import React, { createContext, useEffect, useMemo, useState } from 'react'
import { FRAME_INTERVAL_MS } from '../../core/constants.js'
import { useTerminalFocus } from '../hooks/use-terminal-focus.js'
export type Clock = {
	subscribe: (onChange: () => void, keepAlive: boolean) => () => void
	now: () => number
	setTickInterval: (ms: number) => void
}
export function createClock(tickIntervalMs: number): Clock {
	const subscribers = new Map<() => void, boolean>()
	let interval: ReturnType<typeof setInterval> | null = null
	let currentTickIntervalMs = tickIntervalMs
	let startTime = 0
	let tickTime = 0
	function tick(): void {
		tickTime = Date.now() - startTime
		for (const onChange of subscribers.keys()) {
			onChange()
		}
	}
	function updateInterval(): void {
		const anyKeepAlive = [...subscribers.values()].some(Boolean)
		if (anyKeepAlive) {
			if (interval) {
				clearInterval(interval)
				interval = null
			}
			if (startTime === 0) {
				startTime = Date.now()
			}
			interval = setInterval(tick, currentTickIntervalMs)
		} else if (interval) {
			clearInterval(interval)
			interval = null
		}
	}
	return {
		subscribe(onChange, keepAlive) {
			subscribers.set(onChange, keepAlive)
			updateInterval()
			return () => {
				subscribers.delete(onChange)
				updateInterval()
			}
		},
		now() {
			if (startTime === 0) {
				startTime = Date.now()
			}
			if (interval && tickTime) {
				return tickTime
			}
			return Date.now() - startTime
		},
		setTickInterval(ms) {
			if (ms === currentTickIntervalMs) return
			currentTickIntervalMs = ms
			updateInterval()
		},
	}
}
export const ClockContext = createContext<Clock | null>(null)
const BLURRED_TICK_INTERVAL_MS = FRAME_INTERVAL_MS * 2

export function ClockProvider({ children }: { children: React.ReactNode }) {
	const [clock] = useState(() => createClock(FRAME_INTERVAL_MS))
	const focused = useTerminalFocus()
	useEffect(() => {
		clock.setTickInterval(focused ? FRAME_INTERVAL_MS : BLURRED_TICK_INTERVAL_MS)
	}, [clock, focused])
	return useMemo(
		() => <ClockContext.Provider value={clock}>{children}</ClockContext.Provider>,
		[children, clock],
	)
}