defmodule Logrex do
  @moduledoc """
  An Elixir package for more easily adding Logger metadata and formatting the
  console output so it's easier for humans to parse.

  It integrates with the Elixir Logger to let you write code like this:

  ```
  name = "Matt"
  user_info = %{login_count: 1}
  Logrex.info "New login", [name, user_info.login_count, foo: "bar"]
  ```

  To display this:

  ```
  INFO 20:56:40 New login                    user=Matt login_count=1 foo=bar
  ```
  """

  defmacro __using__(_opts) do
    quote do
      require Logger
      require Logrex
    end
  end

  defmacro debug(chardata_or_fun, metadata \\ []) do
    quote do
      Logger.debug(unquote(chardata_or_fun), unquote(build_metadata(metadata)))
    end
  end

  defmacro error(chardata_or_fun, metadata \\ []) do
    quote do
      Logger.error(unquote(chardata_or_fun), unquote(build_metadata(metadata)))
    end
  end

  defmacro info(chardata_or_fun, metadata \\ []) do
    quote do
      Logger.info(unquote(chardata_or_fun), unquote(build_metadata(metadata)))
    end
  end

  defmacro warn(chardata_or_fun, metadata \\ []) do
    quote do
      Logger.warn(unquote(chardata_or_fun), unquote(build_metadata(metadata)))
    end
  end

  defp build_metadata(metadata) do
    metadata
    |> List.wrap()
    |> Enum.map(fn
      {var, _, _} when is_atom(var) ->
        quote do: {unquote(var), var!(unquote(Macro.var(var, nil)))}

      {_, _} = var ->
        var

      ast ->
        build_path(ast)
    end)
  end

  defp build_path(ast) do
    {_, vars} =
      Macro.prewalk(ast, [], fn
        {var, _, x} = node, acc when x in [nil] ->
          {node, [var | acc]}

        node, acc when node in [:get, Access] ->
          {node, acc}

        node, acc when is_atom(node) or is_binary(node) ->
          {node, [node | acc]}

        node, acc ->
          {node, acc}
      end)

    [meta_key | _tail] = vars
    [var | key_path] = Enum.reverse(vars)

    meta_key =
      case meta_key do
        k when is_binary(k) -> :erlang.binary_to_atom(meta_key, :utf8)
        k -> k
      end

    quote do
      {unquote(meta_key), get_in(var!(unquote(Macro.var(var, nil))), unquote(key_path))}
    end
  end

  defdelegate format(level, message, timestamp, metadata), to: Logrex.Formatter
end