defmodule CCXT.Registry do
  @moduledoc """
  Compile-time exchange lookup registry.

  Maps exchange ID atoms and strings to their generated module names.
  Built from the spec manifest at compile time — recompiles automatically
  when the manifest changes.

  ## Usage

      CCXT.Registry.lookup(:bybit)
      #=> {:ok, CCXT.Bybit}

      CCXT.Registry.lookup!("binance")
      #=> CCXT.Binance

      CCXT.Registry.exchanges()
      #=> ["aftermath", "alpaca", "apex", ...]

      CCXT.Registry.loaded?(:bybit)
      #=> true  # if CCXT.Bybit module is compiled

  """

  @manifest_path CCXT.Spec.manifest_path()
  @external_resource @manifest_path

  @exchange_ids CCXT.Spec.load_manifest!()["exchanges"]

  # Pre-compute the ID-to-module mapping at compile time
  @exchange_modules (for id <- @exchange_ids, into: %{} do
                       {id, Module.concat(CCXT, Macro.camelize(id))}
                     end)

  @doc """
  Looks up the module for an exchange ID.

  Accepts both string and atom IDs.

  ## Examples

      CCXT.Registry.lookup("bybit")
      #=> {:ok, CCXT.Bybit}

      CCXT.Registry.lookup(:unknown)
      #=> {:error, {:unknown_exchange, "unknown"}}

  """
  @spec lookup(String.t() | atom()) :: {:ok, module()} | {:error, {:unknown_exchange, String.t()}}
  def lookup(id) when is_atom(id), do: lookup(Atom.to_string(id))

  for {id, module} <- @exchange_modules do
    def lookup(unquote(id)), do: {:ok, unquote(module)}
  end

  def lookup(id) when is_binary(id), do: {:error, {:unknown_exchange, id}}

  @doc """
  Looks up the module for an exchange ID, raising on unknown.

  ## Examples

      CCXT.Registry.lookup!(:bybit)
      #=> CCXT.Bybit

  """
  @spec lookup!(String.t() | atom()) :: module()
  def lookup!(id) do
    case lookup(id) do
      {:ok, module} -> module
      {:error, _} -> raise ArgumentError, "unknown exchange: #{inspect(id)}"
    end
  end

  @doc """
  Returns the module for an exchange ID, or nil if unknown.

  ## Examples

      CCXT.Registry.module_for("bybit")
      #=> CCXT.Bybit

      CCXT.Registry.module_for("nope")
      #=> nil

  """
  @spec module_for(String.t() | atom()) :: module() | nil
  def module_for(id) do
    case lookup(id) do
      {:ok, module} -> module
      {:error, _} -> nil
    end
  end

  @doc """
  Returns all registered exchange IDs as strings.

  ## Examples

      CCXT.Registry.exchanges()
      #=> ["aftermath", "alpaca", "apex", ...]

  """
  @spec exchanges() :: [String.t()]
  def exchanges, do: Enum.sort(@exchange_ids)

  @doc """
  Checks if an exchange ID is registered.

  ## Examples

      CCXT.Registry.registered?(:bybit)
      #=> true

  """
  @spec registered?(String.t() | atom()) :: boolean()
  def registered?(id) when is_atom(id), do: registered?(Atom.to_string(id))
  def registered?(id) when is_binary(id), do: Map.has_key?(@exchange_modules, id)

  @doc """
  Checks if the exchange module is compiled and loaded.

  Returns true only if the exchange is registered AND its module is
  available in the BEAM. Useful for distinguishing "known exchange"
  from "exchange module exists."

  ## Examples

      CCXT.Registry.loaded?(:bybit)
      #=> true  # if CCXT.Bybit is compiled

  """
  @spec loaded?(String.t() | atom()) :: boolean()
  def loaded?(id) do
    case lookup(id) do
      {:ok, module} -> Code.ensure_loaded?(module)
      {:error, _} -> false
    end
  end
end