71 lines
3.0 KiB
TypeScript
71 lines
3.0 KiB
TypeScript
// paginate (todo §1): pagination math → the model pagination.ejs renders. Pure and
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// URL-free (README signature `paginate(total, page, pageSize)`); the caller maps each
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// page number to an href. Inputs are clamped/guarded so it never produces a broken model:
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// page is pinned to [1, pageCount], total/pageSize coerced to sane integers.
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export interface PageItem {
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current: boolean;
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ellipsis: boolean; // a gap; `page` is null
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page: number | null;
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}
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export interface PageModel {
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from: number; // 1-based index of the first row on this page (0 when empty)
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next: number | null; // next page, or null on the last page
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page: number; // clamped current page (≥ 1)
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pageCount: number; // total pages (≥ 1)
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pageSize: number; // effective page size (≥ 1)
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pages: PageItem[]; // page-number sequence with ellipsis gaps
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prev: number | null; // previous page, or null on the first page
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to: number; // 1-based index of the last row on this page (0 when empty)
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total: number; // effective total rows (≥ 0)
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}
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export interface PaginateOptions {
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boundaries?: number; // pages always shown at each end (default 1)
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siblings?: number; // pages shown each side of the current page (default 1)
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}
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export function paginate(total: number, page: number, pageSize: number, options: PaginateOptions = {}): PageModel {
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const t = Math.max(0, Math.floor(total) || 0);
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const size = Math.max(1, Math.floor(pageSize) || 0);
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const pageCount = Math.max(1, Math.ceil(t / size));
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const reqPage = Number.isFinite(page) ? Math.floor(page) : 1;
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const current = Math.min(Math.max(reqPage, 1), pageCount);
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return {
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from: t === 0 ? 0 : (current - 1) * size + 1,
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next: current < pageCount ? current + 1 : null,
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page: current,
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pageCount,
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pageSize: size,
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pages: pageItems(current, pageCount, options.siblings ?? 1, options.boundaries ?? 1),
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prev: current > 1 ? current - 1 : null,
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to: Math.min(current * size, t),
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total: t,
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};
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}
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const item = (page: number, current = false): PageItem => ({ current, ellipsis: false, page });
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const gap = (): PageItem => ({ current: false, ellipsis: true, page: null });
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// First/last `boundaries` pages + a `siblings`-wide window around current, deduped and sorted;
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// gaps wider than one page become an ellipsis, a lone missing page is shown instead.
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function pageItems(current: number, pageCount: number, siblings: number, boundaries: number): PageItem[] {
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const show = new Set<number>();
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const add = (n: number): void => { if (n >= 1 && n <= pageCount) show.add(n); };
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for (let i = 1; i <= boundaries; i++) { add(i); add(pageCount - i + 1); }
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for (let n = current - siblings; n <= current + siblings; n++) add(n);
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const items: PageItem[] = [];
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let prev = 0;
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for (const n of [...show].sort((a, b) => a - b)) {
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if (prev) {
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if (n - prev === 2) items.push(item(prev + 1)); // single hole → show the page
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else if (n - prev > 2) items.push(gap());
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}
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items.push(item(n, n === current));
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prev = n;
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}
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return items;
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}
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