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src/lib/activitypub/activities.ts

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+/**
+ * ActivityPub Activities
+ * 
+ * Handles creation of ActivityPub activity objects for federation.
+ * See: https://www.w3.org/TR/activitypub/#overview
+ */
+
+import type { posts, users } from '@/db/schema';
+
+type Post = typeof posts.$inferSelect;
+type User = typeof users.$inferSelect;
+
+const ACTIVITY_STREAMS_CONTEXT = 'https://www.w3.org/ns/activitystreams';
+
+export interface ActivityPubNote {
+    '@context': string;
+    id: string;
+    type: 'Note';
+    attributedTo: string;
+    content: string;
+    published: string;
+    to: string[];
+    cc: string[];
+    inReplyTo?: string | null;
+    url: string;
+    attachment?: {
+        type: string;
+        mediaType: string;
+        url: string;
+        name?: string;
+    }[];
+}
+
+export interface ActivityPubActivity {
+    '@context': string | (string | object)[];
+    id: string;
+    type: 'Create' | 'Follow' | 'Like' | 'Announce' | 'Undo' | 'Accept' | 'Reject' | 'Delete' | 'Move';
+    actor: string;
+    object: string | ActivityPubNote | object;
+    target?: string;
+    published?: string;
+    to?: string[];
+    cc?: string[];
+    'synapsis:did'?: string; // Synapsis extension for DID-based migration
+}
+
+/**
+ * Convert a Synapsis post to an ActivityPub Note
+ */
+export function postToNote(post: Post, author: User, nodeDomain: string): ActivityPubNote {
+    const postUrl = `https://${nodeDomain}/posts/${post.id}`;
+    const actorUrl = `https://${nodeDomain}/users/${author.handle}`;
+
+    return {
+        '@context': ACTIVITY_STREAMS_CONTEXT,
+        id: postUrl,
+        type: 'Note',
+        attributedTo: actorUrl,
+        content: escapeHtml(post.content),
+        published: post.createdAt.toISOString(),
+        to: ['https://www.w3.org/ns/activitystreams#Public'],
+        cc: [`${actorUrl}/followers`],
+        inReplyTo: post.replyToId ? `https://${nodeDomain}/posts/${post.replyToId}` : null,
+        url: postUrl,
+    };
+}
+
+/**
+ * Create a Create activity for a new post
+ */
+export function createCreateActivity(
+    post: Post,
+    author: User,
+    nodeDomain: string
+): ActivityPubActivity {
+    const actorUrl = `https://${nodeDomain}/users/${author.handle}`;
+    const note = postToNote(post, author, nodeDomain);
+
+    return {
+        '@context': ACTIVITY_STREAMS_CONTEXT,
+        id: `https://${nodeDomain}/activities/${post.id}`,
+        type: 'Create',
+        actor: actorUrl,
+        published: post.createdAt.toISOString(),
+        to: note.to,
+        cc: note.cc,
+        object: note,
+    };
+}
+
+/**
+ * Create a Follow activity
+ */
+export function createFollowActivity(
+    follower: User,
+    targetActorUrl: string,
+    nodeDomain: string,
+    activityId: string
+): ActivityPubActivity {
+    const actorUrl = `https://${nodeDomain}/users/${follower.handle}`;
+
+    return {
+        '@context': ACTIVITY_STREAMS_CONTEXT,
+        id: `https://${nodeDomain}/activities/${activityId}`,
+        type: 'Follow',
+        actor: actorUrl,
+        object: targetActorUrl,
+    };
+}
+
+/**
+ * Create a Like activity
+ */
+export function createLikeActivity(
+    user: User,
+    targetPostUrl: string,
+    nodeDomain: string,
+    activityId: string
+): ActivityPubActivity {
+    const actorUrl = `https://${nodeDomain}/users/${user.handle}`;
+
+    return {
+        '@context': ACTIVITY_STREAMS_CONTEXT,
+        id: `https://${nodeDomain}/activities/${activityId}`,
+        type: 'Like',
+        actor: actorUrl,
+        object: targetPostUrl,
+    };
+}
+
+/**
+ * Create an Announce (repost) activity
+ */
+export function createAnnounceActivity(
+    user: User,
+    targetPostUrl: string,
+    nodeDomain: string,
+    activityId: string
+): ActivityPubActivity {
+    const actorUrl = `https://${nodeDomain}/users/${user.handle}`;
+
+    return {
+        '@context': ACTIVITY_STREAMS_CONTEXT,
+        id: `https://${nodeDomain}/activities/${activityId}`,
+        type: 'Announce',
+        actor: actorUrl,
+        object: targetPostUrl,
+        to: ['https://www.w3.org/ns/activitystreams#Public'],
+        cc: [`${actorUrl}/followers`],
+    };
+}
+
+/**
+ * Create an Undo activity (for unfollowing, unliking, etc.)
+ */
+export function createUndoActivity(
+    user: User,
+    originalActivity: ActivityPubActivity,
+    nodeDomain: string,
+    activityId: string
+): ActivityPubActivity {
+    const actorUrl = `https://${nodeDomain}/users/${user.handle}`;
+
+    return {
+        '@context': ACTIVITY_STREAMS_CONTEXT,
+        id: `https://${nodeDomain}/activities/${activityId}`,
+        type: 'Undo',
+        actor: actorUrl,
+        object: originalActivity,
+    };
+}
+
+/**
+ * Create an Accept activity (for accepting follow requests)
+ */
+export function createAcceptActivity(
+    user: User,
+    followActivity: ActivityPubActivity,
+    nodeDomain: string,
+    activityId: string
+): ActivityPubActivity {
+    const actorUrl = `https://${nodeDomain}/users/${user.handle}`;
+
+    return {
+        '@context': ACTIVITY_STREAMS_CONTEXT,
+        id: `https://${nodeDomain}/activities/${activityId}`,
+        type: 'Accept',
+        actor: actorUrl,
+        object: followActivity,
+    };
+}
+
+/**
+ * Synapsis namespace for DID extension
+ */
+const SYNAPSIS_CONTEXT = 'https://synapsis.social/ns';
+
+/**
+ * Create a Move activity for account migration
+ * Includes the Synapsis DID extension for automatic follower migration
+ */
+export function createMoveActivity(
+    user: User,
+    oldActorUrl: string,
+    newActorUrl: string,
+    nodeDomain: string
+): ActivityPubActivity {
+    return {
+        '@context': [
+            ACTIVITY_STREAMS_CONTEXT,
+            SYNAPSIS_CONTEXT,
+            {
+                'synapsis': 'https://synapsis.social/ns#',
+                'synapsis:did': {
+                    '@id': 'synapsis:did',
+                    '@type': '@id',
+                },
+            },
+        ],
+        id: `https://${nodeDomain}/activities/move-${user.id}-${Date.now()}`,
+        type: 'Move',
+        actor: oldActorUrl,
+        object: oldActorUrl,
+        target: newActorUrl,
+        'synapsis:did': user.did, // This enables automatic migration for Synapsis nodes
+    };
+}
+
+/**
+ * Escape HTML in content for safety
+ */
+function escapeHtml(text: string): string {
+    return text
+        .replace(/&/g, '&')
+        .replace(/</g, '&lt;')
+        .replace(/>/g, '&gt;')
+        .replace(/"/g, '&quot;')
+        .replace(/'/g, '&#039;')
+        .replace(/\n/g, '<br>');
+}