import { type Accessor, createContext, useContext } from "solid-js";
import type {
	TabsRootChangeEventDetails,
	TabsTabValue,
} from "./tabs-root-context.ts";

/**
 * Context published by `<Tabs.List>`. Child tabs consume this for composite-
 * focus coordination + the `activateOnFocus` hook on focus transitions.
 */
export interface TabsListContextValue {
	/** Whether focusing a tab should activate it. */
	activateOnFocus: Accessor<boolean>;
	/** Index of the highlighted (roving-focus) tab. `-1` if none. */
	highlightedTabIndex: Accessor<number>;
	/** Tab elements register here so the indicator can observe size changes. */
	registerTabResizeObserverElement: (element: HTMLElement) => () => void;
	/**
	 * Child tabs call this when they're activated by click or focus — dispatches
	 * through the root's `onValueChange` channel.
	 */
	onTabActivation: (
		newValue: TabsTabValue,
		eventDetails: TabsRootChangeEventDetails,
	) => void;
	/** Setter for the highlighted tab index (used by child tabs on focus). */
	setHighlightedTabIndex: (index: number) => void;
	/** The `<Tabs.List>` element itself (for indicator measurements). */
	tabsListElement: Accessor<HTMLElement | null>;
	/** Marker — `true` when a real `<Tabs.List>` provided this context. */
	readonly present: boolean;
}

const NOOP = (): void => {};

export const NOOP_TABS_LIST_CONTEXT: TabsListContextValue = {
	activateOnFocus: () => false,
	highlightedTabIndex: () => -1,
	registerTabResizeObserverElement: () => () => {},
	onTabActivation: NOOP,
	setHighlightedTabIndex: NOOP,
	tabsListElement: () => null,
	present: false,
};

export const TabsListContext = createContext<TabsListContextValue>(
	NOOP_TABS_LIST_CONTEXT,
);

/**
 * Read the `<Tabs.List>` context. Throws when no list ancestor is present —
 * every tab / indicator requires a list.
 */
export function useTabsListContext(): TabsListContextValue {
	const context = useContext(TabsListContext);
	if (!context.present) {
		throw new Error(
			"Base UI: TabsListContext is missing. Tabs parts must be placed within <Tabs.List>.",
		);
	}
	return context;
}