-- Assembler for Hack Computer
-- Coursework for Nand2Tetris
-- Author: Yuchen Pei (me@ypei.me)
import Numeric (showIntAtBase)
import Data.Char (intToDigit)
import Data.Map (Map)
import qualified Data.Map as Map
import Data.List.Split (splitOn, splitOneOf)
import System.Environment (getArgs)

parseLine :: Map [Char] [Char] -> [Char] -> [Char]
parseLine table (x:xs)
  | x == '@' && (head xs `elem` ['0'..'9']) = (int2Bin16 $ read xs)
  | x == '@' = table Map.! xs
  | '=' `elem` (x:xs) && ';' `elem` (x:xs) = let [dest, comp, jump] = splitOneOf "=;" (x:xs) in "111" ++ (parseComp comp) ++ (parseDest dest) ++ (parseJump jump)
  | '=' `elem` (x:xs) = let [dest, comp] = splitOn "=" (x:xs) in "111" ++ (parseComp comp) ++ (parseDest dest) ++ "000"
  | ';' `elem` (x:xs) = let [comp, jump] = splitOn ";" (x:xs) in "111" ++ (parseComp comp) ++ "000" ++ (parseJump jump)

parseComp xs = case xs of
  "0" -> "0101010"
  "1" -> "0111111"
  "-1" -> "0111010"
  "D" -> "0001100"
  "A" -> "0110000"
  "!D" -> "0001101"
  "!A" -> "0110001"
  "-D" -> "0001111"
  "-A" -> "0110011"
  "D+1" -> "0011111"
  "A+1" -> "0110111"
  "D-1" -> "0001110"
  "A-1" -> "0110010"
  "D+A" -> "0000010"
  "A+D" -> "0000010"
  "D-A" -> "0010011"
  "A-D" -> "0000111"
  "D&A" -> "0000000"
  "A&D" -> "0000000"
  "D|A" -> "0010101"
  "A|D" -> "0010101"
  "M" -> "1110000"
  "!M" -> "1110001"
  "-M" -> "1110011"
  "M+1" -> "1110111"
  "M-1" -> "1110010"
  "D+M" -> "1000010"
  "M+D" -> "1000010"
  "D-M" -> "1010011"
  "M-D" -> "1000111"
  "D&M" -> "1000000"
  "M&D" -> "1000000"
  "D|M" -> "1010101"
  "M|D" -> "1010101"

parseDest xs = (f 'A'):(f 'D'):(f 'M'):[]
  where f x = if x `elem` xs then '1' else '0'

parseJump xs = case xs of
  "" -> "000"
  "JGT" -> "001"
  "JEQ" -> "010"
  "JGE" -> "011"
  "JLT" -> "100"
  "JNE" -> "101"
  "JLE" -> "110"
  "JMP" -> "111"

int2Bin x = showIntAtBase 2 intToDigit x ""

int2Bin16 :: Int -> [Char]
int2Bin16 x = let xs = int2Bin x in replicate (16 - length xs) '0' ++ xs

initTable :: Map [Char] [Char]
initTable = Map.fromList $ (\(x, y) -> (x, int2Bin16 y)) <$> ("SP", 0):("LCL", 1):("ARG", 2):("THIS", 3):("THAT", 4):("SCREEN", 16384):("KBD", 24576):rs
  where rs = zipWith (,) ((\x -> 'R':(show x)) <$> [0..15]) [0..15]

stripJunk :: [Char] -> [[Char]]
stripJunk xs = filter (not . null) $ (filter (not . (flip elem " \t")) . head . (splitOn "//")) <$> lines (replCrWithNl xs)

stripLabels :: [[Char]] -> [[Char]]
stripLabels = filter (not . (elem '('))

-- For labels
addLabels :: [[Char]] -> Int -> Map [Char] [Char] -> Map [Char] [Char]
addLabels [] _ table = table
addLabels ((hd:tl):rest) addr table
  | hd == '(' = addLabels rest addr (Map.insert (init tl) (int2Bin16 addr) table)
  | otherwise = addLabels rest (addr + 1) table

-- For variables, addr is the current instruction address, vaddr is the
-- variable memory address (to be assigned)
addSyms :: [[Char]] -> Int -> Int -> Map [Char] [Char] -> Map [Char] [Char]
addSyms [] _ _ table = table
addSyms ((hd:tl):rest) addr vaddr table
  | hd == '(' = addSyms rest addr vaddr (Map.insert (init tl) (int2Bin16 addr) table)
  | hd == '@' && head tl `notElem` ['0'..'9'] && tl `Map.notMember` table = addSyms rest (addr + 1) (vaddr + 1) (Map.insert tl (int2Bin16 vaddr) table)
  | otherwise = addSyms rest (addr + 1) vaddr table

parseCode :: [Char] -> [Char]
parseCode code = unlines $ parseLine (addSyms codeWithoutLabels 0 16 (addLabels codeWithoutJunk 0 initTable)) <$> codeWithoutLabels
  where codeWithoutJunk = stripJunk code
        codeWithoutLabels = stripLabels codeWithoutJunk

replCrWithNl = fmap cr2nl 
  where cr2nl '\r' = '\n'
        cr2nl c = c

main = do
  args <- getArgs
  let filename = head args
  code <- readFile $ filename
  writeFile (head (splitOn "." filename) ++ ".hack") (parseCode code)