indiekit-endpoint-activitypub/lib/jf2-to-as2.js

/**
 * Convert Indiekit JF2 post properties to ActivityStreams 2.0 objects.
 *
 * Two export flavors:
 * - jf2ToActivityStreams() — returns plain JSON-LD objects (for content negotiation)
 * - jf2ToAS2Activity()    — returns Fedify vocab instances (for outbox + syndicator)
 */

import { Temporal } from "@js-temporal/polyfill";
import {
  Announce,
  Article,
  Audio,
  Create,
  Hashtag,
  Image,
  Like,
  Mention,
  Note,
  Video,
} from "@fedify/fedify/vocab";

// ---------------------------------------------------------------------------
// Content helpers
// ---------------------------------------------------------------------------

/**
 * Convert bare URLs in HTML content to clickable links.
 * Skips URLs already inside href attributes or anchor tag text.
 */
function linkifyUrls(html) {
  if (!html) return html;
  return html.replace(
    /(?<![=">])(https?:\/\/[^\s<"]+)/g,
    '<a href="$1">$1</a>',
  );
}

/**
 * Parse @user@domain mention patterns from text content.
 * Returns array of { handle: "user@domain", username: "user", domain: "domain.tld" }.
 */
export function parseMentions(text) {
  if (!text) return [];
  // Strip HTML tags for parsing
  const plain = text.replace(/<[^>]*>/g, " ");
  const mentionRegex = /(?<![\/\w])@([\w.-]+)@([\w.-]+\.\w{2,})/g;
  const mentions = [];
  const seen = new Set();
  let match;
  while ((match = mentionRegex.exec(plain)) !== null) {
    const handle = `${match[1]}@${match[2]}`;
    if (!seen.has(handle.toLowerCase())) {
      seen.add(handle.toLowerCase());
      mentions.push({ handle, username: match[1], domain: match[2] });
    }
  }
  return mentions;
}

/**
 * Replace @user@domain patterns in HTML with linked mentions.
 * resolvedMentions: [{ handle, actorUrl, profileUrl? }]
 * Uses profileUrl (human-readable) for href, falls back to Mastodon-style URL.
 */
function linkifyMentions(html, resolvedMentions) {
  if (!html || !resolvedMentions?.length) return html;
  for (const { handle, profileUrl } of resolvedMentions) {
    // Escape handle for regex (dots, hyphens)
    const escaped = handle.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
    // Match @handle not already inside an HTML tag attribute or anchor text
    const pattern = new RegExp(`(?<!["\\/\\w])@${escaped}(?![\\w])`, "gi");
    const parts = handle.split("@");
    const url = profileUrl || `https://${parts[1]}/@${parts[0]}`;
    html = html.replace(
      pattern,
      `<a href="${url}" class="mention" rel="nofollow noopener" target="_blank">@${handle}</a>`,
    );
  }
  return html;
}

// ---------------------------------------------------------------------------
// ActivityPub URL detection
// ---------------------------------------------------------------------------

/**
 * Check whether a URL serves ActivityPub content by doing a quick content
 * negotiation request. Returns true if the server responds with an AP
 * media type (application/activity+json or application/ld+json).
 * Fails silently — any network/timeout error returns false.
 */
async function isApUrl(url) {
  try {
    const res = await fetch(url, {
      headers: { Accept: "application/activity+json, application/ld+json" },
      redirect: "follow",
      signal: AbortSignal.timeout(3000),
    });
    const ct = res.headers.get("content-type") || "";
    return ct.includes("activity+json") || ct.includes("ld+json");
  } catch {
    return false;
  }
}

// ---------------------------------------------------------------------------
// Plain JSON-LD (content negotiation on individual post URLs)
// ---------------------------------------------------------------------------

/**
 * Convert JF2 properties to a plain ActivityStreams JSON-LD object.
 *
 * @param {object} properties - JF2 post properties
 * @param {string} actorUrl - Actor URL (e.g. "https://example.com/activitypub/users/rick")
 * @param {string} publicationUrl - Publication base URL with trailing slash
 * @returns {object} ActivityStreams activity (Create, Like, or Announce)
 */
export function jf2ToActivityStreams(properties, actorUrl, publicationUrl, options = {}) {
  const postType = properties["post-type"];

  // Likes are delivered as bookmarks — fall through to bookmark handling below

  // Reposts are always public — Mastodon and other implementations expect this
  if (postType === "repost") {
    // Same rationale as like — serve as Note for content negotiation.
    const repostOf = properties["repost-of"];
    const postUrl = resolvePostUrl(properties.url, publicationUrl);
    const commentary = linkifyUrls(properties.content?.html || properties.content || "");
    return {
      "@context": "https://www.w3.org/ns/activitystreams",
      type: "Note",
      id: postUrl,
      attributedTo: actorUrl,
      published: properties.published,
      url: postUrl,
      to: ["https://www.w3.org/ns/activitystreams#Public"],
      cc: [`${actorUrl.replace(/\/$/, "")}/followers`],
      content: commentary
        ? `${commentary}<br><br>\u{1F501} <a href="${repostOf}">${repostOf}</a>`
        : `\u{1F501} <a href="${repostOf}">${repostOf}</a>`,
    };
  }

  const isArticle = postType === "article" && properties.name;
  const postUrl = resolvePostUrl(properties.url, publicationUrl);

  const visibility = properties.visibility || options.visibility || "public";
  const followersUrl = `${actorUrl.replace(/\/$/, "")}/followers`;

  const object = {
    type: isArticle ? "Article" : "Note",
    id: postUrl,
    attributedTo: actorUrl,
    published: properties.published,
    url: postUrl,
    to: visibility === "unlisted"
      ? [followersUrl]
      : visibility === "followers"
        ? [followersUrl]
        : ["https://www.w3.org/ns/activitystreams#Public"],
    cc: visibility === "unlisted"
      ? ["https://www.w3.org/ns/activitystreams#Public"]
      : visibility === "followers"
        ? []
        : [followersUrl],
  };

  if (postType === "bookmark" || postType === "like") {
    const bookmarkUrl = properties["bookmark-of"] || properties["like-of"];
    const commentary = linkifyUrls(properties.content?.html || properties.content || "");
    object.content = commentary
      ? `${commentary}<br><br>\u{1F516} <a href="${bookmarkUrl}">${bookmarkUrl}</a>`
      : `\u{1F516} <a href="${bookmarkUrl}">${bookmarkUrl}</a>`;
    object.tag = [
      {
        type: "Hashtag",
        name: "#bookmark",
        href: `${publicationUrl}categories/bookmark`,
      },
    ];
  } else {
    object.content = linkifyUrls(properties.content?.html || properties.content || "");
  }

  // Append permalink to content so fediverse clients show a clickable link
  if (postUrl && object.content) {
    object.content += `<p>\u{1F517} <a href="${postUrl}">${postUrl}</a></p>`;
  }

  // OG image for fediverse preview cards
  const ogMatch = postUrl && postUrl.match(/\/([\w-]+)\/(\d{4})\/(\d{2})\/(\d{2})\/([\w-]+)\/?$/);
  if (ogMatch) {
    object.image = {
      type: "Image",
      url: `${publicationUrl.replace(/\/$/, "")}/og/${ogMatch[5]}.png`,
      mediaType: "image/png",
    };
  }

  if (isArticle) {
    object.name = properties.name;
    if (properties.summary) {
      object.summary = properties.summary;
    }
  }

  if (properties.sensitive || properties["post-status"] === "sensitive") {
    object.sensitive = true;
  }

  // Content warning text for Mastodon CW display
  if (properties["content-warning"]) {
    object.summary = properties["content-warning"];
    object.sensitive = true;
  }

  if (properties["in-reply-to"]) {
    object.inReplyTo = properties["in-reply-to"];
  }

  const attachments = buildPlainAttachments(properties, publicationUrl);
  if (attachments.length > 0) {
    object.attachment = attachments;
  }

  const tags = buildPlainTags(properties, publicationUrl, object.tag);

  // Add Mention tags + cc addressing + content linkification for @mentions
  const resolvedMentions = options.mentions || [];
  for (const { handle, actorUrl: mentionUrl } of resolvedMentions) {
    if (mentionUrl) {
      tags.push({ type: "Mention", href: mentionUrl, name: `@${handle}` });
      if (!object.cc.includes(mentionUrl)) {
        object.cc.push(mentionUrl);
      }
    }
  }

  if (tags.length > 0) {
    object.tag = tags;
  }

  // Linkify @mentions in content (resolved get actor links, unresolved get profile links)
  if (resolvedMentions.length > 0 && object.content) {
    object.content = linkifyMentions(object.content, resolvedMentions);
  }

  return {
    "@context": "https://www.w3.org/ns/activitystreams",
    type: "Create",
    actor: actorUrl,
    object,
  };
}

// ---------------------------------------------------------------------------
// Fedify vocab objects (outbox dispatcher + syndicator delivery)
// ---------------------------------------------------------------------------

/**
 * Convert JF2 properties to a Fedify Activity object.
 *
 * @param {object} properties - JF2 post properties
 * @param {string} actorUrl - Actor URL (e.g. "https://example.com/activitypub/users/rick")
 * @param {string} publicationUrl - Publication base URL with trailing slash
 * @param {object} [options] - Optional settings
 * @param {string} [options.replyToActorUrl] - Original post author's actor URL (for reply addressing)
 * @param {string} [options.replyToActorHandle] - Original post author's handle (for Mention tag)
 * @returns {Promise<import("@fedify/fedify").Activity | null>}
 */
export async function jf2ToAS2Activity(properties, actorUrl, publicationUrl, options = {}) {
  const postType = properties["post-type"];
  const actorUri = new URL(actorUrl);

  // Likes of ActivityPub objects are sent as a proper Like activity.
  // Likes of regular URLs fall through to bookmark-style Create(Note) below.
  if (postType === "like") {
    const likeOfUrl = properties["like-of"];
    if (likeOfUrl && (await isApUrl(likeOfUrl))) {
      // Build a canonical id so remote servers can dereference this activity
      // (ActivityPub §6.2.1 — activities SHOULD have an id URI).
      // Derive the mount path from the actor URL (e.g. "/activitypub") so
      // we don't need mountPath threaded through as an option here.
      const actorPath = new URL(actorUrl).pathname; // e.g. "/activitypub/users/sven"
      const mp = actorPath.replace(/\/users\/[^/]+$/, ""); // → "/activitypub"
      const postRelPath = (properties.url || "")
        .replace(publicationUrl.replace(/\/$/, ""), "")
        .replace(/^\//, "")
        .replace(/\/$/, ""); // e.g. "likes/9acc3"
      const likeActivityId = `${publicationUrl.replace(/\/$/, "")}${mp}/activities/like/${postRelPath}`;
      return new Like({
        id: new URL(likeActivityId),
        actor: actorUri,
        object: new URL(likeOfUrl),
        to: new URL("https://www.w3.org/ns/activitystreams#Public"),
      });
    }
  }

  // Reposts are always public — upstream @rmdes addressing
  if (postType === "repost") {
    const repostOf = properties["repost-of"];
    if (!repostOf) return null;
    const repostContent = properties.content?.html || properties.content || "";
    if (!repostContent) {
      // Pure repost — send as a native Announce (boost) so remote servers
      // can display it as a boost of the original post.
      return new Announce({
        actor: actorUri,
        object: new URL(repostOf),
        to: new URL("https://www.w3.org/ns/activitystreams#Public"),
      });
    }
    // Has commentary — fall through to Create(Note) so the text is federated.
    // The note content block below handles the "repost" post-type.
  }

  const isArticle = postType === "article" && properties.name;
  const postUrl = resolvePostUrl(properties.url, publicationUrl);
  const followersUrl = `${actorUrl.replace(/\/$/, "")}/followers`;
  const { replyToActorUrl, replyToActorHandle } = options;

  const noteOptions = {
    attributedTo: actorUri,
  };

  // Determine visibility: per-post override > option default > "public"
  const visibility = properties.visibility || options.visibility || "public";

  // Addressing based on visibility:
  // - "public":    to: PUBLIC, cc: followers (+ reply author)
  // - "unlisted":  to: followers, cc: PUBLIC (+ reply author)
  // - "followers": to: followers (+ reply author), no PUBLIC
  const PUBLIC = new URL("https://www.w3.org/ns/activitystreams#Public");
  const followersUri = new URL(followersUrl);

  if (replyToActorUrl && properties["in-reply-to"]) {
    const replyAuthor = new URL(replyToActorUrl);
    if (visibility === "unlisted") {
      noteOptions.to = followersUri;
      noteOptions.ccs = [PUBLIC, replyAuthor];
    } else if (visibility === "followers") {
      noteOptions.tos = [followersUri, replyAuthor];
    } else {
      // public (default)
      noteOptions.to = PUBLIC;
      noteOptions.ccs = [followersUri, replyAuthor];
    }
  } else {
    if (visibility === "unlisted") {
      noteOptions.to = followersUri;
      noteOptions.cc = PUBLIC;
    } else if (visibility === "followers") {
      noteOptions.to = followersUri;
    } else {
      // public (default)
      noteOptions.to = PUBLIC;
      noteOptions.cc = followersUri;
    }
  }

  if (postUrl) {
    noteOptions.id = new URL(postUrl);
    noteOptions.url = new URL(postUrl);
  }

  if (properties.published) {
    try {
      noteOptions.published = Temporal.Instant.from(properties.published);
    } catch {
      // Invalid date format — skip
    }
  }

  // Content
  if (postType === "bookmark" || postType === "like") {
    const bookmarkUrl = properties["bookmark-of"] || properties["like-of"];
    const commentary = linkifyUrls(properties.content?.html || properties.content || "");
    noteOptions.content = commentary
      ? `${commentary}<br><br>\u{1F516} <a href="${bookmarkUrl}">${bookmarkUrl}</a>`
      : `\u{1F516} <a href="${bookmarkUrl}">${bookmarkUrl}</a>`;
  } else if (postType === "repost") {
    const repostUrl = properties["repost-of"];
    const repostCommentary = linkifyUrls(properties.content?.html || properties.content || "");
    noteOptions.content = repostCommentary
      ? `${repostCommentary}<br><br>\u{1F501} <a href="${repostUrl}">${repostUrl}</a>`
      : `\u{1F501} <a href="${repostUrl}">${repostUrl}</a>`;
  } else {
    noteOptions.content = linkifyUrls(properties.content?.html || properties.content || "");
  }

  // Append permalink to content so fediverse clients show a clickable link
  // back to the canonical post on the author's site
  if (postUrl && noteOptions.content) {
    noteOptions.content += `<p>\u{1F517} <a href="${postUrl}">${postUrl}</a></p>`;
  }

  if (isArticle) {
    noteOptions.name = properties.name;
    if (properties.summary) {
      noteOptions.summary = properties.summary;
    }
  }

  // Content warning / sensitive flag
  if (properties.sensitive) {
    noteOptions.sensitive = true;
  }
  if (properties["post-status"] === "sensitive") {
    noteOptions.sensitive = true;
  }
  // Content warning text for Mastodon CW display
  if (properties["content-warning"]) {
    noteOptions.summary = properties["content-warning"];
    noteOptions.sensitive = true;
  }

  if (properties["in-reply-to"]) {
    noteOptions.replyTarget = new URL(properties["in-reply-to"]);
  }

  // Attachments
  const fedifyAttachments = buildFedifyAttachments(properties, publicationUrl);
  if (fedifyAttachments.length > 0) {
    noteOptions.attachments = fedifyAttachments;
  }

  // OG image for fediverse preview cards
  const ogMatchF = postUrl && postUrl.match(/\/([\w-]+)\/(\d{4})\/(\d{2})\/(\d{2})\/([\w-]+)\/?$/);
  if (ogMatchF) {
    noteOptions.image = new Image({
      url: new URL(`${publicationUrl.replace(/\/$/, "")}/og/${ogMatchF[5]}.png`),
      mediaType: "image/png",
    });
  }

  // Tags: hashtags + Mention for reply addressing + @mentions
  const fedifyTags = buildFedifyTags(properties, publicationUrl, postType);

  if (replyToActorUrl) {
    fedifyTags.push(
      new Mention({
        href: new URL(replyToActorUrl),
        name: replyToActorHandle ? `@${replyToActorHandle}` : undefined,
      }),
    );
  }

  // Add Mention tags + cc addressing for resolved @mentions
  const resolvedMentions = options.mentions || [];
  const ccUrls = [];
  for (const { handle, actorUrl: mentionUrl } of resolvedMentions) {
    if (mentionUrl) {
      // Skip if same as replyToActorUrl (already added above)
      const alreadyTagged = replyToActorUrl && mentionUrl === replyToActorUrl;
      if (!alreadyTagged) {
        fedifyTags.push(
          new Mention({
            href: new URL(mentionUrl),
            name: `@${handle}`,
          }),
        );
      }
      ccUrls.push(new URL(mentionUrl));
    }
  }

  // Merge mention actors into cc/ccs
  if (ccUrls.length > 0) {
    if (noteOptions.ccs) {
      noteOptions.ccs = [...noteOptions.ccs, ...ccUrls];
    } else if (noteOptions.cc) {
      noteOptions.ccs = [noteOptions.cc, ...ccUrls];
      delete noteOptions.cc;
    } else {
      noteOptions.ccs = ccUrls;
    }
  }

  if (fedifyTags.length > 0) {
    noteOptions.tags = fedifyTags;
  }

  // Linkify @mentions in content
  if (resolvedMentions.length > 0 && noteOptions.content) {
    noteOptions.content = linkifyMentions(noteOptions.content, resolvedMentions);
  }

  const object = isArticle
    ? new Article(noteOptions)
    : new Note(noteOptions);

  return new Create({
    actor: actorUri,
    object,
  });
}

// ---------------------------------------------------------------------------
// URL resolution helpers
// ---------------------------------------------------------------------------

/**
 * Resolve a post URL, ensuring it's absolute.
 * @param {string} url - Post URL (may be relative or absolute)
 * @param {string} publicationUrl - Base publication URL
 * @returns {string} Absolute URL
 */
export function resolvePostUrl(url, publicationUrl) {
  if (!url) return "";
  if (url.startsWith("http")) return url;
  const base = publicationUrl.replace(/\/$/, "");
  return `${base}/${url.replace(/^\//, "")}`;
}

function resolveMediaUrl(url, publicationUrl) {
  if (!url) return "";
  if (url.startsWith("http")) return url;
  const base = publicationUrl.replace(/\/$/, "");
  return `${base}/${url.replace(/^\//, "")}`;
}

// ---------------------------------------------------------------------------
// Attachment builders
// ---------------------------------------------------------------------------

function buildPlainAttachments(properties, publicationUrl) {
  const attachments = [];

  if (properties.photo) {
    for (const photo of asArray(properties.photo)) {
      const url = typeof photo === "string" ? photo : photo.url;
      const alt = typeof photo === "string" ? "" : photo.alt || "";
      attachments.push({
        type: "Image",
        mediaType: guessMediaType(url),
        url: resolveMediaUrl(url, publicationUrl),
        name: alt,
      });
    }
  }

  if (properties.video) {
    for (const video of asArray(properties.video)) {
      const url = typeof video === "string" ? video : video.url;
      attachments.push({
        type: "Video",
        url: resolveMediaUrl(url, publicationUrl),
        name: "",
      });
    }
  }

  if (properties.audio) {
    for (const audio of asArray(properties.audio)) {
      const url = typeof audio === "string" ? audio : audio.url;
      attachments.push({
        type: "Audio",
        url: resolveMediaUrl(url, publicationUrl),
        name: "",
      });
    }
  }

  return attachments;
}

function buildFedifyAttachments(properties, publicationUrl) {
  const attachments = [];

  if (properties.photo) {
    for (const photo of asArray(properties.photo)) {
      const url = typeof photo === "string" ? photo : photo.url;
      const alt = typeof photo === "string" ? "" : photo.alt || "";
      attachments.push(
        new Image({
          url: new URL(resolveMediaUrl(url, publicationUrl)),
          mediaType: guessMediaType(url),
          name: alt,
        }),
      );
    }
  }

  if (properties.video) {
    for (const video of asArray(properties.video)) {
      const url = typeof video === "string" ? video : video.url;
      attachments.push(
        new Video({
          url: new URL(resolveMediaUrl(url, publicationUrl)),
        }),
      );
    }
  }

  if (properties.audio) {
    for (const audio of asArray(properties.audio)) {
      const url = typeof audio === "string" ? audio : audio.url;
      attachments.push(
        new Audio({
          url: new URL(resolveMediaUrl(url, publicationUrl)),
        }),
      );
    }
  }

  return attachments;
}

// ---------------------------------------------------------------------------
// Tag builders
// ---------------------------------------------------------------------------

function buildPlainTags(properties, publicationUrl, existing) {
  const tags = [...(existing || [])];
  if (properties.category) {
    for (const cat of asArray(properties.category)) {
      tags.push({
        type: "Hashtag",
        name: `#${cat.split("/").at(-1).replace(/\s+/g, "")}`,
        href: `${publicationUrl}categories/${encodeURIComponent(cat)}`,
      });
    }
  }
  return tags;
}

function buildFedifyTags(properties, publicationUrl, postType) {
  const tags = [];
  if (postType === "bookmark" || postType === "like") {
    tags.push(
      new Hashtag({
        name: "#bookmark",
        href: new URL(`${publicationUrl}categories/bookmark`),
      }),
    );
  }
  if (properties.category) {
    for (const cat of asArray(properties.category)) {
      tags.push(
        new Hashtag({
          name: `#${cat.split("/").at(-1).replace(/\s+/g, "")}`,
          href: new URL(
            `${publicationUrl}categories/${encodeURIComponent(cat)}`,
          ),
        }),
      );
    }
  }
  return tags;
}

// ---------------------------------------------------------------------------
// Utilities
// ---------------------------------------------------------------------------

function asArray(value) {
  return Array.isArray(value) ? value : [value];
}

function guessMediaType(url) {
  const ext = url.split(".").pop()?.toLowerCase();
  const types = {
    jpg: "image/jpeg",
    jpeg: "image/jpeg",
    png: "image/png",
    gif: "image/gif",
    webp: "image/webp",
    svg: "image/svg+xml",
    avif: "image/avif",
  };
  return types[ext] || "image/jpeg";
}