defmodule CMDC.Agent.Retry do
  @moduledoc """
  Provider 错误分类与重试延迟计算。

  ## 错误分类

  - **Transient（暂时性）** — 限流、服务器过载、网络断开等，等待后重试可能成功。
  - **Permanent（永久性）** — 认证失败、上下文溢出、无效请求，重试无意义。

  永久性错误优先检测——若同一错误同时包含永久与暂时模式，归为永久性。

  ## 退避策略

  指数退避：`delay = base_ms × 2^(attempt-1)`，上限 `max_ms`。
  不引入 jitter——单 Agent 并发请求量不足以受益，且确定性延迟便于测试。
  """

  alias CMDC.Agent.Overflow

  @transient_patterns [
    "overloaded",
    "rate_limit",
    "rate limit",
    "too many requests",
    "429",
    "500",
    "502",
    "503",
    "504",
    "connection",
    "econnreset",
    "econnrefused",
    "etimedout",
    "fetch failed",
    "socket hang up",
    "request timeout",
    "server_error",
    "timeout",
    "recv_timeout",
    "connect_timeout",
    "read_timeout",
    "stream_timeout",
    "closed",
    "transport_error"
  ]

  @permanent_patterns Overflow.overflow_patterns() ++
                        [
                          "unauthorized",
                          "invalid_api_key",
                          "authentication"
                        ]

  # ==========================================================================
  # Public API
  # ==========================================================================

  @doc """
  返回 `true` 如果该错误是暂时性的、可以重试。

  ## 示例

      iex> CMDC.Agent.Retry.retryable?("429 Too Many Requests")
      true

      iex> CMDC.Agent.Retry.retryable?("context_length_exceeded")
      false
  """
  @spec retryable?(term()) :: boolean()
  def retryable?(reason) do
    text = stringify(reason) |> String.downcase()
    not matches_any?(text, @permanent_patterns) and matches_any?(text, @transient_patterns)
  end

  @doc """
  计算第 `attempt` 次重试的延迟毫秒数。

  ## 选项

  - `:base_ms` — 初始延迟（默认 `2_000`）
  - `:max_ms`  — 最大延迟（默认 `60_000`）

  ## 示例

      iex> CMDC.Agent.Retry.delay(1)
      2_000

      iex> CMDC.Agent.Retry.delay(3)
      8_000
  """
  @spec delay(pos_integer(), keyword()) :: pos_integer()
  def delay(attempt, opts \\ []) do
    base = Keyword.get(opts, :base_ms, 2_000)
    max = Keyword.get(opts, :max_ms, 60_000)
    min(base * Integer.pow(2, attempt - 1), max)
  end

  @doc "返回暂时性错误模式列表。"
  @spec transient_patterns() :: [String.t()]
  def transient_patterns, do: @transient_patterns

  @doc "返回永久性错误模式列表。"
  @spec permanent_patterns() :: [String.t()]
  def permanent_patterns, do: @permanent_patterns

  # ==========================================================================
  # 私有辅助
  # ==========================================================================

  defp stringify(reason) when is_binary(reason), do: reason
  defp stringify(reason) when is_atom(reason), do: Atom.to_string(reason)
  defp stringify(reason), do: inspect(reason)

  defp matches_any?(text, patterns) do
    Enum.any?(patterns, &String.contains?(text, &1))
  end
end