elstat/lib/manager.ex

defmodule Elstat.Error.Service do
  defexception message: "default message"
end

defmodule Elstat.ServiceWorker do
  require Logger

  def start_link(service) do
    Logger.info "spawning worker for #{inspect service.id}"

    worker_pid = spawn(fn ->
      worker_func(service)
    end)
    
    {:ok, worker_pid}
  end

  def worker_func(service) do
    adapter = service.adapter
 
    result = adapter.check(service.adapter_opts)
    Logger.info "result from #{inspect adapter} #{inspect service.id}: #{inspect result}"

    man_pid = :global.whereis_name Elstat.Manager
    send man_pid, {:service_info, {service.id, result}}
    
    Process.sleep(service.poll * 1000)
    worker_func(service)
  end
end

defmodule Elstat.Manager do
  @moduledoc """
  Elstat's service manager.
  """
  use GenServer
  require Logger

  def start_link(opts) do
    GenServer.start_link(__MODULE__, :ok, [name: {:global, Elstat.Manager}] ++ opts)
  end

  def build_services() do
    services = Application.fetch_env!(:elstat, :services)

    workers = services
    |> Map.keys
    |> Enum.map(fn service_id ->
      service = Map.put(services[service_id], :id, service_id)

      # each service worker will enter an infinite loop
      # polling the service (via an adapter) and giving
      # information back to the manager, so it can
      # process and show those via its API.
      %{
        id: service_id,
        start: {Elstat.ServiceWorker, :start_link, [service]}
      }
    end)

    # spawn the managere alongside service workers
    [ Elstat.Manager | workers]
  end

  def get_current_state() do
    man_pid = :global.whereis_name Elstat.Manager
    GenServer.call(man_pid, {:get_current})
  end


  # server callbacks

  def get_columns_def do
    %{
      timestamp: "timestamp bigint",
      status: "status bool",
      latency: "latency bigint",
    }
  end

  def get_columns_name do
    %{
      timestamp: "timestamp",
      status: "status",
      latency: "latency",
    }
  end
  
  def init(:ok) do
    services = Application.fetch_env!(:elstat, :services)

    Sqlitex.with_db('elstat.db', fn(db) ->
      services
      |> Map.keys
      |> Enum.each(fn service_id ->
        service = services[service_id]
        adapter = service.adapter

        spec = adapter.adapter_spec

        columns = get_columns_def()

        column_res = spec.db_columns
        |> Enum.map(fn column ->
          columns[column]
        end)
        |> Enum.join(",\n")

        query = """
        CREATE TABLE IF NOT EXISTS #{Atom.to_string service_id} (
        #{column_res}
        );
        """

        Logger.debug "query for #{inspect service_id}: #{query}"

        case Sqlitex.query(db, query) do
          {:ok, _} ->
            Logger.info "created table for #{inspect service_id}"
          {:error, _err} ->
            Logger.error "error making table for #{inspect service_id}"
        end
      end)
    end)
    
    {:ok, %{
        services: services,
        serv_state: %{},
     }}
  end

  def handle_call({:get_current}, _from, state) do
    reply = state.serv_state
    |> Map.keys
    |> Enum.map(fn key ->
      data = state.serv_state[key]
      desc = state.services[key].description

      case data do
        {:map, data_map} ->
          {key, Map.put(data_map, :description, desc)}
        {:bool, data_bool} ->
          {key, %{
              status: data_bool,
              description: desc,
           }}
      end
    end)
    |> Map.new

    {:reply, reply, state}
  end

  def build_insert_query(service_id, state) do
    services = state.services
    service = services[service_id]
    spec = service.adapter.adapter_spec

    columns_str = spec.db_columns
    |> Enum.map(fn atom ->
      Atom.to_string atom
    end)
    |> Enum.join(",")
    
    query_args_str = 1..Enum.count(spec.db_columns)
    |> Enum.map(fn num ->
      "$#{num}"
    end)
    |> Enum.join(",")

    """
    INSERT INTO #{Atom.to_string service_id} (#{columns_str})
    VALUES (#{query_args_str})
    """
  end
  
  def handle_info({:service_info, {sid, sdata}}, state) do
    case sdata do
      {:ok, actual_data} -> 
        new_serv_state = Map.put(state.serv_state, sid, actual_data)

        query = build_insert_query(sid, state)

        adapter = state.services[sid].adapter
        adp_args = adapter.transform_val(actual_data)

        timestamp = :erlang.system_time(:millisecond)

        Logger.debug "query: #{query}, timestamp: #{timestamp}, adp args: #{inspect adp_args}"
        
        Sqlitex.with_db('elstat.db', fn(db) ->
          res = Sqlitex.query(db, query, bind: [timestamp | adp_args])
          IO.puts "#{inspect res}"
        end)
        
        {:noreply, %{state | serv_state: new_serv_state}}
      {:error, err} ->
        Logger.warn "error on #{inspect sid}: #{inspect err}"
    end

  end
  
end