core: relations vector operations (#6459)

* core: relations vector operations

* tests

* simplify

* comment

* remove space

* core: use 1 byte for each member-to-member relation (#6462)

---------

Co-authored-by: Evgeny <evgeny@poberezkin.com>

src/Simplex/Chat/Types/MemberRelations.hs

@@ -0,0 +1,74 @@
+{-# LANGUAGE LambdaCase #-}
+
+module Simplex.Chat.Types.MemberRelations
+  ( MemberRelation (..),
+    getRelation,
+    setRelation,
+    setRelations,
+  )
+where
+
+import Control.Monad
+import Data.Bits ((.&.), (.|.), complement)
+import Data.ByteString (ByteString)
+import qualified Data.ByteString as B
+import Data.ByteString.Internal (toForeignPtr, unsafeCreate)
+import Data.Int (Int64)
+import Data.Word (Word8)
+import Foreign.ForeignPtr (withForeignPtr)
+import Foreign.Marshal.Utils (copyBytes, fillBytes)
+import Foreign.Ptr (plusPtr)
+import Foreign.Storable (peekByteOff, pokeByteOff)
+
+data MemberRelation
+  = MRNew
+  | MRIntroduced
+  | MRConnected
+  deriving (Eq, Show)
+
+toRelationInt :: MemberRelation -> Word8
+toRelationInt = \case
+  MRNew -> 0
+  MRIntroduced -> 1
+  MRConnected -> 2
+
+fromRelationInt :: Word8 -> MemberRelation
+fromRelationInt = \case
+  0 -> MRNew
+  1 -> MRIntroduced
+  2 -> MRConnected
+  _ -> MRNew
+
+-- | Get the relation status of a member at a given index from the relations vector.
+-- Returns 'MRNew' if the vector is not long enough (lazy initialization).
+getRelation :: Int64 -> ByteString -> MemberRelation
+getRelation i v
+  | i < 0 || fromIntegral i >= B.length v = MRNew
+  | otherwise = fromRelationInt $ (v `B.index` fromIntegral i) .&. relationMask
+
+
+-- | Set the relation status of a member at a given index in the relations vector.
+-- Expands the vector lazily if needed (padding with zeros for 'MRNew' relation).
+setRelation :: Int64 -> MemberRelation -> ByteString -> ByteString
+setRelation i r v
+  | i >= 0 = setRelations [(i, r)] v
+  | otherwise = v
+
+-- | Set multiple relations at once.
+-- Expands the vector lazily if needed (padding with zeros for 'MRNew' relation).
+setRelations :: [(Int64, MemberRelation)] -> ByteString -> ByteString
+setRelations [] v = v
+setRelations relations v =
+  let (fp, off, len) = toForeignPtr v
+      newLen = max len $ fromIntegral $ maximum (map fst relations) + 1
+   in unsafeCreate newLen $ \ptr -> do
+        withForeignPtr fp $ \vPtr -> copyBytes ptr (vPtr `plusPtr` off) len
+        when (newLen > len) $ fillBytes (ptr `plusPtr` len) 0 (newLen - len)
+        forM_ relations $ \(ix, r) -> when (ix >= 0) $ do
+          let i = fromIntegral ix
+          b <- peekByteOff ptr i
+          let b' = (b .&. complement relationMask) .|. toRelationInt r
+          pokeByteOff ptr i b'
+
+relationMask :: Word8
+relationMask = 0x07 -- reserving 3 bits