1	# Match an HTTP method and path to a handler. Source: https://github.com/paymog/bend-kit/tree/main/router
2	import Base
3	
4	# route(wantMethod, gotMethod, "/users/:id", path) → Maybe params.
5	
6	def segs.one.if(h: String, acc: List<&2, String>, empty: Bool) -> List<&2, String>:
7	  match empty:
8	    case True{}:
9	      acc
10	    case False{}:
11	      h <> acc
12	
13	def segs.one(+h: String, acc: List<&2, String>) -> List<&2, String>:
14	  segs.one.if(h, acc, String.is_empty(h))
15	
16	def segs.keep(xs: List<&2, String>, acc: List<&2, String>) -> List<&2, String>:
17	  match xs:
18	    case Nil{}:
19	      acc
20	    case Con{h, t}:
21	      segs.keep(t, segs.one(h, acc))
22	
23	def segs(s: String) -> List<&2, String>:
24	  segs.keep(String.split(s, '/'), Nil{})
25	
26	def param(+seg: String) -> Bool:
27	  String.starts_with(seg, ":")
28	
29	@unsafe
30	def zip(pat: List<&2, String>, got: List<&2, String>, +m: Map<&2, String>) -> Maybe<&2, Map<&2, String>>:
31	  match pat:
32	    case Nil{}:
33	      match got:
34	        case Nil{}:
35	          Some{m}
36	        case Con{h, t}:
37	          None{}
38	    case Con{+p, +pt}:
39	      match got:
40	        case Nil{}:
41	          None{}
42	        case Con{+g, +gt}:
43	          Bool.pick(Maybe<&2, Map<&2, String>>, param(p), zip(pt, gt, Map.set(&2, String, m, String.drop(p, 1n), g)), Bool.pick(Maybe<&2, Map<&2, String>>, String.eq(p, g), zip(pt, gt, m), None{}))
44	
45	def route.ok(pattern: String, path: String, same: Bool) -> Maybe<&2, Map<&2, String>>:
46	  match same:
47	    case False{}:
48	      None{}
49	    case True{}:
50	      zip(segs(pattern), segs(path), Map.new(&2, String))
51	
52	def route(want: String, method: String, pattern: String, path: String) -> Maybe<&2, Map<&2, String>>:
53	  route.ok(pattern, path, String.eq(want, method))