thi-ng/umbrella

import { ensureArrayLike } from "@thi.ng/arrays/ensure-array";
import { illegalArgs } from "@thi.ng/errors/illegal-arguments";
import { range } from "./range.js";

/**
 * Iterator yielding the Cartesian Product of the given iterables.
 *
 * @remarks
 * All iterables MUST be finite! If any of the given iterables is
 * empty the iterator yields no values.
 *
 * @example
 * ```ts
 * import { permutations } from "@thi.ng/transducers";
 *
 * [...permutations("ab", range(3))]
 * // [ ['a', 0], ['a', 1], ['a', 2],
 * //   ['b', 0], ['b', 1], ['b', 2] ]
 *
 * [...map((x: any[]) => x.join(""), permutations("ab", "-", range(3)))]
 * // ['a-0', 'a-1', 'a-2', 'b-0', 'b-1', 'b-2']
 *
 * [...permutations([], "", range(0))]
 * // []
 * ```
 *
 * @param a -
 */
export function permutations<A>(a: Iterable<A>): IterableIterator<[A]>;
export function permutations<A, B>(
    a: Iterable<A>,
    b: Iterable<B>
): IterableIterator<[A, B]>;
export function permutations<A, B, C>(
    a: Iterable<A>,
    b: Iterable<B>,
    c: Iterable<C>
): IterableIterator<[A, B, C]>;
export function permutations<A, B, C, D>(
    a: Iterable<A>,
    b: Iterable<B>,
    c: Iterable<C>,
    d: Iterable<D>
): IterableIterator<[A, B, C, D]>;
export function permutations(...src: Iterable<any>[]): IterableIterator<any[]>;
export function* permutations(...src: any[]): IterableIterator<any[]> {
    const n = src.length - 1;
    if (n < 0) {
        return;
    }
    const step = new Array(n + 1).fill(0);
    const realized = src.map(ensureArrayLike);
    const total = realized.reduce((acc, x) => acc * x.length, 1);
    for (let i = 0; i < total; i++) {
        const tuple = [];
        for (let j = n; j >= 0; j--) {
            const r = realized[j];
            let s = step[j];
            if (s === r.length) {
                step[j] = s = 0;
                j > 0 && step[j - 1]++;
            }
            tuple[j] = r[s];
        }
        step[n]++;
        yield tuple;
    }
}

/**
 * Iterator yielding the Cartesian Product for `n` items of `m` values
 * each.
 *
 * @remarks
 * If `m` is not given, defaults to value of `n`. The range of `m` is
 * `0..m-1`. The optional `offsets` array can be used to define start
 * values for each dimension.
 *
 * @example
 * ```ts
 * import { permutationsN } from "@thi.ng/transducers";
 *
 * [...permutationsN(2)]
 * // [ [0, 0], [0, 1], [1, 0], [1, 1] ]
 *
 * [...permutationsN(2, 3)]
 * // [ [0, 0], [0, 1], [0, 2],
 * //   [1, 0], [1, 1], [1, 2],
 * //   [2, 0], [2, 1], [2, 2] ]
 *
 * [...permutationsN(2, 2, [10, 20])]
 * // [ [ 10, 20 ], [ 10, 21 ], [ 11, 20 ], [ 11, 21 ] ]
 * ```
 *
 * @param n -
 * @param m -
 * @param offsets -
 */
export const permutationsN = (
    n: number,
    m = n,
    offsets?: number[]
): IterableIterator<number[]> => {
    if (offsets && offsets.length < n) {
        illegalArgs(`insufficient offsets, got ${offsets.length}, needed ${n}`);
    }
    const seqs = [];
    while (n-- > 0) {
        const o = offsets ? offsets[n] : 0;
        seqs[n] = range(o, o + m);
    }
    return permutations.apply(null, seqs);
};