import browser from 'webextension-polyfill';
import {createValue, type Value} from '@holllo/webextension-storage';

/** A queued item. */
export type Item = {
  /** The date when the item was added. */
  dateAdded: Date;

  /** The unique ID for this item. */
  id: number;

  /**
   * The display text of the item.
   *
   * This can be undefined when the context menu doesn't have access to the text
   * like when a tab's context menu is used.
   */
  text: string | undefined;

  /** The URL of the item. */
  url: string;
};

/** A serialized representation of {@link Item} for use in storage. */
export type SerializedItem = {
  // Create an index signature with every key from Item and the type for each
  // as `string`.
  [k in keyof Item]: string;
};

/** The key prefix for {@link Item}s. */
export const itemKeyPrefix = 'item-';

/** The default storage area to use for {@link Item}s. */
export const storage = browser.storage.sync;

/**
 * Serialize and JSON-stringify an {@link Item}.
 *
 * @param input The {@link Item} to serialize.
 * @returns The serialized {@link Item} string.
 */
export const serializeItem: Value<Item>['serialize'] = (
  input: Item,
): string => {
  const serialized: SerializedItem = {
    dateAdded: input.dateAdded.toISOString(),
    id: input.id.toString(),
    text: input.text ?? '',
    url: input.url,
  };

  return JSON.stringify(serialized);
};

/**
 * Deserialize and JSON-parse an {@link Item} from a string.
 *
 * This function should only ever be used with {@link Value} as this
 * doesn't do any validation. With {@link Value} it's reasonable to assume
 * the input will actually deserialize to an {@link Item}.
 *
 * @param input The {@link Item} string to deserialize.
 * @returns The deserialized {@link Item}.
 */
export const deserializeItem: Value<Item>['deserialize'] = (
  input: string,
): Item => {
  const parsed = JSON.parse(input) as SerializedItem;

  return {
    dateAdded: new Date(parsed.dateAdded),
    id: Number(parsed.id),
    // In `serializeItem()` the item text is set to an empty string when
    // undefined, so revert it back to undefined here if that's the case.
    text: parsed.text === '' ? undefined : parsed.text,
    url: parsed.url,
  };
};

/**
 * Create a new {@link Item} in the default storage.
 *
 * @param text The text of the {@link Item} to create.
 * @param url The URL of the {@link Item} to create.
 * @returns The created {@link Value} with inner {@link Item}.
 */
export async function createItem(
  text: Item['text'],
  url: Item['url'],
): Promise<Value<Item>> {
  const nextId = await nextItemId();

  const item = await createValue<Item>({
    deserialize: deserializeItem,
    serialize: serializeItem,
    storage,
    key: `${itemKeyPrefix}${nextId}`,
    value: {
      dateAdded: new Date(),
      id: nextId,
      text,
      url,
    },
  });

  return item;
}

/**
 * Get all keys from storage that start with the {@link itemKeyPrefix}.
 *
 * @returns The keys as a string array.
 */
export async function getItemKeys(): Promise<string[]> {
  const stored = Object.keys(await storage.get());
  const keys = stored.filter((key) => key.startsWith(itemKeyPrefix));
  return keys;
}

/**
 * Get the next unique {@link Item} ID.
 *
 * @returns The next ID as a number.
 */
export async function nextItemId(): Promise<number> {
  // Get all the item keys and sort them so the highest ID is first.
  const keys = await getItemKeys();
  keys.sort((a, b) => b.localeCompare(a));

  // Get the first key or use 0 if no items exist yet.
  const highestKey = keys[0] ?? `${itemKeyPrefix}0`;

  // Create the next ID by removing the item key prefix and adding 1.
  return Number(highestKey.slice(itemKeyPrefix.length)) + 1;
}

/**
 * Get the next queued {@link Item}.
 *
 * @returns The {@link Value} with inner {@link Item} or `undefined` if the
 * queue is empty.
 */
export async function nextItem(): Promise<Value<Item> | undefined> {
  // Get all the item keys and sort them so the lowest ID is first.
  const keys = await getItemKeys();
  keys.sort((a, b) => a.localeCompare(b));

  // If no keys exist then exit early.
  const key = keys[0];
  if (key === undefined) {
    return undefined;
  }

  return createValue<Item>({
    deserialize: deserializeItem,
    key,
    // We know that an item exists in storage since there is a key for it, which
    // means passing undefined here is fine as it won't be used.
    value: undefined!,
    serialize: serializeItem,
  });
}