FPS

import { to_writable } from "@sveu/shared"

import { raf_fn } from "../raf_fn"
import type { FpsOptions } from "../utils"

/**
 * Reactive FPS (frames per second)
 *
 * @param options - Options
 * - `every` - Calculate the FPS on every x frames. Default: `10`
 *
 * @returns Readable store
 */
export function fps(options: FpsOptions = {}) {
    const { subscribe, set } = to_writable(0)

    if (typeof performance === "undefined") return { subscribe }

    const every = options?.every ?? 10

    let last = performance.now()

    let ticks = 0

    raf_fn(() => {
        ticks += 1

        if (ticks >= every) {
            const now = performance.now()

            const diff = now - last

            set(Math.round(1000 / (diff / ticks)))

            last = now

            ticks = 0
        }
    })

    return { subscribe }
}