import type { ScanOptions } from '../kv-storage/base-kv-storage.js'
import { Keys } from './keys.js'

/**
 * A key and its whole subtree: `[prefix, prefix + '0')`. Escaping guarantees nothing else sorts
 * in that range (not even lookalikes such as `prefix-x`). The empty prefix is every key.
 */
export class KeyRange {
  /** Inclusive lower bound (`undefined` = unbounded). */
  readonly gte: string | undefined
  /** Exclusive upper bound (`undefined` = unbounded). */
  readonly lt: string | undefined

  constructor(readonly prefix: string) {
    this.gte = prefix === '' ? undefined : prefix
    this.lt = prefix === '' ? undefined : prefix + Keys.afterSeparator
  }

  contains(key: string): boolean {
    return this.prefix === '' || key === this.prefix || key.startsWith(this.prefix + Keys.separator)
  }

  /** Whether a scan over `[gte, lt)` stays inside this range. */
  covers(gte: string | undefined, lt: string | undefined): boolean {
    if (this.prefix === '') return true
    return gte !== undefined && lt !== undefined && gte >= this.gte! && lt <= this.lt!
  }

  /** Scan options narrowed to this range, or `undefined` if nothing is left. */
  clamp(options: ScanOptions): ScanOptions | undefined {
    const gte = this.gte !== undefined && (options.gte === undefined || options.gte < this.gte) ? this.gte : options.gte
    const lt = this.lt !== undefined && (options.lt === undefined || options.lt > this.lt) ? this.lt : options.lt
    if (gte !== undefined && lt !== undefined && gte >= lt) return undefined
    return { ...options, gte, lt }
  }
}