Using incomes to compute a fair computation to designate the payer

1 files changed, 76 insertions, 0 deletions

diff --git a/src/client/Model/Income.elm b/src/client/Model/Income.elm
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+++ b/src/client/Model/Income.elm
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+module Model.Income
+  ( Income
+  , incomeDecoder
+  , incomeDefinedForAll
+  , cumulativeIncomesSince
+  ) where
+
+import Json.Decode as Json exposing ((:=))
+import Time exposing (Time, hour)
+import List exposing (..)
+
+import Model.Date exposing (timeDecoder)
+import Model.User exposing (UserId)
+
+import Utils.Maybe exposing (isJust, catMaybes, maybeToList)
+
+type alias Income =
+  { creation : Time
+  , amount : Int
+  }
+
+incomeDecoder : Json.Decoder Income
+incomeDecoder =
+  Json.object2 Income
+    ("creation" := timeDecoder)
+    ("amount" := Json.int)
+
+incomeDefinedForAll : List (UserId, List Income) -> Maybe Time
+incomeDefinedForAll usersIncomes =
+  let firstIncomes = map (head << sortBy .creation << snd) usersIncomes
+  in  if all isJust firstIncomes
+        then head << reverse << List.sort << map .creation << catMaybes <| firstIncomes
+        else Nothing
+
+cumulativeIncomesSince : Time -> Time -> (List Income) -> Int
+cumulativeIncomesSince currentTime since incomes =
+  cumulativeIncome currentTime (getOrderedIncomesSince since incomes)
+
+getOrderedIncomesSince : Time -> List Income -> List Income
+getOrderedIncomesSince time incomes =
+  let mbStarterIncome = getIncomesAt time incomes
+      orderedIncomesSince = filter (\income -> income.creation >= time) incomes
+  in  (maybeToList mbStarterIncome) ++ orderedIncomesSince
+
+getIncomesAt : Time -> List Income -> Maybe Income
+getIncomesAt time incomes =
+  case incomes of
+    [x] ->
+      if x.creation < time
+        then Just { creation = time, amount = x.amount }
+        else Nothing
+    x1 :: x2 :: xs ->
+      if x1.creation < time && x2.creation > time
+        then Just { creation = time, amount = x2.amount }
+        else getIncomesAt time (x2 :: xs)
+    [] ->
+      Nothing
+
+cumulativeIncome : Time -> List Income -> Int
+cumulativeIncome currentTime incomes =
+  getIncomesWithDuration (incomes ++ [{ creation = currentTime, amount = 0 }])
+    |> map durationIncome
+    |> sum
+
+getIncomesWithDuration : List Income -> List (Float, Int)
+getIncomesWithDuration incomes =
+  case incomes of
+    (income1 :: income2 :: xs) ->
+      (income2.creation - income1.creation, income1.amount) :: (getIncomesWithDuration (income2 :: xs))
+    _ ->
+      []
+
+durationIncome : (Float, Int) -> Int
+durationIncome (duration, income) =
+  duration * toFloat income / (hour * 24 * 365 / 12)
+    |> truncate