'use strict';

// reddit gallery images: `s.u` (still) or `s.gif`/`s.mp4` (animated) - URLs come back
// HTML-entity-encoded (e.g. '&' instead of '&')
function resolveMediaUrl(media) {
    const url = media?.s?.u || media?.s?.gif || media?.s?.mp4;

    return url ? url.replace(/&/g, '&') : null;
}

// reddit sends the non-standard 'image/jpg' instead of the real IANA 'image/jpeg' for
// gallery items - left as-is, this silently breaks anything matching against real mime
// types downstream (interpolate.js's extension lookup ends up with a '.false' extension,
// fetch/content.js's addMeta() skips embedding metadata since it only matches 'image/jpeg')
function normalizeType(type) {
    return type === 'image/jpg' ? 'image/jpeg' : type;
}

async function redditAlbum(host, post, { reddit }) {
    // reddit's submission listing already embeds media_metadata/gallery_data for gallery posts,
    // and curate/posts.js carries them through as post.mediaMetadata/post.galleryData - reuse
    // those instead of re-fetching the same post individually through reddit's own client
    // (reservoir: 6/min, maxConcurrent: 1 - see src/reddit/client.js), which would otherwise cost
    // one full throttled round trip per gallery post. Only fall back to a fresh fetch if the
    // listing didn't have it for some reason (e.g. gallery_data null on the listing too).
    const data = post.mediaMetadata
        ? { media_metadata: post.mediaMetadata, gallery_data: post.galleryData }
        : await reddit.getSubmission(post.id);
    const mediaMetadata = data.media_metadata || {};

    // gallery_data (the ordered {media_id, is_deleted, ...} list for this gallery) has been
    // seen coming back null on a freshly-posted gallery even though media_metadata itself
    // was already fully populated - fall back to media_metadata's own keys, in the order the
    // JSON provided them (reddit sends them in gallery order, and object key order is
    // preserved through JSON.parse), skipping anything not (yet, or any longer) valid
    const galleryItems = data.gallery_data?.items
        || Object.entries(mediaMetadata)
            .filter(([, media]) => media.status === 'valid')
            .map(([mediaId]) => ({ media_id: mediaId }));

    const items = galleryItems
        .filter((item) => !item.is_deleted)
        .map((item) => {
            const media = mediaMetadata[item.media_id];
            const url = resolveMediaUrl(media);

            return url && {
                id: item.media_id,
                url,
                datetime: post.datetime,
                type: normalizeType(media.m) || 'image/jpeg',
            };
        })
        .filter(Boolean);

    return {
        album: {
            id: host.id,
            url: host.url,
            title: post.title,
        },
        items,
    };
}

module.exports = redditAlbum;