google_sheets

defmodule GoogleSheets.Loader.FileSystem do

  @moduledoc """
  Implements GoogleSheets.Loader behaviour for reading given spreadsheets in csv format
  from a directory.
  """

  @behaviour GoogleSheets.Loader

  @doc """
  Reads CSV files from config[:dir] directory.
  """
  def load(previous_version, config) when is_list(config) do
    try do
      dir = Keyword.fetch! config, :dir
      sheets = Keyword.get config, :sheets, []
      load_spreadsheet previous_version, dir, sheets
    catch
      result -> result
    end
  end

  defp load_spreadsheet(previous_version, dir, sheets) do
    path = Path.expand dir
    if not File.exists? path do
      throw {:error, "Can't load CSV files from non existing directory #{inspect path}"}
    end

    files = Path.wildcard(path <> "/*.csv")
    worksheets = load_files files, sheets, []

    if not Enum.all?(sheets, fn sheetname -> Enum.any?(worksheets, fn ws -> ws.name == sheetname end) end) do
      loaded = worksheets |> Enum.map(fn ws -> ws.name end) |> Enum.join(",")
      throw {:error, "All requested worksheets were not found, expected to load #{inspect sheets} loaded: #{inspect loaded}"}
    end

    version = calculate_version worksheets
    if version == previous_version do
      throw {:ok, :unchanged}
    end

    {:ok, version, worksheets}
  end

  # Load csv files and filter if only specific sheets should be loaded
  defp load_files([], _sheets, worksheets), do: worksheets
  defp load_files([filename | rest], sheets, worksheets) do
    sheetname = Path.basename filename, ".csv"
    if sheets == [] or sheetname in sheets do
      csv = File.read! filename
      worksheets = [%GoogleSheets.WorkSheet{name: sheetname, csv: csv} | worksheets]
    end
    load_files rest, sheets, worksheets
  end

  # Calculate version based on CSV data
  defp calculate_version(worksheets) when is_list(worksheets) do
    concatenated = worksheets |> Enum.sort(fn a,b -> a.name <= b.name end) |> Enum.reduce("", fn ws, acc -> ws.csv <> acc end)
    :crypto.hash(:sha, concatenated) |> GoogleSheets.Utils.hexstring
  end

end