module Language.Elna.RiscV.CodeGenerator
    ( Directive(..)
    , Statement(..)
    , generateRiscV
    , riscVConfiguration
    ) where

import Control.Monad.Trans.State (State, get, evalState, modify')
import qualified Data.HashMap.Strict as HashMap
import Data.Int (Int32)
import Data.Word (Word32)
import Data.Vector (Vector)
import qualified Data.Vector as Vector
import qualified Language.Elna.Architecture.RiscV as RiscV
import Language.Elna.Backend.Allocator (MachineConfiguration(..), Store(..))
import Language.Elna.Backend.Intermediate
    ( Label(..)
    , Operand(..)
    , ProcedureQuadruples(..)
    , Quadruple(..)
    )
import Language.Elna.Location (Identifier(..))
import Data.Bits (Bits(..))
import Data.Foldable (Foldable(..), foldlM)
import Data.Text (Text)
import qualified Data.Text.Lazy.Builder.Int as Text.Builder
import qualified Data.Text.Lazy.Builder as Text.Builder
import qualified Data.Text.Lazy as Text.Lazy

data Directive
    = GlobalDirective
    | FunctionDirective
    deriving (Eq, Show)

data Statement
    = Instruction RiscV.Instruction
    | JumpLabel Text [Directive]
    deriving Eq

riscVConfiguration :: MachineConfiguration RiscV.XRegister
riscVConfiguration = MachineConfiguration
    { temporaryRegisters =
        [ RiscV.T0
        , RiscV.T1
        , RiscV.T2
        , RiscV.T3
        , RiscV.T4
        , RiscV.T5
        , RiscV.T6
        ]
    }

-- | Reserved register used for calculations to save an immediate temporary.
immediateRegister :: RiscV.XRegister
immediateRegister = RiscV.A7

type RiscVStore = Store RiscV.XRegister
type RiscVQuadruple = Quadruple RiscVStore
type RiscVOperand = Operand RiscVStore

newtype RiscVGenerator a = RiscVGenerator
    { runRiscVGenerator :: State Word32 a }

instance Functor RiscVGenerator
  where
    fmap f (RiscVGenerator x) = RiscVGenerator $ f <$> x

instance Applicative RiscVGenerator
  where
    pure = RiscVGenerator . pure
    (RiscVGenerator f) <*> (RiscVGenerator x) = RiscVGenerator $ f <*> x

instance Monad RiscVGenerator
  where
    (RiscVGenerator x) >>= f = RiscVGenerator $ x >>= (runRiscVGenerator . f)

createLabel :: RiscVGenerator Text
createLabel = do
    currentCounter <- RiscVGenerator get
    RiscVGenerator $ modify' (+ 1)
    pure
        $ mappend ".A"
        $ Text.Lazy.toStrict
        $ Text.Builder.toLazyText
        $ Text.Builder.decimal currentCounter

generateRiscV :: ProcedureQuadruples RiscVStore -> Vector Statement
generateRiscV (ProcedureQuadruples quadruples) = flip evalState 0
    $ runRiscVGenerator
    $ foldlM go Vector.empty
    $ HashMap.toList quadruples
  where
    go accumulator (Identifier key, value) =
        let code = Vector.cons (JumpLabel key [GlobalDirective, FunctionDirective])
                . fold <$> mapM quadruple value
         in (accumulator <>) <$> code

quadruple :: RiscVQuadruple -> RiscVGenerator (Vector Statement)
quadruple StartQuadruple = pure $ Vector.fromList
    [ Instruction (RiscV.BaseInstruction RiscV.OpImm $ RiscV.I RiscV.SP RiscV.ADDI RiscV.SP (negate 4))
    , Instruction (RiscV.BaseInstruction RiscV.Store $ RiscV.S 0 RiscV.SW RiscV.SP RiscV.S0)
    , Instruction (RiscV.BaseInstruction RiscV.Store $ RiscV.S 4 RiscV.SW RiscV.SP RiscV.RA)
    , Instruction (RiscV.BaseInstruction RiscV.OpImm $ RiscV.I RiscV.S0 RiscV.ADDI RiscV.SP 4)
    ]
quadruple (ParameterQuadruple operand1) =
    let (operandRegister, statements) = loadImmediateOrRegister operand1 RiscV.A0
     in pure $ mappend statements $ Vector.fromList
        [ Instruction (RiscV.BaseInstruction RiscV.OpImm $ RiscV.I RiscV.SP RiscV.ADDI RiscV.SP (negate 4))
        , Instruction (RiscV.BaseInstruction RiscV.Store $ RiscV.S 0 RiscV.SW RiscV.SP operandRegister)
        ]
quadruple (CallQuadruple callName numberOfArguments) = pure $ Vector.fromList
    [ Instruction (RiscV.CallInstruction callName)
    , Instruction (RiscV.BaseInstruction RiscV.OpImm $ RiscV.I RiscV.SP RiscV.ADDI RiscV.SP (numberOfArguments * 4))
    ]
quadruple StopQuadruple = pure $ Vector.fromList
    [ Instruction (RiscV.BaseInstruction RiscV.Load $ RiscV.I RiscV.S0 RiscV.LW RiscV.SP 0)
    , Instruction (RiscV.BaseInstruction RiscV.Load $ RiscV.I RiscV.RA RiscV.LW RiscV.SP 4)
    , Instruction (RiscV.BaseInstruction RiscV.OpImm $ RiscV.I RiscV.SP RiscV.ADDI RiscV.SP 4)
    , Instruction (RiscV.BaseInstruction RiscV.Jalr $ RiscV.I RiscV.RA RiscV.JALR RiscV.Zero 0)
    ]
quadruple (AddQuadruple operand1 operand2 store) =
    commutativeBinary (+) RiscV.ADD (RiscV.Funct7 0b0000000) (operand1, operand2) store
quadruple (ProductQuadruple operand1 operand2 store) =
    commutativeBinary (*) RiscV.MUL (RiscV.Funct7 0b0000001) (operand1, operand2) store
quadruple (SubtractionQuadruple operand1 operand2 (Store register))
    | IntOperand immediateOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        pure $ lui (immediateOperand1 - immediateOperand2) register
    | VariableOperand variableOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 =
        let Store operandRegister1 = variableOperand1
            Store operandRegister2 = variableOperand2
        in pure $ Vector.singleton $ Instruction
            $ RiscV.BaseInstruction RiscV.Op
            $ RiscV.R register RiscV.SUB operandRegister1 operandRegister2
            $ RiscV.Funct7 0b0100000
    | IntOperand immediateOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 =
        let statements1 = lui immediateOperand1 register
            Store operandRegister2 = variableOperand2
         in pure $ Vector.snoc statements1
            $ Instruction
            $ RiscV.BaseInstruction RiscV.Op
            $ RiscV.R register RiscV.SUB register operandRegister2
            $ RiscV.Funct7 0b0100000
    | VariableOperand variableOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        let statements2 = lui (negate immediateOperand2) register
            Store operandRegister1 = variableOperand1
         in pure $ Vector.snoc statements2
            $ Instruction
            $ RiscV.BaseInstruction RiscV.Op
            $ RiscV.R register RiscV.ADD register operandRegister1
            $ RiscV.Funct7 0b0000000
quadruple (NegationQuadruple operand1 (Store register))
    | IntOperand immediateOperand1 <- operand1 =
        pure $ lui (negate immediateOperand1) register
    | VariableOperand variableOperand1 <- operand1 =
        let Store operandRegister1 = variableOperand1
         in pure $ Vector.singleton
            $ Instruction
            $ RiscV.BaseInstruction RiscV.Op
            $ RiscV.R register RiscV.SUB RiscV.Zero operandRegister1
            $ RiscV.Funct7 0b0100000
quadruple (DivisionQuadruple operand1 operand2 (Store register))
    | IntOperand immediateOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        if immediateOperand2 == 0
        then pure $ Vector.singleton
            $ Instruction (RiscV.CallInstruction "_divide_by_zero_error")
        else pure $ lui (quot immediateOperand1 immediateOperand2) register
    | VariableOperand variableOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 = do
        let Store operandRegister1 = variableOperand1
            Store operandRegister2 = variableOperand2
            divisionInstruction = Instruction
                $ RiscV.BaseInstruction RiscV.Op
                $ RiscV.R register RiscV.DIV operandRegister1 operandRegister2 (RiscV.Funct7 0b0000001)
        branchLabel <- createLabel
        let branchInstruction = Instruction
                $ RiscV.RelocatableInstruction RiscV.Branch
                $ RiscV.RBranch branchLabel RiscV.BNE RiscV.Zero operandRegister2
        pure $ Vector.fromList
            [ branchInstruction
            , Instruction (RiscV.CallInstruction "_divide_by_zero_error")
            , JumpLabel branchLabel []
            , divisionInstruction
            ]
    | VariableOperand variableOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        let statements2 = lui immediateOperand2 register
            Store operandRegister1 = variableOperand1
            operationInstruction
                | immediateOperand2 == 0 =
                    RiscV.CallInstruction "_divide_by_zero_error"
                | otherwise = RiscV.BaseInstruction RiscV.Op
                    $ RiscV.R register RiscV.DIV operandRegister1 register
                    $ RiscV.Funct7 0b0000001
         in pure $ Vector.snoc statements2
            $ Instruction operationInstruction
    | IntOperand immediateOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 = do
        let statements1 = lui immediateOperand1 register
            Store operandRegister2 = variableOperand2
            divisionInstruction = Instruction
                $ RiscV.BaseInstruction RiscV.Op
                $ RiscV.R register RiscV.DIV register operandRegister2 (RiscV.Funct7 0b0000001)
        branchLabel <- createLabel
        let branchInstruction = Instruction
                $ RiscV.RelocatableInstruction RiscV.Branch
                $ RiscV.RBranch branchLabel RiscV.BNE RiscV.Zero operandRegister2
        pure $ mappend statements1 $ Vector.fromList 
            [ branchInstruction
            , Instruction (RiscV.CallInstruction "_divide_by_zero_error")
            , JumpLabel branchLabel []
            , divisionInstruction
            ]
quadruple (LabelQuadruple (Label label)) = pure $ Vector.singleton $ JumpLabel label mempty
quadruple (GoToQuadruple label) = pure $ Vector.singleton $ unconditionalJal label
quadruple (EqualQuadruple operand1 operand2 goToLabel) =
    commutativeComparison (==) RiscV.BEQ (operand1, operand2) goToLabel
quadruple (NonEqualQuadruple operand1 operand2 goToLabel) =
    commutativeComparison (/=) RiscV.BNE (operand1, operand2) goToLabel
quadruple (LessQuadruple operand1 operand2 goToLabel) =
    lessThan (operand1, operand2) goToLabel
quadruple (GreaterQuadruple operand1 operand2 goToLabel) =
    lessThan (operand2, operand1) goToLabel
quadruple (LessOrEqualQuadruple operand1 operand2 goToLabel) =
    lessOrEqualThan (operand1, operand2) goToLabel
quadruple (GreaterOrEqualQuadruple operand1 operand2 goToLabel) =
    lessOrEqualThan (operand2, operand1) goToLabel
quadruple (AssignQuadruple operand1 (Store register))
    | IntOperand immediateOperand1 <- operand1 = pure
        $ lui immediateOperand1 register
    | VariableOperand variableOperand1 <- operand1 =
        let Store operandRegister1 = variableOperand1
         in pure $ Vector.singleton
            $ Instruction
            $ RiscV.BaseInstruction RiscV.OpImm
            $ RiscV.I register RiscV.ADDI operandRegister1 0

unconditionalJal :: Label -> Statement
unconditionalJal (Label goToLabel) = Instruction
    $ RiscV.RelocatableInstruction RiscV.Jal
    $ RiscV.RJal RiscV.Zero goToLabel

loadImmediateOrRegister :: RiscVOperand -> RiscV.XRegister -> (RiscV.XRegister, Vector Statement)
loadImmediateOrRegister (IntOperand intValue) targetRegister =
    (targetRegister, lui intValue targetRegister)
loadImmediateOrRegister (VariableOperand (Store register)) _ = (register, Vector.empty)

lui :: Int32 -> RiscV.XRegister -> Vector Statement
lui intValue targetRegister
    | intValue >= -2048
    , intValue <= 2047 = Vector.singleton
        $ Instruction (RiscV.BaseInstruction RiscV.OpImm $ RiscV.I targetRegister RiscV.ADDI RiscV.Zero lo)
    | intValue .&. 0x800 /= 0 = Vector.fromList
        [ Instruction (RiscV.BaseInstruction RiscV.Lui $ RiscV.U targetRegister $ fromIntegral $ succ hi)
        , Instruction (RiscV.BaseInstruction RiscV.OpImm $ RiscV.I targetRegister RiscV.ADDI targetRegister lo)
        ]
    | otherwise = Vector.fromList
        [ Instruction (RiscV.BaseInstruction RiscV.Lui $ RiscV.U targetRegister $ fromIntegral hi)
        , Instruction (RiscV.BaseInstruction RiscV.OpImm $ RiscV.I targetRegister RiscV.ADDI targetRegister lo)
        ]
  where
    hi = intValue `shiftR` 12
    lo = fromIntegral intValue

commutativeBinary
    :: (Int32 -> Int32 -> Int32)
    -> RiscV.Funct3
    -> RiscV.Funct7
    -> (Operand RiscVStore, Operand RiscVStore)
    -> Store RiscV.XRegister
    -> RiscVGenerator (Vector Statement)
commutativeBinary immediateOperation funct3 funct7 (operand1, operand2) (Store register)
    | IntOperand immediateOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 = pure
        $ lui (immediateOperation immediateOperand1 immediateOperand2) register
    | VariableOperand variableOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 =
        let Store operandRegister1 = variableOperand1
            Store operandRegister2 = variableOperand2
        in pure $ Vector.singleton $ Instruction
            $ RiscV.BaseInstruction RiscV.Op
            $ RiscV.R register funct3 operandRegister1 operandRegister2 funct7
    | VariableOperand variableOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        commutativeImmediateRegister variableOperand1 immediateOperand2
    | IntOperand immediateOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 =
        commutativeImmediateRegister variableOperand2 immediateOperand1
  where
    commutativeImmediateRegister variableOperand immediateOperand = 
        let statements = lui immediateOperand register
            Store operandRegister = variableOperand
        in pure $ Vector.snoc statements
            $ Instruction
            $ RiscV.BaseInstruction RiscV.Op
            $ RiscV.R register funct3 register operandRegister funct7

commutativeComparison
    :: (Int32 -> Int32 -> Bool)
    -> RiscV.Funct3
    -> (Operand RiscVStore, Operand RiscVStore)
    -> Label
    -> RiscVGenerator (Vector Statement)
commutativeComparison immediateOperation funct3 (operand1, operand2) goToLabel
    | IntOperand immediateOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        if immediateOperation immediateOperand1 immediateOperand2
        then pure $ Vector.singleton $ unconditionalJal goToLabel
        else pure Vector.empty
    | VariableOperand variableOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 = do
        let Store operandRegister1 = variableOperand1
            Store operandRegister2 = variableOperand2
            Label goToLabel' = goToLabel
        pure $ Vector.singleton
            $ Instruction
            $ RiscV.RelocatableInstruction RiscV.Branch
            $ RiscV.RBranch goToLabel' funct3 operandRegister1 operandRegister2
    | VariableOperand variableOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        compareImmediateRegister variableOperand1 immediateOperand2
    | IntOperand immediateOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 =
        compareImmediateRegister variableOperand2 immediateOperand1
  where
    compareImmediateRegister variableOperand immediateOperand = 
        let statements = lui immediateOperand immediateRegister
            Store operandRegister = variableOperand
            Label goToLabel' = goToLabel
        in pure $ Vector.snoc statements
            $ Instruction
            $ RiscV.RelocatableInstruction RiscV.Branch
            $ RiscV.RBranch goToLabel' funct3 operandRegister immediateRegister

lessThan :: (Operand RiscVStore, Operand RiscVStore) -> Label -> RiscVGenerator (Vector Statement)
lessThan (operand1, operand2) goToLabel
    | IntOperand immediateOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        if immediateOperand1 < immediateOperand2
        then pure $ Vector.singleton $ unconditionalJal goToLabel
        else pure Vector.empty
    | VariableOperand variableOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 = do
        let Store operandRegister1 = variableOperand1
            Store operandRegister2 = variableOperand2
            Label goToLabel' = goToLabel
        pure $ Vector.singleton
            $ Instruction
            $ RiscV.RelocatableInstruction RiscV.Branch
            $ RiscV.RBranch goToLabel' RiscV.BLT operandRegister1 operandRegister2
    | VariableOperand variableOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        let statements2 = lui immediateOperand2 immediateRegister
            Store operandRegister1 = variableOperand1
            Label goToLabel' = goToLabel
        in pure $ Vector.snoc statements2
            $ Instruction
            $ RiscV.RelocatableInstruction RiscV.Branch
            $ RiscV.RBranch goToLabel' RiscV.BLT operandRegister1 immediateRegister
    | IntOperand immediateOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 =
        let statements1 = lui immediateOperand1 immediateRegister
            Store operandRegister2 = variableOperand2
            Label goToLabel' = goToLabel
        in pure $ Vector.snoc statements1
            $ Instruction
            $ RiscV.RelocatableInstruction RiscV.Branch
            $ RiscV.RBranch goToLabel' RiscV.BLT immediateRegister operandRegister2

lessOrEqualThan :: (Operand RiscVStore, Operand RiscVStore) -> Label -> RiscVGenerator (Vector Statement)
lessOrEqualThan (operand1, operand2) goToLabel
    | IntOperand immediateOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        if immediateOperand1 <= immediateOperand2
        then pure $ Vector.singleton $ unconditionalJal goToLabel
        else pure Vector.empty
    | VariableOperand variableOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 = do
        let Store operandRegister1 = variableOperand1
            Store operandRegister2 = variableOperand2
            Label goToLabel' = goToLabel
        pure $ Vector.singleton
            $ Instruction
            $ RiscV.RelocatableInstruction RiscV.Branch
            $ RiscV.RBranch goToLabel' RiscV.BGE operandRegister2 operandRegister1
    | VariableOperand variableOperand1 <- operand1
    , IntOperand immediateOperand2 <- operand2 =
        let statements2 = lui immediateOperand2 immediateRegister
            Store operandRegister1 = variableOperand1
            Label goToLabel' = goToLabel
        in pure $ Vector.snoc statements2
            $ Instruction
            $ RiscV.RelocatableInstruction RiscV.Branch
            $ RiscV.RBranch goToLabel' RiscV.BGE immediateRegister operandRegister1
    | IntOperand immediateOperand1 <- operand1
    , VariableOperand variableOperand2 <- operand2 =
        let statements1 = lui immediateOperand1 immediateRegister
            Store operandRegister2 = variableOperand2
            Label goToLabel' = goToLabel
        in pure $ Vector.snoc statements1
            $ Instruction
            $ RiscV.RelocatableInstruction RiscV.Branch
            $ RiscV.RBranch goToLabel' RiscV.BGE operandRegister2 immediateRegister