// Adapted from https://github.com/microsoft/TypeScript/blob/master/lib/lib.es2019.array.d.ts

interface ReadonlyArray<T> {
    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(
        this:
            | readonly U[][][][][]
            | ReadonlyArray<readonly U[][][][]>
            | ReadonlyArray<Array<readonly U[][][]>>
            | ReadonlyArray<Array<Array<readonly U[][]>>>
            | ReadonlyArray<Array<Array<Array<readonly U[]>>>>
            | ReadonlyArray<ReadonlyArray<readonly U[][][]>>
            | ReadonlyArray<ReadonlyArray<Array<Array<readonly U[]>>>>
            | ReadonlyArray<ReadonlyArray<Array<Array<readonly U[]>>>>
            | ReadonlyArray<ReadonlyArray<Array<Array<readonly U[]>>>>
            | ReadonlyArray<ReadonlyArray<Array<readonly U[][]>>>
            | ReadonlyArray<ReadonlyArray<Array<readonly U[][]>>>
            | ReadonlyArray<ReadonlyArray<ReadonlyArray<readonly U[][]>>>
            | ReadonlyArray<ReadonlyArray<ReadonlyArray<Array<readonly U[]>>>>
            | ReadonlyArray<ReadonlyArray<ReadonlyArray<Array<readonly U[]>>>>
            | ReadonlyArray<Array<ReadonlyArray<ReadonlyArray<readonly U[]>>>>
            | ReadonlyArray<ReadonlyArray<ReadonlyArray<ReadonlyArray<readonly U[]>>>>,
        depth: 4,
    ): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(
        this:
            | readonly U[][][][]
            | ReadonlyArray<Array<Array<readonly U[]>>>
            | ReadonlyArray<Array<readonly U[][]>>
            | ReadonlyArray<readonly U[][][]>
            | ReadonlyArray<ReadonlyArray<readonly U[][]>>
            | ReadonlyArray<ReadonlyArray<Array<readonly U[]>>>
            | ReadonlyArray<ReadonlyArray<Array<readonly U[]>>>
            | ReadonlyArray<ReadonlyArray<ReadonlyArray<readonly U[]>>>,
        depth: 3,
    ): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(
        this:
            | readonly U[][][]
            | ReadonlyArray<readonly U[][]>
            | ReadonlyArray<Array<readonly U[]>>
            | ReadonlyArray<ReadonlyArray<readonly U[]>>,
        depth: 2,
    ): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(this: readonly U[][] | ReadonlyArray<readonly U[]>, depth?: 1): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(this: readonly U[], depth: 0): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth. If no depth is provided, flat method defaults to the depth of 1.
     *
     * @param depth The maximum recursion depth
     */
    flat(depth?: number): any[];
}

interface Array<T> {
    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(this: U[][][][][][][][], depth: 7): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(this: U[][][][][][][], depth: 6): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(this: U[][][][][][], depth: 5): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(this: U[][][][][], depth: 4): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(this: U[][][][], depth: 3): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(this: U[][][], depth: 2): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(this: U[][], depth?: 1): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth.
     *
     * @param depth The maximum recursion depth
     */
    flat<U>(this: U[], depth: 0): U[];

    /**
     * Returns a new array with all sub-array elements concatenated into it recursively up to the
     * specified depth. If no depth is provided, flat method defaults to the depth of 1.
     *
     * @param depth The maximum recursion depth
     */
    flat(depth?: number): any[];
}