/**
 * The keyboard contract of the range slider, kept pure and in its own module
 * so the element module holds only DOM wiring and the contract is testable
 * without layout.
 */
import { nth, valueQuantile } from "./quantile.js";
/**
 * Steps one thumb by `delta` positions through the distribution. Pure, so the
 * keyboard contract is testable without layout.
 *
 * Steps to the next *distinct* value rather than the next index. Real
 * distributions are lumpy -- awesome-mcp-explorer's star counts hold ~1500
 * duplicate zeros -- and an index step inside a run of equal values changes the
 * index while leaving the value (and therefore the thumb, and the filter)
 * exactly where it was. That reads as a dead arrow key.
 */
export function steppedValue(values, current, delta) {
    const last = values.length - 1;
    // Round to a real sample index so a thumb sitting between two samples still
    // advances rather than stalling on a fractional step.
    const index = Math.round(valueQuantile(values, current) * last);
    const direction = Math.sign(delta);
    if (direction === 0)
        return nth(values, index);
    let cursor = index;
    for (let taken = 0; taken < Math.abs(delta); taken++) {
        let next = cursor + direction;
        while (next >= 0 && next <= last && nth(values, next) === nth(values, cursor)) {
            next += direction;
        }
        if (next < 0 || next > last)
            break;
        cursor = next;
    }
    return nth(values, cursor);
}
/**
 * The value a thumb at `current` moves to for a key, or `undefined` when the
 * key is not one the slider handles (so the event is left to the browser).
 * Arrow keys step one distinct value, Page keys ten, Home/End jump to the
 * bounds.
 */
export function keyTarget(key, values, current) {
    switch (key) {
        case "ArrowDown":
        case "ArrowLeft": {
            return steppedValue(values, current, -1);
        }
        case "ArrowRight":
        case "ArrowUp": {
            return steppedValue(values, current, 1);
        }
        case "End": {
            return nth(values, values.length - 1);
        }
        case "Home": {
            return nth(values, 0);
        }
        case "PageDown": {
            return steppedValue(values, current, -10);
        }
        case "PageUp": {
            return steppedValue(values, current, 10);
        }
        default: {
            return undefined;
        }
    }
}
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