/**
 * How a period is cut into the buckets a trend is drawn over, and the one rule
 * every chart over dated rows has to obey: a bucket is drawn only when it is
 * COMPLETE. The bucket holding "now" is a partial period, and so is a bucket the
 * period's own edge cuts through; drawing either beside finished ones draws a
 * collapse that is not there.
 */
export type BucketUnit = "day" | "week" | "month";
export interface Bucket {
    /** Inclusive. */
    start: Date;
    /** Exclusive. */
    end: Date;
    /** The bucket holds "now", or runs past the period's edge — its figure is not a whole one. */
    partial: boolean;
}
export declare const startOfDay: (date: Date) => Date;
/** Whole days from `start` to `end`, both included. */
export declare function daySpan(start: Date, end: Date): number;
/** The day `days` whole days after `start`, counting `start` as the first. */
export declare function dayAfter(start: Date, days: number): Date;
/** The unit a span is read in — a month by day, half a year by week, longer by month. */
export declare function bucketUnit(start: Date, end: Date): BucketUnit;
/**
 * The buckets of `[start, end]`, aligned to the unit's own boundaries so a week
 * is a calendar week and a month a calendar month. A bucket is partial when it
 * holds `now` or when the period's edge cuts through it; a bucket that starts
 * after `now` is not returned at all.
 */
export declare function bucketsOf(start: Date, end: Date, now: Date, unit?: BucketUnit): Bucket[];
/** The dates a stored value parses to — `YYYY-MM-DD`, with or without a time. */
export declare function parseWhen(value: string | null | undefined): Date | null;
/** Each bucket's sum of `value` over the rows whose `when` falls in it. */
export declare function sumByBucket<T>(rows: readonly T[], when: (row: T) => string | null | undefined, value: (row: T) => number | null | undefined, buckets: readonly Bucket[]): number[];
/** Whether a stored date falls inside `[start, end]` — both ends inclusive, whole days. */
export declare function inPeriod(value: string | null | undefined, start: Date, end: Date): boolean;
/** The percentage change from `previous` to `current`; `null` when the base is zero. */
export declare function percentChange(current: number, previous: number): number | null;