defmodule Spark.Formatter do
  @moduledoc """
  Formats Spark modules.

  Currently, it is very simple, and will only reorder the outermost sections according to some rules.

  # Plugin

  Include the plugin into your `.formatter.exs` like so `plugins: [Spark.Formatter]`.

  If no configuration is provided, it will sort all top level DSL sections *alphabetically*.

  # Section Order

  To provide a custom section order, add configuration to your app, for example:

  ```elixir
  config :spark, :formatter,
    remove_parens?: true,
    "Ash.Resource": [
      section_order: [
        :resource,
        :postgres,
        :attributes,
        :relationships,
        :aggregates,
        :calculations
      ]
    ],
    "MyApp.Resource": [
      # Use this if you use a module that is not the spark DSL itself.
      # For example, you might have a "base" that you use instead that sets some simple defaults.

      # This tells us what the actual thing is so we know what extensions are included automatically.
      type: Ash.Resource,

      # Tell us what extensions might be added under the hood
      extensions: [MyApp.ResourceExtension],
      section_order: [...]
    ]
  ```

  Any sections found that aren't in that list will be left in the order that they were in, the sections
  in the list will be sorted "around" those sections. E.g the following list: `[:code_interface, :attributes]` can be interpreted as
  "ensure that code_interface comes before attributes, and don't change the rest".
  """
  @behaviour Mix.Tasks.Format

  require Logger

  def features(_opts) do
    [extensions: [".ex", ".exs"]]
  end

  def format(contents, opts) do
    config =
      :spark
      |> Application.get_env(:formatter, [])
      |> Enum.map(fn
        {key, value} when key in [:remove_parens?] ->
          {key, value}

        {key, value} ->
          {Module.concat([key]), value}
      end)

    parse_result =
      try do
        {:ok, Sourceror.parse_string!(contents)}
      rescue
        _ ->
          :error
      end

    case parse_result do
      {:ok, parsed} ->
        parsed
        |> format_resources(opts, config)
        |> then(fn patches ->
          Sourceror.patch_string(contents, patches)
        end)
        |> Code.format_string!(opts_without_plugin(opts))
        |> then(fn iodata ->
          [iodata, ?\n]
        end)
        |> IO.iodata_to_binary()

      :error ->
        contents
    end
  end

  defp format_resources(parsed, opts, config) do
    {_, patches} =
      Spark.CodeHelpers.prewalk(parsed, [], false, fn
        {:defmodule, _, [_, [{{:__block__, _, [:do]}, {:__block__, _, body}}]]} = expr,
        patches,
        false ->
          case get_extensions(body, config) do
            {:ok, extensions, type, using} ->
              replacement = format_resource(body, extensions, config, type, using)

              patches =
                body
                |> Enum.zip(replacement)
                |> Enum.reduce(patches, fn {body_section, replacement_section}, patches ->
                  if body_section == replacement_section do
                    patches
                  else
                    [
                      %{
                        range: Sourceror.get_range(body_section, include_comments: true),
                        change: Sourceror.to_string(replacement_section, opts)
                      }
                      | patches
                    ]
                  end
                end)

              {expr, patches, true}

            _ ->
              {expr, patches, true}
          end

        expr, patches, branch_acc ->
          {expr, patches, branch_acc}
      end)

    patches
  end

  defp format_resource(body, extensions, config, _type, using) do
    sections =
      extensions
      |> Enum.flat_map(fn extension ->
        Enum.map(extension.sections(), fn section ->
          {extension, section}
        end)
      end)
      |> sort_sections(config[using][:section_order])

    section_names = Enum.map(sections, fn {_, section} -> section.name end)

    {section_exprs, non_section_exprs} =
      body
      |> Enum.with_index()
      |> Enum.split_with(fn {{name, _, _}, _index} ->
        name in section_names
      end)

    new_sections =
      if config[using][:section_order] && config[using][:section_order] != [] do
        Enum.sort_by(section_exprs, fn {{name, _, _}, _} ->
          Enum.find_index(section_names, &(&1 == name))
        end)
      else
        section_exprs
      end

    new_section_indexes =
      section_exprs
      |> Enum.map(&elem(&1, 1))
      |> Enum.sort()

    new_sections =
      Enum.zip_with(new_sections, new_section_indexes, fn {new_section, _}, index ->
        {new_section, index}
      end)

    non_section_exprs
    |> Enum.concat(new_sections)
    |> Enum.sort_by(&elem(&1, 1))
    |> Enum.map(&elem(&1, 0))
    |> then(fn sections ->
      if config[:remove_parens?] do
        de_paren(sections, Enum.flat_map(extensions, & &1.sections()), extensions)
      else
        sections
      end
    end)
  end

  defp de_paren(actual_sections, dsl_sections, extensions) do
    actual_sections
    |> Enum.map(fn
      {name, meta, body} ->
        case Enum.find(dsl_sections, &(&1.name == name)) do
          nil ->
            {name, meta, body}

          section ->
            {name, meta, de_paren_section(body, section, extensions)}
        end

      other ->
        other
    end)
  end

  defp de_paren_section(body, section, extensions) do
    builders = all_entity_builders([section], extensions)

    Macro.prewalk(body, fn
      {func, meta, body} = node when is_atom(func) ->
        count = Enum.count(List.wrap(body))

        builders = Keyword.get_values(builders, func)

        if Enum.any?(builders, &(&1 in [count, count - 1])) &&
             Keyword.keyword?(meta) &&
             meta[:closing] do
          {func, Keyword.delete(meta, :closing), body}
        else
          node
        end

      node ->
        node
    end)
  end

  defp sort_sections(sections, nil), do: sections
  defp sort_sections(sections, []), do: sections

  defp sort_sections(sections, section_order) do
    {ordered, unordered} =
      sections
      |> Enum.with_index()
      |> Enum.split_with(fn {{_, section}, _} ->
        section.name in section_order
      end)

    reordered =
      ordered
      |> Enum.map(&elem(&1, 0))
      |> Enum.sort_by(fn {_, section} ->
        Enum.find_index(section_order, &(&1 == section.name))
      end)

    Enum.reduce(unordered, reordered, fn {{extension, section}, i}, acc ->
      List.insert_at(acc, i, {extension, section})
    end)
  end

  defp get_extensions(body, config) do
    Enum.find_value(body, :error, fn
      {:use, _, using} ->
        [using, opts] =
          case Spark.Dsl.Extension.expand_alias(using, __ENV__) do
            [using] ->
              [using, []]

            [using, opts] ->
              [using, opts]
          end

        if Keyword.has_key?(config, using) do
          type = config[using][:type] || using
          {:ok, parse_extensions(opts, config[using], type), type, using}
        end

      _ ->
        nil
    end)
  end

  defp parse_extensions(blocks, config, type) do
    blocks
    |> Enum.flat_map(fn {{:__block__, _, _}, extensions} ->
      extensions
      |> case do
        {:__block__, _, [extensions]} ->
          extensions

        extension when is_atom(extension) ->
          extension

        _ ->
          []
      end
      |> List.wrap()
      |> Enum.flat_map(fn extension ->
        case is_atom(extension) and Code.ensure_compiled(extension) do
          {:module, module} ->
            if Spark.implements_behaviour?(module, Spark.Dsl.Extension) do
              [module]
            else
              []
            end

          _ ->
            []
        end
      end)
    end)
    |> Enum.concat(config[:extensions] || [])
    |> Enum.concat(type.default_extensions() || [])
  end

  defp opts_without_plugin(opts) do
    Keyword.update(opts, :plugins, [], &(&1 -- [__MODULE__]))
  end

  @doc false
  def all_entity_builders(sections, extensions, path \\ []) do
    Enum.flat_map(sections, fn section ->
      Enum.concat([
        all_entity_option_builders(section),
        all_patch_entity_builders(extensions, section, path),
        section_option_builders(section),
        section_entity_builders(section, extensions, path)
      ])
    end)
    |> Enum.uniq()
    |> Enum.sort()
  end

  defp all_patch_entity_builders(extensions, section, path) do
    match_path = path ++ [section.name]

    extensions
    |> Enum.flat_map(& &1.dsl_patches())
    |> tap(fn patches ->
      Enum.map(patches, & &1.section_path)
    end)
    |> Enum.filter(fn
      %Spark.Dsl.Patch.AddEntity{section_path: ^match_path} ->
        true

      _ ->
        false
    end)
    |> Enum.map(& &1.entity)
    |> Enum.flat_map(&entity_option_builders/1)
  end

  defp section_entity_builders(section, extensions, path) do
    match_path = path ++ [section.name]

    mixed_in_entities =
      extensions
      |> Enum.flat_map(& &1.dsl_patches())
      |> Enum.filter(fn
        %Spark.Dsl.Patch.AddEntity{section_path: ^match_path} ->
          true

        _ ->
          false
      end)
      |> Enum.map(& &1.entity)

    Enum.flat_map(section.entities ++ mixed_in_entities, fn entity ->
      entity_builders(entity)
    end) ++ all_entity_builders(section.sections, extensions, path ++ [section.name])
  end

  defp entity_builders(entity) do
    arg_count = Enum.count(entity.args)
    non_optional_arg_count = Enum.count(entity.args, &is_atom/1)

    non_optional_arg_count..arg_count
    |> Enum.flat_map(&[{entity.name, &1}, {entity.name, &1 + 1}])
    |> Enum.concat(flat_map_nested_entities(entity, &entity_builders/1))
  end

  defp all_entity_option_builders(section) do
    Enum.flat_map(section.entities, fn entity ->
      entity_option_builders(entity)
    end)
  end

  defp entity_option_builders(entity) do
    entity_args_to_drop = Spark.Dsl.Entity.arg_names(entity)

    entity.schema
    |> Keyword.drop(entity_args_to_drop)
    |> Enum.map(fn {key, _schema} ->
      {key, 1}
    end)
    |> Kernel.++(flat_map_nested_entities(entity, &entity_option_builders/1))
  end

  defp section_option_builders(section) do
    Enum.map(section.schema, fn {key, _} ->
      {key, 1}
    end)
  end

  defp flat_map_nested_entities(entity, mapper) do
    Enum.flat_map(entity.entities, fn {_, nested_entities} ->
      nested_entities
      |> List.wrap()
      |> Enum.flat_map(fn nested_entity ->
        mapper.(nested_entity)
      end)
    end)
  end
end