bun-activitypub/src/inbox.ts

import { idsFromValue } from "./activitypub"
import * as db from "./db"
import outbox from "./outbox"
import { send } from "./request"
import ACTOR from "../actor"

export default async function inbox(activity:any) {
  const date = new Date()
  // get the main recipients ([...new Set()] is to dedupe)
  const recipientList = [...new Set([...idsFromValue(activity.to), ...idsFromValue(activity.cc), ...idsFromValue(activity.audience)])]

  // if my list of followers in the list of recipients, then forward to them as well
  if(recipientList.includes(ACTOR.url + "/followers")) {
    (await db.listFollowers()).forEach(f => send(f, activity, activity.attributedTo))
  }

  // save this activity to my inbox
  const id =  `${date.getTime().toString(16)}`
  db.createInboxActivity(activity, id)

  // TODO: process the activity and update local data
  switch(activity.type) {
    case "Follow": follow(activity, id); break;
    case "Accept": accept(activity); break;
    case "Reject": reject(activity); break;
    case "Undo": undo(activity); break;
  }

  return new Response("", { status: 204 })
}

const follow = async (activity:any, id:string) => {
  // someone is following me
  // save this follower locally
  db.createFollower(activity.actor, id)
  // send an accept message to the outbox
  await outbox({
    "@context": "https://www.w3.org/ns/activitystreams",
    type: "Accept",
    actor: ACTOR.id,
    to: [activity.actor],
    object: activity,
  });
}

const undo = async (activity:any) => {
  switch (activity.object.type) {
    // someone is undoing their follow of me
    case "Follow": await db.deleteFollower(activity.actor); break
  }
}

const accept = async (activity:any) => {
  switch (activity.object.type) {
    // someone accepted my follow of them
    case "Follow": await db.acceptFollowing(activity.actor); break
  }
}

const reject = async (activity:any) => {
  switch (activity.object.type) {
    // someone rejected my follow of them
    case "Follow": await db.deleteFollowing(activity.actor); break
  }
}