[bugfix] Parse `scheduled_at` as ISO8601 with offset if RFC3339 parse fails (#4431)

# Description

> If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.
>
> If this is a documentation change, please briefly describe what you've changed and why.

Closes https://codeberg.org/superseriousbusiness/gotosocial/issues/4409 by reattempting `scheduled_at` parsing using ISO8601 offset.

## Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: `[ ]` -> `[x]`

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [x] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4431
Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Co-committed-by: tobi <tobi.smethurst@protonmail.com>

5 files changed, 89 insertions, 12 deletions

diff --git a/docs/api/swagger.yaml b/docs/api/swagger.yaml
index b84a3e21b..ae8888af4 100644
--- a/docs/api/swagger.yaml
+++ b/docs/api/swagger.yaml
@@ -11291,8 +11291,6 @@ paths:
                     description: unprocessable content
                 "500":
                     description: internal server error
-                "501":
-                    description: scheduled_at was set, but this feature is not yet implemented
             security:
                 - OAuth2 Bearer:
                     - write:statuses
diff --git a/internal/api/client/statuses/statuscreate.go b/internal/api/client/statuses/statuscreate.go
index 167b59b23..de06d2d8b 100644
--- a/internal/api/client/statuses/statuscreate.go
+++ b/internal/api/client/statuses/statuscreate.go
@@ -21,6 +21,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"time"
 
 	apimodel "code.superseriousbusiness.org/gotosocial/internal/api/model"
 	apiutil "code.superseriousbusiness.org/gotosocial/internal/api/util"
@@ -259,8 +260,6 @@ import (
 //			description: unprocessable content
 //		'500':
 //			description: internal server error
-//		'501':
-//			description: scheduled_at was set, but this feature is not yet implemented
 func (m *Module) StatusCreatePOSTHandler(c *gin.Context) {
 	authed, errWithCode := apiutil.TokenAuth(c,
 		true, true, true, true,
@@ -414,5 +413,30 @@ func parseStatusCreateForm(c *gin.Context) (*apimodel.StatusCreateRequest, gtser
 		form.Poll.ExpiresIn = util.PtrOrZero(expiresIn)
 	}
 
+	// Parse scheduled_at if given.
+	if form.ScheduledAtRaw != "" {
+		// Try RFC3339 initially, which
+		// is a stricter UTC subset of ISO8601.
+		scheduledAt, err := time.Parse(
+			time.RFC3339, form.ScheduledAtRaw,
+		)
+		if err != nil {
+			// Try ISO8601 with offset
+			// (many clients use this).
+			scheduledAt, err = time.Parse(
+				util.ISO8601Offset, form.ScheduledAtRaw,
+			)
+		}
+
+		// If we still have an error
+		// we can't use this time.
+		if err != nil {
+			text := "could not parse scheduled_at value " + form.ScheduledAtRaw + " as ISO8601 time"
+			return nil, gtserror.NewErrorBadRequest(errors.New(text), text)
+		}
+
+		form.ScheduledAt = &scheduledAt
+	}
+
 	return form, nil
 }
diff --git a/internal/api/client/statuses/statuscreate_test.go b/internal/api/client/statuses/statuscreate_test.go
index 84a6622a2..ca82502c2 100644
--- a/internal/api/client/statuses/statuscreate_test.go
+++ b/internal/api/client/statuses/statuscreate_test.go
@@ -467,7 +467,7 @@ func (suite *StatusCreateTestSuite) TestPostNewStatusMessedUpIntPolicy() {
 }`, out)
 }
 
-func (suite *StatusCreateTestSuite) TestPostNewScheduledStatus() {
+func (suite *StatusCreateTestSuite) TestPostNewScheduledStatusRFC3339() {
 	out, recorder := suite.postStatus(map[string][]string{
 		"status":       {"this is a brand new status! #helloworld"},
 		"spoiler_text": {"hello hello"},
@@ -497,6 +497,56 @@ func (suite *StatusCreateTestSuite) TestPostNewScheduledStatus() {
 }`, out)
 }
 
+func (suite *StatusCreateTestSuite) TestPostNewScheduledStatusISO8601Offset() {
+	out, recorder := suite.postStatus(map[string][]string{
+		"status":       {"this is a brand new status! #helloworld"},
+		"spoiler_text": {"hello hello"},
+		"sensitive":    {"true"},
+		"visibility":   {string(apimodel.VisibilityMutualsOnly)},
+		"scheduled_at": {"2080-09-05T19:38:00+0400"},
+	}, "")
+
+	// We should have OK from
+	// our call to the function.
+	suite.Equal(http.StatusOK, recorder.Code)
+
+	// A scheduled status with scheduled_at and status params should be returned.
+	suite.Equal(`{
+  "id": "ZZZZZZZZZZZZZZZZZZZZZZZZZZ",
+  "media_attachments": [],
+  "params": {
+    "application_id": "01F8MGY43H3N2C8EWPR2FPYEXG",
+    "language": "",
+    "scheduled_at": null,
+    "sensitive": true,
+    "spoiler_text": "hello hello",
+    "text": "this is a brand new status! #helloworld",
+    "visibility": "private"
+  },
+  "scheduled_at": "2080-09-05T15:38:00.000Z"
+}`, out)
+}
+
+func (suite *StatusCreateTestSuite) TestPostNewScheduledStatusNonsenseTime() {
+	out, recorder := suite.postStatus(map[string][]string{
+		"status":       {"this is a brand new status! #helloworld"},
+		"spoiler_text": {"hello hello"},
+		"sensitive":    {"true"},
+		"visibility":   {string(apimodel.VisibilityMutualsOnly)},
+		"scheduled_at": {"pee pee poo poo"},
+	}, "")
+
+	// We should have 400 from
+	// our call to the function.
+	suite.Equal(http.StatusBadRequest, recorder.Code)
+
+	// We should have a helpful error
+	// message telling us how we screwed up.
+	suite.Equal(`{
+  "error": "Bad Request: could not parse scheduled_at value pee pee poo poo as ISO8601 time"
+}`, out)
+}
+
 func (suite *StatusCreateTestSuite) TestPostNewBackfilledStatus() {
 	// A time in the past.
 	scheduledAtStr := "2020-10-04T15:32:02.018Z"
diff --git a/internal/api/model/status.go b/internal/api/model/status.go
index 3edb4be5f..3ce5913bd 100644
--- a/internal/api/model/status.go
+++ b/internal/api/model/status.go
@@ -248,14 +248,18 @@ type StatusCreateRequest struct {
 	// Deprecated: Only used if LocalOnly is not set.
 	Federated *bool `form:"federated" json:"federated"`
 
-	// ISO 8601 Datetime at which to schedule a status.
+	// ISO8601 datetime string at which to schedule a status.
 	//
-	// Providing this parameter with a *future* time will cause ScheduledStatus to be returned instead of Status.
-	// Must be at least 5 minutes in the future.
+	// Providing this parameter with a *future* time will cause ScheduledStatus
+	// to be returned instead of Status (must be at least 5 minutes in the future).
 	//
 	// Providing this parameter with a *past* time will cause the status to be backdated,
 	// and will not push it to the user's followers. This is intended for importing old statuses.
-	ScheduledAt *time.Time `form:"scheduled_at" json:"scheduled_at"`
+	ScheduledAtRaw string `form:"scheduled_at" json:"scheduled_at"`
+
+	// ScheduledAtParsed is the parsed version
+	// of scheduled_at, if scheduled_at was set.
+	ScheduledAt *time.Time `form:"-" json:"-"`
 
 	// ISO 639 language code for this status.
 	Language string `form:"language" json:"language"`
diff --git a/internal/util/time.go b/internal/util/time.go
index 9ea8d0c93..7f75920e8 100644
--- a/internal/util/time.go
+++ b/internal/util/time.go
@@ -20,9 +20,10 @@ package util
 import "time"
 
 const (
-	ISO8601     = "2006-01-02T15:04:05.000Z"
-	ISO8601Date = "2006-01-02"
-	RFC2822     = "Mon, 02 Jan 2006 15:04:05 -0700"
+	ISO8601       = "2006-01-02T15:04:05.000Z"
+	ISO8601Offset = "2006-01-02T15:04:05-0700"
+	ISO8601Date   = "2006-01-02"
+	RFC2822       = "Mon, 02 Jan 2006 15:04:05 -0700"
 )
 
 // FormatISO8601 converts the given time to UTC and then formats it