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A functional toolkit for authoring resource-leveling algorithms — compose constraint and scoring blocks, enumerate feasible schedules
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TypeScript
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206// Lazy schedule enumeration.// Wraps an AsyncIterable<Schedule> so that filter/map/take/branch stay lazy// and only the terminal ops (bestBy, bestByLex, kBestByLex, paretoFrontier,// collect) actually drain.
import type { Schedule, ScheduleStream, Scorer } from "./types.ts";
export class ScheduleStreamImpl implements ScheduleStream { private readonly source: AsyncIterable<Schedule>;
constructor(source: AsyncIterable<Schedule>) { this.source = source; }
[Symbol.asyncIterator](): AsyncIterator<Schedule> { return this.source[Symbol.asyncIterator](); }
filter(pred: (s: Schedule) => boolean): ScheduleStream { const source = this.source; return new ScheduleStreamImpl({ async *[Symbol.asyncIterator]() { for await (const s of source) { if (pred(s)) yield s; } }, }); }
map(fn: (s: Schedule) => Schedule): ScheduleStream { const source = this.source; return new ScheduleStreamImpl({ async *[Symbol.asyncIterator]() { for await (const s of source) yield fn(s); }, }); }
take(k: number): ScheduleStream { const source = this.source; return new ScheduleStreamImpl({ async *[Symbol.asyncIterator]() { if (k <= 0) return; let n = 0; for await (const s of source) { yield s; if (++n >= k) return; } }, }); }
branch(fork: (s: Schedule) => ScheduleStream): ScheduleStream { const source = this.source; return new ScheduleStreamImpl({ async *[Symbol.asyncIterator]() { for await (const s of source) { for await (const child of fork(s)) yield child; } }, }); }
async bestBy(scorer: Scorer): Promise<Schedule | null> { let bestSchedule: Schedule | null = null; let bestScore: number | null = null; for await (const s of this.source) { const score = scorer.score(s); if ( bestScore === null || (scorer.direction === "min" ? score < bestScore : score > bestScore) ) { bestScore = score; bestSchedule = s; } } return bestSchedule; }
async bestByLex(scorers: readonly Scorer[]): Promise<Schedule | null> { let bestSchedule: Schedule | null = null; let bestScores: number[] | null = null; for await (const s of this.source) { const scores = scorers.map((sc) => sc.score(s)); if (bestScores === null || lexBetter(scores, bestScores, scorers)) { bestScores = scores; bestSchedule = s; } } return bestSchedule; }
async kBestByLex( scorers: readonly Scorer[], k: number, ): Promise<readonly Schedule[]> { if (k <= 0) return []; const scored: { schedule: Schedule; scores: number[] }[] = []; for await (const s of this.source) { scored.push({ schedule: s, scores: scorers.map((sc) => sc.score(s)) }); } // Stable sort (ES2019 guarantees it): equal-on-all-tiers keeps stream // order, matching bestByLex where first seen wins. scored.sort((a, b) => lexBetter(a.scores, b.scores, scorers) ? -1 : lexBetter(b.scores, a.scores, scorers) ? 1 : 0, ); return scored.slice(0, k).map((x) => x.schedule); }
async paretoFrontier( scorers: readonly Scorer[], ): Promise<readonly Schedule[]> { const collected: { schedule: Schedule; scores: number[] }[] = []; for await (const s of this.source) { collected.push({ schedule: s, scores: scorers.map((sc) => sc.score(s)), }); } const frontier: Schedule[] = []; for (const candidate of collected) { let dominated = false; for (const other of collected) { if (other === candidate) continue; if (dominates(other.scores, candidate.scores, scorers)) { dominated = true; break; } } if (!dominated) frontier.push(candidate.schedule); } return frontier; }
async collect(limit?: number): Promise<readonly Schedule[]> { const out: Schedule[] = []; for await (const s of this.source) { out.push(s); if (limit !== undefined && out.length >= limit) break; } return out; }}
// `a` beats `b` on the first tier where they differ; equal on all tiers is// not better (first seen wins, keeping selection deterministic).function lexBetter( a: readonly number[], b: readonly number[], scorers: readonly Scorer[],): boolean { for (let i = 0; i < scorers.length; i++) { const ai = a[i]!; const bi = b[i]!; if (ai === bi) continue; return scorers[i]!.direction === "min" ? ai < bi : ai > bi; } return false;}
// `a` dominates `b` iff a is at least as good on every scorer and strictly// better on at least one.function dominates( a: readonly number[], b: readonly number[], scorers: readonly Scorer[],): boolean { let strictlyBetter = false; for (let i = 0; i < scorers.length; i++) { const dir = scorers[i]!.direction; const ai = a[i]!; const bi = b[i]!; const aBetter = dir === "min" ? ai < bi : ai > bi; const aWorse = dir === "min" ? ai > bi : ai < bi; if (aWorse) return false; if (aBetter) strictlyBetter = true; } return strictlyBetter;}
export function streamFromFactory( factory: () => AsyncGenerator<Schedule>,): ScheduleStream { return new ScheduleStreamImpl({ [Symbol.asyncIterator]: factory, });}
/** Lazily concatenate streams in declaration order. A later factory is not * invoked until every schedule from the preceding stream has been consumed. */export function concatStreams( factories: readonly (() => ScheduleStream)[],): ScheduleStream { return new ScheduleStreamImpl({ async *[Symbol.asyncIterator]() { for (const factory of factories) { for await (const schedule of factory()) yield schedule; } }, });}