joystream/storage-node/packages/util/pagination.js

/*
 * This file is part of the storage node for the Joystream project.
 * Copyright (C) 2019 Joystream Contributors
 *
 * 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 3 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, see <https://www.gnu.org/licenses/>.
 */

'use strict'

const debug = require('debug')('joystream:middleware:pagination')

// Pagination definitions
const _api_defs = {
	parameters: {
		paginationLimit: {
			name: 'limit',
			in: 'query',
			description: 'Number of items per page.',
			required: false,
			schema: {
				type: 'integer',
				minimum: 1,
				maximum: 50,
				default: 20,
			},
		},
		paginationOffset: {
			name: 'offset',
			in: 'query',
			description: 'Page number (offset)',
			schema: {
				type: 'integer',
				minimum: 0,
			},
		},
	},
	schemas: {
		PaginationInfo: {
			type: 'object',
			required: ['self'],
			properties: {
				self: {
					type: 'string',
				},
				next: {
					type: 'string',
				},
				prev: {
					type: 'string',
				},
				first: {
					type: 'string',
				},
				last: {
					type: 'string',
				},
			},
		},
	},
}

/**
 * Silly pagination because it's faster than getting other modules to work.
 *
 * Usage:
 * - apiDoc.parameters = pagination.parameters
 *   -> Validates pagination parameters
 * - apiDoc.responses.200.schema.pagination = pagination.response
 *   -> Generates pagination info on response
 * - paginate(req, res, [last_offset])
 *   -> add (valid) pagination fields to response object
 *      If last_offset is given, create a last link with that offset
 **/
module.exports = {
	// Add pagination parameters and pagination info responses.
	parameters: [
		{ $ref: '#/components/parameters/paginationLimit' },
		{ $ref: '#/components/parameters/paginationOffset' },
	],

	response: {
		$ref: '#/components/schema/PaginationInfo',
	},

	// Update swagger/openapi specs with our own parameters and definitions
	openapi(api) {
		api.components = api.components || {}
		api.components.parameters = { ...(api.components.parameters || {}), ..._api_defs.parameters }
		api.components.schemas = { ...(api.components.schemas || {}), ..._api_defs.schemas }
		return api
	},

	// Pagination function
	paginate(req, res, last_offset) {
		// Skip if the response is not an object.
		if (Object.prototype.toString.call(res) != '[object Object]') {
			debug('Cannot paginate non-objects.')
			return res
		}

		// Defaults for parameters
		const offset = req.query.offset || 0
		const limit = req.query.limit || 20
		debug('Create pagination links from offset=' + offset, 'limit=' + limit)

		// Parse current url
		const url = require('url')
		const req_url = url.parse(req.protocol + '://' + req.get('host') + req.originalUrl)
		const params = new url.URLSearchParams(req_url.query)

		// Pagination object
		const pagination = {
			self: req_url.href,
		}

		const prev = offset - limit
		if (prev >= 0) {
			params.set('offset', prev)
			req_url.search = params.toString()
			pagination.prev = url.format(req_url)
		}

		const next = offset + limit
		if (next >= 0) {
			params.set('offset', next)
			req_url.search = params.toString()
			pagination.next = url.format(req_url)
		}

		if (last_offset) {
			params.set('offset', last_offset)
			req_url.search = params.toString()
			pagination.last = url.format(req_url)
		}

		// First
		params.set('offset', 0)
		req_url.search = params.toString()
		pagination.first = url.format(req_url)

		debug('pagination', pagination)

		// Now set pagination values in response.
		res.pagination = pagination
		return res
	},
}