Showing exceeding payers

1 files changed, 57 insertions, 0 deletions

diff --git a/src/client/Model/Payers.elm b/src/client/Model/Payers.elm
new file mode 100644
index 0000000..6550eaa
--- /dev/null
+++ b/src/client/Model/Payers.elm
@@ -0,0 +1,57 @@
+module Model.Payers
+  ( Payers
+  , ExceedingPayer
+  , payersDecoder
+  , updatePayers
+  , getOrderedExceedingPayers
+  ) where
+
+import Json.Decode as Json exposing (..)
+import Dict exposing (..)
+import List
+import Maybe
+
+type alias Payers = Dict String Int
+
+payersDecoder : Decoder Payers
+payersDecoder = Json.map Dict.fromList (list payerDecoder)
+
+payerDecoder : Decoder (String, Int)
+payerDecoder =
+  object2 (,)
+    ("userName" := string)
+    ("totalPayment" := int)
+
+updatePayers : Payers -> String -> Int -> Payers
+updatePayers payers userName amountDiff =
+  Dict.update
+    userName
+    (\mbAmount ->
+      case mbAmount of
+        Just amount -> Just (amount + amountDiff)
+        Nothing -> Nothing
+    )
+    payers
+
+type alias ExceedingPayer =
+  { userName : String
+  , amount : Int
+  }
+
+getOrderedExceedingPayers : Payers -> List ExceedingPayer
+getOrderedExceedingPayers payers =
+  let orderedPayers =
+        Dict.toList payers
+          |> List.map (\(userName, amount) -> ExceedingPayer userName amount)
+          |> List.sortBy .amount
+      maybeMinAmount =
+        List.head orderedPayers
+          |> Maybe.map .amount
+  in  case maybeMinAmount of
+        Just minAmount ->
+          orderedPayers
+            |> List.map (\payer -> { payer | amount <- payer.amount - minAmount })
+            |> List.filter (\payer -> payer.amount /= 0)
+            |> List.reverse
+        Nothing ->
+          []