// Browser-side like / unlike calls and the pure card update they drive.

import type { CardPost } from "./feed-model";

export interface LikeOutcome {
  isLiked: boolean;
  likesCount: number | null;
}

export class LikeError extends Error {
  constructor(public readonly signedOut: boolean) {
    super(signedOut ? "sign_in" : "like_failed");
  }
}

export async function sendLike(
  postId: string,
  liked: boolean,
  fetchImpl: typeof fetch = fetch,
): Promise<LikeOutcome> {
  let res: Response;
  try {
    res = await fetchImpl(`/api/posts/${encodeURIComponent(postId)}/like`, {
      method: liked ? "POST" : "DELETE",
      credentials: "same-origin",
    });
  } catch {
    throw new LikeError(false);
  }
  if (res.status === 401) throw new LikeError(true);
  if (!res.ok) throw new LikeError(false);
  try {
    const b = (await res.json()) as { isLiked?: unknown; likesCount?: unknown };
    return {
      isLiked: typeof b.isLiked === "boolean" ? b.isLiked : liked,
      likesCount:
        typeof b.likesCount === "number" && Number.isInteger(b.likesCount) && b.likesCount >= 0
          ? b.likesCount
          : null,
    };
  } catch {
    throw new LikeError(false);
  }
}

/** The card after a successful call: the server count when present, else flip and adjust by one. */
export function applyLikeOutcome(post: CardPost, wanted: boolean, out: LikeOutcome): CardPost {
  if (out.likesCount !== null) return { ...post, isLiked: out.isLiked, likesCount: out.likesCount };
  const changed = post.isLiked !== wanted;
  const delta = changed ? (wanted ? 1 : -1) : 0;
  return { ...post, isLiked: wanted, likesCount: Math.max(0, post.likesCount + delta) };
}