import {
    clampNumber,
    roundToStepPrecision,
} from '$shared/lib/utils';

/**
 * Geometry/range options shared by the math helpers.
 */
type SliderMathOpts = {
    /**
     * Minimum value (inclusive)
     */
    min: number;
    /**
     * Maximum value (inclusive)
     */
    max: number;
    /**
     * Step increment
     */
    step: number;
};

/**
 * Snap a raw value onto the step grid, then clamp to [min, max].
 *
 * Snapping is anchored to `min` so non-zero ranges land on valid stops.
 * `roundToStepPrecision` removes IEEE-754 drift from fractional steps.
 */
export function snapToStep(raw: number, { min, max, step }: SliderMathOpts): number {
    if (step <= 0) {
        return clampNumber(raw, min, max);
    }
    const snapped = min + Math.round((raw - min) / step) * step;
    return clampNumber(roundToStepPrecision(snapped, step), min, max);
}

/**
 * Convert a pointer coordinate into a slider value.
 *
 * Horizontal maps left→min, right→max. Vertical is inverted so that
 * up→max, matching natural slider expectations. The DOMRect is passed in
 * to keep this pure and unit-testable without layout.
 */
export function pointerToValue(
    point: { clientX: number; clientY: number },
    rect: DOMRect,
    opts: SliderMathOpts & { orientation: 'horizontal' | 'vertical' },
): number {
    const { min, max, orientation } = opts;
    const size = orientation === 'vertical' ? rect.height : rect.width;
    if (size <= 0) {
        return snapToStep(min, opts);
    }
    const ratio = orientation === 'vertical'
        ? (rect.bottom - point.clientY) / size
        : (point.clientX - rect.left) / size;
    return snapToStep(min + clampNumber(ratio, 0, 1) * (max - min), opts);
}