defmodule Indexer do
  @moduledoc """
  Indexes an Ethereum-based chain using JSONRPC.
  """
  require Logger

  alias Explorer.Chain

  @doc """
  The maximum `t:Explorer.Chain.Block.t/0` `number` that was indexed

  If blocks are skipped and inserted out of number order, the max number is still returned

      iex> insert(:block, number: 2)
      iex> insert(:block, number: 1)
      iex> Indexer.max_block_number()
      2

  If there are no blocks, `0` is returned to indicate to index from genesis block.

      iex> Indexer.max_block_number()
      0

  """
  def max_block_number do
    case Chain.max_block_number() do
      {:ok, number} -> number
      {:error, :not_found} -> 0
    end
  end

  @doc """
  The next `t:Explorer.Chain.Block.t/0` `number` that needs to be indexed (excluding skipped blocks)

  When there are no blocks the next block is the 0th block

      iex> Indexer.max_block_number()
      0
      iex> Indexer.next_block_number()
      0

  When there is a block, it is the successive block number

      iex> insert(:block, number: 2)
      iex> insert(:block, number: 1)
      iex> Indexer.next_block_number()
      3

  """
  def next_block_number do
    case max_block_number() do
      0 -> 0
      num -> num + 1
    end
  end

  @doc """
  Logs debug message if `:debug_logs` have been enabled.
  """
  def debug(message_func) when is_function(message_func, 0) do
    if debug_logs_enabled?() do
      Logger.debug(message_func)
    else
      :noop
    end
  end

  @doc """
  Enables debug logs for indexing system.
  """
  def enable_debug_logs do
    Application.put_env(:indexer, :debug_logs, true)
  end

  @doc """
  Disables debug logs for indexing system.
  """
  def disable_debug_logs do
    Application.put_env(:indexer, :debug_logs, false)
  end

  @doc """
  Starts a child task of `Indexer.TaskSupervisor` and monitors it, instead of linking to it.
  """
  @spec start_monitor((() -> term())) :: {:ok, pid, reference}
  def start_monitor(task_function) when is_function(task_function, 0) do
    {:ok, pid} = Task.Supervisor.start_child(Indexer.TaskSupervisor, task_function)
    ref = Process.monitor(pid)
    {:ok, pid, ref}
  end

  defp debug_logs_enabled? do
    Application.fetch_env!(:indexer, :debug_logs)
  end
end