windmill/frontend/src/lib/history.ts

import { deepEqual } from "fast-equals"
import { get, writable, type Writable } from "svelte/store"

export type History<T> = Writable<{ history: T[], index: number }>

export function initHistory<T>(initial: T): History<T> {
    return writable({ history: [initial], index: 0 })
}

export function undo<T>(history: History<T> | undefined, now: T): T {
    if (history) {

        let chistory = get(history)
        if (chistory.index == 0) return now
        if (!deepEqual(chistory.history[chistory.index], now)) {
            push(history, now, true)
        } else {
            history.update((history) => {
                history.index--
                return history
            })
        }
        let nhistory = get(history)
        let r = nhistory.history[nhistory.index]
        if (!r) {
            console.log('undo failed', nhistory, now)
            return now
        } else {
            return r
        }
    } else {
        return now
    }
}

export function redo<T>(history: History<T> | undefined): T {
    if (history) {
        history?.update((history) => {
            if (history.index < history.history.length - 1) {
                history.index++
            }
            return history
        })
        let nhistory = get(history)
        return nhistory.history[nhistory.index]
    } else {
        return undefined as T
    }
}

export function push<T>(history: History<T> | undefined, value: T, noSetIndex: boolean = false, skipCopy: boolean = false) {
    history?.update((history) => {
        history.history = JSON.parse(JSON.stringify(history.history.slice(0, history.index + 1)))
        const toPush = skipCopy ? value : JSON.parse(JSON.stringify(value))
        history.history.push(toPush)
        if (!noSetIndex) {
            history.index = history.history.length - 1
        }
        if (history.history.length > 20) {
            history.history = history.history.slice(history.history.length - 20)
            history.index -= 1
        }
        return history

    })

}