# Regenerates the per-method JSON docs in priv/docs/methods/ by scraping
# https://docs.slack.dev/reference/methods.md and each linked method page.
#
#     mix run lib/mix/tasks/update_slack_api.exs                    # all methods
#     mix run lib/mix/tasks/update_slack_api.exs chat.postMessage   # subset
#
# The universal `token` argument is excluded — Slack.Web injects it at call time.

defmodule UpdateSlackApi do
  @base_url "https://docs.slack.dev"
  @index_url "https://docs.slack.dev/reference/methods.md"
  @out_dir "priv/docs/methods"
  @common_errors_path "priv/docs/common_errors.json"
  @common_errors_markdown_path "guides/common_errors.md"
  # An error code is "common" if it appears on at least this fraction of the
  # method pages we successfully scraped. In practice ~30 boilerplate errors
  # hit ~86% of pages and the next most common (channel_not_found) hits ~33%,
  # so any threshold in (0.34, 0.85) yields the same set. 0.70 leaves
  # headroom against Slack tweaking a handful of pages without shifting it.
  @common_errors_threshold 0.70
  @user_agent "slack_kit-doc-generator"

  @method_link_re ~r"\[([A-Za-z][\w.]*)\]\((https://docs\.slack\.dev/reference/methods/[\w.]+\.md)\)"
  @desc_re ~r/\*\*Description\*\*\s*([^\n]+)/
  @args_section_re ~r/##\s*Arguments\s*\{#arguments\}(.*?)(?=\n##\s|\z)/s
  @errors_section_re ~r/##\s*Errors\s*\{#errors\}(.*?)(?=\n##\s|\z)/s
  @arg_header_re ~r/\*\*`([^`]+)`\*\*(?:`([^`]+)`)?(Required|Optional)/
  @example_re ~r/_Example:_\s*`([^`]+)`/
  @default_re ~r/_Default:_\s*`([^`]+)`/
  @meta_split_re ~r/_(?:Example|Default):_/
  @subsection_re ~r/\n###\s.*\z/s
  @error_name_re ~r/^`([a-z][a-z0-9_]*)`$/
  @trailing_rule_re ~r/\s*\*\s*\*\s*\*\s*\z/
  @markdown_link_re ~r/\[([^\]]+)\]\([^)]+\)/

  @scopes_section_re ~r/\*\*Scopes\*\*(.*?)(?=\n\n\*\*|\n##\s)/s
  @no_scopes_re ~r/_No scopes required_/
  @scope_token_split_re ~r/\b(Bot token|User token|App token):\s*/
  @scope_link_re ~r/\[`([^`]+)`\]\(([^)]+)\)/
  @rate_limit_re ~r/\*\*Rate Limits\*\*\s*\[([^\]]+)\]\(([^)]+)\)/

  @usage_section_re ~r/##\s*Usage info\s*\{#usage-info\}(.*?)(?=\n##\s|\z)/s
  @code_block_re ~r/```.*?```/s
  @heading_line_re ~r/^#+\s+.*$/m
  @hr_line_re ~r/^\s*\*\s*\*\s*\*\s*$/m
  @bullet_line_re ~r/\n[ \t]*\*[ \t]+/
  @sentence_split_re ~r/(?<=[.!?])\s+(?=[A-Z])/
  @arg_ref_re ~r/`([a-z][a-z0-9_]*)`/

  def run(args) do
    Application.ensure_all_started(:req)

    methods = list_methods() |> filter(args)
    IO.puts("Fetching #{length(methods)} methods...")

    File.mkdir_p!(@out_dir)

    parsed = fetch_all(methods)

    common_errors =
      case args do
        [] ->
          # Full regen — derive the common-error set from the fetched data and
          # rewrite both the JSON source of truth and the human-facing guide.
          common = compute_common_errors(parsed)
          write_common_errors_files(common)
          common

        _ ->
          # Subset regen — keep the existing curated/derived set intact;
          # we don't have enough data to redetermine "common" from one method.
          load_common_errors()
      end

    common_names = MapSet.new(Map.keys(common_errors))
    Enum.each(parsed, &write_parsed(&1, common_names))
  end

  defp fetch_all(methods) do
    methods
    |> Task.async_stream(&fetch_and_parse/1,
      max_concurrency: 8,
      timeout: 60_000,
      on_timeout: :kill_task
    )
    |> Enum.flat_map(fn
      {:ok, {:ok, _name, _data} = ok} ->
        [ok]

      {:ok, {:error, name, reason}} ->
        IO.puts(:stderr, "err #{name}: #{reason}")
        []

      {:exit, reason} ->
        IO.puts(:stderr, "exit: #{inspect(reason)}")
        []
    end)
  end

  defp fetch_and_parse({name, url}) do
    data = url |> fetch!() |> parse_method_page()
    {:ok, name, data}
  rescue
    e -> {:error, name, Exception.message(e)}
  end

  defp write_parsed({:ok, name, data}, common_names) do
    stripped = strip_common_errors(data, common_names)
    json = (stripped |> :json.format() |> IO.iodata_to_binary()) <> "\n"
    File.write!(Path.join(@out_dir, "#{name}.json"), json)
    IO.puts("ok  #{name}")
  end

  # Picks every error code that appears on >= @common_errors_threshold of the
  # successfully parsed method pages, and chooses each one's canonical
  # description as the most-frequent variant (ties broken by longest).
  defp compute_common_errors([]), do: %{}

  defp compute_common_errors(parsed) do
    total = length(parsed)
    threshold = max(1, ceil(total * @common_errors_threshold))

    parsed
    |> Enum.flat_map(fn
      {:ok, _name, %{"errors" => errs}} when is_map(errs) -> Map.to_list(errs)
      _ -> []
    end)
    |> Enum.group_by(fn {name, _} -> name end, fn {_, desc} -> desc end)
    |> Enum.filter(fn {_name, descs} -> length(descs) >= threshold end)
    |> Map.new(fn {name, descs} -> {name, canonical_description(descs)} end)
  end

  defp canonical_description(descs) do
    descs
    |> Enum.frequencies()
    |> Enum.max_by(fn {desc, count} -> {count, String.length(desc)} end)
    |> elem(0)
  end

  defp write_common_errors_files(common) do
    json = (common |> :json.format() |> IO.iodata_to_binary()) <> "\n"
    File.write!(@common_errors_path, json)
    File.mkdir_p!(Path.dirname(@common_errors_markdown_path))
    File.write!(@common_errors_markdown_path, render_common_errors_markdown(common))
  end

  defp render_common_errors_markdown(common) do
    body =
      common
      |> Enum.sort()
      |> Enum.map_join("\n", fn {name, desc} -> "* `#{name}` — #{desc}" end)

    """
    # Common Errors

    Slack documents the same set of errors on nearly every Web API method page —
    authentication failures, rate limiting, deprecated endpoints, transport
    problems, and so on. To keep per-method docs focused, those shared errors
    are listed here once and stripped from each method's own error list.
    Method-specific errors (e.g. `channel_not_found`, `is_archived`) remain on
    the method itself.

    ## Errors

    #{body}
    """
  end

  defp load_common_errors do
    @common_errors_path
    |> File.read!()
    |> JSON.decode!()
  end

  defp filter(methods, []), do: methods

  defp filter(methods, args) do
    set = MapSet.new(args)
    Enum.filter(methods, fn {name, _} -> name in set end)
  end

  defp list_methods do
    @index_url
    |> fetch!()
    |> then(&Regex.scan(@method_link_re, &1))
    |> Enum.reduce(%{}, fn [_, name, url], acc ->
      # Method names always contain a dot (e.g. chat.postMessage).
      # Skip incidental links to other reference pages.
      if String.contains?(name, "."), do: Map.put_new(acc, name, url), else: acc
    end)
    |> Enum.sort()
  end

  defp strip_common_errors(%{"errors" => errors} = data, common_errors) when is_map(errors) do
    Map.put(data, "errors", Map.reject(errors, fn {k, _} -> MapSet.member?(common_errors, k) end))
  end

  defp strip_common_errors(data, _common_errors), do: data

  defp fetch!(url) do
    %{body: body} = Req.get!(url, headers: [{"user-agent", @user_agent}])
    if is_binary(body), do: body, else: to_string(body)
  end

  defp parse_method_page(text) do
    %{
      "desc" => extract(text, @desc_re),
      "args" => parse_args(text),
      "errors" => parse_errors(text),
      "scopes" => parse_scopes(text),
      "rate_limit" => parse_rate_limit(text)
    }
  end

  defp parse_scopes(text) do
    case Regex.run(@scopes_section_re, text) do
      [_, section] ->
        if Regex.match?(@no_scopes_re, section),
          do: %{},
          else: extract_scope_groups(section)

      _ ->
        %{}
    end
  end

  # The section opens with `**Scopes**` followed by zero or more
  # `Bot token:` / `User token:` / `App token:` blocks. For each labeled
  # block, the body runs from the label's end to the next label or section end.
  defp extract_scope_groups(section) do
    matches = Regex.scan(@scope_token_split_re, section, return: :index)
    section_len = byte_size(section)

    matches
    |> Enum.with_index()
    |> Enum.reduce(%{}, fn {[{m_start, m_len}, {label_start, label_len}], i}, acc ->
      body_start = m_start + m_len

      body_end =
        case Enum.at(matches, i + 1) do
          [{next_start, _} | _] -> next_start
          _ -> section_len
        end

      label = binary_part(section, label_start, label_len)
      body = binary_part(section, body_start, body_end - body_start)
      maybe_add_scopes(acc, scope_token_key(label), extract_scope_links(body))
    end)
  end

  defp scope_token_key("Bot token"), do: "bot"
  defp scope_token_key("User token"), do: "user"
  defp scope_token_key("App token"), do: "app"
  defp scope_token_key(_), do: nil

  defp extract_scope_links(body) do
    @scope_link_re
    |> Regex.scan(body, capture: :all_but_first)
    |> Enum.map(fn [name, url] ->
      %{"name" => name, "url" => absolute_url(url)}
    end)
  end

  defp maybe_add_scopes(acc, nil, _scopes), do: acc
  defp maybe_add_scopes(acc, _key, []), do: acc
  defp maybe_add_scopes(acc, key, scopes), do: Map.put(acc, key, scopes)

  defp parse_rate_limit(text) do
    case Regex.run(@rate_limit_re, text) do
      [_, label, url] ->
        %{"label" => String.trim(label), "url" => absolute_url(url)}

      _ ->
        nil
    end
  end

  defp absolute_url("/" <> _ = path), do: @base_url <> path
  defp absolute_url(url), do: url

  defp extract(text, re) do
    case Regex.run(re, text) do
      [_, value] -> value |> String.trim() |> strip_links()
      _ -> ""
    end
  end

  defp strip_links(text), do: Regex.replace(@markdown_link_re, text, "\\1")

  # Argument descriptions must be single-line: the upstream docs sometimes
  # interleave horizontal rules or stray scalar values (e.g. a lone `0` minimum)
  # between the prose and the `_Example:_` marker, and we don't want those
  # smuggled into the JSON as newline-separated cruft.
  defp normalize_whitespace(text) do
    text
    |> then(&Regex.replace(@trailing_rule_re, &1, ""))
    |> String.replace(~r/\s+/, " ")
    |> String.trim()
  end

  defp parse_args(text) do
    case Regex.run(@args_section_re, text) do
      [_, section] ->
        section
        |> do_parse_args()
        |> Map.delete("token")
        |> apply_usage_constraints(text)

      _ ->
        %{}
    end
  end

  # Slack documents cross-argument constraints (e.g. "Exactly one of `team_id`
  # or `enterprise_id` is required") as prose in the Usage info section rather
  # than per-argument. Scan that section for sentences that reference one or
  # more known argument names in backticks and append each such sentence to the
  # matching arg's desc, so the constraint is visible at the call site.
  defp apply_usage_constraints(args, _text) when map_size(args) == 0, do: args

  defp apply_usage_constraints(args, text) do
    case Regex.run(@usage_section_re, text) do
      [_, usage] -> append_constraints(args, usage)
      _ -> args
    end
  end

  defp append_constraints(args, usage) do
    arg_names = MapSet.new(Map.keys(args))

    usage
    |> sanitize_usage()
    |> extract_sentences()
    |> Enum.reduce(args, fn sentence, acc ->
      case mentioned_args(sentence, arg_names) do
        # Cross-argument constraints reference two or more args by name in the
        # same sentence — skip single-arg mentions, which are usually just
        # descriptive prose covered by the arg's own description.
        mentioned when length(mentioned) >= 2 ->
          Enum.reduce(mentioned, acc, &append_constraint(&2, &1, sentence))

        _ ->
          acc
      end
    end)
  end

  defp sanitize_usage(usage) do
    usage
    |> then(&Regex.replace(@code_block_re, &1, ""))
    |> then(&Regex.replace(@heading_line_re, &1, ""))
    |> then(&Regex.replace(@hr_line_re, &1, ""))
    # Promote each bullet item to its own paragraph so the sentence splitter
    # treats them independently instead of merging the whole list.
    |> then(&Regex.replace(@bullet_line_re, &1, "\n\n"))
    |> String.replace("**", "")
    |> strip_links()
  end

  defp extract_sentences(text) do
    text
    |> String.split(~r/\n\s*\n/)
    |> Enum.flat_map(&split_paragraph/1)
    |> Enum.map(&String.trim/1)
    |> Enum.reject(&(&1 == ""))
  end

  defp split_paragraph(paragraph) do
    paragraph
    |> String.replace(~r/\s+/, " ")
    |> String.trim()
    |> String.split(@sentence_split_re)
  end

  defp mentioned_args(sentence, arg_names) do
    @arg_ref_re
    |> Regex.scan(sentence, capture: :all_but_first)
    |> List.flatten()
    |> Enum.filter(&MapSet.member?(arg_names, &1))
    |> Enum.uniq()
  end

  defp append_constraint(args, arg_name, sentence) do
    Map.update!(args, arg_name, fn entry ->
      Map.update(entry, "desc", sentence, &append_sentence(&1, sentence))
    end)
  end

  defp append_sentence("", sentence), do: sentence

  defp append_sentence(desc, sentence) do
    separator = if String.ends_with?(desc, [".", "!", "?"]), do: " ", else: ". "
    desc <> separator <> sentence
  end

  defp do_parse_args(section) do
    section
    |> then(&Regex.replace(@arg_header_re, &1, "\u{0000}\\0"))
    |> String.split("\u{0000}", trim: true)
    |> Enum.flat_map(&parse_arg_chunk/1)
    |> Map.new()
  end

  defp parse_arg_chunk(chunk) do
    case Regex.run(@arg_header_re, chunk) do
      [matched, name, type, required] ->
        body =
          chunk
          |> String.replace_prefix(matched, "")
          |> then(&Regex.replace(@subsection_re, &1, ""))
          |> String.trim()

        desc =
          body
          |> String.split(@meta_split_re, parts: 2)
          |> hd()
          |> String.trim()
          |> strip_links()
          |> normalize_whitespace()

        entry =
          %{"required" => required == "Required", "desc" => desc}
          |> maybe_put("type", non_empty(type))
          |> maybe_put("example", capture(@example_re, body))
          |> maybe_put("default", capture(@default_re, body))

        [{name, entry}]

      _ ->
        []
    end
  end

  defp parse_errors(text) do
    case Regex.run(@errors_section_re, text) do
      [_, section] -> do_parse_errors(section)
      _ -> %{}
    end
  end

  defp do_parse_errors(section) do
    {name, lines, errors} =
      section
      |> String.split("\n")
      |> Enum.reduce({nil, [], %{}}, &reduce_error_line/2)

    flush_error(name, lines, errors)
  end

  defp reduce_error_line(line, {current, lines, errors}) do
    stripped = String.trim(line)

    case Regex.run(@error_name_re, stripped) do
      [_, new_name] -> {new_name, [], flush_error(current, lines, errors)}
      _ -> accumulate_error_line(stripped, current, lines, errors)
    end
  end

  defp accumulate_error_line(_stripped, nil, lines, errors), do: {nil, lines, errors}
  defp accumulate_error_line("", current, lines, errors), do: {current, lines, errors}

  defp accumulate_error_line(stripped, current, lines, errors),
    do: {current, [stripped | lines], errors}

  defp flush_error(nil, _, errors), do: errors

  defp flush_error(name, lines, errors) do
    joined =
      lines
      |> Enum.reverse()
      |> Enum.join(" ")
      |> String.trim()
      |> then(&Regex.replace(@trailing_rule_re, &1, ""))
      |> String.trim()
      |> strip_links()

    if joined == "" or Map.has_key?(errors, name) do
      errors
    else
      Map.put(errors, name, joined)
    end
  end

  defp capture(re, text) do
    case Regex.run(re, text) do
      [_, value] -> value
      _ -> nil
    end
  end

  defp non_empty(nil), do: nil
  defp non_empty(""), do: nil
  defp non_empty(string), do: string

  defp maybe_put(map, _key, nil), do: map
  defp maybe_put(map, key, value), do: Map.put(map, key, value)
end

UpdateSlackApi.run(System.argv())