module.exports = function(Self) {
    Self.installMethod = function(methodName, filterCb, filterResult) {
        this.remoteMethod(methodName, {
            description: 'List items using a filter',
            accessType: 'READ',
            accepts: [
                {
                    arg: 'filter',
                    type: 'object',
                    required: true,
                    description: 'Filter defining where',
                    http: function(ctx) {
                        return ctx.req.query;
                    }
                }
            ],
            returns: {
                arg: 'data',
                type: [this.modelName],
                root: true
            },
            http: {
                verb: 'get',
                path: `/${methodName}`
            }
        });

        this[methodName] = (params, cb) => {
            let filter = removeEmpty(filterCb(params));

            var response = {};

            function returnValues() {
                if (response.instances !== undefined && response.count !== undefined) {
                    if (filterResult)
                        cb(null, filterResult(response));
                    else
                        cb(null, response);
                }
            }

            function error() {
                cb(null, response);
            }

            this.find(filter, function(err, instances) {
                if (err) {
                    error();
                } else {
                    response.instances = instances;
                    returnValues();
                }
            });

            this.count(filter.where, function(err, totalCount) {
                if (err) {
                    error();
                } else {
                    response.count = totalCount;
                    returnValues();
                }
            });
        };
    };
};

function removeEmpty(o) {
    if (Array.isArray(o)) {
        let array = [];
        for (let item of o) {
            let i = removeEmpty(item);
            if (!isEmpty(i))
                array.push(i);
        }
        if (array.length > 0)
            return array;
    } else if (typeof o === 'object') {
        let object = {};
        for (let key in o) {
            let i = removeEmpty(o[key]);
            if (!isEmpty(i))
                object[key] = i;
        }
        if (Object.keys(object).length > 0)
            return object;
    } else if (!isEmpty(o))
        return o;

    return undefined;
}

function isEmpty(value) {
    return value === undefined || value === '';
}