module Model.Payer
  ( Payers
  , Payer
  , ExceedingPayer
  , getOrderedExceedingPayers
  ) where

import Json.Decode as Json exposing (..)
import Dict exposing (..)
import List
import Maybe
import Time exposing (Time)
import Date

import Model.Payment exposing (Payments, totalPayments)
import Model.User exposing (Users, UserId, userIdDecoder)
import Model.Income exposing (..)

import Utils.Dict exposing (mapValues)
import Utils.Maybe exposing (isJust)

type alias Payers = Dict UserId Payer

type alias Payer =
  { preIncomePaymentSum : Int
  , postIncomePaymentSum : Int
  , incomes : List Income
  }

type alias ExceedingPayer =
  { userId : UserId
  , amount : Int
  }

getOrderedExceedingPayers : Time -> Users -> Incomes -> Payments -> List ExceedingPayer
getOrderedExceedingPayers currentTime users incomes payments =
  let payers = getPayers currentTime users incomes payments
      exceedingPayersOnPreIncome =
        payers
          |> mapValues .preIncomePaymentSum
          |> Dict.toList
          |> exceedingPayersFromAmounts
  in  case incomeDefinedForAll (Dict.keys users) incomes of
        Just since ->
          let postPaymentPayers = mapValues (getPostPaymentPayer currentTime since) payers
              mbMaxRatio =
                postPaymentPayers
                  |> Dict.toList
                  |> List.map (.ratio << snd)
                  |> List.maximum
          in  case mbMaxRatio of
                Just maxRatio ->
                  postPaymentPayers
                    |> mapValues (getFinalDiff maxRatio)
                    |> Dict.toList
                    |> exceedingPayersFromAmounts
                Nothing ->
                  exceedingPayersOnPreIncome
        Nothing ->
          exceedingPayersOnPreIncome

getPayers : Time -> Users -> Incomes -> Payments -> Payers
getPayers currentTime users incomes payments =
  let incomesDefined = incomeDefinedForAll (Dict.keys users) incomes
  in  Dict.keys users
        |> List.map (\userId ->
             ( userId
             , { preIncomePaymentSum =
                   totalPayments
                     (\p -> (Date.toTime p.creation) < (Maybe.withDefault currentTime incomesDefined))
                     userId
                     payments
               , postIncomePaymentSum =
                   totalPayments
                     (\p ->
                       case incomesDefined of
                         Nothing -> False
                         Just t -> (Date.toTime p.creation) >= t
                     )
                     userId
                     payments
               , incomes = List.filter ((==) userId << .userId) (Dict.values incomes)
               }
             )
           )
        |> Dict.fromList

exceedingPayersFromAmounts : List (UserId, Int) -> List ExceedingPayer
exceedingPayersFromAmounts userAmounts =
  let mbMinAmount = List.minimum << List.map snd <| userAmounts
  in  case mbMinAmount of
        Nothing ->
          []
        Just minAmount ->
          userAmounts
            |> List.map (\userAmount ->
                 { userId = fst userAmount
                 , amount = snd userAmount - minAmount
                 }
               )
            |> List.filter (\payer -> payer.amount > 0)

type alias PostPaymentPayer =
  { preIncomePaymentSum : Int
  , cumulativeIncome : Int
  , ratio : Float
  }

getPostPaymentPayer : Time -> Time -> Payer -> PostPaymentPayer
getPostPaymentPayer currentTime since payer =
  let cumulativeIncome = cumulativeIncomesSince currentTime since payer.incomes
  in  { preIncomePaymentSum = payer.preIncomePaymentSum
      , cumulativeIncome = cumulativeIncome
      , ratio = toFloat payer.postIncomePaymentSum / toFloat cumulativeIncome
      }

getFinalDiff : Float -> PostPaymentPayer -> Int
getFinalDiff maxRatio payer =
  let postIncomeDiff =
        -1 * (maxRatio - payer.ratio) * toFloat payer.cumulativeIncome
          |> truncate
  in  postIncomeDiff + payer.preIncomePaymentSum