import { useCallback, useEffect, useRef, useState } from 'react';
import { invoke } from '@tauri-apps/api/core';

import {
    createThumbnailRequestKey,
    startOwnedThumbnailGeneration,
    ThumbnailRequestGeneration,
    thumbnailIdsFromRequestKey,
} from '../lib/thumbnailRequests';
import { windowAsyncScope } from '../lib/asyncOwnership';

/**
 * Per-id cache for cover thumbnails belonging to the supplied game ids.
 * Returns `null` until the value is known; returns the empty string when the
 * backend has nothing for the id, so callers can use the placeholder cover.
 */
export const useThumbnails = (ids: readonly string[]) => {
    const [thumbnails, setThumbnails] = useState<Map<string, string>>(new Map());
    const thumbnailsRef = useRef(thumbnails);
    const requestKey = createThumbnailRequestKey(ids);

    useEffect(() => {
        const generation = new ThumbnailRequestGeneration(
            id => invoke<string>('get_game_thumbnail', { gameId: id }),
            (id, url) => {
                const next = new Map(thumbnailsRef.current).set(id, url);
                thumbnailsRef.current = next;
                setThumbnails(next);
            },
        );
        const missingIds = thumbnailIdsFromRequestKey(requestKey)
            .filter(id => !thumbnailsRef.current.has(id));

        return startOwnedThumbnailGeneration(windowAsyncScope, generation, missingIds);
    }, [requestKey]);

    const get = useCallback((id: string): string | null => {
        if (thumbnails.has(id)) return thumbnails.get(id) ?? '';
        return null;
    }, [thumbnails]);

    return { get };
};