1	import Base
2	import ./Db.bend as Db
3	import ./Wal.bend as Wal
4	
5	# Identifies the durability boundary reached by a commit.
6	type Stage is Data:
7	  EncodingRejected{error: Wal.Error}
8	  AppendRejected{code: U32, message: String}
9	  AppendUnknown{code: U32, message: String}
10	  DurableAppend{}
11	
12	# Applies mutations only after the WAL commit stage is durable.
13	def apply(pair: Stage & List<&2, Wal.Mut>, +db: Db.Db) -> Db.Db & Stage:
14	  match pair:
15	    case (stage, muts):
16	      match stage:
17	        case EncodingRejected{error}:
18	          (db, EncodingRejected{error})
19	        case AppendRejected{code, message}:
20	          (db, AppendRejected{code, message})
21	        case AppendUnknown{code, message}:
22	          (db, AppendUnknown{code, message})
23	        case DurableAppend{}:
24	          match db:
25	            case Db.Db{dir, mem, frozen, batch_cap, bcache, levels, flushed, manifest_token, mem_count, frozen_count}:
26	              (Db.apply_done(Db.apply_and_rotate(muts, mem, frozen, mem_count, frozen_count), dir,
27	                batch_cap, bcache, levels, flushed, manifest_token), DurableAppend{})