1	import Base
2	import ./DurableError.bend as DurableError
3	
4	# Tracks whether the handle accepts data operations.
5	type HandleState is Data:
6	  Open{}
7	  Poisoned{}
8	  MaintenanceBlocked{}
9	
10	# Increments the per-handle operation error count.
11	def next_operation_errors(count: Nat) -> Nat:
12	  Nat.add(count, 1n)
13	
14	# Distinguishes failures before and after WAL append begins.
15	type AppendPhase is Data:
16	  BeforeAppend{}
17	  AppendStarted{}
18	
19	# Tracks whether failed maintenance blocks later writes.
20	type MaintenanceState is Data:
21	  MaintenanceSucceeded{}
22	  MaintenanceFailed{error: DurableError.Error}
23	
24	# Checks whether accepts data operation.
25	def accepts_data_operation(state: HandleState) -> Bool:
26	  match state:
27	    case Open{}:
28	      True{}
29	    case Poisoned{}:
30	      False{}
31	    case MaintenanceBlocked{}:
32	      False{}
33	
34	# Selects handle state from the write failure stage.
35	def state_after_write_failure(phase: AppendPhase, current: HandleState) -> HandleState:
36	  match phase:
37	    case BeforeAppend{}:
38	      current
39	    case AppendStarted{}:
40	      Poisoned{}
41	
42	# Blocks writes when maintenance fails.
43	def state_after_maintenance(result: MaintenanceState) -> HandleState:
44	  match result:
45	    case MaintenanceSucceeded{}:
46	      Open{}
47	    case MaintenanceFailed{_}:
48	      MaintenanceBlocked{}
49	
50	# Reports maintenance separately from the confirmed commit.
51	def committed_maintenance(commit_error: Maybe<&2, DurableError.Error>) -> Bool:
52	  match commit_error:
53	    case Some{_}:
54	      False{}
55	    case None{}:
56	      True{}