Joins.elm

module Joins exposing (..)

import Dict exposing (..)


join : List a -> List b -> (a -> b -> Bool) -> List (a, List b)
join left right joinTest =
  left
  |> List.map (\leftItem ->
    right
    |> List.filter (joinTest leftItem)
    |> (\rightItems -> (leftItem, rightItems))
  )

--splitApplyCombine : (item -> key) -> (List item -> combined) -> List item -> List combined
--splitApplyCombine getKey combine items =
--  items
--  |> List.map (\item -> (getKey item, item))
--  |> List.foldl (\(key, item) soFar -> multimapPut key item) Dict.empty


multimapPut : comparable -> v -> Dict comparable (List v) -> Dict comparable (List v)
multimapPut key value dict =
  Dict.update
    key
    (\maybeEntry ->
      case maybeEntry of
        Just entry ->
          Just (value :: entry)

        Nothing ->
          Just [value]
    )
    dict


-- testing

blogPosts =
  [ { id = 1, title = "title 1", body = "body 1" }
  , { id = 2, title = "title 2", body = "body 2" }
  ]


comments =
  [ { id = 1, postId = 1, timeStamp = 1, body = "yo" }
  , { id = 2, postId = 1, timeStamp = 2, body = "yo yourself" }
  , { id = 3, postId = 2, timeStamp = 1, body = "whazzup" }
  ]


joined =
  join
    blogPosts
    comments
    (\post comment -> comment.postId == post.id)


{-
[ ( { id = 1, title = "title 1", body = "body 1" }
  , [ { id = 1, postId = 1, timeStamp = 1, body = "yo" }
    , { id = 2, postId = 1, timeStamp = 2, body = "yo yourself" }
    ]
  ),
  ( { id = 2, title = "title 2", body = "body 2" }
  , [ { id = 3, postId = 2, timeStamp = 1, body = "whazzup" } ]
  )
]
    : List
        ( { body : String, id : number, title : String }
        , List
            { body : String, id : number, postId : number, timeStamp : number'
            }
        )
-}