import type { ConversationView, InboxState, LiveState } from "@earendil-works/pi-durable";
import type { Scope } from "./ui.ts";

/** Acknowledge the settled messages actually drawn in a visible conversation pane. */
export function readWhenVisible(
  scope: Scope,
  acknowledge: (entryId: number) => Promise<unknown>,
): (view: ConversationView) => void {
  let current = 0;
  let readThrough = 0;
  let sending = false;
  let disposed = false;
  const read = async () => {
    if (disposed || document.visibilityState !== "visible" || sending || current <= readThrough) {
      return;
    }
    const entryId = current;
    sending = true;
    try {
      await acknowledge(entryId);
      readThrough = Math.max(readThrough, entryId);
    } catch (error) {
      console.error("[berry] read receipt:", error);
    } finally {
      sending = false;
      if (current !== entryId) void read();
    }
  };
  const onVisibility = () => void read();
  document.addEventListener("visibilitychange", onVisibility);
  scope.add(() => {
    disposed = true;
    document.removeEventListener("visibilitychange", onVisibility);
  });
  return ({ entries, docs }) => {
    const live = docs["pi.live"] as LiveState | undefined;
    const inbox = docs["pi.inbox"] as InboxState | undefined;
    current = live?.run || inbox?.items.length
      ? 0
      : entries.findLast((entry) => entry.kind === "pi.assistant" || entry.kind === "pi.user")
        ?.id ?? 0;
    void read();
  };
}