xterm.js/src/common/CircularList.ts

/**
 * Copyright (c) 2016 The xterm.js authors. All rights reserved.
 * @license MIT
 */

import { EventEmitter } from './EventEmitter';
import { ICircularList } from './Types';

export interface IInsertEvent {
  index: number;
  amount: number;
}

export interface IDeleteEvent {
  index: number;
  amount: number;
}

/**
 * Represents a circular list; a list with a maximum size that wraps around when push is called,
 * overriding values at the start of the list.
 */
export class CircularList<T> extends EventEmitter implements ICircularList<T> {
  protected _array: (T | undefined)[];
  private _startIndex: number;
  private _length: number;

  constructor(
    private _maxLength: number
  ) {
    super();
    this._array = new Array<T>(this._maxLength);
    this._startIndex = 0;
    this._length = 0;
  }

  public get maxLength(): number {
    return this._maxLength;
  }

  public set maxLength(newMaxLength: number) {
    // There was no change in maxLength, return early.
    if (this._maxLength === newMaxLength) {
      return;
    }

    // Reconstruct array, starting at index 0. Only transfer values from the
    // indexes 0 to length.
    const newArray = new Array<T | undefined>(newMaxLength);
    for (let i = 0; i < Math.min(newMaxLength, this.length); i++) {
      newArray[i] = this._array[this._getCyclicIndex(i)];
    }
    this._array = newArray;
    this._maxLength = newMaxLength;
    this._startIndex = 0;
  }

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

  public set length(newLength: number) {
    if (newLength > this._length) {
      for (let i = this._length; i < newLength; i++) {
        this._array[i] = undefined;
      }
    }
    this._length = newLength;
  }

  /**
   * Gets the value at an index.
   *
   * Note that for performance reasons there is no bounds checking here, the index reference is
   * circular so this should always return a value and never throw.
   * @param index The index of the value to get.
   * @return The value corresponding to the index.
   */
  public get(index: number): T | undefined {
    return this._array[this._getCyclicIndex(index)];
  }

  /**
   * Sets the value at an index.
   *
   * Note that for performance reasons there is no bounds checking here, the index reference is
   * circular so this should always return a value and never throw.
   * @param index The index to set.
   * @param value The value to set.
   */
  public set(index: number, value: T | undefined): void {
    this._array[this._getCyclicIndex(index)] = value;
  }

  /**
   * Pushes a new value onto the list, wrapping around to the start of the array, overriding index 0
   * if the maximum length is reached.
   * @param value The value to push onto the list.
   */
  public push(value: T): void {
    this._array[this._getCyclicIndex(this._length)] = value;
    if (this._length === this._maxLength) {
      this._startIndex = ++this._startIndex % this._maxLength;
      this.emitMayRemoveListeners('trim', 1);
    } else {
      this._length++;
    }
  }

  /**
   * Advance ringbuffer index and return current element for recycling.
   * Note: The buffer must be full for this method to work.
   * @throws When the buffer is not full.
   */
  public recycle(): T {
    if (this._length !== this._maxLength) {
      throw new Error('Can only recycle when the buffer is full');
    }
    this._startIndex = ++this._startIndex % this._maxLength;
    this.emitMayRemoveListeners('trim', 1);
    return this._array[this._getCyclicIndex(this._length - 1)]!;
  }

  /**
   * Ringbuffer is at max length.
   */
  public get isFull(): boolean {
    return this._length === this._maxLength;
  }

  /**
   * Removes and returns the last value on the list.
   * @return The popped value.
   */
  public pop(): T | undefined {
    return this._array[this._getCyclicIndex(this._length-- - 1)];
  }

  /**
   * Deletes and/or inserts items at a particular index (in that order). Unlike
   * Array.prototype.splice, this operation does not return the deleted items as a new array in
   * order to save creating a new array. Note that this operation may shift all values in the list
   * in the worst case.
   * @param start The index to delete and/or insert.
   * @param deleteCount The number of elements to delete.
   * @param items The items to insert.
   */
  public splice(start: number, deleteCount: number, ...items: T[]): void {
    // Delete items
    if (deleteCount) {
      for (let i = start; i < this._length - deleteCount; i++) {
        this._array[this._getCyclicIndex(i)] = this._array[this._getCyclicIndex(i + deleteCount)];
      }
      this._length -= deleteCount;
    }

    // Add items
    for (let i = this._length - 1; i >= start; i--) {
      this._array[this._getCyclicIndex(i + items.length)] = this._array[this._getCyclicIndex(i)];
    }
    for (let i = 0; i < items.length; i++) {
      this._array[this._getCyclicIndex(start + i)] = items[i];
    }

    // Adjust length as needed
    if (this._length + items.length > this._maxLength) {
      const countToTrim = (this._length + items.length) - this._maxLength;
      this._startIndex += countToTrim;
      this._length = this._maxLength;
      this.emitMayRemoveListeners('trim', countToTrim);
    } else {
      this._length += items.length;
    }
  }

  /**
   * Trims a number of items from the start of the list.
   * @param count The number of items to remove.
   */
  public trimStart(count: number): void {
    if (count > this._length) {
      count = this._length;
    }
    this._startIndex += count;
    this._length -= count;
    this.emitMayRemoveListeners('trim', count);
  }

  public shiftElements(start: number, count: number, offset: number): void {
    if (count <= 0) {
      return;
    }
    if (start < 0 || start >= this._length) {
      throw new Error('start argument out of range');
    }
    if (start + offset < 0) {
      throw new Error('Cannot shift elements in list beyond index 0');
    }

    if (offset > 0) {
      for (let i = count - 1; i >= 0; i--) {
        this.set(start + i + offset, this.get(start + i));
      }
      const expandListBy = (start + count + offset) - this._length;
      if (expandListBy > 0) {
        this._length += expandListBy;
        while (this._length > this._maxLength) {
          this._length--;
          this._startIndex++;
          this.emitMayRemoveListeners('trim', 1);
        }
      }
    } else {
      for (let i = 0; i < count; i++) {
        this.set(start + i + offset, this.get(start + i));
      }
    }
  }

  /**
   * Gets the cyclic index for the specified regular index. The cyclic index can then be used on the
   * backing array to get the element associated with the regular index.
   * @param index The regular index.
   * @returns The cyclic index.
   */
  private _getCyclicIndex(index: number): number {
    return (this._startIndex + index) % this._maxLength;
  }
}