/** Shared, versioned status-line contract. Vendored copies communicate through the same global symbol. */
export const STATUS_LINE_CHANNEL = Symbol.for("@stagefright5/pi-status-line/v1");

export type StatusLineHost = {
	/** True only while the host is focused and drew the line in its latest render. */
	hostsStatusLine(): boolean;
};

export type StatusAction = {
	/** Short verb shown while the status has keyboard focus, for example "jobs". */
	label: string;
	activate(): void;
};

/** Columns `[start, end)` of one extension status, relative to the start of the rendered line. */
export type StatusRegion = { id: string; start: number; end: number };

export type StatusLineChannel = {
	/**
	 * One status line exactly `width` cells wide. `extras` (already styled, most important first,
	 * e.g. a mode label then hints) follow the directory; the last is dropped first when narrow.
	 */
	render?: (width: number, extras?: readonly string[]) => string;
	host?: StatusLineHost;
	/** Clickable statuses, keyed by their `ctx.ui.setStatus` id. */
	statusActions?: Map<string, StatusAction>;
	/** Status positions in the latest rendered line; replaced on every layout. */
	regions?: readonly StatusRegion[];
	/** The status with keyboard focus, drawn highlighted. */
	focusedStatus?: string;
	/** Bumped whenever actions or focus change, so renderers can key caches on it. */
	version?: number;
	/** Model-adjacent status ids. Consumers may retain fallbacks for older producers. */
	modelStatuses?: Set<string>;
};

export function statusLineChannel(): StatusLineChannel {
	const store = globalThis as typeof globalThis & { [STATUS_LINE_CHANNEL]?: StatusLineChannel };
	return (store[STATUS_LINE_CHANNEL] ??= {});
}

export function registerModelStatus(id: string): () => void {
	const channel = statusLineChannel();
	(channel.modelStatuses ??= new Set()).add(id);
	channel.version = (channel.version ?? 0) + 1;
	return () => {
		channel.modelStatuses?.delete(id);
		channel.version = (channel.version ?? 0) + 1;
	};
}

/** Make the status with this id clickable; returns a function that removes exactly this action. */
export function registerStatusAction(id: string, action: StatusAction): () => void {
	const channel = statusLineChannel();
	(channel.statusActions ??= new Map()).set(id, action);
	channel.version = (channel.version ?? 0) + 1;
	return () => {
		if (channel.statusActions?.get(id) !== action) return;
		channel.statusActions.delete(id);
		if (channel.focusedStatus === id) channel.focusedStatus = undefined;
		channel.version = (channel.version ?? 0) + 1;
	};
}

/** The clickable status drawn at `column` (relative to the line start) in the latest render. */
export function statusAt(column: number): string | undefined {
	const channel = statusLineChannel();
	if (!channel.statusActions?.size || !channel.regions) return undefined;
	for (const region of channel.regions) {
		if (column >= region.start && column < region.end && channel.statusActions.has(region.id)) return region.id;
	}
	return undefined;
}

/** Run the action of the clickable status at `column`; true when one ran. */
export function activateStatusAt(column: number): boolean {
	const id = statusAt(column);
	const action = id === undefined ? undefined : statusLineChannel().statusActions?.get(id);
	if (!action) return false;
	action.activate();
	return true;
}