add m.location support

Needs cross-platform testing. Currently only tested on Android.

lib/models/content/message.dart

@@ -4,6 +4,7 @@ import "package:nexus/models/content/content.dart";
 import "package:nexus/models/info/file.dart";
 import "package:nexus/models/info/image.dart";
 import "package:nexus/models/info/video.dart";
+import "package:nexus/models/location.dart";
 part "message.freezed.dart";
 part "message.g.dart";
 
@@ -90,8 +91,12 @@ sealed class MessageContent extends Content with _$MessageContent {
   }) = VideoMessageContent;
 
   @FreezedUnionValue("m.location")
-  factory MessageContent.location({required String body, required Uri geoUri}) =
-      LocationMessageContent;
+  factory MessageContent.location({
+    required String body,
+    required Uri geoUri,
+    @JsonKey(name: "m.location", includeIfNull: false) LocationInfo? location,
+    @JsonKey(name: "m.asset", includeIfNull: false) LocationAsset? asset,
+  }) = LocationMessageContent;
 
   factory MessageContent.fromJson(Map<String, Object?> json) =>
       _$MessageContentFromJson(json);

lib/models/location.dart

@@ -0,0 +1,84 @@
+import "package:freezed_annotation/freezed_annotation.dart";
+import "package:latlong2/latlong.dart";
+import "package:nexus/models/content/message.dart";
+
+part "location.freezed.dart";
+part "location.g.dart";
+
+/// A location message's `m.location` block.
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable(includeIfNull: false)
+class const LocationInfo({required final Uri uri, final String? description})
+    with _$LocationInfo {
+  Map<String, Object?> toJson() => _$LocationInfoToJson(this);
+
+  factory LocationInfo.fromJson(Map<String, Object?> json) =>
+      _$LocationInfoFromJson(json);
+}
+
+/// A location message's `m.asset` block.
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable()
+class const LocationAsset({
+  @JsonKey(unknownEnumValue: LocationAssetType.pin)
+  final LocationAssetType type = .self,
+}) with _$LocationAsset {
+  Map<String, Object?> toJson() => _$LocationAssetToJson(this);
+
+  factory LocationAsset.fromJson(Map<String, Object?> json) =>
+      _$LocationAssetFromJson(json);
+}
+
+enum LocationAssetType {
+  @JsonValue("m.self")
+  self,
+
+  @JsonValue("m.pin")
+  pin,
+}
+
+extension LocationMessagePoint on LocationMessageContent {
+  LatLng? get point => location?.uri.latLng ?? geoUri.latLng;
+
+  String? get description => switch (location?.description?.trim()) {
+    final description? when description.isNotEmpty => description,
+    _ => null,
+  };
+
+  LocationAssetType get assetType => asset?.type ?? .self;
+}
+
+extension FormatLatLng on LatLng {
+  String get formatted =>
+      "${latitude.toStringAsFixed(5)}, ${longitude.toStringAsFixed(5)}";
+}
+
+extension GeoUri on Uri {
+  /// The coordinates of a geo: URI, like `geo:51.5,-0.12;u=35`.
+  LatLng? get latLng {
+    if (scheme != "geo") return null;
+    final coordinates = path.split(";").first.split(",");
+    if (coordinates.length < 2) return null;
+
+    return switch ((
+      double.tryParse(coordinates[0]),
+      double.tryParse(coordinates[1]),
+    )) {
+      (final latitude?, final longitude?)
+          when latitude.abs() <= 90 && longitude.abs() <= 180 =>
+        LatLng(latitude, longitude),
+      _ => null,
+    };
+  }
+
+  static Uri openStreetMap(LatLng point) => Uri.https(
+    "www.openstreetmap.org",
+    "/",
+    {"mlat": "${point.latitude}", "mlon": "${point.longitude}"},
+  ).replace(fragment: "map=16/${point.latitude}/${point.longitude}");
+
+  static Uri fromLatLng(LatLng point, {double? uncertainty}) => Uri.parse(
+    "geo:${point.latitude},${point.longitude}"
+    "${uncertainty == null ? "" : ";u=${uncertainty.round()}"}",
+  );
+}

lib/models/location_exception.dart

@@ -0,0 +1,11 @@
+enum LocationException(final String message) implements Exception {
+  servicesOff("Location services are turned off."),
+  denied("Nexus doesn't have permission to see your location."),
+  timedOut("Couldn't get your location in time."),
+  failed(
+    "Couldn't get your location. Check that location services are on, and that Nexus is allowed to use them.",
+  );
+
+  @override
+  String toString() => message;
+}