1	import Base
2	import ./ordinary_declaration.bend as C
3	import ./persistence_declaration.bend as Decl
4	import ./decode_data.bend as D
5	import ./decode.bend as Decode
6	
7	type Leaf<-S:Data,-P:Type,-identity:C.Declaration<S,P>,-project:P -> P & D.Raw> is Type:
8	  Plain{}
9	  Transient{}
10	  Constructed{declaration:Decl.Constructed<S,P,identity,project>}
11	type Refusal is Data:
12	  PlainUnserializable{key:String}
13	  InvalidProjection{key:String,error:D.Error}
14	  MalformedColumn{key:String}
15	  DescriptorMismatch{expected:String,actual:String}
16	type Field is Data:
17	  Omitted{}
18	  Saved{field:D.Field}
19	  Refused{reason:Refusal}
20	
21	def plain(~S:Data,~P:Type,~identity:C.Declaration<S,P>,~project:P -> P & D.Raw,declaration:Decl.Plain<S,P,identity>) -> Leaf<S,P,identity,project>:Plain{}
22	def transient(~S:Data,~P:Type,~identity:C.Declaration<S,P>,~project:P -> P & D.Raw,declaration:Decl.Transient<S,P,identity>) -> Leaf<S,P,identity,project>:Transient{}
23	def constructed(~S:Data,~P:Type,~identity:C.Declaration<S,P>,~project:P -> P & D.Raw,declaration:Decl.Constructed<S,P,identity,project>) -> Leaf<S,P,identity,project>:Constructed{declaration}
24	def eligibility(~S:Data,~P:Type,~identity:C.Declaration<S,P>,~project:P -> P & D.Raw,recipe:Leaf<S,P,identity,project>) -> Leaf<S,P,identity,project> & Maybe<&2,Refusal>:
25	  match recipe:
26	    case Plain{}:(Plain{},Some{PlainUnserializable{C.key(~S,~P,identity)}})
27	    case Transient{}:(Transient{},None{})
28	    case Constructed{declaration}:(Constructed{declaration},None{})
29	def projected(~S:Data,~P:Type,~identity:C.Declaration<S,P>,~project:P -> P & D.Raw,declaration:Decl.Constructed<S,P,identity,project>,result:D.Receipt<P>) -> Leaf<S,P,identity,project> & (P & Field):
30	  match result:
31	    case D.Receipt{owner,D.Accepted{value}}:(Constructed{declaration},(owner,Saved{D.Field{C.key(~S,~P,identity),value}}))
32	    case D.Receipt{owner,D.Rejected{error}}:(Constructed{declaration},(owner,Refused{InvalidProjection{C.key(~S,~P,identity),error}}))
33	# The same retained ordinary declaration supplies codec and actual-owner
34	# projection. Transient and Plain never evaluate the projection.
35	def export(~S:Data,~P:Type,~identity:C.Declaration<S,P>,~project:P -> P & D.Raw,recipe:Leaf<S,P,identity,project>,owner:P) -> Leaf<S,P,identity,project> & (P & Field):
36	  match recipe:
37	    case Plain{}:(Plain{},(owner,Refused{PlainUnserializable{C.key(~S,~P,identity)}}))
38	    case Transient{}:(Transient{},(owner,Omitted{}))
39	    case Constructed{+declaration}:projected(~S,~P,~identity,~project,declaration,Decode.decode_owner(~P,~project,Decl.codec(~S,~P,~identity,~project,declaration),owner))