import { Transaction } from 'prosemirror-state'

export interface TrackerResult {
  position: number,
  deleted: boolean,
}

export class Tracker {

  transaction: Transaction

  currentStep: number

  constructor(transaction: Transaction) {
    this.transaction = transaction
    this.currentStep = this.transaction.steps.length
  }

  map(position: number): TrackerResult {
    let deleted = false

    const mappedPosition = this.transaction.steps
      .slice(this.currentStep)
      .reduce((newPosition, step) => {
        const mapResult = step
          .getMap()
          .mapResult(newPosition)

        if (mapResult.deleted) {
          deleted = true
        }

        return mapResult.pos
      }, position)

    return {
      position: mappedPosition,
      deleted,
    }
  }

}