From a769e80808113b02f4b71bd9f22a095ab6cf60eb Mon Sep 17 00:00:00 2001
From: Bohdan Horbeshko <bodqhrohro@gmail.com>
Date: Thu, 10 Feb 2022 21:08:43 -0500
Subject: [PATCH] Add /schedule command to send a message in certain time

---
 telegram/commands.go | 81 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)

diff --git a/telegram/commands.go b/telegram/commands.go
index 74c2cfa..61cd2f9 100644
--- a/telegram/commands.go
+++ b/telegram/commands.go
@@ -57,6 +57,7 @@ var chatCommands = map[string]command{
 	"d":          command{"[n]", "delete your last message(s)"},
 	"s":          command{"edited message", "edit your last message"},
 	"silent":     command{"message", "send a message without sound"},
+	"schedule":   command{"{online | 2006-01-02T15:04:05 | 15:04:05} message", "schedules a message either to timestamp or to whenever the user goes online"},
 	"add":        command{"@username", "add @username to your chat list"},
 	"join":       command{"https://t.me/invite_link", "join to chat via invite link"},
 	"group":      command{"title", "create groupchat «title» with current user"},
@@ -471,6 +472,86 @@ func (c *Client) ProcessChatCommand(chatID int64, cmdline string) (string, bool)
 		} else {
 			return "Message processing error", true
 		}
+	// schedule a message to timestamp or to going online
+	case "schedule":
+		if len(args) < 2 {
+			return "Not enough arguments", true
+		}
+
+		var state client.MessageSchedulingState
+		var result string
+		due := args[0]
+		if due == "online" {
+			state = &client.MessageSchedulingStateSendWhenOnline{}
+			result = due
+		} else {
+			if c.Session.Timezone == "" {
+				due += "Z"
+			} else {
+				due += c.Session.Timezone
+			}
+
+			switch 0 {
+			default:
+				// try bare time first
+				timestamp, err := time.Parse("15:04:05Z07:00", due)
+				if err == nil {
+					now := time.Now().In(c.Session.TimezoneToLocation())
+					// combine timestamp's time with today's date
+					timestamp = time.Date(
+						now.Year(),
+						now.Month(),
+						now.Day(),
+						timestamp.Hour(),
+						timestamp.Minute(),
+						timestamp.Second(),
+						0,
+						timestamp.Location(),
+					)
+					diff := timestamp.Sub(now)
+					if diff < 0 { // set to tomorrow
+						timestamp = timestamp.AddDate(0, 0, 1)
+					}
+					state = &client.MessageSchedulingStateSendAtDate{
+						SendDate: int32(timestamp.Unix()),
+					}
+					result = timestamp.Format(time.RFC3339)
+
+					break
+				}
+
+				timestamp, err = time.Parse(time.RFC3339, due)
+				if err == nil {
+					// 2038 doomsday again
+					state = &client.MessageSchedulingStateSendAtDate{
+						SendDate: int32(timestamp.Unix()),
+					}
+					result = timestamp.Format(time.RFC3339)
+
+					break
+				}
+
+				return "Invalid schedule time specifier", true
+			}
+		}
+
+		content := c.ProcessOutgoingMessage(0, rawCmdArguments(cmdline, 1), "")
+
+		if content != nil {
+			_, err := c.client.SendMessage(&client.SendMessageRequest{
+				ChatId:              chatID,
+				InputMessageContent: content,
+				Options: &client.MessageSendOptions{
+					SchedulingState: state,
+				},
+			})
+			if err != nil {
+				return err.Error(), true
+			}
+			return "Scheduled to " + result, true
+		} else {
+			return "Message processing error", true
+		}
 	// add @contact
 	case "add":
 		if len(args) < 1 {