add Blob.slice

Author: safareli

src/DOM/File/Blob.js

@@ -3,3 +3,13 @@
 exports.typeImpl = function (blob) { return blob.type; };
 
 exports.size = function (blob) { return blob.size; };
+
+exports._slice = function (blob) {
+  return function (start) {
+    return function (end) {
+      return function (contentType) {
+        return blob.slice(start, end, contentType);
+      }
+    }
+  }
+}

src/DOM/File/Blob.purs

@@ -1,12 +1,23 @@
 module DOM.File.Blob
   ( type_
   , size
+  , StartByte(..)
+  , EndByte(..)
+  , idxFromInt
+  , idxFromNumber
+  , ByteIdx
+  , slice
+  , slice'
   ) where
 
-import Prelude ((==))
+import DOM.File.Types (Blob)
+import Data.Int (toNumber)
 import Data.Maybe (Maybe(..))
 import Data.MediaType (MediaType(..))
-import DOM.File.Types (Blob)
+import Data.Newtype (unwrap)
+import Math (round)
+import Prelude ((==), (>>>))
+import Unsafe.Coerce (unsafeCoerce)
 
 foreign import typeImpl :: Blob -> String
 
@@ -23,3 +34,40 @@ type_ blob =
 
 -- | The size (in bytes) of the data contained in the `Blob`.
 foreign import size :: Blob -> Number
+
+-- | An index into the Blob indicating the first byte to include in the new Blob.
+-- | If you specify a negative value, it's treated as an offset from the end of the
+-- | string toward the beginning. For example, -10 would be the 10th from last byte
+-- | in the Blob. If you specify a value for start that is larger than the size
+-- | of the source Blob, the returned Blob has size 0 and contains no data.
+newtype StartByte = StartByte ByteIdx
+
+-- | An index into the Blob indicating the first byte that will *not* be included
+-- | in the new Blob (i.e. the byte exactly at this index is not included).
+-- | If you specify a negative value, it's treated as an offset from the end of
+-- | the string toward the beginning. For example, -10 would be the 10th from
+-- | last byte in the Blob. The default value is size.
+newtype EndByte = EndByte ByteIdx
+
+foreign import data ByteIdx :: Type
+
+-- | Creates `ByteIdx` from `Int` value
+idxFromInt :: Int -> ByteIdx
+idxFromInt = toNumber >>> unsafeCoerce
+
+-- | Creates `ByteIdx` from `Number` value using `Math.round`.
+idxFromNumber :: Number -> ByteIdx
+idxFromNumber = round >>> unsafeCoerce
+
+-- | Creates a new `Blob` object (with specified `MediaType`), containing the
+-- | data in the specified range of bytes of the source Blob, by setting .
+slice ∷ MediaType -> StartByte -> EndByte -> Blob -> Blob
+slice mediaType (StartByte start) (EndByte end) blob =
+  _slice blob start end (unwrap mediaType)
+
+-- | Creates a new `Blob` object containing the data in the specified range
+-- | of bytes of the source Blob.
+slice' ∷ StartByte -> EndByte -> Blob -> Blob
+slice' (StartByte start) (EndByte end) blob = _slice blob start end ""
+
+foreign import _slice ∷ Blob -> ByteIdx -> ByteIdx -> String -> Blob