Add Timestamp data type

elm.json

@@ -8,12 +8,14 @@
         "Matrix",
         "Internal.Tools.Hashdict",
         "Internal.Tools.Iddict",
+        "Internal.Tools.Timestamp",
         "Internal.Tools.VersionControl"
     ],
     "elm-version": "0.19.0 <= v < 0.20.0",
     "dependencies": {
         "elm/core": "1.0.0 <= v < 2.0.0",
         "elm/json": "1.0.0 <= v < 2.0.0",
+        "elm/time": "1.0.0 <= v < 2.0.0",
         "miniBill/elm-fast-dict": "1.0.0 <= v < 2.0.0"
     },
     "test-dependencies": {}

src/Internal/Tools/Timestamp.elm

@@ -0,0 +1,43 @@
+module Internal.Tools.Timestamp exposing
+    ( Timestamp
+    , encode, decoder
+    )
+
+{-| The Timestamp module is a simplification of the Timetsamp as delivered by
+elm/time. This module offers ways to work with the timestamp in meaningful ways.
+
+
+## Timetstamp
+
+@docs Timestamp
+
+
+## JSON coders
+
+@docs encode, decoder
+
+-}
+
+import Json.Decode as D
+import Json.Encode as E
+import Time
+
+
+{-| The Timetstamp data type representing a moment in time.
+-}
+type alias Timestamp =
+    Time.Posix
+
+
+{-| Encode a timestamp into a JSON value.
+-}
+encode : Timestamp -> E.Value
+encode =
+    Time.posixToMillis >> E.int
+
+
+{-| Decode a timestamp from a JSON value.
+-}
+decoder : D.Decoder Timestamp
+decoder =
+    D.map Time.millisToPosix D.int