1	import Base
2	import ./Protocol.bend as Protocol
3	import ./CursorCodec.bend as CursorCodec
4	import bend-kit-bytes@0.3.2.0/bytes.bend as Bytes
5	
6	# Reports one owner-issued cursor identifier or a rejected open response.
7	type OpenDecision is Type:
8	  Opened{cursor_id: U32}
9	  OpenRejected{status: Protocol.ResponseStatus}
10	  OpenMalformed{}
11	
12	# Reports one decoded cursor frame or a rejected next response.
13	type NextDecision is Type:
14	  NextFrame{frame: CursorCodec.Frame}
15	  NextRejected{status: Protocol.ResponseStatus}
16	  NextMalformed{}
17	
18	# Reports whether an owner acknowledged cursor closure with an exact body.
19	type CloseDecision is Data:
20	  CloseSucceeded{}
21	  CloseRejected{status: Protocol.ResponseStatus}
22	  CloseMalformed{}
23	
24	# Decodes the owner cursor ID only from a successful exact token payload.
25	# Converts an exact token parse into a typed cursor-open decision.
26	def open.parsed(parsed: Maybe<&2, U32>) -> OpenDecision:
27	  match parsed:
28	    case Some{cursor_id}: Opened{cursor_id}
29	    case None{}: OpenMalformed{}
30	
31	# Decodes a successful owner cursor-open response or preserves its rejection.
32	def open(status: Protocol.ResponseStatus, payload: Bytes.Bytes) -> OpenDecision:
33	  match status:
34	    case Protocol.Success{}:
35	      open.parsed(Protocol.snapshot.id.read(payload))
36	    case _: OpenRejected{status}
37	
38	# Converts one exact cursor frame decode into a typed client decision.
39	def next.decoded(decision: CursorCodec.Decision) -> NextDecision:
40	  match decision:
41	    case CursorCodec.Decoded{frame}: NextFrame{frame}
42	    case CursorCodec.Malformed{}: NextMalformed{}
43	
44	# Decodes a raw-byte cursor frame only from a successful owner response.
45	def next(status: Protocol.ResponseStatus, payload: Bytes.Bytes) -> NextDecision:
46	  match status:
47	    case Protocol.Success{}:
48	      next.decoded(CursorCodec.decode(payload))
49	    case _: NextRejected{status}
50	
51	# Accepts one close payload only when its measured length is zero.
52	def close.measured(measured: Bytes.Bytes & U32) -> CloseDecision:
53	  match measured:
54	    case (_, 0): CloseSucceeded{}
55	    case _: CloseMalformed{}
56	
57	# Accepts cursor close only when success carries no trailing payload.
58	def close(status: Protocol.ResponseStatus, payload: Bytes.Bytes) -> CloseDecision:
59	  match status:
60	    case Protocol.Success{}:
61	      close.measured(Bytes.length(payload))
62	    case _: CloseRejected{status}