/**
 * Keyboard-wedge scanners type like superhuman typists: a burst of characters
 * with tiny inter-key gaps, terminated by Enter. This detector distinguishes a
 * scan from human typing purely from timing + length, with injected timestamps
 * so it is testable without a DOM or a clock.
 */
export interface WedgeOptions {
  /** Max gap between scanner keystrokes; humans are slower. */
  maxInterKeyMs: number
  /** Bursts shorter than this are treated as typed input. */
  minLength: number
}

export const DEFAULT_WEDGE: WedgeOptions = { maxInterKeyMs: 35, minLength: 6 }

export type WedgeResult = { type: 'scan'; code: string } | { type: 'typed'; text: string }

export class WedgeDetector {
  private chars: string[] = []
  private lastAtMs: number | undefined
  private maxGapMs = 0

  constructor(private readonly opts: WedgeOptions = DEFAULT_WEDGE) {}

  feed(char: string, atMs: number): void {
    if (char.length !== 1) throw new Error('feed() takes single characters')
    if (this.lastAtMs !== undefined) {
      this.maxGapMs = Math.max(this.maxGapMs, atMs - this.lastAtMs)
    }
    this.lastAtMs = atMs
    this.chars.push(char)
  }

  /** Call on Enter. Decides scan vs typed and resets for the next burst. */
  terminate(): WedgeResult {
    const text = this.chars.join('')
    const isScan =
      this.chars.length >= this.opts.minLength && this.maxGapMs <= this.opts.maxInterKeyMs
    this.reset()
    return isScan ? { type: 'scan', code: text } : { type: 'typed', text }
  }

  reset(): void {
    this.chars = []
    this.lastAtMs = undefined
    this.maxGapMs = 0
  }
}