/*!
 * @license
 * Copyright Squiz Australia Pty Ltd. All Rights Reserved.
 */

import 'reflect-metadata';
import { provideSingleton } from '../../../singletonProvider';
import { BaseItem, BaseDto } from '../../../model/Base/Base';
import { PaginationInfo } from '../model/PaginationInfo';
import { PaginationTokens } from '../model/PaginationLinks';
import { PaginationResponse } from '../model/PaginationResponse';
import { PAGINATION_DIRECTION_TYPE_BEFORE } from '../model/PaginationTypes';
import { encodeTokenString, getPaginationLinks } from '../utils/PaginationUtils';

/**
 * Helper service to handle pagination.
 * @export
 * @abstract
 * @class PaginationService
 */
@provideSingleton(PaginationService)
export class PaginationService<T extends BaseItem> {
  public addPaginationLinksToResponse(
    data: Array<T>,
    paginationInfo: PaginationInfo,
    lastEvaluatedKey: string | null,
    convertToDynamoDbItem: (item: T) => BaseDto,
  ): PaginationResponse<T> {
    const { direction, limit, requestUrl } = paginationInfo;

    const paginationTokens = this.getPaginationTokens(data, paginationInfo, lastEvaluatedKey, convertToDynamoDbItem);
    const links = getPaginationLinks(requestUrl, paginationTokens);
    data = data.slice(0, limit);

    if (direction === PAGINATION_DIRECTION_TYPE_BEFORE) {
      data = data.reverse();
    }

    return { links, data };
  }

  protected getPaginationTokens(
    data: Array<T>,
    paginationInfo: PaginationInfo,
    lastEvaluatedKey: string | null,
    convertToDynamoDbItem: (item: T) => BaseDto,
  ): PaginationTokens {
    const { token, direction, limit } = paginationInfo;

    let firstItemToken: string | null = null;
    let lastItemToken: string | null = null;

    if (token || direction === PAGINATION_DIRECTION_TYPE_BEFORE) {
      firstItemToken = this.getTokenForDto(convertToDynamoDbItem(data[0]));
    }

    if (data.length <= limit) {
      lastItemToken = lastEvaluatedKey;
    } else {
      data = data.slice(0, limit);
      lastItemToken = this.getTokenForDto(convertToDynamoDbItem(data[data.length - 1]));
    }

    let nextToken = lastItemToken;
    let prevToken = firstItemToken;

    if (direction === PAGINATION_DIRECTION_TYPE_BEFORE) {
      nextToken = firstItemToken;
      prevToken = lastItemToken;
    }

    return {
      next: nextToken ? encodeURIComponent(nextToken) : null,
      prev: prevToken ? encodeURIComponent(prevToken) : null,
    };
  }

  /**
   * Get the encoded token for the first item of the data array.
   * @param {BaseDto} dto The array of items.
   * @returns {string} The token string.
   * @memberof Repository
   */
  protected getTokenForDto(dto: BaseDto): string {
    const { pk, sk } = dto;
    const primaryKey = {
      pk,
      sk,
    };

    return encodeTokenString(primaryKey);
  }
}