Turns follower options into the request for GET|POST /{db}/_changes.

The CouchDB changes API takes its parameters in the query string, with two exceptions that need a POST and a JSON body: the _doc_ids and _selector filters. This module encodes the documented parameters the way CouchDB expects them, see https://docs.couchdb.org/en/stable/api/database/changes.html

Options

Every option is sent as the query parameter of the same name, encoded as:

• booleans, integers and atoms become their string form (true, 5, all_docs, now)
• strings are sent verbatim, so style: "all_docs" works as well
• nil drops the parameter, so heartbeat: nil lets the server side timeout end the response. Dropping both is refused, as nothing would ever end a quiet feed and a dead connection would go unnoticed

A few options are special:

• :feed defaults to :continuous. :longpoll and :normal are the alternatives
• longpoll: true is shorthand for feed: :longpoll
• :heartbeat defaults to 60 000 ms and :timeout to 7 200 000 ms
• :since is kept on the struct so the follower can advance it between reconnects. It is sent verbatim and never parsed. Only :now or an opaque sequence string are accepted. Anything else raises an ArgumentError. Omitting it leaves since as nil and drops the parameter, which begins at the start of the feed
• doc_ids: [...] switches to POST with filter=_doc_ids and the ids in the body, overriding any :filter
• selector: %{...} does the same with filter=_selector
• query_params: [k: v] adds raw parameters, as used for filter function arguments

Examples

iex> Sofa.Changes.Query.new([]) |> Sofa.Changes.Query.params()
[{"feed", "continuous"}, {"heartbeat", "60000"}, {"timeout", "7200000"}]

iex> Sofa.Changes.Query.new(longpoll: true, since: "42", heartbeat: nil)
...> |> Sofa.Changes.Query.params()
[{"feed", "longpoll"}, {"timeout", "7200000"}, {"since", "42"}]

iex> %Sofa.Changes.Query{method: :post, body: body} =
...>   Sofa.Changes.Query.new(doc_ids: ["a", "b"], filter: "ignored")
iex> body
%{"doc_ids" => ["a", "b"]}