import type { Accessor } from "solid-js";

/**
 * Tracks whether a streaming response has stalled (no new tokens for a while)
 * and produces a smooth 0→1 intensity value suitable for color interpolation
 * (e.g. fading the spinner glyph toward red).
 *
 * Driven by an external clock signal rather than its own interval, so it
 * automatically slows down when the terminal is backgrounded (no ticks = no
 * updates) and doesn't create a second timer alongside the animation clock.
 *
 * ```ts
 * const time = useClock(50);
 * const stalled = useStalled(time, () => responseLength());
 * // stalled.isStalled()  — boolean
 * // stalled.intensity()  — 0..1
 * ```
 */

export type StalledState = {
	isStalled: Accessor<boolean>;
	intensity: Accessor<number>;
};

export function useStalled(
	time: Accessor<number>,
	getLength: Accessor<number>,
	opts?: { delayMs?: number; rampMs?: number },
): StalledState {
	const delay = opts?.delayMs ?? 3000;
	const ramp = opts?.rampMs ?? 2000;

	let lastLength = getLength();
	let lastChangeTime = 0;
	let smoothIntensity = 0;
	let lastSmoothTime = 0;

	const isStalled = (): boolean => {
		const t = time(); // subscribe to clock
		const len = getLength();

		if (len > lastLength) {
			lastLength = len;
			lastChangeTime = t;
		}

		return t - lastChangeTime > delay;
	};

	const intensity = (): number => {
		const t = time(); // subscribe to clock
		const len = getLength();

		if (len > lastLength) {
			lastLength = len;
			lastChangeTime = t;
			smoothIntensity = 0;
			lastSmoothTime = t;
			return 0;
		}

		const idle = t - lastChangeTime;
		const target = idle > delay ? Math.min((idle - delay) / ramp, 1) : 0;

		// Smooth approach — step at ~50ms granularity
		const dt = t - lastSmoothTime;
		if (dt >= 50 && (target > 0 || smoothIntensity > 0)) {
			const diff = target - smoothIntensity;
			if (Math.abs(diff) < 0.01) {
				smoothIntensity = target;
			} else {
				smoothIntensity += diff * 0.1;
			}
			lastSmoothTime = t;
		}

		return smoothIntensity;
	};

	return { isStalled, intensity };
}