{-# LANGUAGE TypeApplications #-}

module Extism.PDK.Bindings where

import Data.ByteString.Internal
import Foreign.ForeignPtr
import Foreign.Ptr
import Foreign.Storable
import Control.Monad

import System.Exit
import Data.Word
import Data.Int
import Foreign.C.Types

import Data.ByteString as B


type MemoryOffset = Word64
type InputOffset = Word64
type MemoryLength = Word64
type InputLength = Word64

foreign import ccall "extism_output_set" extismSetOutput :: MemoryOffset -> MemoryLength -> IO ()
foreign import ccall "extism_error_set" extismSetError :: MemoryOffset -> IO ()
foreign import ccall "extism_log_info" extismLogInfo :: MemoryOffset -> IO ()
foreign import ccall "extism_log_warn" extismLogWarn :: MemoryOffset -> IO ()
foreign import ccall "extism_log_debug" extismLogDebug :: MemoryOffset -> IO ()
foreign import ccall "extism_log_error" extismLogError :: MemoryOffset -> IO ()
foreign import ccall "extism_store_u8" extismStoreU8 :: MemoryOffset -> Word8 -> IO ()
foreign import ccall "extism_store_u64" extismStoreU64 :: MemoryOffset -> Word64 -> IO ()
foreign import ccall "extism_load_u8" extismLoadU8 :: MemoryOffset -> IO Word8
foreign import ccall "extism_load_u64" extismLoadU64 :: MemoryOffset -> IO Word64
foreign import ccall "extism_alloc" extismAlloc :: MemoryLength -> IO MemoryOffset
foreign import ccall "extism_length" extismLength :: MemoryOffset -> IO MemoryLength
foreign import ccall "extism_free" extismFree :: MemoryOffset -> IO ()
foreign import ccall "extism_input_length" extismInputLength :: IO InputLength
foreign import ccall "extism_input_load_u8" extismInputLoadU8 :: InputOffset -> IO Word8
foreign import ccall "extism_input_load_u64" extismInputLoadU64 :: InputOffset -> IO Word64
foreign import ccall "extism_config_get" extismGetConfig :: MemoryOffset -> IO MemoryOffset
foreign import ccall "extism_var_get" extismGetVar :: MemoryOffset -> IO MemoryOffset
foreign import ccall "extism_var_set" extismSetVar :: MemoryOffset -> MemoryOffset -> IO ()
foreign import ccall "extism_http_request" extismHTTPRequest :: MemoryOffset -> MemoryOffset -> IO MemoryOffset
foreign import ccall "extism_http_status_code" extismHTTPStatusCode :: IO Int32
foreign import ccall "__wasm_call_ctors" wasmConstructor :: IO ()
foreign import ccall "__wasm_call_dtors" wasmDestructor :: IO ()


bsToWord64 :: ByteString -> IO Word64
bsToWord64 (BS fp len) =
  if len /= 8 then error "invalid bytestring"
  else
    withForeignPtr fp (\p ->
      peek $ castPtr @Word8 @Word64 p)

word64ToBS :: Word64 -> ByteString
word64ToBS word = unsafeCreate 8 (\p ->
  poke (castPtr @Word8 @Word64 p) word)

readLoop :: (Word64 -> IO Word8) -> (Word64 -> IO Word64) -> Word64 -> Word64 -> [ByteString] -> IO ByteString
readLoop f1 f8 total index acc =
  if index >= total then
    return $ B.concat . Prelude.reverse $ acc
  else
    let diff = total - index in
    do
      (n, x) <- if diff >= 8 then do
                    u <- f8 index
                    return (8, word64ToBS u)
                  else do
                    b <- f1 index
                    return (1, B.singleton b)
      readLoop f1 f8 total (index + n) (x : acc)

readInputBytes :: InputLength -> IO ByteString
readInputBytes len =
  readLoop extismInputLoadU8 extismInputLoadU64 len 0 []

readBytes :: MemoryOffset -> MemoryLength -> IO ByteString
readBytes offs len =
  readLoop extismLoadU8 extismLoadU64 (offs + len) offs []

writeBytesLoop :: MemoryOffset -> MemoryOffset -> ByteString -> IO ()
writeBytesLoop index total src =
  if index >= total then
    return ()
  else
    let diff = total - index in
    do
      (n, sub) <- if diff >= 8 then do
                    let (curr, next) = B.splitAt 8 src
                    u <- bsToWord64 curr
                    extismStoreU64 index u
                    return (8, next)
                  else do
                    let u = B.head src
                    extismStoreU8 index u
                    return (1, B.tail src)
      writeBytesLoop (index + n) total sub

writeBytes :: MemoryOffset -> MemoryLength -> ByteString -> IO ()
writeBytes offs len src =
  writeBytesLoop offs (offs + len) src