/**
 * `<gen type="stat">` — one number for the WHOLE run, on every row.
 *
 * `accumulate=` totals a list inside one record. `<gen type="running">` totals a
 * column as it goes, so row i knows about rows 1..i. This is the third and last
 * axis: a row that knows something about EVERY row, including the ones after it.
 *
 *     <sequence name="Price"><gen type="number" value="10..200"/></sequence>
 *     <sequence name="Average"><gen type="stat" of="Price" op="mean"/></sequence>
 *     <sequence name="Flag">
 *       <gen if="Price > Average" type="text" value="above average"/>
 *       <gen type="text" value="ordinary"/>
 *     </sequence>
 *
 * "Is this row above average" cannot be asked any other way: the average is not
 * knowable until the last row exists, and a conditional gen is evaluated while
 * the row is being built.
 *
 * ── What it costs, said out loud ──────────────────────────────────────────────
 *
 * A statistic over the whole run is the strongest form of the thing `running`
 * already is: it cannot be answered one row at a time, and unlike `running` it
 * cannot even be answered by the rows SO FAR. So the streaming builder refuses
 * it by name and the router hands the config to the in-memory engine — the same
 * road `running`, `uniq` on a composed value and every other whole-column
 * construct takes.
 *
 * ── Where the arithmetic comes from ───────────────────────────────────────────
 *
 * `sum`, `min` and `max` are the last value of the corresponding RUNNING column,
 * computed by {@link accumulateColumn}. That is not a shortcut — it is how the
 * two features are kept from drifting: the fixed-point scale rule, the treatment
 * of an empty cell and the "min returns the winning element's own spelling" rule
 * are written once and used twice. A column of `19.99`s totals to the same bytes
 * whether it is read row by row or all at once.
 *
 * `mean`, `median` and `stddev` are ratios and cannot be exact, so they are
 * computed in floating point over the numeric values — the same three formulas
 * the expression language's list functions use, including the POPULATION
 * standard deviation. `decimals=` rounds the answer; without it the full value
 * is printed, because a mean that quietly lost digits is worse than an ugly one.
 */
import type { Sequence, SequenceSpec } from './types.js';
/** What a statistic can be. */
export type StatOp = 'sum' | 'mean' | 'median' | 'min' | 'max' | 'count' | 'stddev';
export declare const STAT_OPS: readonly StatOp[];
export declare class StatError extends Error {
    readonly name = "StatError";
}
/** The column a statistic reads, or `''` when the generator did not say. */
export declare function statOf(spec: SequenceSpec): string;
/**
 * Read `op=` where an unknown op simply means "none".
 *
 * The engine path uses this one: by the time a value is drawn the validator has
 * already refused a misspelled op, so throwing here would turn a reported
 * problem into a crash.
 */
export declare function readStatOp(attrs: Record<string, string | undefined>): StatOp | undefined;
/** The same, but strict — the validator's copy, which turns a bad op into a diagnostic. */
export declare function parseStatOp(attrs: Record<string, string | undefined>): StatOp | undefined;
/** `decimals=`, or undefined when the answer is printed at full precision. */
export declare function statDecimals(attrs: Record<string, string | undefined>): number | undefined;
/**
 * The statistic itself, as the text that goes in every cell.
 *
 * A cell the parent filter emptied does not take part — the same rule
 * `accumulateColumn` follows, so a filtered column has one meaning across the
 * three features rather than three.
 */
export declare function statisticOf(values: readonly (string | undefined)[], op: StatOp, decimals: number | undefined): string;
/**
 * Publish the statistic column.
 *
 * Reads `of=` out of the registry rather than drawing anything: a statistic
 * consumes no randomness at all, which is why adding one leaves every other
 * column exactly where it was.
 */
export declare function registerStat(spec: SequenceSpec, registry: Record<string, Sequence>, count: number): void;
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