thi-ng/umbrella

import type { IObjectOf } from "@thi.ng/api";
import type { GroupByOpts, Reducer } from "./api.js";
import { __groupByOpts } from "./internal/group-opts.js";
import { $$reduce } from "./reduce.js";

export function groupByObj<SRC, GROUP>(
    opts?: Partial<GroupByOpts<SRC, PropertyKey, GROUP>>
): Reducer<SRC, IObjectOf<GROUP>>;
export function groupByObj<SRC>(src: Iterable<SRC>): IObjectOf<SRC[]>;
export function groupByObj<SRC, GROUP>(
    opts: Partial<GroupByOpts<SRC, PropertyKey, GROUP>>,
    src: Iterable<SRC>
): IObjectOf<GROUP>;
export function groupByObj<SRC, GROUP>(...args: any[]): any {
    const res = $$reduce(groupByObj, args);
    if (res) return res;

    const opts = __groupByOpts<SRC, PropertyKey, GROUP>(args[0]);
    const [_init, complete, _reduce] = opts.group;
    return <Reducer<SRC, IObjectOf<GROUP>>>[
        () => ({}),
        (acc) => {
            for (let k in acc) {
                acc[k] = complete(acc[k]);
            }
            return acc;
        },
        (acc, x: SRC) => {
            const k: any = opts.key(x);
            acc[k] = acc[k]
                ? <GROUP>_reduce(acc[k], x)
                : <GROUP>_reduce(_init(), x);
            return acc;
        },
    ];
}