import type { IOutput } from './io/output';

/**
 * Command history. Also maintains a current index in the history for scrolling through it.
 */
export class History {
  add(command: string) {
    this._current = null;

    if (
      !command.trim() ||
      (this._ignoreInitialWhitespace && command.startsWith(' ')) ||
      (this._ignoreDuplicates && command === this.at(-1))
    ) {
      // Do not store.
      return;
    }

    if (this._history.length >= this._maxSize) {
      this._history.shift();
    }
    this._history.push(command);
  }

  // Supports negative indexing from end.
  at(index: number): string | null {
    return this._history.at(index) ?? null;
  }

  clear() {
    this._current = null;
    this._history = [];
  }

  scrollCurrent(next: boolean): string | null {
    if (next) {
      this._current = this._current === null ? null : this._current + 1;
    } else {
      this._current = this._current === null ? this._history.length - 1 : this._current - 1;
    }

    if (this._current !== null) {
      if (this._current < 0) {
        this._current = 0;
      } else if (this._current >= this._history.length) {
        this._current = null;
      }
    }

    return this._current === null ? null : this.at(this._current);
  }

  setMaxSize(maxSize: number) {
    this._maxSize = Math.max(maxSize, 0);
    if (this._history.length > this._maxSize) {
      this._current = null;
      this._history = this._history.slice(this._maxSize);
    }
  }

  write(output: IOutput): void {
    for (let i = 0; i < this._history.length; i++) {
      const index = String(i).padStart(5, ' ');
      output.write(`${index}  ${this._history[i]}\n`);
    }
  }

  private _history: string[] = [];
  private _current: number | null = null;
  private _ignoreInitialWhitespace: boolean = true;
  private _ignoreDuplicates: boolean = true;
  private _maxSize: number = 1000;
}