rating-service.js

var Promise = require('promise');
var PouchDB = require('pouchdb');
var path = require('path');
var ratingsDB = new PouchDB(path.join(__dirname, 'ratings_db'));

// ratings service
function RatingService() {}
RatingService.prototype = {

    getRatings: function(titleIds, userId) {
        userId = userId || 'all';
        
        return ratingsDB.allDocs({
            keys: titleIds.map(function(id) {
                return userId + "," + id;
            }),
            include_docs: true
        }).then(function(dbResponse) {
            var ratings = {};
            dbResponse.rows.forEach(function(row) {
				if (row.error) {
					if (row.error == "not_found") {
						ratings[row.key.substr((userId + ",").length)] = {doc: null};
					} else {
						ratings[row.key.substr((userId + ",").length)] = {error: row.error};
					}
				} else if (row.doc) {
                    ratings[row.key.substr((userId + ",").length)] = row;					
				} else {
					ratings[row.key.substr((userId + ",").length)] = {doc: null};
				}                
            });
            return ratings;
        });
	},
    
    setRatings: function(userId, titlesIdsAndRating) {        
		
        function coerce(rating) {
            if (rating > 5)
            	return 5;
            else if (rating < 1)
            	return 1;
            else
            	return rating;
        }

        var ids = Object.keys(titlesIdsAndRating);

        return ratingsDB.allDocs({
            keys: ids.map(function(id) {
                return userId + "," + id;
            }),
            include_docs: true
        }).then(function(getResponse) {
            return ratingsDB.bulkDocs(
                ids.filter(function(id, index) {
                    return !(getResponse.rows[index].doc == null || getResponse.rows[index].error == "not_found");
                }).map(function(id, index) {
                    return {
                        _id: userId + "," + id,
                        _rev: (!getResponse.rows[index].error ? getResponse.rows[index].value.rev : undefined),
                        userRating: coerce(titlesIdsAndRating[id].userRating)
                    };
                })
            ).then(function(setResponse) {
                
                var results = {};
                getResponse.rows.forEach(function(response, index) {
                    if (!setResponse[index]) {
                        results[response.key.substr((userId + ",").length)] = {doc: null};
                    } else if (setResponse[index].ok) {
                        if (getResponse.rows[index].doc == null || getResponse.rows[index].error) {
                            results[response.key.substr((userId + ",").length)] = {
                              id: setResponse[index].id,
                              key: setResponse[index].id,
                              value: {
                                 rev: setResponse[index].rev
                              },
                              doc: {
                                 userRating: coerce(titlesIdsAndRating[response.key.substr((userId + ",").length)].userRating),
                                 _id: setResponse[index].id,
                                 _rev: setResponse[index].rev
                              }
                           };
                        } else {
                            response.doc.userRating = coerce(titlesIdsAndRating[response.key.substr((userId + ",").length)].userRating);
                            results[response.key.substr((userId + ",").length)] = response;
                        }
                    } else {
                        results[response.key.substr((userId + ",").length)] = {error: setResponse[index].message};
                    }
                });
                return results;
            });
        });	
	}
};

module.exports = new RatingService();