defmodule EditorConfig.Resolver do
  @moduledoc "Resolves EditorConfig properties for a file path."

  alias EditorConfig.FileSystem
  alias EditorConfig.FileSystem.Memory
  alias EditorConfig.Glob
  alias EditorConfig.Parser

  @spec properties(Path.t(), keyword()) :: {:ok, map()} | {:error, term()}
  def properties(path, opts \\ []) do
    with {:ok, props, _sources} <- properties_with_sources(path, opts), do: {:ok, props}
  end

  @spec properties_with_sources(Path.t(), keyword()) :: {:ok, map(), list()} | {:error, term()}
  def properties_with_sources(path, opts \\ []) do
    fs = Keyword.get(opts, :fs, FileSystem)
    config_name = Keyword.get(opts, :config_name, ".editorconfig")
    path = normalize_path(path)

    result =
      path
      |> candidate_config_paths(config_name)
      |> Enum.reduce_while({[], false}, &collect_config(&1, &2, fs))

    case result do
      {:error, reason} -> {:error, reason}
      {configs, _root_found?} -> apply_configs(configs, path, opts)
    end
  end

  defp normalize_path(path) do
    Path.expand(path)
  end

  defp candidate_config_paths(path, config_name) do
    path
    |> Path.dirname()
    |> ancestors()
    |> Enum.map(&Path.join(&1, config_name))
  end

  defp ancestors("/"), do: ["/"]
  defp ancestors(dir), do: [dir | ancestors(Path.dirname(dir))]

  defp collect_config(_candidate, {configs, true}, _fs), do: {:halt, {configs, true}}

  defp collect_config(candidate, {configs, false}, fs) do
    if exists?(fs, candidate) do
      with {:ok, body} <- read(fs, candidate),
           {:ok, file} <- Parser.parse(body) do
        {:cont, {[{candidate, file} | configs], file.root?}}
      else
        {:error, reason} -> {:halt, {:error, reason}}
      end
    else
      {:cont, {configs, false}}
    end
  end

  defp apply_configs(configs, path, opts) do
    {props, sources} =
      Enum.reduce(configs, {%{}, []}, fn {config_path, file}, acc ->
        config_dir = Path.dirname(config_path)
        Enum.reduce(file.sections, acc, &apply_section(&1, &2, path, config_path, config_dir))
      end)

    {:ok, normalize_props(props, opts), sources}
  end

  defp apply_section(section, {props, sources}, path, config_path, config_dir) do
    if Glob.match?(section.name, path, config_dir) do
      {merge_props(props, section.properties), sources ++ [{config_path, section.name}]}
    else
      {props, sources}
    end
  end

  defp merge_props(props, section_props) do
    Enum.reduce(section_props, props, fn
      {key, value}, acc -> Map.put(acc, key, value)
    end)
  end

  defp normalize_props(props, opts) do
    props
    |> downcase_known_values()
    |> apply_defaults(Keyword.get(opts, :version, "0.17.2"))
  end

  defp downcase_known_values(props) do
    always_lowercase =
      ~w(charset end_of_line indent_style insert_final_newline trim_trailing_whitespace)

    Map.new(props, fn {key, value} ->
      cond do
        key in always_lowercase ->
          {key, String.downcase(value)}

        key == "indent_size" and String.downcase(value) in ["tab", "unset"] ->
          {key, String.downcase(value)}

        true ->
          {key, value}
      end
    end)
  end

  defp apply_defaults(props, version) do
    if before_0_9_0?(version) do
      props
    else
      props
      |> default_indent_size()
      |> default_tab_width()
    end
  end

  defp default_indent_size(%{"indent_style" => "tab"} = props) do
    Map.put_new(props, "indent_size", Map.get(props, "tab_width", "tab"))
  end

  defp default_indent_size(props), do: props

  defp default_tab_width(%{"indent_size" => "tab"} = props), do: props

  defp default_tab_width(%{"indent_size" => indent_size} = props) do
    Map.put_new(props, "tab_width", indent_size)
  end

  defp default_tab_width(props), do: props

  defp before_0_9_0?(version) do
    Version.compare(version, "0.9.0") == :lt
  rescue
    Version.InvalidVersionError -> false
  end

  defp exists?(%Memory{} = fs, path), do: Memory.exists?(fs, path)
  defp exists?(module, path), do: module.exists?(path)

  defp read(%Memory{} = fs, path), do: Memory.read(fs, path)
  defp read(module, path), do: module.read(path)
end