1 files changed, 119 insertions, 0 deletions
diff --git a/ui/lib/state/local/conversations.svelte.js b/ui/lib/state/local/conversations.svelte.js
new file mode 100644
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--- /dev/null
+++ b/ui/lib/state/local/conversations.svelte.js
@@ -0,0 +1,119 @@
+import { DateTime } from 'luxon';
+import { SvelteMap } from 'svelte/reactivity';
+
+import * as iter from '$lib/iterator.js';
+
+// Conversations were called "channels" in previous iterations. Support loading
+// data saved under that name to prevent the change from resetting everyone's
+// unread tracking.
+export const STORE_KEY_CHANNELS = 'pilcrow:channelsData';
+export const STORE_KEY_CONVERSATIONS = 'pilcrow:conversations';
+
+class Conversation {
+  draft = $state();
+  lastReadAt = $state(null);
+  scrollPosition = $state(null);
+
+  static fromStored({ draft, lastReadAt, scrollPosition }) {
+    return new Conversation({
+      draft,
+      lastReadAt: lastReadAt == null ? null : DateTime.fromISO(lastReadAt),
+      scrollPosition,
+    });
+  }
+
+  constructor({ draft = '', lastReadAt = null, scrollPosition = null } = {}) {
+    this.draft = draft;
+    this.lastReadAt = lastReadAt;
+    this.scrollPosition = scrollPosition;
+  }
+
+  toStored() {
+    const { draft, lastReadAt, scrollPosition } = this;
+    return {
+      draft,
+      lastReadAt: lastReadAt?.toISO(),
+      scrollPosition,
+    };
+  }
+}
+
+export class Conversations {
+  // Store conversationId -> { draft = '', lastReadAt = null, scrollPosition = null }
+  all = $state();
+
+  static fromLocalStorage() {
+    const stored =
+      localStorage.getItem(STORE_KEY_CONVERSATIONS) ?? localStorage.getItem(STORE_KEY_CHANNELS);
+    if (stored !== null) {
+      return Conversations.fromStored(JSON.parse(stored));
+    }
+    return Conversations.empty();
+  }
+
+  static fromStored(stored) {
+    const loaded = Object.keys(stored).map((conversationId) => [
+      conversationId,
+      Conversation.fromStored(stored[conversationId]),
+    ]);
+    const all = new SvelteMap(loaded);
+    return new Conversations({ all });
+  }
+
+  static empty() {
+    return new Conversations({ all: new SvelteMap() });
+  }
+
+  constructor({ all }) {
+    this.all = all;
+  }
+
+  conversation(conversationId) {
+    let conversation = this.all.get(conversationId);
+    if (conversation === undefined) {
+      conversation = new Conversation();
+      this.all.set(conversationId, conversation);
+    }
+    return conversation;
+  }
+
+  updateLastReadAt(conversationId, at) {
+    const conversation = this.conversation(conversationId);
+    // Do it this way, rather than with Math.max tricks, to avoid assignment
+    // when we don't need it, to minimize reactive changes:
+    if (conversation.lastReadAt === null || at > conversation.lastReadAt) {
+      conversation.lastReadAt = at;
+      this.save();
+    }
+  }
+
+  retainConversations(conversations) {
+    const conversationIds = conversations.map((conversation) => conversation.id);
+    const retain = new Set(conversationIds);
+    for (const conversationId of Array.from(this.all.keys())) {
+      if (!retain.has(conversationId)) {
+        this.all.delete(conversationId);
+      }
+    }
+    this.save();
+  }
+
+  toStored() {
+    return iter.reduce(
+      this.all.entries(),
+      (stored, [conversationId, conversation]) => ({
+        ...stored,
+        [conversationId]: conversation.toStored(),
+      }),
+      {},
+    );
+  }
+
+  save() {
+    let stored = this.toStored();
+    localStorage.setItem(STORE_KEY_CONVERSATIONS, JSON.stringify(stored));
+    // If we were able to save the data under `pilcrow:conversations`, then remove the old data;
+    // it is no longer needed and wouldn't be loaded anyways.
+    localStorage.removeItem(STORE_KEY_CHANNELS);
+  }
+}