1 files changed, 118 insertions, 0 deletions
diff --git a/ui/lib/state/local/channels.svelte.js b/ui/lib/state/local/channels.svelte.js
new file mode 100644
index 0000000..9040685
--- /dev/null
+++ b/ui/lib/state/local/channels.svelte.js
@@ -0,0 +1,118 @@
+import { DateTime } from 'luxon';
+import { SvelteMap } from 'svelte/reactivity';
+
+import * as iter from '$lib/iterator.js';
+
+export const STORE_KEY_CHANNELS_DATA = 'pilcrow:channelsData';
+
+class Channel {
+  draft = $state();
+  lastReadAt = $state(null);
+  scrollPosition = $state(null);
+
+  static fromStored({ draft, lastReadAt, scrollPosition }) {
+    return new Channel({
+      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 Channels {
+  // Store channelId -> { draft = '', lastReadAt = null, scrollPosition = null }
+  all = $state();
+
+  static fromLocalStorage() {
+    const stored = localStorage.getItem(STORE_KEY_CHANNELS_DATA);
+    if (stored !== null) {
+      return Channels.fromStored(stored);
+    }
+    return Channels.empty();
+  }
+
+  static fromStored(stored) {
+    const loaded = Object.keys(stored).map((channelId) => [
+      channelId,
+      Channel.fromStored(stored[channelId])
+    ]);
+    const all = new SvelteMap(loaded);
+    return new Channels({ all });
+  }
+
+  static empty() {
+    return new Channels({ all: new SvelteMap() });
+  }
+
+  constructor({ all }) {
+    this.all = all;
+  }
+
+  channel(channelId) {
+    let channel = this.all.get(channelId);
+    if (channel === undefined) {
+      channel = new Channel();
+      this.all.set(channelId, channel);
+    }
+    return channel;
+  }
+
+  updateLastReadAt(channelId, at) {
+    const channel = this.channel(channelId);
+    // Do it this way, rather than with Math.max tricks, to avoid assignment
+    // when we don't need it, to minimize reactive changes:
+    if (channel.lastReadAt === null || at > channel.lastReadAt) {
+      channel.lastReadAt = at;
+      this.save();
+    }
+  }
+
+  retainChannels(channelIds) {
+    const retain = new Set(channelIds);
+    for (const channelId of Array.from(this.all.keys())) {
+      if (!retain.has(channelId)) {
+        this.all.delete(channelId);
+      }
+    }
+    this.save();
+  }
+
+  toStored() {
+    return iter.reduce(
+      this.all.entries(),
+      (stored, [channelId, channel]) => ({
+        ...stored,
+        [channelId]: channel.toStored()
+      }),
+      {}
+    );
+  }
+
+  save() {
+    let stored = this.toStored();
+    console.log(this, stored);
+    localStorage.setItem(STORE_KEY_CHANNELS_DATA, JSON.stringify(stored));
+  }
+}
+
+function objectMap(object, mapFn) {
+  return Object.keys(object).reduce((result, key) => {
+    result[key] = mapFn(object[key]);
+    return result;
+  }, {});
+}