import { isPresent, isNotNullOrEmptyString } from './utils';
import { SortDescriptor } from './sort-descriptor';
import { State } from './state';
import { serializeFilter } from './odata-filtering.operators';
import { ifElse, constant } from './funcs';

const serializeSort = (orderby: Array<SortDescriptor>): string => {
    const str = orderby
        .filter(sort => isPresent(sort.dir))
        .map(sort => {
            const order = sort.field.replace(/\./g, "/");
            return sort.dir === "desc" ? order + " desc" : order;
        }).join(",");

    return str ? `$orderby=${str}` : str;
};

const emptyString = constant('');
const concat = a => b => a + b;

const serializeKey = (strings, val) => ifElse(isPresent, concat(strings[0]), emptyString)(val);

const rules = (settings, state) => (key) => ({
    "filter": serializeFilter(state.filter || {}, settings),
    "skip": serializeKey`$skip=${state.skip}`,
    "sort": serializeSort(state.sort || []),
    "take": serializeKey`$top=${state.take}`
}[key]);

// tslint:disable:max-line-length
/**
 * The settings for the ODataString serialization.
 */
export interface ODataSettings {
    /**
     * Determines if the dates that are set in the filter descriptors will be serialized as UTC by subtracting the offset for the current time zone. Defaults to `false` which means that the dates will be serialized without modification.
     */
    utcDates?: boolean;
}
// tslint:enable:max-line-length

/**
 * Converts a [`State`]({% slug api_kendo-data-query_state %}) into an OData v4 compatible string.
 *
 * @param {State} state - The state that will be serialized.
 * @param {ODataSettings} settings - The settings that are used during the serialization.
 * @returns {string} - The serialized state.
 */
export const toODataString = (state: State, settings: ODataSettings = {}): string => (
    Object.keys(state)
        .map(rules(settings, state))
        .filter(isNotNullOrEmptyString)
        .join('&')
);