feat(@angular-ru/common): support nullable for array utils

[splincode]

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PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

[Markiewic]

Generates tuples with given length. [type] and [type, ...type[]].

type Tuple<T, N extends number = 1, R extends unknown[] = []> = R['length'] extends N ? R : Tuple<T, N, [T, ...R]>;
type InfiniteTuple<T, N extends number = 1> = [...Tuple<T, N>, ...T[]];

Returns type of Indexs item of array or fallbacks to undefined. if there is no certainty that the element is presented, append undefined.

type ItemOrUndefined<ArrayType, Index extends number> = ArrayType extends unknown[]
    ? ArrayType extends [unknown, ...InfiniteTuple<unknown, Index>]
        ? ArrayType[0]
        : ArrayType[0] | undefined
    : undefined;

Now let's use it in our function return type:

export function takeFirstItem<ArrayType extends Nullable<unknown[]>>(array: ArrayType): ItemOrUndefined<ArrayType, 0> {
    return (Array.isArray(array) ? array[0] : undefined) as ItemOrUndefined<ArrayType, 0>;
}

And another functions:

export function takeSecondItem<ArrayType extends Nullable<unknown[]>>(array: ArrayType): ItemOrUndefined<ArrayType, 1> {
    return (Array.isArray(array) ? array[1] : undefined) as ItemOrUndefined<ArrayType, 1>;
}

[Markiewic]

#684