Start work on storing notifications in the database

crates/rpc/src/notification.rs

@@ -0,0 +1,105 @@
+use strum::{Display, EnumIter, EnumString, IntoEnumIterator};
+
+// An integer indicating a type of notification. The variants' numerical
+// values are stored in the database, so they should never be removed
+// or changed.
+#[repr(i32)]
+#[derive(Copy, Clone, Debug, EnumIter, EnumString, Display)]
+pub enum NotificationKind {
+    ContactRequest = 0,
+    ChannelInvitation = 1,
+    ChannelMessageMention = 2,
+}
+
+pub enum Notification {
+    ContactRequest {
+        requester_id: u64,
+    },
+    ChannelInvitation {
+        inviter_id: u64,
+        channel_id: u64,
+    },
+    ChannelMessageMention {
+        sender_id: u64,
+        channel_id: u64,
+        message_id: u64,
+    },
+}
+
+#[derive(Copy, Clone)]
+pub enum NotificationEntityKind {
+    User,
+    Channel,
+    ChannelMessage,
+}
+
+impl Notification {
+    pub fn from_fields(kind: NotificationKind, entity_ids: [Option<u64>; 3]) -> Option<Self> {
+        use NotificationKind::*;
+
+        Some(match kind {
+            ContactRequest => Self::ContactRequest {
+                requester_id: entity_ids[0]?,
+            },
+            ChannelInvitation => Self::ChannelInvitation {
+                inviter_id: entity_ids[0]?,
+                channel_id: entity_ids[1]?,
+            },
+            ChannelMessageMention => Self::ChannelMessageMention {
+                sender_id: entity_ids[0]?,
+                channel_id: entity_ids[1]?,
+                message_id: entity_ids[2]?,
+            },
+        })
+    }
+
+    pub fn to_fields(&self) -> (NotificationKind, [Option<(u64, NotificationEntityKind)>; 3]) {
+        use NotificationKind::*;
+
+        match self {
+            Self::ContactRequest { requester_id } => (
+                ContactRequest,
+                [
+                    Some((*requester_id, NotificationEntityKind::User)),
+                    None,
+                    None,
+                ],
+            ),
+
+            Self::ChannelInvitation {
+                inviter_id,
+                channel_id,
+            } => (
+                ChannelInvitation,
+                [
+                    Some((*inviter_id, NotificationEntityKind::User)),
+                    Some((*channel_id, NotificationEntityKind::User)),
+                    None,
+                ],
+            ),
+
+            Self::ChannelMessageMention {
+                sender_id,
+                channel_id,
+                message_id,
+            } => (
+                ChannelMessageMention,
+                [
+                    Some((*sender_id, NotificationEntityKind::User)),
+                    Some((*channel_id, NotificationEntityKind::ChannelMessage)),
+                    Some((*message_id, NotificationEntityKind::Channel)),
+                ],
+            ),
+        }
+    }
+}
+
+impl NotificationKind {
+    pub fn all() -> impl Iterator<Item = Self> {
+        Self::iter()
+    }
+
+    pub fn from_i32(i: i32) -> Option<Self> {
+        Self::iter().find(|kind| *kind as i32 == i)
+    }
+}