defmodule Polymarket.Schemas.BookEvent do
  @moduledoc """
  Book event. A full order book snapshot for an asset.
  """

  use TypedEctoSchema

  alias Polymarket.Schemas.Ask
  alias Polymarket.Schemas.Bid
  alias Polymarket.Schemas.BookEvent
  alias Polymarket.Schemas.Coerce

  @primary_key false

  @derive Jason.Encoder
  typed_embedded_schema do
    field(:market, :string)
    field(:asset_id, :string)
    field(:hash, :string)
    # Unix epoch in milliseconds, delivered as a string (e.g. "1779658820355").
    field(:timestamp, :integer)
    field(:event_type, :string)
    field(:last_trade_price, :float)
    field(:tick_size, :float)

    embeds_many(:bids, Bid)
    embeds_many(:asks, Ask)
  end

  @required [:market, :asset_id, :hash, :timestamp, :event_type]

  @doc """
  Builds a `BookEvent` from a decoded (atom-keyed) websocket message.

  Constructs the struct directly — no `Ecto.Changeset` — for the websocket hot
  path. Numeric fields (delivered as JSON strings) are coerced via
  `Polymarket.Schemas.Coerce`. Returns `{:error, {:missing_fields, fields}}` when
  a required field is absent.
  """
  @spec from_attrs(map()) :: {:ok, t()} | {:error, {:missing_fields, [atom()]}}
  def from_attrs(attrs) do
    %BookEvent{
      market: attrs[:market],
      asset_id: attrs[:asset_id],
      hash: attrs[:hash],
      timestamp: Coerce.to_int(attrs[:timestamp]),
      event_type: attrs[:event_type],
      last_trade_price: Coerce.to_float(attrs[:last_trade_price]),
      tick_size: Coerce.to_float(attrs[:tick_size]),
      bids: bids(attrs[:bids]),
      asks: asks(attrs[:asks])
    }
    |> Coerce.require_fields(@required)
  end

  @spec bids([map()] | nil) :: [Bid.t()]
  defp bids(nil), do: []

  defp bids(levels) do
    Enum.map(levels, fn level ->
      %Bid{price: Coerce.to_float(level[:price]), size: Coerce.to_float(level[:size])}
    end)
  end

  @spec asks([map()] | nil) :: [Ask.t()]
  defp asks(nil), do: []

  defp asks(levels) do
    Enum.map(levels, fn level ->
      %Ask{price: Coerce.to_float(level[:price]), size: Coerce.to_float(level[:size])}
    end)
  end
end