@spec delete_group(Celery.t() | Celery.Config.t(), String.t()) :: :ok

Deletes group metadata from celery-taskset-meta-<group_id>.

@spec encode_result_meta(
  Celery.t() | Celery.Config.t(),
  String.t(),
  term(),
  String.t(),
  keyword()
) :: {:ok, String.t(), map()} | {:error, term()}

Encodes a task result metadata dictionary into the exact JSON format stored in Redis by Python Celery.

@spec exception_to_elixir(term(), String.t() | nil) :: Exception.t()

Converts a stored exception dictionary (%{"exc_type" => ..., "exc_message" => ..., "exc_module" => ...}) into an Elixir exception struct (%Celery.RemoteError{} or %Celery.TaskRevokedError{}).

@spec forget(Celery.t() | Celery.Config.t(), String.t()) :: :ok

Deletes the task's result metadata from Redis.

@spec get_key_for_chord(Celery.t() | Celery.Config.t(), String.t(), String.t()) ::
  String.t()

Returns the Redis key for a chord ID ("chord-unlock-<group_id>").

@spec get_key_for_group(Celery.t() | Celery.Config.t(), String.t(), String.t()) ::
  String.t()

Returns the Redis key for a group/taskset ID ("celery-taskset-meta-<group_id>").

@spec get_key_for_task(Celery.t() | Celery.Config.t(), String.t(), String.t()) ::
  String.t()

Returns the Redis key for a task ID ("celery-task-meta-<task_id>", prefixed with global_keyprefix if configured).

@spec get_many(Celery.t() | Celery.Config.t(), [String.t()]) :: %{
  required(String.t()) => map()
}

Fetches metadata for multiple task IDs in a single MGET call.

@spec get_result(Celery.t() | Celery.Config.t(), String.t()) :: term()

Returns the task result (or reconstructed %Celery.RemoteError{} if failed).

@spec get_state(Celery.t() | Celery.Config.t(), String.t()) :: String.t()

Returns the current task state ("PENDING", "SUCCESS", "FAILURE", etc.).

@spec get_task_meta(Celery.t() | Celery.Config.t(), String.t()) :: map()

Fetches the decoded task metadata dictionary from Redis. If the task does not exist in Redis, returns %{"status" => "PENDING", "result" => nil}.

@spec get_traceback(Celery.t() | Celery.Config.t(), String.t()) :: String.t() | nil

Returns the task traceback string (or nil).

@spec mark_as_done(Celery.t() | Celery.Config.t(), String.t(), term(), keyword()) ::
  {:ok, term()} | {:error, term()}

Marks a task as SUCCESS in the result backend and triggers chord completion if the request is part of a chord.

@spec mark_as_failure(Celery.t() | Celery.Config.t(), String.t(), term(), keyword()) ::
  {:ok, term()} | {:error, term()}

Marks a task as FAILURE in the result backend, triggers chord failure handling if part of a chord, propagates failure down any attached chain, and invokes errbacks.

@spec mark_as_retry(Celery.t() | Celery.Config.t(), String.t(), term(), keyword()) ::
  {:ok, term()} | {:error, term()}

Marks a task as RETRY in the result backend.

@spec mark_as_revoked(
  Celery.t() | Celery.Config.t(),
  String.t(),
  String.t(),
  keyword()
) ::
  {:ok, term()} | {:error, term()}

Marks a task as REVOKED in the result backend.

@spec mark_as_started(Celery.t() | Celery.Config.t(), String.t(), map(), keyword()) ::
  {:ok, term()} | {:error, term()}

Marks a task as STARTED in the result backend (meta typically includes %{pid: ..., hostname: ...}).

@spec on_chord_part_return(
  Celery.t() | Celery.Config.t(),
  Celery.Task.Context.t(),
  String.t(),
  term()
) ::
  :ok

Handles completion of a chord header part (on_chord_part_return in celery/backends/redis.py).

Records [1, task_id, state, encoded_result] in celery-taskset-meta-<gid>.j (using ZADD when result_chord_ordered is true and group_index is present, or RPUSH otherwise) and triggers the chord callback once all parts have completed.

@spec prepare_exception(term()) :: map()

Serializes an Elixir exception or error term into Python Celery's JSON exception dictionary: %{"exc_type" => ..., "exc_message" => [...], "exc_module" => ...}.

@spec restore_group(Celery.t() | Celery.Config.t(), String.t()) :: map() | nil

Restores group result metadata from celery-taskset-meta-<group_id>.

@spec save_group(Celery.t() | Celery.Config.t(), String.t(), map()) ::
  :ok | {:error, term()}

Saves group result metadata under celery-taskset-meta-<group_id>.

@spec set_chord_size(Celery.t() | Celery.Config.t(), String.t(), non_neg_integer()) ::
  :ok

Sets the expected chord size in Redis (celery-taskset-meta-<group_id>.s), matching Python Celery's RedisBackend.set_chord_size/2.

@spec store_result(
  Celery.t() | Celery.Config.t(),
  String.t(),
  term(),
  String.t(),
  keyword()
) :: {:ok, term()} | {:error, term()}

Stores task state and result in Redis and publishes the metadata to the task's Redis Pub/Sub channel (SETEX key expires value + PUBLISH key value).

Matches Python Celery's deduplication behavior: if the existing state in Redis is already "SUCCESS", does not overwrite it.

@spec wait_for(Celery.t() | Celery.Config.t(), String.t(), keyword()) :: term()

Waits for a task to reach one of States.ready_states() (SUCCESS, FAILURE, REVOKED), returning the result or raising if propagate: true (default) and the task failed/revoked.

Options:

• :timeout - timeout in milliseconds or seconds (float, e.g. 5.0, or integer ms 5000, or :infinity; default :infinity)
• :interval - polling interval in milliseconds (default 50)
• :propagate - whether to raise on FAILURE / REVOKED (default true)