1	# ezsys/src/step: every decision the file and environment helpers make. It
2	# does no IO; src/sys.bend runs the effects and acts on these answers
3	# (SYS-TRUST-4).
4	import Base
5	
6	# after one read: read again with the text so far, or stop with an answer
7	type Read is Type:
8	  ReadMore{text: String}
9	  ReadStop{answer: Result<&1, &1, U32 & String, String>}
10	
11	# after the temporary file is written: rename it, or stop with a failure
12	type Save is Type:
13	  SaveMove{}
14	  SaveStop{error: U32 & String}
15	
16	# the bytes one read asks for: the file's size, and at least 64 KiB
17	def read.chunk(size: U32) -> U32:
18	  U32.max(size, 65536)
19	
20	# a chunk that is empty ends the file; any other is appended
21	def read.more(empty: Bool, text: String, got: String) -> Read:
22	  match empty:
23	    case True{}:
24	      ReadStop{Done{got}}
25	    case False{}:
26	      ReadMore{got ++ text}
27	
28	# what one read's answer means, with the text read before it
29	def read.step(res: Result<&1, &1, U32 & String, String>, got: String) -> Read:
30	  match res:
31	    case Fail{error}:
32	      ReadStop{Fail{error}}
33	    case Done{+text}:
34	      read.more(String.is_empty(text), text, got)
35	
36	# the answer when a file has not ended after every read file.read makes
37	def read.spent() -> Result<&1, &1, U32 & String, String>:
38	  Fail{(27, "ezsys: file.read: the file did not end")}
39	
40	# where file.save writes before it renames
41	def save.tmp(path: String) -> String:
42	  path ++ ".tmp"
43	
44	# what the temporary file's write answer means
45	def save.step(res: Result<&1, &1, U32 & String, Unit>) -> Save:
46	  match res:
47	    case Fail{error}:
48	      SaveStop{error}
49	    case Done{_u}:
50	      SaveMove{}
51	
52	# an environment variable's value, or the fallback when it is unset
53	def env.pick(
54	  res: Result<&1, &1, U32 & String, String>,
55	  fallback: String
56	) -> String:
57	  match res:
58	    case Fail{_error}:
59	      fallback
60	    case Done{value}:
61	      value