message: add utc-offset field

Add a new db field for storing UTC-offset for the Date: field.

lib/message/mu-fields.hh

@@ -68,7 +68,7 @@ struct Field {
 
 		// XXX: re-order when we update the db-schema.
 		Labels,         /**< Labels */
-
+		UtcOffset,      /**< Offset from UTC for the sent Date */
 		//
 		_count_         /**< Number of Ids */
 	};
@@ -465,6 +465,8 @@ inline constexpr std::array<Field, Field::id_size()>
 		Field::Flag::NormalTerm |
 		Field::Flag::PhrasableTerm,
 	    },
+	    // at the end for now; reordering when we're bumping
+	    // the db schema version.
 	    {
 		Field::Id::Labels,
 		Field::Type::StringList,
@@ -475,7 +477,16 @@ inline constexpr std::array<Field, Field::id_size()>
 		Field::Flag::BooleanTerm |
 		Field::Flag::Value |
 		Field::Flag::IncludeInSexp
-,
+	    },
+	    {
+		Field::Id::UtcOffset,
+		Field::Type::Integer,
+		"utc-offset", {},
+		"UTC offset for Date in seconds:",
+		{},
+		'u',
+		Field::Flag::Value |
+		Field::Flag::IncludeInSexp
 	    },
 
 	}};

lib/message/mu-message.cc

@@ -741,7 +741,10 @@ fill_document(Message::Private& priv)
 				doc.add(field.id, priv.ctime);
 			break;
 		case Field::Id::Date:
-			doc.add(field.id, mime_msg.date());
+			if (const auto& date{mime_msg.date()}; date) {
+				doc.add(field.id, date->first);
+				doc.add(Field::Id::UtcOffset, date->second);
+			}
 			break;
 		case Field::Id::EmbeddedText:
 			doc.add(field.id, priv.embedded);
@@ -801,6 +804,8 @@ fill_document(Message::Private& priv)
 		case Field::Id::To:
 			doc.add(field.id, mime_msg.contacts(Contact::Type::To));
 			break;
+		case Field::Id::UtcOffset:
+			break; // handle already as part of Date:
 		/* LCOV_EXCL_START */
 		case Field::Id::_count_:
 		default:

lib/message/mu-mime-object.cc

@@ -334,13 +334,17 @@ MimeMessage::make_from_text(const std::string& text)
 		return make_from_stream(std::move(stream));
 }
 
-Option<int64_t>
+Option<MimeMessage::Date>
 MimeMessage::date() const noexcept
 {
 	if (/*const*/GDateTime *dt{g_mime_message_get_date(self())}; !dt)
 		return Nothing;
-	else
-		return g_date_time_to_unix(dt);
+	else {
+		constexpr auto usecs_per_sec = 1'000'000;
+		return Date{ g_date_time_to_unix(dt),
+			     g_date_time_get_utc_offset(dt) / usecs_per_sec };
+
+	}
 }
 
 constexpr Option<GMimeAddressType>
@@ -431,7 +435,8 @@ MimeMessage::contacts(Contact::Type ctype) const noexcept
 		return {};
 
 	Contacts contacts;
-	add_contacts(addrs, ctype, date().value_or(0), contacts);
+	const auto mdate{date()};
+	add_contacts(addrs, ctype, mdate ? mdate->first : 0, contacts);
 
 	return contacts;
 }

lib/message/mu-mime-object.hh

@@ -1047,12 +1047,19 @@ public:
 		return Mu::to_string_opt(g_mime_message_get_subject(self()));
 	}
 
+	using Date = std::pair<int64_t/*unix-time*/, int64_t/*utc-offset in secs*/>;
+	/**< Date type */
+
 	/**
-	 * Gets the date if it exists, or nullopt otherwise.
+	 * Gets a date, utf-offset pair if it exists, or nullopt otherwise.
+	 *
+	 * The date is the number of seconds since epoch (i.e., unix time),
+	 * while utf-offset is the number of seconds offset from UTC
+	 * (i.e., negative numbers west of GMT, positive numbers for east)
 	 *
 	 * @return a time_t value (expressed as a 64-bit number) or nullopt
 	 */
-	Option<int64_t> date() const noexcept;
+	Option<Date> date() const noexcept;
 
 
 	/**