From 5e7c3ad7ed8c287b538de97d4de3a4df87e9a100 Mon Sep 17 00:00:00 2001 From: nsfisis Date: Sun, 8 Feb 2026 21:18:55 +0900 Subject: feat(study): use seeded PRNG for deterministic card shuffle order Shuffle order is now fixed within a study day by seeding mulberry32 with the study day boundary timestamp (3:00 AM rollover). Co-Authored-By: Claude Opus 4.6 --- src/client/utils/random.ts | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) create mode 100644 src/client/utils/random.ts (limited to 'src/client/utils/random.ts') diff --git a/src/client/utils/random.ts b/src/client/utils/random.ts new file mode 100644 index 0000000..53de45e --- /dev/null +++ b/src/client/utils/random.ts @@ -0,0 +1,32 @@ +/** + * Mulberry32 seeded PRNG. + * Returns a function that produces deterministic values in [0, 1). + */ +export function createSeededRandom(seed: number): () => number { + let s = seed | 0; + return () => { + s = (s + 0x6d2b79f5) | 0; + let t = Math.imul(s ^ (s >>> 15), 1 | s); + t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t; + return ((t ^ (t >>> 14)) >>> 0) / 4294967296; + }; +} + +/** + * Fisher-Yates shuffle algorithm. + * Returns a new shuffled array (does not mutate the original). + * Accepts an optional `random` function for deterministic shuffling. + */ +export function shuffle( + array: T[], + random: () => number = Math.random, +): T[] { + const result = [...array]; + for (let i = result.length - 1; i > 0; i--) { + const j = Math.floor(random() * (i + 1)); + const temp = result[i] as T; + result[i] = result[j] as T; + result[j] = temp; + } + return result; +} -- cgit v1.3-1-g0d28