@spec background(term(), (-> term())) :: :ok

Start fun under key in the background unless one is already running; return at once.

@spec cached?(String.t()) :: boolean()

Whether url is already in the cache.

@spec dir() :: Path.t()

Where fetched files are kept.

@spec fetch(String.t()) :: {:ok, Path.t()} | {:error, term()}

The local path of url, fetched if it is not in the cache yet. A fetch of the same URL already under way is waited for rather than repeated.

The cache is $XDG_CACHE_HOME/tuning_fork/samples, or ~/.cache/tuning_fork/samples. {:error, reason} when the fetch fails or the cache cannot be written.

@spec get(String.t()) :: {:ok, binary()} | {:error, term()}

Fetch the body of url. Spaces and other characters a URL cannot carry are percent-encoded; what is already percent-encoded is left as it is.

@spec once(term(), (-> term())) :: :done

Run fun in a task registered under key, or wait for the one already running under that key, and return when it is done.

@spec prefetch([String.t()]) :: :ok

Start fetching every URL not yet in the cache, one after another in the background, and return at once. A list already being walked is not walked again.

@spec settle() :: :ok

Wait until every fetch and background task under way has finished.