feat(client/helpers/pagination-props): Add function to determine pagi…

…nation props

src/client/helpers/pagination-props.js

@@ -0,0 +1,154 @@
+/*
+ * Copyright (C) 2018 Shivam Tripathi
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+// @flow
+
+/*
+ ______                _    ______              _
+| ___ \              | |   | ___ \            (_)
+| |_/ /  ___    ___  | | __| |_/ / _ __  __ _  _  _ __   ____
+| ___ \ / _ \  / _ \ | |/ /| ___ \| '__|/ _` || || '_ \ |_  /
+| |_/ /| (_) || (_) ||   < | |_/ /| |  | (_| || || | | | / /
+\____/  \___/  \___/ |_|\_\\____/ |_|   \__,_||_||_| |_|/___|
+
+*/
+
+import _ from 'lodash';
+
+
+type getPaginationPropsGeneratorType = {
+	displayedPagesRange: number,
+	itemsPerPage: number
+};
+
+/** Pagination::validateDefault - Validates, if invalid passed default
+ * @param  {number} currentPage - The current active page
+ * @param  {number} totalResults - Total number of results
+ * @param {number} itemsPerPage - number of items per page
+ * @returns {Object} - Returns an object encapsulating validated
+ * 		currentPage, totalResults, totalPages
+ */
+function validatePaginationArgs(
+	currentPage: number,
+	totalResults: number,
+	itemsPerPage: number
+) {
+	const totalPages: number = Math.ceil(totalResults / itemsPerPage);
+	const args = {currentPage, totalPages, totalResults};
+	if (!args.currentPage ||
+		!_.isNumber(args.currentPage) ||
+		args.currentPage < 1
+	) {
+		args.currentPage = 1;
+	}
+
+	if (!args.totalPages ||
+		!_.isNumber(args.totalPages) ||
+		args.totalPages < 1
+	) {
+		args.totalPages = 1;
+		args.totalResults = itemsPerPage;
+	}
+
+	if (args.currentPage > args.totalPages) {
+		args.currentPage = args.totalPages;
+	}
+	return args;
+}
+
+/** getPaginationPropsGenerator - Takes in number of pages and items per page,
+ * 		defaults to 10, 25 and returns propsGenerator function
+ * @param {object} args - encapsulates args
+ * @param  {number} args.displayedPagesRange - Range of pages surrounding the
+ * 		current page to be displayed
+ * @param  {number} args.itemsPerPage - Number of items per page
+ * @returns {function} - Returns a function which give pagination props given
+ * 		currentPage and totalResults
+ */
+export default function getPaginationPropsGenerator(
+	args: getPaginationPropsGeneratorType
+) {
+	const {displayedPagesRange = 10, itemsPerPage = 25} = args;
+
+	/**
+	 * @param  {number} totalRes - Total number of results
+	 * @param  {number} curPage - Current page
+	 * @returns {object} Returns result encapsulating pagination details
+	 */
+	return function getDetails(totalRes: number, curPage: number) {
+		// Extract results, clean them up
+		const {currentPage, totalPages, totalResults} =
+			validatePaginationArgs(curPage, totalRes, itemsPerPage);
+
+		// The first and last page links to be displayed, exactly halfway left
+		//		and right from the currentpage
+		const halfwayDistance: number =
+			Math.floor(displayedPagesRange / 2);
+		let firstPage: number = Math.max(1, currentPage - halfwayDistance);
+		let lastPage: number =
+			Math.min(totalPages, currentPage + halfwayDistance);
+
+		// Incase number of pages lying in [firstPage, lastPage] are not
+		//		covering the range due to being at extremes, we adjust the range
+		const defaultRange: number = lastPage - firstPage + 1;
+		const defaultDiffInRange = displayedPagesRange - defaultRange;
+		if (defaultDiffInRange) {
+			if (lastPage < totalPages) {
+				lastPage = Math.min(lastPage + defaultDiffInRange, totalPages);
+			}
+			if (firstPage > 1) {
+				firstPage = Math.max(firstPage - defaultDiffInRange, 1);
+			}
+		}
+
+		// First result on current page
+		const firstResultOnCurrentPage: number = _.clamp(
+			displayedPagesRange * (currentPage - 1), 1, totalResults
+		);
+		const lastResultOnCurrentPage: number = _.clamp(
+			displayedPagesRange * currentPage, 1, totalResults
+		);
+
+		return {
+			beginningPage: 1,
+			currentPage,
+			endPage: totalPages,
+			firstPage,
+			firstResultOnCurrentPage,
+			hasBeginningPage: totalPages > 1,
+			hasEndPage: totalPages > 1,
+			hasNextPage: currentPage < totalPages,
+			hasPreviousPage: (currentPage - 1) > 0,
+			itemsPerPage,
+			lastPage,
+			lastResultOnCurrentPage,
+			nextPage: currentPage + 1,
+			pagesRange: _.clamp(
+				lastPage - firstPage + 1,
+				1, totalPages
+			),
+			previousPage: currentPage - 1,
+			resultsRange: _.clamp(
+				lastResultOnCurrentPage - firstResultOnCurrentPage + 1,
+				1, totalResults
+			),
+			totalPages,
+			totalResults
+		};
+	};
+}