openreplay/frontend/app/player/common/ListWalker.ts

import type { Timed } from 'Player';

export default class ListWalker<T extends Timed> {
  /* Pointer to the "current" item */
  private p = 0;

  constructor(private _list: Array<T> = []) {}

  append(m: T): void {
    if (this.length > 0 && this.last && m.time < this.last.time) {
      console.error(
        'Trying to append message with the less time then the list tail:',
        m.time,
        'vs',
        this.last.time,
        m,
        this.last,
        this,
      );
      return;
    }
    this.list.push(m);
  }

  unshift(m: T): void {
    this.list.unshift(m);
  }

  insert(m: T): void {
    let index = this.list.findIndex((om) => om.time > m.time);
    if (index === -1) {
      index = this.length;
    }
    const oldList = this.list;
    this._list = [...oldList.slice(0, index), m, ...oldList.slice(index)];
  }

  reset(): void {
    this.p = 0;
  }

  sort(comparator: (a: T, b: T) => number): void {
    // @ts-ignore
    this.list.sort((m1, m2) => comparator(m1, m2) || m1._index - m2._index); // indexes for sort stability (TODO: fix types???)
  }

  forEach(f: (item: T) => void): void {
    this.list.forEach(f);
  }

  get last(): T | null {
    if (this.list.length === 0) {
      return null;
    }
    return this.list.slice(-1)[0];
  }

  get current(): T | null {
    if (this.p === 0) {
      return null;
    }
    return this.list[this.p - 1];
  }

  get timeNow(): number {
    if (this.p === 0) {
      return 0;
    }
    return this.list[this.p - 1].time;
  }

  get length(): number {
    return this.list.length;
  }

  get maxTime(): number {
    if (this.length === 0) {
      return 0;
    }
    return this.list[this.length - 1].time;
  }

  get minTime(): number {
    if (this.length === 0) {
      return 0;
    }
    return this.list[0].time;
  }

  get listNow(): Array<T> {
    return this.list.slice(0, this.p);
  }

  get list(): Array<T> {
    return this._list;
  }

  get count(): number {
    return this.length;
  }

  get countNow(): number {
    return this.p;
  }

  private hasNext() {
    return this.p < this.length;
  }

  private hasPrev() {
    return this.p > 0;
  }

  protected moveNext(): T | null {
    return this.hasNext() ? this.list[this.p++] : null;
  }

  protected movePrev(): T | null {
    return this.hasPrev() ? this.list[--this.p] : null;
  }

  /**
   * @returns last message with the time <= t.
   * Assumed that the current message is already handled so
   * if pointer doesn't change <null> is returned.
   */
  moveGetLast(t: number, index?: number, force?: boolean, debug?: boolean): T | null {
    const key: string = index ? '_index' : 'time';
    const val = index ? index : t;

    let changed = false;
    // @ts-ignore
    while (this.p < this.length && this.list[this.p][key] <= val) {
      this.moveNext();
      changed = true;
    }
    // @ts-ignore
    while (this.p > 0 && this.list[this.p - 1][key] > val) {
      this.movePrev();
      changed = true;
    }
    if (debug) {
      console.log(this.list[this.p - 1])
    }
    return changed || force ? this.list[this.p - 1] : null;
  }

  prevTs = 0;

  getNew(t: number, index?: number): T | null {
    const key: string = 'time'; // TODO
    const val = t;

    let changed = this.prevTs > t;
    this.prevTs = t;
    // @ts-ignore
    while (this.p < this.length && this.list[this.p][key] <= val) {
      this.moveNext();
      changed = true;
    }
    // @ts-ignore
    while (this.p > 0 && this.list[this.p - 1][key] > val) {
      this.movePrev();
      changed = true;
    }
    return changed ? this.list[this.p - 1] : null;
  }

  findLast(t: number): T | null {
    let left = 0;
    let right = this.list.length - 1;
    let result: T | null = null;

    while (left <= right) {
      const mid = Math.floor((left + right) / 2);
      const currentItem = this.list[mid];

      if (currentItem.time <= t) {
        result = currentItem;
        left = mid + 1;
      } else {
        right = mid - 1;
      }
    }

    return result;
  }

  /**
   * Moves over the messages starting from the current+1 to the last one with the time <= t
   * applying callback on each of them
   * @param t - max message time to move to; will move & apply callback while msg.time <= t
   * @param callback - a callback to apply on each message passing by while moving
   */
  moveApply(t: number, callback: (msg: T) => void): void {
    // Applying only in increment order for now
    if (t < this.timeNow) {
      this.reset();
    }

    const { list } = this;
    while (list[this.p] && list[this.p].time <= t) {
      callback(this.list[this.p++]);
    }
  }
}