defmodule Dexcord do
  @moduledoc """
  A reliability-first Discord bot library for Elixir.

  Dexcord is a library, not an auto-starting application - you add a single child
  to your own supervision tree:

      children = [
        {Dexcord, token: System.fetch_env!("DISCORD_TOKEN"),
                   handler: MyBot.Handler,
                   intents: :all}
      ]

  ## Options

    * `:token` (required) - the bot token
    * `:handler` (required) - a module using `Dexcord.Handler`
    * `:intents` - `:all`, `:default`, a list of intent atoms, or an integer
      bitmask (default `:default`); see `Dexcord.Intents`
    * `:cache_presences` - cache PRESENCE_UPDATE (default `false`)
    * `:request_guild_members` - request full member lists on GUILD_CREATE
      (default `false`)
    * `:slash` - a module using `Dexcord.Slash`. When set, `Dexcord.Slash.Registrar`
      registers its `commands/0` at startup and `INTERACTION_CREATE`s are
      auto-routed to it (the raw event still reaches the handler).
    * `:slash_guild_ids` - a list of guild ids (strings or integers). When present,
      slash commands are registered per guild (instant) instead of globally (~1h).
    * `:gateway_url` - override the gateway URL (e.g. `"ws://127.0.0.1:4000"`);
      when set, `GET /gateway/bot` is skipped. Primarily for testing.

  `child_spec/1` validates these options and stashes the resolved config in
  `Dexcord.Config` (`:persistent_term`) before the supervision tree starts.
  """

  @doc "Sends a presence update (op 3) through the gateway's send budget."
  @spec update_presence(map()) :: :ok
  defdelegate update_presence(presence), to: Dexcord.Gateway

  @doc """
  Builds the supervisor child spec, validating options first.

  Raises `ArgumentError` on missing/invalid required options.
  """
  @spec child_spec(keyword()) :: Supervisor.child_spec()
  def child_spec(opts) do
    config = validate(opts)

    %{
      id: __MODULE__,
      start: {Dexcord.Supervisor, :start_link, [config]},
      type: :supervisor
    }
  end

  @doc false
  def validate(opts) do
    token = require_opt(opts, :token)

    unless is_binary(token) do
      raise ArgumentError, "Dexcord :token must be a string"
    end

    handler = require_opt(opts, :handler)

    unless is_atom(handler) do
      raise ArgumentError, "Dexcord :handler must be a module"
    end

    intents = Keyword.get(opts, :intents, :default)
    intents_bits = resolve_intents(intents)

    cache_presences = boolean_opt(opts, :cache_presences, false)
    request_guild_members = boolean_opt(opts, :request_guild_members, false)

    gateway_url = Keyword.get(opts, :gateway_url)
    validate_gateway_url(gateway_url)

    slash = Keyword.get(opts, :slash)
    validate_slash(slash)

    slash_guild_ids = Keyword.get(opts, :slash_guild_ids)
    validate_slash_guild_ids(slash_guild_ids)

    allowed_mentions = validate_allowed_mentions(Keyword.get(opts, :allowed_mentions))

    %{
      token: token,
      handler: handler,
      intents: intents_bits,
      intents_spec: intents,
      cache_presences: cache_presences,
      request_guild_members: request_guild_members,
      slash: slash,
      slash_guild_ids: slash_guild_ids,
      gateway_url: gateway_url,
      allowed_mentions: allowed_mentions
    }
  end

  # `Intents.resolve/1` raises a `FunctionClauseError` for a wrong-typed spec
  # (a tuple, a negative integer, ...). Convert that into a friendly message; a
  # list carrying an unknown intent already raises a helpful `ArgumentError`,
  # which we let through.
  defp resolve_intents(intents) do
    Dexcord.Intents.resolve(intents)
  rescue
    FunctionClauseError ->
      reraise ArgumentError,
              [
                message:
                  "Dexcord :intents must be :all, :default, a list of intent atoms, or a " <>
                    "non-negative integer, got: #{inspect(intents)}"
              ],
              __STACKTRACE__
  end

  defp validate_gateway_url(nil), do: :ok

  defp validate_gateway_url(url) when is_binary(url) do
    unless String.starts_with?(url, ["ws://", "wss://", "http://", "https://"]) do
      raise ArgumentError,
            "Dexcord :gateway_url must start with ws://, wss://, http:// or https://, " <>
              "got: #{inspect(url)}"
    end

    :ok
  end

  defp validate_gateway_url(other) do
    raise ArgumentError,
          "Dexcord :gateway_url must be a URL string or nil, got: #{inspect(other)}"
  end

  defp validate_slash(nil), do: :ok
  defp validate_slash(mod) when is_atom(mod), do: :ok

  defp validate_slash(other) do
    raise ArgumentError, "Dexcord :slash must be a module, got: #{inspect(other)}"
  end

  defp validate_slash_guild_ids(nil), do: :ok

  defp validate_slash_guild_ids(ids) when is_list(ids) do
    unless Enum.all?(ids, &(is_binary(&1) or is_integer(&1))) do
      raise ArgumentError,
            "Dexcord :slash_guild_ids must be a list of guild ids (strings or integers), " <>
              "got: #{inspect(ids)}"
    end

    :ok
  end

  defp validate_slash_guild_ids(other) do
    raise ArgumentError,
          "Dexcord :slash_guild_ids must be a list of guild ids (strings or integers), " <>
            "got: #{inspect(other)}"
  end

  # Accepts a keyword, a map, or a `%Dexcord.AllowedMentions{}`, normalized to a
  # string-keyed wire map (only explicitly-provided keys). Absent -> nil.
  defp validate_allowed_mentions(nil), do: nil

  defp validate_allowed_mentions(spec)
       when is_list(spec) or is_map(spec) do
    Dexcord.AllowedMentions.normalize(spec)
  end

  defp validate_allowed_mentions(other) do
    raise ArgumentError,
          "Dexcord :allowed_mentions must be a keyword list, map, or %Dexcord.AllowedMentions{}, " <>
            "got: #{inspect(other)}"
  end

  defp boolean_opt(opts, key, default) do
    value = Keyword.get(opts, key, default)

    unless is_boolean(value) do
      raise ArgumentError, "Dexcord :#{key} must be a boolean, got: #{inspect(value)}"
    end

    value
  end

  defp require_opt(opts, key) do
    case Keyword.fetch(opts, key) do
      {:ok, value} -> value
      :error -> raise ArgumentError, "Dexcord requires the :#{key} option"
    end
  end
end