Performance Observer

import { on_destroy, unstore } from "@sveu/shared"

import { support } from "../support"
import type { PerformanceObserverOptions } from "../utils"

/**
 * Observe performance metrics.
 *
 * @param fn - Callback function to be invoked when a performance entry is added to the performance entry buffer.

* @see https://developer.mozilla.org/en-US/docs/Web/API/PerformanceObserver
* @param options - Options for the observer.
* - `immediate` - Start the observer immediate.
*
* @returns
* - `supported` - Whether the browser supports the PerformanceObserver API.
* - `start` - Start the observer.
* - `stop` - Stop the observer.
*/
export function performance_observer(
    fn: PerformanceObserverCallback,
    options: PerformanceObserverOptions = {}
) {
    const { immediate = true, ...performance_options } = options

    const supported = support("PerformanceObserver", "window")

    let observer: PerformanceObserver | undefined

    function stop() {
        observer?.disconnect()
    }

    function start() {
        if (unstore(supported)) {
            stop()

            observer = new PerformanceObserver(fn)

            observer.observe(performance_options)
        }
    }

    on_destroy(stop)

    if (immediate) start()

    return {
        supported,
        start,
        stop,
    }
}