Add CST to UTC (#135)

Author: mitchpaulus

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   Example: `` [sort -u] `file.txt` <> ! ``
 - Functions
   - `chomp`
+  - `cstToUtc`
   - `fromOleDate`
   - `toOleDate`
   - `__gitCompletion`

doc/functions.inc.html

@@ -302,6 +302,7 @@ <h1 id="functions-dates">Dates <a class="section-link" href="#functions-dates" a
         <tr> <td><code>fromOleDate</code></td> <td>Create a date from an OLE Automation date float. This is equivalent to Excel dates (<a href="https://learn.microsoft.com/en-us/troubleshoot/microsoft-365-apps/excel/wrongly-assumes-1900-is-leap-year">Less some early time bugs</a>).</td> <td><code>(<span class="sig-type sig-type-numeric">numeric</span> -- <span class="sig-type sig-type-date">date</span>)</code></td> </tr>
         <tr> <td><code>addDays</code></td> <td>Add days to a date.</td> <td><code>(<span class="sig-type sig-type-date">date</span> <span class="sig-type sig-type-numeric">numeric</span> -- <span class="sig-type sig-type-date">date</span>)</code></td> </tr>
         <tr> <td><code>utcToCst</code></td> <td>Convert a UTC datetime to US Central Time.</td> <td><code>(<span class="sig-type sig-type-date">date</span> -- <span class="sig-type sig-type-date">date</span>)</code></td> </tr>
+        <tr> <td><code>cstToUtc</code></td> <td>Convert a US Central Time datetime to UTC.</td> <td><code>(<span class="sig-type sig-type-date">date</span> -- <span class="sig-type sig-type-date">date</span>)</code></td> </tr>
     </tbody>
 </table>
 

doc/mshell.md

@@ -380,6 +380,7 @@ Metadata values must be static: strings (single or double quoted), integers, flo
 - `fromOleDate`: Convert an OLE Automation date float to a date `(numeric -- date)`
 - `addDays`: Add days to date `(date numeric -- date)`
 - `utcToCst`: Convert a UTC datetime to US Central Time `(date -- date)`
+- `cstToUtc`: Convert a US Central Time datetime to UTC `(date -- date)`
 
 ## Regular Expression Functions
 

mshell/BuiltInList.go

@@ -21,6 +21,7 @@ var BuiltInList = map[string]struct{}{
 	"ceil": {},
 	"countSubStr": {},
 	"cp": {},
+	"cstToUtc": {},
 	"date": {},
 	"dateFmt": {},
 	"day": {},

mshell/Evaluator.go

@@ -3089,6 +3089,36 @@ MainLoop:
 					dateTimeObj.Time = dateTimeObj.Time.In(cstLocation)
 					dateTimeObj.OriginalString = ""
 					stack.Push(dateTimeObj)
+				} else if t.Lexeme == "cstToUtc" {
+					obj1, err := stack.Pop()
+					if err != nil {
+						return state.FailWithMessage(fmt.Sprintf("%d:%d: Cannot do 'toUtc' operation on an empty stack.\n", t.Line, t.Column))
+					}
+
+					// Convert the datetime to UTC from assumed CST
+					dateTimeObj, ok := obj1.(*MShellDateTime)
+					if !ok {
+						return state.FailWithMessage(fmt.Sprintf("%d:%d: Cannot convert a %s to UTC.\n", t.Line, t.Column, obj1.TypeName()))
+					}
+
+					cstLocation, err := time.LoadLocation("America/Chicago")
+					if err != nil {
+						return state.FailWithMessage(fmt.Sprintf("%d:%d: Error loading CST location: %s\n", t.Line, t.Column, err.Error()))
+					}
+
+					cstTime := time.Date(
+						dateTimeObj.Time.Year(),
+						dateTimeObj.Time.Month(),
+						dateTimeObj.Time.Day(),
+						dateTimeObj.Time.Hour(),
+						dateTimeObj.Time.Minute(),
+						dateTimeObj.Time.Second(),
+						dateTimeObj.Time.Nanosecond(),
+						cstLocation,
+					)
+					dateTimeObj.Time = cstTime.In(time.UTC)
+					dateTimeObj.OriginalString = ""
+					stack.Push(dateTimeObj)
 				} else if t.Lexeme == "floor" {
 					// Round a number down to the nearest integer
 					obj1, err := stack.Pop()

tests/tz.msh

@@ -1,2 +1,17 @@
 2025-05-29T16:00 utcToCst str wl
 2025-01-02T16:00 utcToCst str wl
+2025-05-29T11:00 cstToUtc str wl
+2025-01-02T10:00 cstToUtc str wl
+
+# DST problems
+"Spring Forward" wl
+$"1 AM: {2025-03-09T01:00 cstToUtc isoDateTimeFmt}" wl
+$"2 AM: {2025-03-09T02:00 cstToUtc isoDateTimeFmt}" wl
+$"2:30 AM (doesn't actually exist): {2025-03-09T02:30 cstToUtc isoDateTimeFmt}" wl
+$"3 AM: {2025-03-09T03:00 cstToUtc isoDateTimeFmt}" wl
+
+"Fall Back" wl
+$"1 AM: {2025-11-02T01:00 cstToUtc isoDateTimeFmt}" wl
+$"2 AM: {2025-11-02T02:00 cstToUtc isoDateTimeFmt}" wl
+$"2:30 AM: {2025-11-02T02:30 cstToUtc isoDateTimeFmt}" wl
+$"3 AM: {2025-11-02T03:00 cstToUtc isoDateTimeFmt}" wl

tests/tz.msh.stdout

@@ -1,2 +1,14 @@
 2025-05-29T11:00:00
 2025-01-02T10:00:00
+2025-05-29T16:00:00
+2025-01-02T16:00:00
+Spring Forward
+1 AM: 2025-03-09T07:00:00
+2 AM: 2025-03-09T07:00:00
+2:30 AM (doesn't actually exist): 2025-03-09T07:30:00
+3 AM: 2025-03-09T08:00:00
+Fall Back
+1 AM: 2025-11-02T06:00:00
+2 AM: 2025-11-02T08:00:00
+2:30 AM: 2025-11-02T08:30:00
+3 AM: 2025-11-02T09:00:00