import uuid1 from "uuid/v1";

/**
 * Standard interface for the simplest key-value store
 */
export interface KeyValueStorage {
  get(key: string): Promise<string | null>
  set(key: string, value: string | null): Promise<void>
}

/**
 * Basic memory implementation
 */
export class MemoryStorage implements KeyValueStorage {
  private store: { [key: string]: string } = {}

  async get(key: string): Promise<string | null> {
    const result = this.store[key];
    return (typeof result == "undefined") ? null : result;
  }

  async set(key: string, value: string | null): Promise<void> {
    if (value === null) {
      delete this.store[key];
    } else {
      this.store[key] = value;
    }
  }
}

type StorageDelegate = KeyValueStorage | (() => KeyValueStorage)

function fromDelegate(delegate: StorageDelegate): KeyValueStorage {
  return (typeof delegate === "function") ? delegate() : delegate;
}

/**
 * Use a target unscoped storage, scoping the keys in a virtual namespace
 *
 * The namespace is persisted in a reference storage (used unscoped)
 */
export class ScopedStorage implements KeyValueStorage {
  private readonly reference: KeyValueStorage
  private readonly target: KeyValueStorage
  private suffix?: string

  constructor(reference: StorageDelegate, target: StorageDelegate) {
    this.reference = fromDelegate(reference);
    this.target = fromDelegate(target);
  }

  private async init(): Promise<void> {
    const refkey = "tk-storage-scope-suffix"
    const suffix = await this.reference.get(refkey);
    if (suffix) {
      this.suffix = suffix;
    } else {
      const suffix = "#" + uuid1();
      await this.reference.set(refkey, suffix);
      this.suffix = suffix;
    }
  }

  async get(key: string): Promise<string | null> {
    if (!this.suffix) {
      await this.init();
    }

    return await this.target.get(key + this.suffix);
  }

  async set(key: string, value: string | null): Promise<void> {
    if (!this.suffix) {
      await this.init();
    }

    return await this.target.set(key + this.suffix, value);
  }
}