Calendar.hs

module Grocery.Calendar where

import Data.Time
import Grocery.Types.Meal
import Control.Lens
import Data.Ord
import Data.List (sortBy)


type Calendar = [(Day, [Meal])]

createMealCalendar :: [Meal] -> Calendar
createMealCalendar [] = []
createMealCalendar meals = createMealCalendar' [] [firstDay..lastDay] sortedMeals
  where
  firstDay = (head meals) ^. day
  lastDay  = (last meals) ^. day
  sortedMeals = sortBy (comparing (^. day)) meals

  -- first case, empty calendar, create the first day & meal
  createMealCalendar' []  dds@(d:ds) (m:ms) = createMealCalendar' [(d, [m])] dds ms

  -- base case, when we run out of meals to add, we're done
  createMealCalendar' cal _ [] = cal

  -- base case, when we run out of days, something odd happened
  createMealCalendar' _ [] _ = error "Ran out of days!?"

  -- recursive case. init & last are safe due to previous check.
  createMealCalendar' cal dds@(d:ds) mms@(m:ms) = -- if this meal belongs on this day, add it and recurse
                                          if m ^. day == d
                                          then let previousCal      = init cal
                                                   previousMealList = (snd . last) cal
                                                   updatedDay       = (d, previousMealList ++ [m])
                                                   newCal           = previousCal ++ [updatedDay]
                                               in  createMealCalendar' newCal dds ms

                                          -- Advance one day when the meal doesn't belong
                                          else let newCal = (cal ++ [(d, [])])
                                               in  createMealCalendar' newCal ds mms