import { type Accessor, createContext, useContext } from "solid-js";

/**
 * Context value provided by `<Meter.Root>` to its compound parts.
 *
 * Reactive values are exposed as `Accessor`s (not plain numbers/strings) so
 * descendants stay reactive to upstream prop changes without having to
 * subscribe through a signal wrapper.
 *
 * `setLabelId` is the registration channel used by `<Meter.Label>` to report
 * its generated id into the root, so the root can wire up `aria-labelledby`.
 */
export interface MeterRootContextValue {
	/** Accessor for the current meter value. */
	value: Accessor<number>;
	/** Accessor for the minimum value of the range. */
	min: Accessor<number>;
	/** Accessor for the maximum value of the range. */
	max: Accessor<number>;
	/**
	 * Accessor for the formatted (human-readable) current value — either the
	 * value formatted via the root's `format` / `locale` props, or the default
	 * percentage form when no explicit format is provided.
	 */
	formattedValue: Accessor<string>;
	/**
	 * Register/deregister the label id that drives `<Meter.Root>`'s
	 * `aria-labelledby`. Called by `<Meter.Label>` from its mount/unmount
	 * lifecycle.
	 */
	setLabelId: (id: string | undefined) => void;
}

/**
 * Meter root context. Solid 2's `useContext` throws `ContextNotFoundError`
 * when the resolved value is `undefined`, so the sentinel for "no provider
 * mounted" is `null` — a custom message after `useContext` would never fire
 * against the default `undefined`.
 */
export const MeterRootContext = createContext<MeterRootContextValue | null>(
	null,
);

export function useMeterRootContext(): MeterRootContextValue {
	const context = useContext(MeterRootContext);
	if (context == null) {
		throw new Error(
			"Base UI: <Meter.*> parts must be used within <Meter.Root>.",
		);
	}
	return context;
}