defmodule Hologram.Template.DOM do
  @moduledoc false

  alias Hologram.Compiler.AST
  alias Hologram.Template.Helpers
  alias Hologram.Template.Parser

  # 'dom_node' name used instead of 'node" because type node/0 is a built-in type and it cannot be redefined.
  @type dom_node ::
          {:component, module, list({String.t(), t}), t}
          | {:element, String.t(), list({String.t(), t}), t}
          | {:expression, {any}}
          | {:page, module, list({String.t(), t}), []}
          | {:public_comment, t}
          | {:text, String.t()}

  @type t :: dom_node | list(dom_node())

  @doc """
  Builds DOM AST from the given parsed tags.

  ## Examples

      iex> tags = [{:start_tag, {"div, []}}, {:text, "abc"}, {:end_tag, "div"}]
      iex> build_ast(tags)
      [{:{}, [line: 1], [:element, "div", [], [{:text, "abc"}]]}]
  """
  @spec build_ast(list(Parser.parsed_tag())) :: AST.t()
  def build_ast(tags) do
    {code, _last_tag_type} =
      Enum.reduce(tags, {"", nil}, fn tag, {code_acc, last_tag_type} ->
        current_tag_type = if is_tuple(tag), do: elem(tag, 0), else: tag

        # :skip items are fully elided, as if they did not appear
        case render_code(tag) do
          :skip ->
            {code_acc, last_tag_type}

          current_tag_code ->
            {append_code(code_acc, current_tag_code, last_tag_type), current_tag_type}
        end
      end)

    "[#{code}]"
    |> AST.for_code()
    |> substitute_module_attributes()
  end

  defp append_code(code_acc, code, last_tag_type)
       when last_tag_type in [
              :block_end,
              :doctype,
              :end_tag,
              :expression,
              :public_comment_end,
              :self_closing_tag,
              :text
            ] do
    code_acc <> ", " <> code
  end

  defp append_code(code_acc, code, _last_tag_type) do
    code_acc <> code
  end

  defp extract_expression_content(expr_str) do
    expr_str
    |> String.slice(1, String.length(expr_str) - 2)
    |> String.trim()
  end

  defp render_code({:block_start, "else"}) do
    "] else ["
  end

  defp render_code({:block_start, {"for", expr_str}}) do
    "(for #{extract_expression_content(expr_str)} do ["
  end

  defp render_code({:block_end, "for"}) do
    "] end)"
  end

  defp render_code({:block_start, {"if", expr_str}}) do
    "(if #{extract_expression_content(expr_str)} do ["
  end

  defp render_code({:block_end, "if"}) do
    "] end)"
  end

  # `raw` blocks are useful only in the handling of template sources.
  # `Parser` emits them so that such source can be reconstructed.
  # They can be skipped in the building of the AST here.
  defp render_code({:block_start, "raw"}) do
    :skip
  end

  defp render_code({:block_end, "raw"}) do
    :skip
  end

  defp render_code({:doctype, content}) do
    "{:doctype, \"#{content}\"}"
  end

  defp render_code({:end_tag, _tag_name}) do
    "]}"
  end

  # Wraps implicit keyword list.
  # {a: 1, b: 2} is not valid Elixir code, although {123, a: 1, b: 2} is allowed.
  defp render_code({:expression, templ_expr}) do
    regex = ~r/^\{(([a-zA-Z][a-zA-Z0-9]*|"[^"]+"): .+)\}$/

    elixir_expr =
      case Regex.run(regex, templ_expr) do
        [_full, content, _beginning] ->
          "{[#{content}]}"

        nil ->
          templ_expr
      end

    "{:expression, #{elixir_expr}}"
  end

  defp render_code(:public_comment_end) do
    "]}"
  end

  defp render_code(:public_comment_start) do
    "{:public_comment, ["
  end

  defp render_code({:self_closing_tag, {tag_name, attributes}}) do
    render_code({:start_tag, {tag_name, attributes}}) <> render_code({:end_tag, tag_name})
  end

  defp render_code({:start_tag, {tag_name, attributes}}) do
    tag_type = Helpers.tag_type(tag_name)

    tag_name_code =
      if tag_type == :element do
        "\"#{tag_name}\""
      else
        "alias!(#{tag_name})"
      end

    attributes_code =
      Enum.map_join(attributes, ", ", fn {name, value_parts} ->
        "{\"#{name}\", [" <> Enum.map_join(value_parts, ", ", &render_code/1) <> "]}"
      end)

    "{:#{tag_type}, #{tag_name_code}, [#{attributes_code}], ["
  end

  defp render_code({:text, str}) do
    escaped_str =
      str
      |> HtmlEntities.decode()
      |> String.replace(~s("), ~s(\\"))

    ~s({:text, "#{escaped_str}"})
  end

  defp substitute_module_attributes({:@, meta_1, [{name, _meta_2, _args}]}) do
    {{:., meta_1, [{:vars, meta_1, nil}, name]}, [{:no_parens, true} | meta_1], []}
  end

  defp substitute_module_attributes(ast) when is_list(ast) do
    Enum.map(ast, &substitute_module_attributes/1)
  end

  defp substitute_module_attributes(ast) when is_tuple(ast) do
    ast
    |> Tuple.to_list()
    |> Enum.map(&substitute_module_attributes/1)
    |> List.to_tuple()
  end

  defp substitute_module_attributes(ast), do: ast
end