"use client";

/**
 * SharePostProvider — single source of truth for "share a post" routing.
 *
 * Any component in the tree calls `useSharePost().openShareSheet(post)`
 * and the provider decides what actually happens:
 *
 *   • Mobile + navigator.share supported → short-URL fetch happens
 *     inside the user gesture, then navigator.share fires
 *     immediately so iOS Safari's activation token is preserved.
 *     The OS share sheet appears with the canonical "Source:" payload.
 *   • Desktop, or no navigator.share → mount the custom SharePostSheet
 *     drawer/modal (handles its own URL shortening + image pre-fetch
 *     for the More-button file-attach path).
 *   • Native share fails non-AbortError (e.g. activation already
 *     expired) → graceful fallback to the custom sheet so the user
 *     never gets stranded.
 *
 * Callers used to get away with a synchronous `openShareSheet(post)`
 * that just mounted the sheet. The function is now async because the
 * native path awaits the URL shortener inside the gesture. Callers
 * that show a loading spinner (the Send icon in PostActionsFooter)
 * await the returned promise; callers that don't (the post-create
 * success toast) can fire-and-forget.
 *
 * Used today by:
 *   • PostActionsFooter — owner + resharer "Send" buttons.
 *   • compose-post.tsx success toast — "Share" action after a post is
 *     created.
 *   • Any future surface (profile cards, etc.) — same one-line API.
 */

import {
  createContext,
  useCallback,
  useContext,
  useState,
} from "react";
import type { Post } from "@/lib/social";
import { buildPostShareText } from "@/lib/post-share-text";
import { useAuth } from "@/components/auth/auth-provider";
import { useMediaQuery } from "@/components/selection-toolbar/shared";
import { SharePostSheet } from "./share-post-sheet";

type SharePostContextValue = {
  /** Open the right share surface for the current platform. Returns
   *  a promise so callers can render loading state during the short-URL
   *  fetch on the mobile native-share path. Always resolves; never
   *  rejects. */
  openShareSheet: (post: Post) => Promise<void>;
};

/**
 * Fetch the post's first image via our same-origin proxy and wrap it
 * in a File so navigator.share can attach it. The proxy at
 * /api/share-image/<id> sits in front of R2 and serves the bytes
 * without CORS, which sidesteps the cached-without-Vary issue R2
 * custom domains hit when a browser previously loaded the same image
 * via an <img> tag. Returns null on any failure so the caller falls
 * back to a text-only share.
 */
async function fetchShareImageFile(postId: string): Promise<File | null> {
  try {
    const res = await fetch(`/api/share-image/${encodeURIComponent(postId)}`);
    if (!res.ok) return null;
    const blob = await res.blob();
    const ext = (blob.type.split("/")[1] || "jpg").toLowerCase();
    return new File([blob], `share.${ext}`, {
      type: blob.type || "image/jpeg",
      lastModified: Date.now(),
    });
  } catch {
    return null;
  }
}

const SharePostContext = createContext<SharePostContextValue | null>(null);

export function useSharePost(): SharePostContextValue {
  const v = useContext(SharePostContext);
  if (!v) {
    throw new Error("useSharePost must be used inside <SharePostProvider>");
  }
  return v;
}

export function SharePostProvider({
  children,
}: {
  children: React.ReactNode;
}) {
  const [activePost, setActivePost] = useState<Post | null>(null);
  const isMobile = useMediaQuery("(max-width: 767px)");
  const { user } = useAuth();
  // Capability check once — the result doesn't change at runtime.
  const nativeShareSupported =
    typeof navigator !== "undefined" &&
    typeof navigator.share === "function";

  const openShareSheet = useCallback<SharePostContextValue["openShareSheet"]>(
    async (post) => {
      // Path A — desktop or no native share API: drop straight into
      // the custom sheet. It handles its own URL shortening + image
      // pre-fetch.
      if (!isMobile || !nativeShareSupported) {
        setActivePost(post);
        return;
      }

      // Resolve the author handle. For owner posts the BFF Create
      // response doesn't include author_handle, so fall back to the
      // signed-in user's handle (the post creator IS the auth user
      // in the toast-after-post case). For reshared posts the handle
      // arrives populated.
      const handle = post.author_handle ?? user?.handle ?? "";
      if (!handle) {
        // Can't build a post URL without a handle — bail to the
        // custom sheet which has its own fallback path.
        setActivePost(post);
        return;
      }

      // Path B — mobile native share:
      //   1. Fetch short URL AND image-file proxy in parallel — the
      //      wait is bounded by the slower of the two. Both target
      //      same-origin Next routes so they're typically <300ms.
      //   2. Fire navigator.share synchronously after, with image
      //      attached as a File when the platform's canShare accepts
      //      it.
      //   3. On any non-AbortError, fall back to the custom sheet.
      try {
        const hasImage = !!post.images?.[0];
        const [share, imageFile] = await Promise.all([
          buildPostShareText(post, handle),
          hasImage ? fetchShareImageFile(post.id) : Promise.resolve(null),
        ]);
        if (!share) {
          setActivePost(post);
          return;
        }

        const payload: ShareData = { title: share.title, text: share.text };
        // Only attach files when the platform actually accepts them.
        // canShare returns false on Chrome desktop / Firefox even
        // though navigator.share itself exists, and we want to fail
        // gracefully there.
        if (
          imageFile &&
          typeof navigator.canShare === "function" &&
          navigator.canShare({ files: [imageFile] })
        ) {
          payload.files = [imageFile];
        }

        try {
          await navigator.share(payload);
        } catch (err) {
          if (err instanceof DOMException && err.name === "AbortError") {
            return;
          }
          // Most likely NotAllowedError — iOS Safari refused the call
          // because user activation lapsed during the parallel fetch
          // on a slow network. The custom sheet has no activation
          // requirement, so falling back gets the user unstuck.
          console.warn(
            "[share] navigator.share failed, opening custom sheet",
            err,
          );
          setActivePost(post);
        }
      } catch {
        // Short URL fetch itself blew up — same fallback.
        setActivePost(post);
      }
    },
    [isMobile, nativeShareSupported, user?.handle],
  );

  return (
    <SharePostContext.Provider value={{ openShareSheet }}>
      {children}
      {activePost ? (
        <SharePostSheet
          open={true}
          onClose={() => setActivePost(null)}
          post={activePost}
          isMobile={isMobile}
        />
      ) : null}
    </SharePostContext.Provider>
  );
}