1	import Base
2	import ../types/model.bend as T
3	import ../spec/clock.bend as Clock
4	import ./cache.bend as C
5	import ./public.bend as Pub
6	
7	# Deterministic model of the host clock loop over an explicit provider-event
8	# list. Only the neutral Clock.ClockEvent/Clock.Error datatypes are imported from the
9	# clock specification; no specification function is used. The adapter runs
10	# this machine through src/host.bend begin/answer (proofs/host_loop.bend).
11	type Outcome<-K: Data, -V: Data> is Data:
12	  Returned{cache: C.Cache<K, V>, answer: Pub.Answer<K, V>, remaining: List<&2, Clock.ClockEvent>, requests: Nat}
13	  Failed{cache: C.Cache<K, V>, error: Clock.Error, remaining: List<&2, Clock.ClockEvent>, requests: Nat}
14	
15	def bump(-K: Data, -V: Data, outcome: Outcome<K, V>) -> Outcome<K, V>:
16	  match outcome:
17	    case Returned{c, answer, events, requests}: Returned{c, answer, events, 1n+requests}
18	    case Failed{c, error, events, requests}: Failed{c, error, events, 1n+requests}
19	
20	# One step: the provider event answering a Waiting progress either resumes the
21	# machine or stops it with the retained state and the error. drive is its
22	# iteration (drive_advance in END_TO_END.bend); src/host.bend answer uses it.
23	type Step<-K: Data, -V: Data> is Data:
24	  Continue{progress: Pub.Progress<K, V>}
25	  Stopped{cache: C.Cache<K, V>, error: Clock.Error}
26	
27	def advance(-K: Data, -V: Data, zero_value: V, pending: Pub.Pending<K, V>, event: Clock.ClockEvent) -> Step<K, V>:
28	  match event:
29	    case Clock.Sample{now}: Continue{Pub.resume(K, V, zero_value, pending, now)}
30	    case Clock.InvalidSample{reason}: Stopped{Pub.abandon(K, V, pending), Clock.Invalid{reason}}
31	    case Clock.ProviderException{reason}: Stopped{Pub.abandon(K, V, pending), Clock.Thrown{reason}}
32	
33	def drive(-K: Data, -V: Data, +zero_value: V, events: List<&2, Clock.ClockEvent>, progress: Pub.Progress<K, V>) -> Outcome<K, V>:
34	  match events progress:
35	    case remaining Pub.Finished{c, answer}: Returned{c, answer, remaining, 0n}
36	    case Nil{} Pub.Waiting{pending}: Failed{Pub.abandon(K, V, pending), Clock.Exhausted{}, Nil{}, 1n}
37	    case Con{Clock.InvalidSample{reason}, tail} Pub.Waiting{pending}: Failed{Pub.abandon(K, V, pending), Clock.Invalid{reason}, tail, 1n}
38	    case Con{Clock.ProviderException{reason}, tail} Pub.Waiting{pending}: Failed{Pub.abandon(K, V, pending), Clock.Thrown{reason}, tail, 1n}
39	    case Con{Clock.Sample{now}, tail} Pub.Waiting{pending}: bump(K, V, drive(K, V, zero_value, tail, Pub.resume(K, V, zero_value, pending, now)))
40	
41	def execute(~K: Data, ~encode: K -> String, -V: Data, zero_key: K, +zero_value: V, c: C.Cache<K, V>, events: List<&2, Clock.ClockEvent>, request: Pub.Request<K, V>) -> Outcome<K, V>:
42	  drive(K, V, zero_value, events, Pub.start(K, V, encode, zero_key, zero_value, c, request))
43	
44	def cache(-K: Data, -V: Data, outcome: Outcome<K, V>) -> C.Cache<K, V>:
45	  match outcome:
46	    case Returned{c, answer, events, requests}: c
47	    case Failed{c, error, events, requests}: c
48	
49	def remaining(-K: Data, -V: Data, outcome: Outcome<K, V>) -> List<&2, Clock.ClockEvent>:
50	  match outcome:
51	    case Returned{c, answer, events, requests}: events
52	    case Failed{c, error, events, requests}: events
53	
54	def requests(-K: Data, -V: Data, outcome: Outcome<K, V>) -> Nat:
55	  match outcome:
56	    case Returned{c, answer, events, count}: count
57	    case Failed{c, error, events, count}: count
58	
59	# A caller may catch a failed command and continue from the retained state.
60	type Trace<-K: Data, -V: Data> is Data:
61	  Ran{cache: C.Cache<K, V>, remaining: List<&2, Clock.ClockEvent>, outcomes: List<&2, Outcome<K, V>>, requests: Nat}
62	
63	def prepend(-K: Data, -V: Data, +outcome: Outcome<K, V>, rest: Trace<K, V>) -> Trace<K, V>:
64	  Ran{c, events, outcomes, count} = rest
65	  Ran{c, events, Con{outcome, outcomes}, Nat.add(requests(K, V, outcome), count)}
66	
67	def run(~K: Data, ~encode: K -> String, -V: Data, requests: List<&2, Pub.Request<K, V>>, c: C.Cache<K, V>, +zero_key: K, +zero_value: V, events: List<&2, Clock.ClockEvent>) -> Trace<K, V>:
68	  match requests:
69	    case Nil{}: Ran{c, events, Nil{}, 0n}
70	    case Con{request, tail}:
71	      +outcome = execute(~K, ~encode, V, zero_key, zero_value, c, events, request)
72	      prepend(K, V, outcome, run(~K, ~encode, V, tail, cache(K, V, outcome), zero_key, zero_value, remaining(K, V, outcome)))