/**
 * When a document's slug changes, appends the OLD slug to a `slugHistory` array
 * field. The project reads slugHistory to serve a 301 redirect from old URLs to
 * the current one — so changing a slug doesn't 404 the old address (a real SEO
 * loss / audit finding).
 *
 * Requires a `slugHistory` field on the collection:
 *   { name: 'slugHistory', type: 'array', fields: [{ name: 'slug', type: 'text' }],
 *     admin: { readOnly: true } }
 *
 *   hooks: { beforeChange: [trackSlugHistoryHook] }
 *
 * The project then, in resolveRoute or a redirect check, looks up slugHistory and
 * 301s to the current slug. See docs/hooks.md.
 */ export const trackSlugHistoryHook = ({ data, originalDoc })=>{
    const oldSlug = originalDoc?.slug;
    const newSlug = data.slug;
    if (typeof oldSlug === 'string' && typeof newSlug === 'string' && oldSlug !== newSlug && oldSlug.length > 0) {
        const history = Array.isArray(data.slugHistory) ? data.slugHistory : Array.isArray(originalDoc?.slugHistory) ? originalDoc.slugHistory : [];
        // Avoid duplicates; don't record the new slug itself.
        if (!history.some((h)=>h?.slug === oldSlug)) {
            data.slugHistory = [
                ...history,
                {
                    slug: oldSlug
                }
            ];
        }
    }
    return data;
};

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