/** How a period is cut into buckets, and the one rule for charts over dated rows: the buckets partition the
 *  window, starting on its first day, so they add up to its figure. The bucket holding now and one cut by
 *  the period's edge are partial, and beside finished ones read as a collapse; they are marked, never
 *  dropped unsaid. */
export type BucketUnit = "day" | "week" | "month";
export interface Bucket {
    start: Date;
    end: Date;
    /** Holds now or runs past the edge: not a whole figure. */
    partial: boolean;
}
export declare const startOfDay: (date: Date) => Date;
export declare function daySpan(start: Date, end: Date): number;
export declare function dayAfter(start: Date, days: number): Date;
/**
 * The unit that cuts a window into about twelve periods at most, so a sparse count reads as a shape rather
 * than a comb of single days: a fortnight by day, a month to a quarter by week, longer by month.
 */
export declare function bucketUnit(start: Date, end: Date): BucketUnit;
/**
 * Where a window's first period starts: a day or a week on the window's own first day, so its periods
 * partition it and add up to its figure (a month's weeks run 01–07, 08–14…); a month on the calendar
 * month holding it.
 */
export declare function periodStart(date: Date, unit: BucketUnit): Date;
/** Anchored on the window's start (`periodStart`). Partial when holding now or cut by the edge; buckets
 *  starting after now are not returned. */
export declare function bucketsOf(start: Date, end: Date, now: Date, unit?: BucketUnit): Bucket[];
/** `YYYY-MM-DD`, with or without a time. */
export declare function parseWhen(value: string | null | undefined): Date | null;
export declare function sumByBucket<T>(rows: readonly T[], when: (row: T) => string | null | undefined, value: (row: T) => number | null | undefined, buckets: readonly Bucket[]): number[];
/** Both ends inclusive, whole days. */
export declare function inPeriod(value: string | null | undefined, start: Date, end: Date): boolean;
/** `null` when the base is zero. */
export declare function percentChange(current: number, previous: number): number | null;
export interface TrendPoint {
    /** What a chart labels the point by. */
    start: Date;
    value: number;
}
export interface TrendSeries {
    unit: BucketUnit;
    /** A running or cut bucket is not among them. */
    points: readonly TrendPoint[];
    /** A bucket still filling or cut by the edge was left out. */
    partial: boolean;
    /** The bucket holding now, summed so far: drawn marked as running, never beside the points as a peer. */
    running: TrendPoint | null;
}
/** One definition for both readings of a period — a trend chart and a register band's change — so they
 *  agree on which buckets count. */
export declare function trendBuckets<T>(rows: readonly T[], window: {
    start: Date;
    end: Date;
    now: Date;
}, when: (row: T) => string | null | undefined, value: (row: T) => number | null | undefined): TrendSeries;
/** The later half of the buckets against the earlier, as a percentage; nothing without a base. Halves, not
 *  the last bucket, since day-on-day is noise; per bucket, since an odd count would read as growth. */
export declare function seriesChange(points: readonly TrendPoint[]): number | null;