1	import Base
2	import ./change_tick.bend as Tick
3	
4	# Metadata is Data; payload ownership stays in the typed column. Identity is
5	# the caller's closed typed column lens, never the family's display name.
6	type Stamp is Data:
7	  Stamp{added: Maybe<&2,Tick.Tick>,changed: Maybe<&2,Tick.Tick>}
8	type Entry is Data:
9	  Entry{id: U32,stamp: Stamp}
10	
11	def choose(found: Bool,stamp: Stamp,other: Stamp) -> Stamp:
12	  match found:
13	    case True{}: stamp
14	    case False{}: other
15	
16	def get_selected(entries: List<&2,Entry>,+id: U32,found: Bool,stamp: Stamp) -> Stamp:
17	  match entries found:
18	    case _ True{}: stamp
19	    case Nil{} False{}: Stamp{None{},None{}}
20	    case Con{Entry{key,current},rest} False{}: get_selected(rest,id,U32.is_eq(key,id),current)
21	
22	def get(entries: List<&2,Entry>,id: U32) -> Stamp:
23	  get_selected(entries,id,False{},Stamp{None{},None{}})
24	
25	
26	def keep(equal: Bool,entry: Entry,rest: List<&2,Entry>) -> List<&2,Entry>:
27	  match equal:
28	    case True{}: rest
29	    case False{}: entry <> rest
30	
31	def entry_id(entry:Entry) -> U32:
32	  match entry:
33	    case Entry{id,_}:id
34	
35	def clear_reversed(entries: List<&2,Entry>,+id: U32,acc: List<&2,Entry>) -> List<&2,Entry>:
36	  match entries:
37	    case []: List.reverse(&2,Entry,acc)
38	    case +entry <> rest: clear_reversed(rest,id,keep(U32.is_eq(entry_id(entry),id),entry,acc))
39	
40	def clear(entries: List<&2,Entry>,id: U32) -> List<&2,Entry>:
41	  clear_reversed(entries,id,[])
42	
43	def set(entries: List<&2,Entry>,+id: U32,stamp: Stamp) -> List<&2,Entry>:
44	  Entry{id,stamp} <> clear(entries,id)
45	
46	def written(wasPresent: Bool,stamp: Stamp,+tick: Tick.Tick) -> Stamp:
47	  match wasPresent stamp:
48	    case False{} _: Stamp{Some{tick},Some{tick}}
49	    case True{} Stamp{added,_}: Stamp{added,Some{tick}}
50	
51	def after_write(incoming: Bool,wasPresent: Bool,stamp: Stamp,tick: Tick.Tick) -> Stamp:
52	  match incoming:
53	    case False{}: Stamp{None{},None{}}
54	    case True{}: written(wasPresent,stamp,tick)
55	
56	# Presence is explicit: wrapped tick zero is a valid component timestamp.
57	def selected_age(+stamp:Tick.Tick,cursor:Maybe<&2,Tick.Tick>,+this:Tick.Tick) -> Bool:
58	  match cursor:
59	    case None{}:Bool.and(Tick.not_future(stamp,this),U32.is_lt(Tick.age(stamp,this),Tick.max_change_age()))
60	    case Some{last}:Tick.newer(stamp,last,this)
61	def selected(stamp:Maybe<&2,Tick.Tick>,cursor:Maybe<&2,Tick.Tick>,this:Tick.Tick) -> Bool:
62	  match stamp:
63	    case None{}:False{}
64	    case Some{tick}:selected_age(tick,cursor,this)
65	
66	# Compare bounded true ages against this captured run; None is a first-run cursor.
67	def added(stamp:Stamp,cursor:Maybe<&2,Tick.Tick>,this:Tick.Tick) -> Bool:
68	  match stamp:
69	    case Stamp{value,_}:selected(value,cursor,this)
70	def changed(stamp:Stamp,cursor:Maybe<&2,Tick.Tick>,this:Tick.Tick) -> Bool:
71	  match stamp:
72	    case Stamp{_,value}:selected(value,cursor,this)