defmodule PostCSS.Parser do
  @moduledoc """
  CSS Parser for PostCSS.

  Converts tokens from the tokenizer into an Abstract Syntax Tree (AST).
  """

  alias PostCSS.{Tokenizer, Root, Rule, Declaration, AtRule, Comment, CssSyntaxError, Raws}

  @doc """
  Parses CSS string into a PostCSS AST.
  """
  def parse(css) when is_binary(css) do
    css
    |> Tokenizer.tokenize()
    |> parse_tokens()
  end

  defp parse_tokens(tokens) do
    tokens
    |> filter_meaningful_tokens()
    |> parse_root()
  end

  defp filter_meaningful_tokens(tokens) do
    # Keep spaces for selector parsing, remove only standalone spaces not between words
    tokens
  end

  defp parse_root(tokens) do
    {nodes, remaining} = parse_nodes(tokens)

    # Collect any trailing whitespace
    trailing_whitespace = collect_trailing_whitespace(remaining, "")

    unless Enum.empty?(remaining) and trailing_whitespace == "" do
      # If we have trailing whitespace, that's fine
      # If we have other tokens, that's an error
      non_whitespace_remaining =
        Enum.reject(remaining, fn
          {:space, _, _} -> true
          {:space, _, _, _} -> true
          _ -> false
        end)

      unless Enum.empty?(non_whitespace_remaining) do
        raise CssSyntaxError.new("Unexpected tokens at end of input")
      end
    end

    root = %Root{nodes: nodes}

    # Add trailing whitespace to raws.after if present
    if trailing_whitespace != "" do
      Raws.put(root, :after, trailing_whitespace)
    else
      root
    end
  end

  defp collect_trailing_whitespace([], acc), do: acc

  defp collect_trailing_whitespace([{:space, space, _} | rest], acc) do
    collect_trailing_whitespace(rest, acc <> space)
  end

  defp collect_trailing_whitespace([{:space, space, _, _} | rest], acc) do
    collect_trailing_whitespace(rest, acc <> space)
  end

  defp collect_trailing_whitespace(_, acc), do: acc

  defp parse_nodes(tokens) do
    parse_nodes_with_whitespace(tokens, [], "")
  end

  defp parse_nodes_with_whitespace([], acc, whitespace) do
    # If we have trailing whitespace, preserve it as remaining space tokens
    remaining =
      if whitespace != "" do
        [{:space, whitespace, 0}]
      else
        []
      end

    {Enum.reverse(acc), remaining}
  end

  defp parse_nodes_with_whitespace([{:close_brace, _, _} | _] = tokens, acc, _whitespace) do
    {Enum.reverse(acc), tokens}
  end

  defp parse_nodes_with_whitespace([{:space, space, _} | rest], acc, whitespace) do
    # Collect whitespace for the next node
    parse_nodes_with_whitespace(rest, acc, whitespace <> space)
  end

  defp parse_nodes_with_whitespace([{:space, space, _, _} | rest], acc, whitespace) do
    # Collect whitespace for the next node
    parse_nodes_with_whitespace(rest, acc, whitespace <> space)
  end

  defp parse_nodes_with_whitespace(tokens, acc, whitespace) do
    case parse_node(tokens) do
      {node, remaining} ->
        # Add collected whitespace to node's raws.before
        node_with_raws =
          if whitespace != "" do
            Raws.put(node, :before, whitespace)
          else
            node
          end

        parse_nodes_with_whitespace(remaining, [node_with_raws | acc], "")

      :error ->
        raise CssSyntaxError.new("Failed to parse node")
    end
  end

  defp parse_node(tokens) do
    case tokens do
      # Comment
      [{:comment, comment_text, _, _} | rest] ->
        parse_comment(comment_text, rest)

      # At-rule: @import, @media, etc.
      [{:at_word, at_rule_text, _, _} | rest] ->
        parse_at_rule(at_rule_text, rest)

      # Simple declaration: word : value
      [{:word, prop, _, _} | rest] ->
        rest = skip_spaces(rest)

        case rest do
          [{:colon, _, _} | value_tokens] ->
            # This is a declaration
            case parse_declaration_value(value_tokens) do
              {value, important, remaining} ->
                decl = %Declaration{prop: prop, value: value, important: important}
                {decl, remaining}

              :error ->
                raise CssSyntaxError.new("Failed to parse declaration value")
            end

          _ ->
            # This might be a selector, collect all tokens until we find an open brace
            case collect_selector_tokens(tokens) do
              {[_ | _] = selector_tokens, [{:open_brace, _, _} | rule_rest]} ->
                selector = extract_selector_from_tokens(selector_tokens)
                {declarations, remaining} = parse_declarations(rule_rest, [])

                case remaining do
                  [{:close_brace, _, _} | rest_tokens] ->
                    rule = %Rule{selector: selector, nodes: declarations}
                    {rule, rest_tokens}

                  [] ->
                    raise CssSyntaxError.new("Unclosed rule: missing '}'")

                  _ ->
                    raise CssSyntaxError.new("Expected '}' after rule declarations")
                end

              {[_ | _] = tokens_found, _} ->
                [first_token | _] = tokens_found
                raise CssSyntaxError.new("Unexpected token: #{inspect(first_token)}")

              _ ->
                :error
            end
        end

      # Other tokens - try to parse as selector
      _ ->
        case collect_selector_tokens(tokens) do
          {[_ | _] = selector_tokens, [{:open_brace, _, _} | rule_rest]} ->
            selector = extract_selector_from_tokens(selector_tokens)
            {declarations, remaining} = parse_declarations(rule_rest, [])

            case remaining do
              [{:close_brace, _, _} | rest_tokens] ->
                rule = %Rule{selector: selector, nodes: declarations}
                {rule, rest_tokens}

              [] ->
                raise CssSyntaxError.new("Unclosed rule: missing '}'")

              _ ->
                raise CssSyntaxError.new("Expected '}' after rule declarations")
            end

          {[_ | _] = tokens_found, _} ->
            [first_token | _] = tokens_found
            raise CssSyntaxError.new("Unexpected token: #{inspect(first_token)}")

          _ ->
            :error
        end
    end
  end

  defp collect_selector_tokens(tokens) do
    collect_selector_tokens(tokens, [])
  end

  defp collect_selector_tokens([], acc), do: {Enum.reverse(acc), []}

  defp collect_selector_tokens([{:open_brace, _, _} | _] = tokens, acc),
    do: {Enum.reverse(acc), tokens}

  defp collect_selector_tokens([token | rest], acc),
    do: collect_selector_tokens(rest, [token | acc])

  defp extract_selector_from_tokens(tokens) do
    tokens
    |> Enum.map(fn
      {:word, value, _, _} -> value
      {:at_word, value, _, _} -> value
      {:space, value, _} -> value
      {:space, value, _, _} -> value
      {:comma, value, _} -> value
      {:colon, value, _} -> value
      {_, value, _} -> value
      {_, value, _, _} -> value
    end)
    |> Enum.join("")
    |> String.trim()
  end

  defp parse_declarations(tokens, acc) do
    parse_declarations_with_whitespace(tokens, acc, "")
  end

  defp parse_declarations_with_whitespace(tokens, acc, whitespace) do
    case tokens do
      [{:close_brace, _, _} | _] ->
        {Enum.reverse(acc), tokens}

      [] ->
        {Enum.reverse(acc), []}

      [{:space, space, _} | rest] ->
        # Collect whitespace for the next node
        parse_declarations_with_whitespace(rest, acc, whitespace <> space)

      [{:space, space, _, _} | rest] ->
        # Collect whitespace for the next node
        parse_declarations_with_whitespace(rest, acc, whitespace <> space)

      [{:comment, comment_text, _, _} | rest] ->
        # Handle comments inside rule blocks
        {comment, remaining} = parse_comment(comment_text, rest)

        comment_with_raws =
          if whitespace != "" do
            Raws.put(comment, :before, whitespace)
          else
            comment
          end

        parse_declarations_with_whitespace(remaining, [comment_with_raws | acc], "")

      _ ->
        case parse_declaration(tokens) do
          {decl, remaining} ->
            # Add collected whitespace to declaration's raws.before
            decl_with_raws =
              if whitespace != "" do
                Raws.put(decl, :before, whitespace)
              else
                decl
              end

            # Skip semicolon if present, but preserve whitespace for next declaration
            remaining = skip_semicolon_preserve_whitespace(remaining)
            parse_declarations_with_whitespace(remaining, [decl_with_raws | acc], "")

          :error ->
            {Enum.reverse(acc), tokens}
        end
    end
  end

  defp parse_declaration([{:word, prop, _, _} | rest]) do
    # Collect spaces before colon
    {before_colon, after_spaces} = collect_spaces_before_colon(rest, "")

    case after_spaces do
      [{:colon, _, _} | value_tokens] ->
        # Collect spaces after colon
        {after_colon, value_tokens} = collect_spaces(value_tokens, "")

        case parse_declaration_value(value_tokens) do
          {value, important, remaining} ->
            # Build the between string (spaces + colon + spaces)
            between = before_colon <> ":" <> after_colon

            decl = %Declaration{prop: prop, value: value, important: important}
            decl_with_raws = Raws.put(decl, :between, between)
            {decl_with_raws, remaining}

          :error ->
            :error
        end

      _ ->
        :error
    end
  end

  defp collect_spaces_before_colon([{:space, space, _} | rest], acc) do
    collect_spaces_before_colon(rest, acc <> space)
  end

  defp collect_spaces_before_colon([{:space, space, _, _} | rest], acc) do
    collect_spaces_before_colon(rest, acc <> space)
  end

  defp collect_spaces_before_colon(tokens, acc), do: {acc, tokens}

  defp collect_spaces([{:space, space, _} | rest], acc) do
    collect_spaces(rest, acc <> space)
  end

  defp collect_spaces([{:space, space, _, _} | rest], acc) do
    collect_spaces(rest, acc <> space)
  end

  defp collect_spaces(tokens, acc), do: {acc, tokens}

  defp skip_spaces([{:space, _, _} | rest]), do: skip_spaces(rest)
  defp skip_spaces([{:space, _, _, _} | rest]), do: skip_spaces(rest)
  defp skip_spaces(tokens), do: tokens

  defp parse_declaration_value(tokens) do
    case collect_value_tokens(tokens, []) do
      {value_tokens, remaining} ->
        {value, important} = process_value_tokens(value_tokens)
        {value, important, remaining}

      :error ->
        :error
    end
  end

  defp collect_value_tokens([], acc), do: {Enum.reverse(acc), []}

  defp collect_value_tokens([{:semicolon, _, _} | _] = tokens, acc) do
    {Enum.reverse(acc), tokens}
  end

  defp collect_value_tokens([{:close_brace, _, _} | _] = tokens, acc) do
    {Enum.reverse(acc), tokens}
  end

  defp collect_value_tokens([token | rest], acc) do
    collect_value_tokens(rest, [token | acc])
  end

  defp process_value_tokens(tokens) do
    # Check for !important
    case Enum.reverse(tokens) do
      [{:word, "!important", _, _} | rest_tokens] ->
        value = extract_value_from_tokens(Enum.reverse(rest_tokens))
        {value, true}

      _ ->
        value = extract_value_from_tokens(tokens)
        {value, false}
    end
  end

  defp extract_value_from_tokens(tokens) do
    tokens
    |> Enum.map(fn
      {:word, value, _, _} -> value
      {:string, value, _, _} -> value
      {:colon, value, _} -> value
      {:at_word, value, _, _} -> value
      {_, value, _} -> value
      {_, value, _, _} -> value
    end)
    |> Enum.join("")
    |> String.trim()
  end

  # Skip semicolon but preserve whitespace (for use in parse_declarations_with_whitespace)
  defp skip_semicolon_preserve_whitespace([{:semicolon, _, _} | rest]), do: rest
  defp skip_semicolon_preserve_whitespace(tokens), do: tokens

  defp parse_at_rule(at_rule_text, tokens) do
    # Extract the rule name (remove the @ symbol)
    name = String.slice(at_rule_text, 1..-1//1)

    # Collect parameters until we hit a semicolon or opening brace
    {param_tokens, remaining} = collect_at_rule_params(tokens, [])

    # Convert parameter tokens to a string
    params =
      if Enum.empty?(param_tokens) do
        nil
      else
        extract_params_from_tokens(param_tokens)
      end

    case remaining do
      [{:semicolon, _, _} | rest] ->
        # Simple at-rule like @import url(...);
        at_rule = %AtRule{name: name, params: params, nodes: []}
        {at_rule, rest}

      [{:open_brace, _, _} | rest] ->
        # Block at-rule like @media (...) { ... }
        # Use parse_nodes to handle both rules and declarations inside at-rules
        {nodes, remaining} = parse_nodes_with_whitespace(rest, [], "")

        case remaining do
          [{:close_brace, _, _} | rest_tokens] ->
            at_rule = %AtRule{name: name, params: params, nodes: nodes}
            {at_rule, rest_tokens}

          [] ->
            raise CssSyntaxError.new("Unclosed at-rule: missing '}'")

          _ ->
            raise CssSyntaxError.new("Expected '}' after at-rule content")
        end

      [] ->
        # At-rule at end of input
        at_rule = %AtRule{name: name, params: params, nodes: []}
        {at_rule, []}

      _ ->
        raise CssSyntaxError.new("Expected ';' or '{' after at-rule")
    end
  end

  defp collect_at_rule_params([], acc), do: {Enum.reverse(acc), []}

  defp collect_at_rule_params([{:semicolon, _, _} | _] = tokens, acc),
    do: {Enum.reverse(acc), tokens}

  defp collect_at_rule_params([{:open_brace, _, _} | _] = tokens, acc),
    do: {Enum.reverse(acc), tokens}

  defp collect_at_rule_params([token | rest], acc),
    do: collect_at_rule_params(rest, [token | acc])

  defp extract_params_from_tokens(tokens) do
    tokens
    |> Enum.map(fn
      {:word, value, _, _} -> value
      {:string, value, _, _} -> value
      {:open_paren, value, _} -> value
      {:close_paren, value, _} -> value
      {:space, value, _} -> value
      {:space, value, _, _} -> value
      {:comma, value, _} -> value
      {:colon, value, _} -> value
      {_, value, _} -> value
      {_, value, _, _} -> value
    end)
    |> Enum.join("")
    |> String.trim()
  end

  defp parse_comment(comment_text, remaining_tokens) do
    # Extract comment content (remove /* and */)
    # comment_text is like "/* comment */"
    text =
      comment_text
      # Remove /* and */
      |> String.slice(2..-3//1)

    # Parse whitespace like PostCSS does
    if String.trim(text) == "" do
      # Empty comment, preserve all whitespace as left
      comment = %Comment{text: "", raws: %{left: text, right: ""}}
      {comment, remaining_tokens}
    else
      # Parse leading and trailing whitespace
      case Regex.run(~r/^(\s*)(.*?\S)(\s*)$/s, text) do
        [_, left, content, right] ->
          comment = %Comment{text: content, raws: %{left: left, right: right}}
          {comment, remaining_tokens}

        nil ->
          # Fallback if regex doesn't match
          comment = %Comment{text: text, raws: %{}}
          {comment, remaining_tokens}
      end
    end
  end
end