import Promise from 'bluebird';
import { remove, assign } from 'lodash';

const DEFAULT_LIMIT = 10;
const DEFAULT_OFFSET = 0;
const DEFAULT_PAGE = 1;

/**
 * Exports a plugin to pass into the bookshelf instance, i.e.:
 *
 *      import config from './knexfile';
 *      import knex from 'knex';
 *      import bookshelf from 'bookshelf';
 *
 *      const ORM = bookshelf(knex(config));
 *
 *      ORM.plugin('bookshelf-pagination-plugin');
 *
 *      export default ORM;
 *
 * The plugin attaches two instance methods to the bookshelf
 * Model object: orderBy and fetchPage.
 *
 * Model#orderBy calls the underlying query builder's orderBy method, and
 * is useful for ordering the paginated results.
 *
 * Model#fetchPage works like Model#fetchAll, but returns a single page of
 * results instead of all results, as well as the pagination information
 *
 * See methods below for details.
 */
module.exports = function paginationPlugin (bookshelf) {

  /**
   * @method Model#fetchPage
   * @belongsTo Model
   *
   * Similar to {@link Model#fetchAll}, but fetches a single page of results
   * as specified by the limit (page size) and offset or page number.
   *
   * Any options that may be passed to {@link Model#fetchAll} may also be passed
   * in the options to this method.
   *
   * To perform pagination, you may include *either* an `offset` and `limit`, **or**
   * a `page` and `pageSize`.
   *
   * By default, with no parameters or missing parameters, `fetchPage` will use an
   * options object of `{page: 1, pageSize: 10}`
   *
   *
   * Below is an example showing the user of a JOIN query with sort/ordering,
   * pagination, and related models.
   *
   * @example
   *
   * Car
   * .query(function (qb) {
   *    qb.innerJoin('manufacturers', 'cars.manufacturer_id', 'manufacturers.id');
   *    qb.groupBy('cars.id');
   *    qb.where('manufacturers.country', '=', 'Sweden');
   * })
   * .orderBy('-productionYear') // Same as .orderBy('cars.productionYear', 'DESC')
   * .fetchPage({
   *    pageSize: 15, // Defaults to 10 if not specified
   *    page: 3, // Defaults to 1 if not specified
   *
   *    // OR
   *    // limit: 15,
   *    // offset: 30,
   *
   *    withRelated: ['engine'] // Passed to Model#fetchAll
   * })
   * .then(function (results) {
   *    console.log(results); // Paginated results object with metadata example below
   * })
   *
   * // Pagination results:
   *
   * {
   *    models: [<Car>], // Regular bookshelf Collection
   *    // other standard Collection attributes
   *    ...
   *    pagination: {
   *        rowCount: 53, // Total number of rows found for the query before pagination
   *        pageCount: 4, // Total number of pages of results
   *        page: 3, // The requested page number
   *        pageSze: 15, // The requested number of rows per page
   *
   *  // OR, if limit/offset pagination is used instead of page/pageSize:
   *        // offset: 30, // The requested offset
   *        // limit: 15 // The requested limit
   *    }
   * }
   *
   * @param options {object}
   *    The pagination options, plus any additional options that will be passed to
   *    {@link Model#fetchAll}
   * @returns {Promise<Model|null>}
   */
  function fetchPage (options = {}) {
    const {page, pageSize, limit, offset, ...fetchOptions} = options;

    let usingPageSize = false; // usingPageSize = false means offset/limit, true means page/pageSize
    let _page;
    let _pageSize;
    let _limit;
    let _offset;

    function ensureIntWithDefault (val, def) {
      if (!val) {
        return def;
      }

      const _val = parseInt(val);
      if (Number.isNaN(_val)) {
        return def;
      }

      return _val;
    }

    if (!limit && !offset) {
      usingPageSize = true;

      _pageSize = ensureIntWithDefault(pageSize, DEFAULT_LIMIT);
      _page = ensureIntWithDefault(page, DEFAULT_PAGE);

      _limit = _pageSize;
      _offset = _limit * (_page - 1);
    } else {
      _pageSize = _limit; // not used, just for eslint `const` error
      _limit = ensureIntWithDefault(limit, DEFAULT_LIMIT);
      _offset = ensureIntWithDefault(offset, DEFAULT_OFFSET);
    }

    const tableName = this.constructor.prototype.tableName;
    const idAttribute = this.constructor.prototype.idAttribute ?
      this.constructor.prototype.idAttribute : 'id';

    const paginate = () => {
      // const pageQuery = clone(this.query());
      const pager = this.constructor.forge();

      return pager

        .query(qb => {
          assign(qb, this.query().clone());
          qb.limit.apply(qb, [_limit]);
          qb.offset.apply(qb, [_offset]);
          return null;
        })

      .fetchAll(fetchOptions);
    };

    const count = () => {
      const notNeededQueries = [
        'orderByBasic',
        'orderByRaw',
        'groupByBasic',
        'groupByRaw'
      ];
      const counter = this.constructor.forge();

      return counter.query(qb => {
        assign(qb, this.query().clone());

        // Remove grouping and ordering. Ordering is unnecessary
        // for a count, and grouping returns the entire result set
        // What we want instead is to use `DISTINCT`
        remove(qb._statements, statement => {
          return (notNeededQueries.indexOf(statement.type) > -1) ||
            statement.grouping === 'columns';
        });
        qb.countDistinct.apply(qb, [`${tableName}.${idAttribute}`]);

      }).fetchAll().then(result => {

        const metadata = usingPageSize
          ? {page: _page, pageSize: _limit}
          : {offset: _offset, limit: _limit};

        if (result && result.length == 1) {
          // We shouldn't have to do this, instead it should be
          // result.models[0].get('count')
          // but SQLite uses a really strange key name.
          const count = result.models[0];
          const keys = Object.keys(count.attributes);
          if (keys.length === 1) {
            const key = Object.keys(count.attributes)[0];
            metadata.rowCount = parseInt(count.attributes[key]);
          }
        }

        return metadata;
      });
    };

    return Promise.join(paginate(), count())
      .then(([rows, metadata]) => {
        const pageCount = Math.ceil(metadata.rowCount / _limit);
        const pageData = assign(metadata, {pageCount});
        return assign(rows, {pagination: pageData});
      });
  }

  bookshelf.Model.prototype.fetchPage = fetchPage;

  bookshelf.Model.fetchPage = function (...args) {
    return this.forge().fetchPage(...args);
  }

  bookshelf.Collection.prototype.fetchPage = function (...args) {
    return fetchPage.apply(this.model.forge(), args);
  };

}