomment' rest
        '\\' : '"' : rest -> "\\\"" ++ ignoreString rest
        b          : rest -> b : ignoreString rest

-- | A simple `define preprocessor.
preprocess :: [(String, String)] -> FilePath -> String -> String
preprocess env file content = unlines $ pp True [] env $ lines $ uncomment
    file
    content
  where
    pp :: Bool -> [Bool] -> [(String, String)] -> [String] -> [String]
    pp _  _     _    []         = []
    pp on stack env_ (a : rest) = case words a of
        "`define" : name : value ->
            ""
                : pp
                      on
                      stack
                      (if on
                          then (name, ppLine env_ $ unwords value) : env_
                          else env_
                      )
                      rest
        "`ifdef" : name : _ ->
            "" : pp (on && elem name (map fst env_)) (on : stack) env_ rest
        "`ifndef" : name : _ ->
            "" : pp (on && notElem name (map fst env_)) (on : stack) env_ rest
        "`else" : _
            | not $ null stack
            -> "" : pp (head stack && not on) stack env_ rest
            | otherwise
            -> error $ "`else  without associated `ifdef/`ifndef: " ++ file
        "`endif" : _
            | not $ null stack
            -> "" : pp (head stack) (tail stack) env_ rest
            | otherwise
            -> error $ "`endif  without associated `ifdef/`ifndef: " ++ file
        _ -> (if on then ppLine env_ a else "") : pp on stack env_ rest

ppLine :: [(String, String)] -> String -> String
ppLine _   ""        = ""
ppLine env ('`' : a) = case lookup name env of
    Just value -> value ++ ppLine env rest
    Nothing    -> error $ "Undefined macro: `" ++ name ++ "  Env: " ++ show env
  where
    name = takeWhile
        (flip elem $ ['A' .. 'Z'] ++ ['a' .. 'z'] ++ ['0' .. '9'] ++ ['_'])
        a
    rest = drop (length name) a
ppLine env (a : b) = a : ppLine env b