import { derived, readable, writable, type Updater, type Writable } from "svelte/store"
import { page } from "$app/stores"
import { browser } from "$app/environment"
import deepEquals from "fast-deep-equal"

let oldState: App.PageState = {}

export const pageState = derived<typeof page, App.PageState>(
    page,
    (_, set) => {
        if (!browser) return
        setTimeout(() => {
            const newState = history.state["sveltekit:states"] ?? {}
            if (!deepEquals(oldState, newState)) {
                oldState = newState
                set(newState)
            }
        })
    },
    {},
)

_: typeof page extends Readable<infer U> ? U : never, set: (value: App.PageState) => void)