1	import Base
2	
3	# Encode one byte as a percent escape. The SQL library used this representation;
4	# keeping it preserves existing query and form-body behavior.
5	def hex_digit_kind(n: U32, decimal: Bool) -> U32:
6	    match decimal:
7	        case True{}: (48 + n : U32)
8	        case False{}: (55 + n : U32)
9	
10	def hex_digit(+n: U32) -> U32:
11	    hex_digit_kind(n, U32.is_lt(n, 10))
12	
13	def percent_byte(+byte: U32) -> String:
14	    SCon{Chr{37}, SCon{Chr{hex_digit(U32.div(byte, 16))}, SCon{Chr{hex_digit(U32.mod(byte, 16))}, SNil{}}}}
15	
16	def percent_codepoint_width(+codepoint: U32, width: U32) -> String:
17	    match width:
18	        case 1: percent_byte(codepoint)
19	        case 2: percent_byte((192 + U32.shrn(codepoint, 6n) : U32)) ++
20	                percent_byte((128 + U32.and(codepoint, 63) : U32))
21	        case 3: percent_byte((224 + U32.shrn(codepoint, 12n) : U32)) ++
22	                percent_byte((128 + U32.and(U32.shrn(codepoint, 6n), 63) : U32)) ++
23	                percent_byte((128 + U32.and(codepoint, 63) : U32))
24	        case _: percent_byte((240 + U32.shrn(codepoint, 18n) : U32)) ++
25	                percent_byte((128 + U32.and(U32.shrn(codepoint, 12n), 63) : U32)) ++
26	                percent_byte((128 + U32.and(U32.shrn(codepoint, 6n), 63) : U32)) ++
27	                percent_byte((128 + U32.and(codepoint, 63) : U32))
28	
29	def percent_codepoint(+codepoint: U32) -> String:
30	    +width = Bool.pick(U32, U32.is_lt(codepoint, 128), 1,
31	        Bool.pick(U32, U32.is_lt(codepoint, 2048), 2,
32	            Bool.pick(U32, U32.is_lt(codepoint, 65536), 3, 4)))
33	    percent_codepoint_width(codepoint, width)
34	
35	def percent_characters(text: String) -> String:
36	    match text:
37	        case SNil{}: ""
38	        case SCon{Chr{+codepoint}, tail}:
39	            percent_codepoint(codepoint) ++ percent_characters(tail)
40	
41	# Percent-encode a URL component as UTF-8 bytes. This deliberately encodes
42	# every byte, matching the former SQL.percent_component behavior.
43	def percent_component(text: String) -> String:
44	    percent_characters(text)