live_view.ex

defmodule AppWeb.PageLive do
  use AppWeb, :live_view
  alias App.Posts
  alias App.Posts.Post
  alias App.Votes

  @impl true
  def mount(_params, session, socket) do
    socket = maybe_assign_user(session, socket)

    days = 5
    votes = get_votes(socket)

    if connected?(socket) do
      AppWeb.Endpoint.subscribe("post")
    end

    {:ok,
     assign(socket, %{
       days: get_days(days),
       votes: votes
     })}
  end

  @impl true
  def handle_info(
        %{topic: "post", event: "upvoted", payload: %{post_id: post_id, day: day, month: month}},
        socket
      ) do
    post = find_post_in_socket(post_id, day, month, socket)
    post = %Post{post | upvotes: post.upvotes + 1}

    {:noreply,
     assign(socket, %{
       days: upvote_post_in_days(post, day, month, socket.assigns.days)
     })}
  end

  @impl true
  def handle_event("upvote", %{"id" => post_id, "day" => day, "month" => month}, socket) do
    socket =
      if(socket.assigns[:current_user]) do
        day = String.to_integer(day)
        month = String.to_integer(month)
        post_id = String.to_integer(post_id)
        post = find_post_in_socket(post_id, day, month, socket)

        {:ok, post} =
          Posts.update_post(post, %{
            upvotes: post.upvotes + 1
          })

        {:ok, vote} =
          Votes.create_vote(%{
            user_id: socket.assigns.current_user.id,
            post_id: post_id
          })

        AppWeb.Endpoint.broadcast("post", "upvoted", %{
          day: day,
          month: month,
          post_id: post.id
        })

        assign(socket, %{
          votes: socket.assigns.votes ++ [vote]
        })
      else
        socket
      end

    {:noreply, socket}
  end

  defp get_votes(socket) do
    if socket.assigns[:current_user] do
      App.Repo.preload(socket.assigns.current_user, :votes).votes
    else
      []
    end
  end

  defp get_days(count) do
    now = Timex.beginning_of_day(Timex.now())

    Enum.map(0..(count - 1), fn i ->
      date = Timex.shift(now, days: -i)

      %{
        date: date,
        day: date.day,
        month: date.month,
        posts: Posts.most_popular_for_date(date)
      }
    end)
  end

  defp find_post_in_socket(post_id, day, month, socket) do
    get_in(socket.assigns.days, [
      Access.filter(&(&1.day == day && &1.month == month)),
      :posts,
      Access.filter(&(&1.id == post_id))
    ])
    |> List.flatten()
    |> List.first()
  end

  defp upvote_post_in_days(post, day, month, days) do
    put_in(
      days,
      [
        Access.filter(&(&1.day == day && &1.month == month)),
        :posts,
        Access.filter(&(&1.id == post.id)),
        Access.key!(:upvotes)
      ],
      post.upvotes
    )
  end
end