1 files changed, 74 insertions, 0 deletions
diff --git a/ui/lib/store/messages.svelte.js b/ui/lib/store/messages.svelte.js
new file mode 100644
index 0000000..c0db71b
--- /dev/null
+++ b/ui/lib/store/messages.svelte.js
@@ -0,0 +1,74 @@
+const RUN_COALESCE_MAX_INTERVAL = 10 /* min */ * 60 /* sec */ * 1000; /* ms */
+
+export class Messages {
+  channels = $state({});
+
+  inChannel(channel) {
+    return this.channels[channel];
+  }
+
+  addMessage(channel, id, { at, sender, body }) {
+    let parsedAt = new Date(at);
+    const message = { id, at: parsedAt, body };
+
+    // You might be thinking, can't this be
+    //
+    //     let runs = (this.channels[channel] ||= []);
+    //
+    // Let me tell you, I thought that too. Javascript's semantics allow it. It
+    // didn't work - the first message in each channel was getting lost as the
+    // update to `this.channels` wasn't actually happening. I suspect this is
+    // due to the implementation of Svelte's `$state` rune, but I don't know it
+    // for sure.
+    //
+    // In any case, splitting the read and write up like this has the same
+    // semantics, and _works_. (This time, for sure!)
+    let runs = this.channels[channel] || [];
+
+    let currentRun = runs.slice(-1)[0];
+    if (currentRun === undefined) {
+      currentRun = { sender, messages: [message] };
+      runs.push(currentRun);
+    } else {
+      let lastMessage = currentRun.messages.slice(-1)[0];
+      let newRun =
+        currentRun.sender !== sender || parsedAt - lastMessage.at > RUN_COALESCE_MAX_INTERVAL;
+
+      if (newRun) {
+        currentRun = { sender, messages: [message] };
+        runs.push(currentRun);
+      } else {
+        currentRun.messages.push(message);
+      }
+    }
+
+    this.channels[channel] = runs;
+
+    return this;
+  }
+
+  setMessages(messages) {
+    this.channels = {};
+    for (let { channel, id, at, sender, body } of messages) {
+      this.addMessage(channel, id, { at, sender, body });
+    }
+    return this;
+  }
+
+  deleteMessage(messageId) {
+    for (let channel in this.channels) {
+      this.channels[channel] = this.channels[channel]
+        .map(({ sender, messages }) => ({
+          sender,
+          messages: messages.filter(({ id }) => id != messageId)
+        }))
+        .filter(({ messages }) => messages.length > 0);
+    }
+    return this;
+  }
+
+  deleteChannel(id) {
+    delete this.channels[id];
+    return this;
+  }
+}