add an ID field to Player

elm.json

@@ -14,6 +14,7 @@
             "elm/json": "1.1.3",
             "elm/random": "1.0.0",
             "ohanhi/keyboard": "2.0.1",
+            "robinheghan/murmur3": "1.0.0",
             "rtfeldman/elm-css": "16.1.0",
             "tesk9/accessible-html-with-css": "2.1.1"
         },

src/Player.elm

@@ -3,18 +3,21 @@ module Player exposing (Player, decoder, encode, incrementMatchesPlayed, init, s
 import Elo
 import Json.Decode as Decode exposing (Decoder)
 import Json.Encode as Encode exposing (Value)
+import Murmur3
 
 
 type alias Player =
-    { name : String
+    { id : Int
+    , name : String
     , rating : Int
     , matches : Int
     }
 
 
 init : String -> Player
 init name =
-    { name = name
+    { id = Murmur3.hashString 0 name
+    , name = name
     , rating = Elo.initialRating
     , matches = 0
     }
@@ -32,16 +35,23 @@ incrementMatchesPlayed player =
 
 decoder : Decoder Player
 decoder =
-    Decode.map3 Player
+    Decode.map4 Player
+        (Decode.oneOf
+            [ Decode.field "id" Decode.int
+            , Decode.field "name" Decode.string
+                |> Decode.map (Murmur3.hashString 0)
+            ]
+        )
         (Decode.field "name" Decode.string)
         (Decode.field "rating" Decode.int)
         (Decode.field "matches" Decode.int)
 
 
 encode : Player -> Value
-encode { name, rating, matches } =
+encode { id, name, rating, matches } =
     Encode.object
-        [ ( "name", Encode.string name )
+        [ ( "id", Encode.int id )
+        , ( "name", Encode.string name )
         , ( "rating", Encode.int rating )
         , ( "matches", Encode.int matches )
         ]

tests/PlayerTest.elm

@@ -3,6 +3,8 @@ module PlayerTest exposing (..)
 import Expect
 import Fuzz exposing (Fuzzer)
 import Json.Decode as Decode
+import Json.Encode as Encode
+import Murmur3
 import Player exposing (Player)
 import Test exposing (..)
 
@@ -18,7 +20,8 @@ roundTripDecoderTest =
 
 playerFuzzer : Fuzzer Player
 playerFuzzer =
-    Fuzz.map3 Player
+    Fuzz.map4 Player
+        (Fuzz.map (Murmur3.hashString 0) nameFuzzer)
         nameFuzzer
         (Fuzz.intRange 1000 3000)
         (Fuzz.intRange 0 50)
@@ -33,3 +36,21 @@ nameFuzzer =
     in
     Fuzz.map2 (::) chars (Fuzz.list chars)
         |> Fuzz.map String.fromList
+
+
+decoderTest : Test
+decoderTest =
+    describe "decoder"
+        [ describe "id"
+            [ test "fills in the ID if it's missing" <|
+                \_ ->
+                    Encode.object
+                        [ ( "name", Encode.string "Test" )
+                        , ( "rating", Encode.int 1200 )
+                        , ( "matches", Encode.int 0 )
+                        ]
+                        |> Decode.decodeValue Player.decoder
+                        |> Result.map .id
+                        |> Expect.equal (Ok 123038886)
+            ]
+        ]