import { invoke, isTauri } from "@tauri-apps/api/core";
import { writable } from "svelte/store";

/**
 * Guard the Tauri runtime. When the page is served by `vite dev`
 * for browser-only preview (no Tauri webview), `__TAURI_INTERNALS__`
 * is undefined and the bare `invoke` call throws
 * `TypeError: Cannot read properties of undefined (reading
 * 'invoke')`. That error fired inside `onMount` during
 * `session.load()` and crashed the entire Svelte mount, leaving
 * the user with a white page. We wrap every Tauri call in two
 * helpers:
 *   - `tauriCall(cmd, fallback)` for loads — returns the fallback
 *     when no Tauri runtime is present (e.g. session.load() returns
 *     null).
 *   - `safeInvoke(cmd, args)` for actions that MUST hit the runtime
 *     (login, register, etc.) — throws a friendly error so the UI
 *     can show a "running in browser preview" notice.
 */
async function tauriCall<T>(cmd: string, fallback: T, args?: Record<string, unknown>): Promise<T> {
  if (!isTauri()) {
    return fallback;
  }
  return invoke<T>(cmd, args);
}

/// Base URLs the Tauri shell was started with. Exposed via the
/// `get_api_urls` command so the Svelte components can build
/// absolute fetch URLs — a relative `/api/...` resolves against
/// the Vite dev origin (port 1430), not the AppView (port 2584),
/// and `response.json()` then throws `SyntaxError` on the 404
/// HTML page. Cached after the first successful call.
let _apiUrlsCache: { pdsUrl: string; appviewUrl: string } | null = null;

export type ApiUrls = { pdsUrl: string; appviewUrl: string };

/// Fetch the AppView + PDS base URLs from the Rust shell. Returns
/// the cached value on subsequent calls.
export async function getApiUrls(): Promise<ApiUrls> {
  if (_apiUrlsCache) return _apiUrlsCache;
  const urls = await safeInvoke<ApiUrls>("get_api_urls");
  _apiUrlsCache = urls;
  return urls;
}

/// Convenience: just the AppView base URL (the only one the UI
/// currently needs for direct fetch calls). Same caching as
/// `getApiUrls`.
export async function getAppviewUrl(): Promise<string> {
  const { appviewUrl } = await getApiUrls();
  return appviewUrl;
}

/**
 * Strict variant of `tauriCall` for actions that MUST hit the
 * Tauri runtime (login, register, logout, post, like, etc.). In
 * the browser preview this throws a friendly Error so the UI can
 * show a "running in browser preview" notice. In the Tauri
 * webview it falls through to a normal `invoke` call.
 *
 * **Auto-refresh on 401**: the access JWT expires after 1 hour. When
 * the PDS rejects our token with `TokenInvalid` (the rusty
 * `routes::auth` handlers return `{"error":"TokenInvalid",...}`),
 * we ask the Rust shell for a fresh access JWT via the
 * `auth_refresh` Tauri command. The Rust side reads the stored
 * refresh JWT (valid for 90 days) and rotates both. We retry
 * exactly once on the same `cmd` + `args`. The `auth_*` commands
 * themselves are skipped so a failing login doesn't trigger an
 * infinite refresh loop.
 */
async function safeInvoke<T>(cmd: string, args?: Record<string, unknown>): Promise<T> {
  if (!isTauri()) {
    throw new Error(`Tauri command ${cmd} requires the desktop runtime`);
  }
  try {
    return await invoke<T>(cmd, args);
  } catch (e: unknown) {
    if (!isTokenInvalid(e) || cmd.startsWith("auth_")) throw e;
    const fresh = await session.refresh();
    if (!fresh) throw e;
    return await invoke<T>(cmd, args);
  }
}

/// Sniff out a `TokenInvalid` response from the Rust error string.
/// Returns true when the error message looks like an expired/
/// invalid JWT (the PDS uses a stable `"TokenInvalid"` code in its
/// JSON error body, which `@tauri-apps/api/core` surfaces verbatim).
function isTokenInvalid(e: unknown): boolean {
  if (typeof e !== "object" || e === null) return false;
  const msg = (e as { message?: string }).message ?? String(e);
  if (!msg) return false;
  return msg.includes("TokenInvalid") || msg.includes("ExpiredSignature");
}

export type Session = {
  did: string;
  handle: string;
  access_jwt: string;
  refresh_jwt: string;
};

function createSessionStore() {
  const { subscribe, set } = writable<Session | null>(null);
  // Coalesce concurrent refresh requests into one — every safeInvoke
  // call that hits a 401 would otherwise race to call auth_refresh in
  // parallel. The pending promise is reset to `null` exactly once in
  // the finally block; subsequent callers await the same one.
  let pendingRefresh: Promise<Session | null> | null = null;

  return {
    subscribe,
    /// Mint a fresh access JWT from the stored refresh JWT. Called
    /// automatically by [`safeInvoke`] on `TokenInvalid` responses.
    /// Returns the new session, or `null` if the refresh itself failed
    /// (e.g. refresh JWT expired; at that point the user has to log
    /// in again).
    async refresh(): Promise<Session | null> {
      if (pendingRefresh) return pendingRefresh;
      pendingRefresh = (async () => {
        try {
          const s = await invoke<Session>("auth_refresh");
          set(s);
          return s;
        } catch (e) {
          console.warn("session refresh failed", e);
          return null;
        } finally {
          pendingRefresh = null;
        }
      })();
      return pendingRefresh;
    },
    async load() {
      const s = await tauriCall<Session | null>("current_session", null);
      set(s);
    },
    async login(handle: string, password: string) {
      if (!isTauri()) {
        throw new Error("login requires the Tauri desktop runtime");
      }
      const s = await safeInvoke<Session>("auth_login", { identifier: handle, password });
      set(s);
      return s;
    },
    async register(handle: string, password: string) {
      if (!isTauri()) {
        throw new Error("register requires the Tauri desktop runtime");
      }
      const s = await safeInvoke<Session>("auth_register", { handle, password });
      set(s);
      return s;
    },
    async logout() {
      try {
        await safeInvoke("auth_logout");
      } catch (e) {
        console.error("logout failed", e);
      }
      set(null);
    },
  };
}

export const session = createSessionStore();

/// AT-Protocol embed variants. We keep the on-the-wire JSON verbatim
/// (instead of narrowing to one specific shape per variant) so that
/// adding a new embed type upstream doesn't require a frontend change.
/// The UI sniffs `embed.$type` to decide which sub-component to render.
export type Embed = {
  $type: string;
  images?: EmbedImage[];
  external?: EmbedExternal;
  record?: EmbedRecord;
  media?: EmbedRecordWithMedia;
  [k: string]: unknown;
};

export type EmbedImage = {
  alt?: string;
  image?: unknown;
  aspectRatio?: { width: number; height: number };
};

export type EmbedExternal = {
  uri: string;
  title?: string;
  description?: string;
  thumb?: string;
};

export type EmbedRecord = {
  uri: string;
  cid?: string;
  author?: { did: string; handle?: string };
  value?: { text?: string; createdAt?: string };
};

export type EmbedRecordWithMedia = Embed & {
  record: EmbedRecord;
  media: { images?: EmbedImage[]; external?: EmbedExternal };
};

/// Post shape returned by the AppView REST API. The Tauri command
/// (also named `Post` on the Rust side) re-exports this as
/// `appview_client::PostDto` and the frontend receives it as-is.
export type Post = {
  uri: string;
  did: string;
  handle: string;
  rkey: string;
  collection: string;
  text: string;
  cid: string;
  parent_uri?: string | null;
  root_uri?: string | null;
  embed?: Embed | null;
  langs: string[];
  created_at: string;
  like_count?: number;
  repost_count?: number;
  /// Resolved author-avatar CID from the AppView's `profiles`
  /// cache. NULL when the user has no profile record yet.
  avatar_cid?: string | null;
};

export type TimelineResponse = {
  posts: Post[];
  cursor: string | null;
};

export type ProfileResponse = {
  did: string;
  handle: string;
  posts: Post[];
  followers: number;
  following: number;
  display_name?: string | null;
  description?: string | null;
  avatar_cid?: string | null;
  banner_cid?: string | null;
  post_count: number;
};

export type SearchResponse = {
  posts: Post[];
  q: string;
};

/// `GET /api/post/{uri}` response. Used by the UI when the user
/// expands a reply to fetch the parent + root in one round trip.
///
/// `like_count` and `repost_count` are present when the post was
/// found; they're `undefined` (or absent) for the "not in index"
/// sentinel response (where `post` is null). AppView has no auth
/// yet, so `viewer_liked` / `viewer_reposted` aren't returned.
export type ThreadResponse = {
  post: Post | null;
  thread: {
    parent: Post | null;
    root: Post | null;
  };
  like_count?: number;
  repost_count?: number;
};

/// Reply block for `app.bsky.feed.post#reply`. Both `root` and
/// `parent` are `com.atproto.repo.strongRef`s (uri + cid). For a
/// top-level reply to a single post, `root` and `parent` point at
/// the same strongRef. The Rust `post_create` command wires this
/// onto the record's `reply` field.
export type ReplyRef = {
  root: { uri: string; cid: string };
  parent: { uri: string; cid: string };
};

export async function createPost(
  text: string,
  embed?: unknown | null,
  reply?: ReplyRef | null,
): Promise<Post> {
  // The Rust post_create command returns a different shape (uri+cid
  // only), but we keep the call simple: it gives us the cid we need
  // to show the "ok" toast.
  // `embed` is forwarded verbatim; the caller is responsible for
  // shaping it as an `app.bsky.embed.images` / `.external` / etc.
  // record. Pass `null` or `undefined` to omit.
  // `reply` is the reply block (root + parent strongRefs); `null` or
  // `undefined` means "top-level post" (no reply block on the record).
  return await safeInvoke<any>("post_create", {
    text,
    embed: embed ?? null,
    reply: reply ?? null,
  });
}

/// `com.atproto.uploadBlob` wrapped with a file picker. Opens a
/// native OS dialog (via `tauri-plugin-dialog`), uploads the chosen
/// file to the user's PDS, and returns the parsed blob reference.
///
/// Returns `null` when the user cancels the picker. The Tauri shell
/// enforces a 1 MiB cap (matching the PDS's `MAX_BLOB_SIZE`) and
/// surfaces other errors via the rejected promise.
export async function pickAndUploadImage(): Promise<{
  cid: string;
  mimeType: string;
  size: number;
} | null> {
  const r = await safeInvoke<{
    blob: {
      $type: string;
      ref: { $link: string };
      mimeType: string;
      size: number;
    };
  } | null>("pick_and_upload_image");
  if (!r) return null;
  return {
    cid: r.blob.ref.$link,
    mimeType: r.blob.mimeType,
    size: r.blob.size,
  };
}

/// Helper that builds the `app.bsky.embed.images` embed for a single
/// image blob, ready to drop into a post record.
export function makeImagesEmbed(blob: {
  cid: string;
  mimeType: string;
  size: number;
}): Record<string, unknown> {
  return {
    $type: "app.bsky.embed.images",
    images: [
      {
        alt: "",
        image: {
          $type: "blob",
          ref: { $link: blob.cid },
          mimeType: blob.mimeType,
          size: blob.size,
        },
      },
    ],
  };
}

export async function describeServer(): Promise<any> {
  return await safeInvoke("pds_describe");
}

export async function pdsStatus(): Promise<any> {
  return await safeInvoke("status_pds");
}

export async function fetchTimeline(
  did: string,
  cursor: string | null = null,
  limit: number = 30,
): Promise<TimelineResponse> {
  return await safeInvoke<TimelineResponse>("timeline_home", {
    did,
    cursor,
    limit,
  });
}

export async function fetchProfile(handle: string): Promise<ProfileResponse> {
  return await safeInvoke<ProfileResponse>("profile_get", { handle });
}

/// Resolve a profile by DID (`GET /api/profile?did=…`) instead of by
/// handle.
///
/// Use this — not [`fetchProfile`] — whenever the actor came out of a
/// notification or a follower/following list. The AppView synthesises
/// a placeholder `handle` for actors it has neither a profile row nor
/// an indexed post for: a truncated DID with an ellipsis, e.g.
/// `"did:plc:f5…"`. That string matches nothing on the way back in, and
/// the server answers with a synthetic empty profile (`did: ""`, zero
/// posts) rather than an error — so a handle-based navigation from
/// those lists is a silent dead end. The DID in the DTO is always
/// real, so navigate by that.
export async function fetchProfileByDid(
  did: string,
): Promise<ProfileResponse> {
  return await safeInvoke<ProfileResponse>("profile_get_by_did", { did });
}

export async function fetchSearch(
  q: string,
  limit: number = 30,
): Promise<SearchResponse> {
  return await safeInvoke<SearchResponse>("search", { q, limit });
}

export async function fetchPost(uri: string): Promise<ThreadResponse> {
  return await safeInvoke<ThreadResponse>("post_get", { uri });
}

/// `GET /api/thread?uri=…` — the *full* thread around a post: the
/// entire ancestor chain plus the direct replies, in one round trip.
///
/// `parents` is ordered root-first (so `parents[parents.length - 1]`
/// is the immediate parent) and `replies` oldest-first. A `parents[0]`
/// whose own `parent_uri` is non-null means "the chain continues
/// above but wasn't loaded" — the walk is depth-limited server-side.
///
/// `post` is `null` when the URI isn't in the index; the counters are
/// then absent too, so a single field check renders "post not found".
/// `viewer_liked` / `viewer_reposted` are `undefined` when no
/// `viewerDid` was passed — that means "unknown", not "false".
export type ThreadFullResponse = {
  post: Post | null;
  parents: Post[];
  root: Post | null;
  replies: Post[];
  like_count?: number;
  repost_count?: number;
  viewer_liked?: boolean;
  viewer_reposted?: boolean;
};

export async function fetchThread(
  uri: string,
  viewerDid: string | null = null,
): Promise<ThreadFullResponse> {
  return await safeInvoke<ThreadFullResponse>("fetch_thread", {
    uri,
    viewerDid,
  });
}

/// One row of `GET /api/notifications`, hydrated server-side with the
/// author's profile and the subject post's text so the list renders
/// without any follow-up fetch.
///
/// `kind` is typed as the four known values plus `string` so an
/// unknown kind added upstream still type-checks here; the UI's
/// `notificationText` falls back to a generic line.
export type NotificationKind = "like" | "repost" | "follow" | "reply";

export type Notification = {
  id: number;
  kind: NotificationKind | string;
  author_did: string;
  /// Without a leading `@` (the UI renders `@{handle}`). Never null —
  /// the AppView falls back to a truncated DID.
  author_handle: string;
  author_display_name?: string | null;
  author_avatar_cid?: string | null;
  /// The post this is about. `null` for `"follow"`. For
  /// `"like"`/`"repost"` it's the recipient's own post; for `"reply"`
  /// it's the reply itself.
  subject_uri: string | null;
  subject_text?: string | null;
  created_at: string;
  /// When the AppView indexed it — the list's sort key and the value
  /// to echo back as `seenAt`.
  indexed_at: string;
  /// `null` while unread.
  read_at: string | null;
};

export type NotificationsResponse = {
  notifications: Notification[];
  cursor: string | null;
};

/// German UI copy for a notification row. Kept next to the type (and
/// exported) so the mapping is unit-testable without mounting a
/// component. An unrecognised `kind` gets a neutral fallback rather
/// than an empty line.
export function notificationText(kind: string): string {
  switch (kind) {
    case "like":
      return "hat deinen Post geliked";
    case "repost":
      return "hat repostet";
    case "follow":
      return "folgt dir jetzt";
    case "reply":
      return "hat geantwortet";
    default:
      return "hat interagiert";
  }
}

/// Single-glyph icon for a notification row, same switch as
/// [`notificationText`]. Monospace glyphs rather than SVGs so the
/// list keeps the terminal look of the rest of the UI.
export function notificationIcon(kind: string): string {
  switch (kind) {
    case "like":
      return "♥";
    case "repost":
      return "⇄";
    case "follow":
      return "+";
    case "reply":
      return "↩";
    default:
      return "•";
  }
}

/// One page of notifications, newest first. Same opaque-cursor
/// contract as [`fetchTimeline`]: pass the previous response's
/// `cursor` to page down, and `cursor === null` means end of list.
export async function fetchNotifications(
  did: string,
  cursor: string | null = null,
  limit: number = 30,
): Promise<NotificationsResponse> {
  return await safeInvoke<NotificationsResponse>("fetch_notifications", {
    did,
    cursor,
    limit,
  });
}

/// Unread-notification count for the NavRail badge. Cheap enough to
/// poll on the same cadence as the timeline refresh.
export async function notificationCount(did: string): Promise<number> {
  const r = await safeInvoke<{ count: number }>("notification_count", { did });
  return r.count;
}

/// Mark every notification indexed at or before `seenAt` as read.
/// Pass the `indexed_at` of the topmost row the user actually sees, so
/// a notification arriving mid-scroll isn't swallowed. `null` marks
/// everything currently unread. Idempotent — a repeat call reports
/// `updated: 0`.
export async function markNotificationsSeen(
  did: string,
  seenAt: string | null = null,
): Promise<{ ok: boolean; updated: number }> {
  return await safeInvoke<{ ok: boolean; updated: number }>(
    "mark_notifications_seen",
    { did, seenAt },
  );
}

/// A minimal profile card from `GET /api/followers` / `/api/following`.
/// Deliberately not a full `ProfileResponse` — a page of 30 followers
/// would otherwise be 30 post queries server-side. Click a row and the
/// UI navigates to the full profile by `handle`.
export type ActorProfile = {
  did: string;
  handle: string;
  display_name?: string | null;
  avatar_cid?: string | null;
};

export type ActorListResponse = {
  profiles: ActorProfile[];
  cursor: string | null;
};

export async function fetchFollowers(
  did: string,
  cursor: string | null = null,
  limit: number = 30,
): Promise<ActorListResponse> {
  return await safeInvoke<ActorListResponse>("fetch_followers", {
    did,
    cursor,
    limit,
  });
}

export async function fetchFollowing(
  did: string,
  cursor: string | null = null,
  limit: number = 30,
): Promise<ActorListResponse> {
  return await safeInvoke<ActorListResponse>("fetch_following", {
    did,
    cursor,
    limit,
  });
}

/// `app.bsky.feed.like.create` — Tauri command. Builds the
/// flat-shape like body on the Rust side, signs a commit, pushes
/// to the AppView. Returns the new like's `uri` and `cid`.
export type RepoWriteResult = { uri: string; cid: string };

/// `com.atproto.repo.deleteRecord` — Tauri command. Used for
/// both unlike and unrepost. The Rust side splits the URI into
/// `rkey` and sends it.
export type DeleteRecordResult = { commit: { cid: string; rev: string } };

export async function likePost(
  subjectUri: string,
  subjectCid: string,
): Promise<RepoWriteResult> {
  return await safeInvoke<RepoWriteResult>("like_post", {
    subjectUri,
    subjectCid,
  });
}

export async function unlikePost(likeUri: string): Promise<DeleteRecordResult> {
  return await safeInvoke<DeleteRecordResult>("unlike_post", { likeUri });
}

export async function repostPost(
  subjectUri: string,
  subjectCid: string,
): Promise<RepoWriteResult> {
  return await safeInvoke<RepoWriteResult>("repost_post", {
    subjectUri,
    subjectCid,
  });
}

export async function unrepostPost(
  repostUri: string,
): Promise<DeleteRecordResult> {
  return await safeInvoke<DeleteRecordResult>("unrepost_post", { repostUri });
}

/// `followUser(targetDid)` — create an `app.bsky.graph.follow` record
/// on the user's PDS. Returns `{ uri, cid }` — the client caches
/// `uri` in localStorage so `unfollowUser(uri)` can delete the
/// record without needing a "list my follows" round-trip.
export async function followUser(
  targetDid: string,
): Promise<RepoWriteResult> {
  return await safeInvoke<RepoWriteResult>("follow_user", { targetDid });
}

export async function unfollowUser(
  followUri: string,
): Promise<DeleteRecordResult> {
  return await safeInvoke<DeleteRecordResult>("unfollow_user", {
    followUri,
  });
}

/// Fire-and-forget user-visible toast. Implemented as a `window`
/// `CustomEvent` so any component can show toasts without pulling
/// in a global store. `App.svelte` listens for the event and
/// renders the toast UI.
export function showError(text: string): void {
  if (typeof window === "undefined") return;
  window.dispatchEvent(
    new CustomEvent("maarcadetweet:toast", { detail: { kind: "error", text } }),
  );
}

export function showInfo(text: string): void {
  if (typeof window === "undefined") return;
  window.dispatchEvent(
    new CustomEvent("maarcadetweet:toast", { detail: { kind: "info", text } }),
  );
}

/// Show a native OS notification. Thin wrapper around the
/// `show_notification` Tauri command. The Rust side also emits an
/// `app://notification` event with the same payload, so the click
/// listener (registered via `listenNotification`) can route to a URL.
///
/// Pass `url` to make the notification clickable: when the user
/// clicks, the Rust command focuses the main window and the JS
/// listener navigates.
export async function showNotification(
  title: string,
  body: string,
  url?: string,
): Promise<void> {
  try {
    await safeInvoke("show_notification", { title, body, url: url ?? null });
  } catch (e) {
    console.error("show_notification failed", e);
  }
}

/// Subscribe to system-tray menu events. The Tauri tray menu emits
/// `app://show` ("Show maarcadetweet") and `app://compose` ("Compose");
/// the Rust side already turns left-clicks into `app://show` and the
/// "Quit" menu item into a clean `app.exit(0)`.
///
/// The handler receives the event payload (empty object for these
/// cases). Returns an unsubscribe function.
export async function listenTrayEvents(
  handler: (event: "show" | "home" | "compose" | "profile" | "search" | "settings") => void,
): Promise<() => void> {
  const { listen } = await import("@tauri-apps/api/event");
  const unlisteners: Array<() => void> = [];
  const u1 = await listen("app://show", () => handler("show"));
  const u2 = await listen("app://navigate", (e) => {
    handler(e.payload as "home" | "profile" | "search" | "settings");
  });
  const u3 = await listen("app://compose", () => handler("compose"));
  unlisteners.push(u1, u2, u3);
  return () => {
    for (const u of unlisteners) u();
  };
}

/// Open an external URL in the user's default browser. The Rust
/// `open_external_url` command enforces http(s) only; in the
/// browser preview where no Tauri runtime is present, fall back
/// to `window.open` and treat a popup-blocker denial as
/// "fine, user can copy the URL themselves".
export type ProfileRecord = {
  displayName?: string;
  description?: string;
  avatar?: { ref: { $link: string }; mimeType?: string; size?: number };
  banner?: { ref: { $link: string }; mimeType?: string; size?: number };
};

/// Read the authenticated user's `app.bsky.actor.profile` record.
/// Returns `null` if no profile record exists yet (a brand-new
/// account, or a user whose PDS hasn't pushed one).
export async function getMyProfile(): Promise<ProfileRecord | null> {
  return await safeInvoke<ProfileRecord | null>("profile_get_record");
}

/// Read-modify-write the authenticated user's profile. The Rust
/// `profile_set` command fetches the existing record, overlays
/// the supplied fields, and writes a new commit. `undefined` fields
/// are preserved.
export async function setMyProfile(fields: {
  displayName?: string;
  description?: string;
  avatarBlobCid?: string;
  bannerBlobCid?: string;
}): Promise<ProfileRecord | null> {
  return await safeInvoke<ProfileRecord | null>("profile_set", fields);
}

export async function openExternalUrl(url: string): Promise<void> {
  try {
    if (isTauri()) {
      await safeInvoke("open_external_url", { url });
      return;
    }
  } catch (e) {
    console.warn("open_external_url failed", e);
  }
  // Browser fallback (vite dev preview).
  try {
    window.open(url, "_blank", "noopener,noreferrer");
  } catch (e) {
    console.warn("window.open failed (popup blocker?)", e);
  }
}

/// Subscribe to `app://notification` events emitted by the Rust
/// `show_notification` command. Used to focus the window and
/// navigate when the user clicks the notification.
export async function listenNotification(
  handler: (payload: {
    title: string;
    body: string;
    url: string | null;
  }) => void,
): Promise<() => void> {
  const { listen } = await import("@tauri-apps/api/event");
  const u = await listen<{ title: string; body: string; url: string | null }>(
    "app://notification",
    (e) => handler(e.payload),
  );
  return u;
}

// -- blob fetch + cache -----------------------------------------------------
//
// Image embeds reference blobs by CID. The blob bytes themselves
// live on the user's PDS — the AppView only has the CID. The Tauri
// shell handles the PDS HTTP call (`fetch_blob` command) so the
// frontend never has to know the PDS URL.
//
// We cache the *resolved object URL* (not the raw bytes) keyed
// by `(did, cid)`, NOT just `cid`:
//   * the blob *bytes* are addressed by content hash, so the same
//     CID *usually* resolves to the same bytes regardless of DID;
//   * BUT in the atproto sync spec, `com.atproto.sync.getBlob` is
//     intentionally unauthenticated and keyed by `(did, cid)` on
//     the server. A future change to a per-DID access control
//     model would make the bytes differ per DID — caching by CID
//     alone would then leak the first responder's bytes to every
//     subsequent viewer.
//   * the `<img>` element takes an object URL, not raw bytes, so
//     handing the URL straight back to the caller saves a
//     Blob/URL.createObjectURL call per render.
const _blobUrlCache = new Map<string, string>();
const _blobKey = (did: string, cid: string) => `${did}/${cid}`;

/// Fetch the raw blob bytes for `cid` and return an object URL
/// suitable for `<img src={...}>`. Caches the URL in-process so
/// navigating the timeline doesn't re-download already-seen
/// images. Keyed by `(did, cid)` for the security reason above.
export async function fetchBlob(
  did: string,
  cid: string,
): Promise<string> {
  const key = _blobKey(did, cid);
  const cached = _blobUrlCache.get(key);
  if (cached) return cached;
  const bytes: number[] = await safeInvoke<number[]>("fetch_blob", {
    did,
    cid,
  });
  const u8 = new Uint8Array(bytes);
  if (u8.length === 0) {
    throw new Error(`empty blob for cid ${cid}`);
  }
  const blob = new Blob([u8]);
  const url = URL.createObjectURL(blob);
  _blobUrlCache.set(key, url);
  return url;
}

/// Drop the cached object URL and remove it. Components should
/// call this when an `<img>` is unmounted to avoid leaking the
/// underlying Blob. For a Tauri WebView with at most a few
/// dozen visible images the OS cleans up anyway, but explicit
/// revocation makes long sessions friendlier on memory.
export function releaseBlob(did: string, cid: string): void {
  const url = _blobUrlCache.get(_blobKey(did, cid));
  if (url) {
    URL.revokeObjectURL(url);
    _blobUrlCache.delete(_blobKey(did, cid));
  }
}

/// Test/internal: clear the in-memory blob cache.
export function clearBlobCache(): void {
  for (const url of _blobUrlCache.values()) {
    URL.revokeObjectURL(url);
  }
  _blobUrlCache.clear();
}