flatten.exs

# Declarative File Parser written in Elixir
require Poison.Parser

defmodule Flatten do

  def transpose([[]|_]), do: []

  def transpose(a) do
    [Enum.map(a, &hd/1) | transpose(Enum.map(a, &tl/1))]
  end


  def parse_file(data) do
    lines = Enum.map(data["m_LStudentData"], &student_map(&1))

    [first_student | _] = data["m_LStudentData"] |> Enum.to_list

    table = [headers(first_student) | lines]


    #IO.puts "sep=," # Excel
    table
    |> transpose
    |> Enum.map(&Enum.join(&1, ";"))
  end

  def headers(student) do
    ["Student name"] ++ student_hmap(student) |> List.flatten
  end

  def student_map(student) do
    chapters = Enum.map(student["m_LChapReport"], &chapter_map(&1))
    [student["m_StudentProfileName"] | List.flatten(chapters)]
  end

  def chapter_map(chapter) do
    chapter["m_ChapterName"]
    actions = Enum.map(chapter["m_LReportAct"], &action_map(&1))
    actions
  end

  def action_map(action) do
    [
      action["m_PctProgression"],
      action["m_TimeSpent"],
      action["m_ErrorPerStep"] |> Enum.join(":")
    ]
  end

  def student_hmap(student) do
    student["m_LChapReport"]
    |> Enum.map(&chapter_hmap/1)
  end

  def chapter_hmap(chapter) do
    Enum.map(chapter["m_LReportAct"], &action_hmap(chapter["m_ChapterName"], &1))
  end

  def action_hmap(chapter_name, action) do

    action_name = action["m_Name"]
    action_config = action["m_Config"]
    ~w(Progression TimeSpent ErrorsPerStep)
    |> Enum.map(fn type -> Enum.join([chapter_name, action_name, action_config, type], "::") end)

  end


  def process([id, create_date, data]) do
    case Poison.Parser.parse(data) do
      {:ok, data} ->
        teacher = data["m_TeacherProfileName"]
        IO.puts "#{id}:#{create_date}:#{teacher}"
        try do
          data = Flatten.parse_file(data)
          |> Enum.join("\n")

          File.write!("#{id}.csv", data)
        rescue
          e -> IO.puts "Cannot be parsed"
        end

      {:error, _} ->
        IO.puts "Cannot be parsed"
    end
  end
end

{:ok, pid} = Postgrex.start_link(database: "DATABASE", username: "USERNAME", password: "PASSWORD", hostname: "HOST", sync_connect: true, port: 5452, ssl: true)
{:ok, result} = Postgrex.query(pid, "SELECT * FROM edu_report", [])


Enum.each(result.rows, &Flatten.process/1)