Add preserves/datehooks for handling dates and times

preserves.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version = "20230504"
+version = "20230512"
 author        = "Emery Hemingway"
 description   = "data model and serialization format"
 license       = "Unlicense"

src/preserves/Tupfile

@@ -1,3 +1,4 @@
 include_rules
 : foreach preserves_schema_nim.nim schemac.nim |> !nim |> $(BIN_DIR)/%B | $(BIN_DIR)/<%B>
+NIM_FLAGS += --path:$(TUP_CWD)/..
 : foreach *hooks.nim |> !nim_check |>

src/preserves/datehooks.nim

@@ -0,0 +1,44 @@
+# SPDX-FileCopyrightText: ☭ Emery Hemingway
+# SPDX-License-Identifier: Unlicense
+
+import std/times
+import ../preserves
+
+const
+  label = "rfc3339"
+  fullDateFormat = "yyyy-MM-dd"
+  partialTimeFormat = "HH:mm:ss"
+  fullTimeFormat = "HH:mm:sszzz"
+  dateTimeFormat = "yyyy-MM-dd'T'HH:mm:sszzz"
+
+proc toPreserveHook*(dt: DateTime; E: typedesc): Preserve[E] =
+  initRecord[E](toSymbol("rfc3339", E), toPreserve($dt, E))
+
+proc fromPreserveHook*[E](dt: var DateTime; pr: Preserve[E]): bool =
+  result = pr.isRecord(label, 1) and pr.record[0].isString
+  if result:
+    try:
+      let
+        s = pr.record[0].string
+        n = len(s)
+      if n == len(fullDateFormat):
+        dt = parse(s, fullDateFormat)
+      elif n == len(partialTimeFormat):
+        dt = parse(s, partialTimeFormat)
+      elif len(partialTimeFormat) < n and n <= len(fullTimeFormat):
+        dt = parse(s, fullTimeFormat)
+      elif len(fullTimeFormat) < n:
+        dt = parse(s, dateTimeFormat)
+      else:
+        result = false
+    except ValueError:
+      result = false
+
+runnableExamples:
+  import std/[times, unittest]
+  import preserves
+  var a, b: DateTime
+  a = now()
+  var pr = a.toPreserveHook(void)
+  check fromPreserveHook(b, pr)
+  check $a == $b