// Round-14 frontend micro-pack (benches/ROUND14.md §F1, §F2).
//
// Each section is BEFORE (verbatim replica of the shipped shape) vs AFTER
// (proposed shape), with an equivalence gate and a wall-time perf gate — the
// same discipline as the Rust micro-packs: an AFTER that doesn't beat its
// BEFORE fails the gate.

import { describe, expect, it } from 'vitest';

// ────────────────────────────────────────────────────────────────────────────
// [F2] favorites `favoriteIds` — rebuild-a-fresh-Set-per-page vs incremental
// ────────────────────────────────────────────────────────────────────────────
//
// Audit finding: the favorites route derived `favoriteIds = new SvelteSet(
// items.map(i => i.id))`. Every infinite-scroll page (`raw = [...raw, ...page]`)
// rebuilt a brand-new set over the WHOLE accumulated list — O(N) per page,
// O(N²) across a P-page drain — and, being a new instance each page,
// invalidated every mounted star reader. The fix keeps one persistent set and
// `add`s only the fresh page's ids (clear on reset). Since every item on the
// page is a favorite and removed items aren't rendered, the set only has to be
// a superset of the displayed ids, so `add`-only is correct.

/** A page of ids (50/page, the default page size). */
function pageOf(start: number, n: number): string[] {
	return Array.from({ length: n }, (_, i) => `fav-${start + i}`);
}

/** BEFORE: rebuild a fresh Set over the whole accumulated list each page. */
function rebuildPerPage(pages: string[][]): Set<string> {
	let acc: string[] = [];
	let set = new Set<string>();
	for (const page of pages) {
		acc = [...acc, ...page]; // the route's `raw = [...raw, ...page]`
		set = new Set(acc.map((id) => id)); // new instance + O(N) rebuild
	}
	return set;
}

/** AFTER: one persistent set, add only the fresh page's ids. */
function incrementalPerPage(pages: string[][]): Set<string> {
	const set = new Set<string>();
	for (const page of pages) {
		for (const id of page) set.add(id);
	}
	return set;
}

describe('round14 §F2 — favorites favoriteIds incremental set', () => {
	it('final membership is identical (equivalence gate)', () => {
		const pages = Array.from({ length: 20 }, (_, p) => pageOf(p * 50, 50));
		const before = rebuildPerPage(pages);
		const after = incrementalPerPage(pages);
		expect(after.size).toBe(before.size);
		for (const id of before) expect(after.has(id)).toBe(true);
		for (const id of after) expect(before.has(id)).toBe(true);
	});

	it('a P-page drain builds the set ≥5x faster incrementally (perf gate)', () => {
		const PAGES = 40;
		const PER = 50; // 2 000 items total
		const pages = Array.from({ length: PAGES }, (_, p) => pageOf(p * PER, PER));

		const run = (f: (p: string[][]) => Set<string>): number => {
			const t0 = performance.now();
			// A few repetitions so the measurement isn't dominated by timer noise.
			for (let r = 0; r < 20; r++) f(pages);
			return performance.now() - t0;
		};

		// Warm-up (JIT) then measure.
		run(rebuildPerPage);
		run(incrementalPerPage);
		const beforeMs = run(rebuildPerPage);
		const afterMs = run(incrementalPerPage);

		console.info(
			`§F2 ${PAGES} pages × ${PER}: rebuild-per-page ${beforeMs.toFixed(1)} ms vs incremental ${afterMs.toFixed(1)} ms (${(beforeMs / afterMs).toFixed(1)}x)`
		);
		expect(afterMs).toBeLessThan(beforeMs / 5);
	});
});

// ────────────────────────────────────────────────────────────────────────────
// [F1] t() params — throwaway `{}` per call vs a shared frozen empty object
// ────────────────────────────────────────────────────────────────────────────
//
// The ubiquitous inline-fallback form `t('k', 'Fallback')` and the bare
// `t('k')` (default param `= {}`) allocated a fresh params object on every
// call, though for a cache-hit string with no `{{…}}` `interpolate` returns
// before ever reading params. t() runs ~10×/row. The fix hoists a shared
// frozen `EMPTY_PARAMS` for both no-param branches.

const EMPTY_PARAMS: Record<string, unknown> = Object.freeze({});

/** Model of the shipped t() param selection + a representative params read
 * (interpolate's `params[name]` lookup), isolated from dictionary I/O. */
function tBefore(paramsOrFallback: string | Record<string, unknown> = {}): unknown {
	const isStringForm = typeof paramsOrFallback === 'string';
	const params = isStringForm ? {} : paramsOrFallback;
	return (params as Record<string, unknown>)['n'];
}
function tAfter(paramsOrFallback: string | Record<string, unknown> = EMPTY_PARAMS): unknown {
	const isStringForm = typeof paramsOrFallback === 'string';
	const params = isStringForm ? EMPTY_PARAMS : paramsOrFallback;
	return (params as Record<string, unknown>)['n'];
}

describe('round14 §F1 — t() shared empty params', () => {
	it('produces identical results for the no-param call forms (equivalence gate)', () => {
		expect(tAfter()).toBe(tBefore());
		expect(tAfter('Owner')).toBe(tBefore('Owner'));
		expect(tAfter({ n: 5 })).toBe(tBefore({ n: 5 }));
	});

	it('the string/bare forms are not slower with a shared empty (perf gate)', () => {
		const N = 4_000_000;
		const run = (f: (a?: string | Record<string, unknown>) => unknown): number => {
			let sink: unknown;
			const t0 = performance.now();
			for (let i = 0; i < N; i++) {
				// Alternate the two no-param call forms (bare + string fallback).
				sink = i & 1 ? f('Fallback') : f();
			}
			void sink;
			return performance.now() - t0;
		};
		// Warm-up then measure (best-of-3 to damp GC/JIT noise).
		run(tBefore);
		run(tAfter);
		const beforeMs = Math.min(run(tBefore), run(tBefore), run(tBefore));
		const afterMs = Math.min(run(tAfter), run(tAfter), run(tAfter));
		console.info(
			`§F1 ${N} no-param t() calls: fresh {} ${beforeMs.toFixed(1)} ms vs shared frozen ${afterMs.toFixed(1)} ms (${(beforeMs / afterMs).toFixed(2)}x)`
		);
		// Zero-risk alloc reduction: the shared-empty arm must be no slower.
		expect(afterMs).toBeLessThanOrEqual(beforeMs * 1.05);
	});
});