Raf Fn

import { on_destroy, to_readable, to_writable, unstore } from "@sveu/shared"
import type { Fn, Pauseable } from "@sveu/shared"

import type { RafFnOptions } from "../utils"

/**
 * Call function on every `requestAnimationFrame` with controls.
 *
 * @param fn - Function to call on every `requestAnimationFrame`
 *
 * @param options - Options
 * - `immediate` - Start the requestAnimationFrame loop immediately on creation
 *
 * @returns Pauseable object.
 * - `pause` - Pause the requestAnimationFrame loop
 * - `resume` - Resume the requestAnimationFrame loop
 * - `active` - Readable store of the active state
 */
export function raf_fn(fn: Fn, options: RafFnOptions = {}): Pauseable {
    const { immediate = true } = options

    const active = to_writable(false)

    let raf_id: null | number = null

    function loop() {
        if (!unstore(active) || !window) return

        fn()
        raf_id = window.requestAnimationFrame(loop)
    }

    function resume() {
        if (!unstore(active) && window) {
            active.set(true)
            loop()
        }
    }

    function pause() {
        active.set(false)
        if (raf_id != null && window) {
            window.cancelAnimationFrame(raf_id)
            raf_id = null
        }
    }

    if (immediate) resume()

    on_destroy(pause)

    return {
        pause,
        resume,
        active: to_readable(active),
    }
}