import { parseDocumentAnnotationHash } from "@/lib/document-annotation-hash";
import { type ThreadScrollAnchor, threadScrollAnchorDelta } from "./scroll-anchor";
import { createContext, useContext } from "react";

export const TaskChatScrollNavigation = createContext<{ key: string; restore: boolean; hash: string } | null>(null);
export const TaskChatScrollReady = createContext(true);

/** Decision links name the conversation anchor separately from the artifact. */
export function taskChatHashAnchor(hash: string): string | null {
  const documentTarget = parseDocumentAnnotationHash(hash);
  if (documentTarget?.interactionId) return `interaction-${documentTarget.interactionId}`;
  if (documentTarget) return null;
  try { return hash ? decodeURIComponent(hash.slice(1).split("&")[0]!) : null; } catch { return null; }
}

/** Document navigation opens a pane without starting a new thread reading. */
export function taskChatScrollEntry(location: { key: string; hash: string; pathname: string; state: unknown }): { key: string; hash: string; pathname: string } {
  if (parseDocumentAnnotationHash(location.hash)?.interactionId) {
    return { key: location.key, hash: location.hash, pathname: location.pathname };
  }
  const saved = location.state && typeof location.state === "object" && "taskDocumentScrollEntry" in location.state
    ? location.state.taskDocumentScrollEntry : null;
  if (saved && typeof saved === "object" && "key" in saved && "hash" in saved && "pathname" in saved && saved.pathname === location.pathname && typeof saved.key === "string" && typeof saved.hash === "string") {
    return { key: saved.key, hash: saved.hash, pathname: location.pathname };
  }
  return { key: location.key, hash: location.hash, pathname: location.pathname };
}

// Scoped to browser-history entries, not issues: opening the same task from a
// new Inbox click starts at latest, while Back restores the previous reading.
const positions = new Map<string, { top: number; anchor: ThreadScrollAnchor | null; followBottom: boolean }>();

export function useTaskChatScrollNavigation() {
  const navigation = useContext(TaskChatScrollNavigation);
  const ready = useContext(TaskChatScrollReady);
  // Native hash links can reuse React Router's history key. Keep those entries
  // separate so their POP event does not restore the previous hash's position.
  const positionKey = navigation ? JSON.stringify([navigation.key, navigation.hash]) : null;
  return {
    key: navigation?.key,
    hash: navigation?.hash,
    ready,
    initialPosition(root: Element, viewportTop: number, scrollTop: number, options?: { restore?: boolean }): number | null {
      if (!navigation) return null;
      if (options?.restore !== false && navigation.restore && positionKey && positions.has(positionKey)) {
        const saved = positions.get(positionKey)!;
        // A saved pixel offset goes stale when rotation changes text wrapping.
        // Bottom-follow needs no row measurements, even across navigation.
        if (saved.followBottom) return Math.max(0, root.scrollHeight - root.clientHeight);
        if (saved.anchor && [...root.querySelectorAll<HTMLElement>("[data-thread-anchor]")].some((row) => row.dataset.threadAnchor === saved.anchor?.id)) {
          return scrollTop + threadScrollAnchorDelta(root, saved.anchor, viewportTop);
        }
        return saved.top;
      }
      if (navigation.hash) {
        const id = taskChatHashAnchor(navigation.hash);
        const target = id ? document.getElementById(id) : null;
        if (target && root.contains(target)) return scrollTop + target.getBoundingClientRect().top - viewportTop;
      }
      return null;
    },
    remember(top: number, anchor: ThreadScrollAnchor | null, followBottom: boolean) {
      if (!positionKey || !ready) return;
      positions.set(positionKey, { top, anchor, followBottom });
      if (positions.size > 100) positions.delete(positions.keys().next().value!);
    },
  };
}