Type-level integer to base-26 converter, excel column number style A = 0, AA = 26, AB = 27, etc

to-excel-number.ts

type Tuple<L extends number, T extends any[] = []> =
    T["length"] extends L ? T : Tuple<L, [...T, void]>;


type Keys = [
    "Z", "Y", "X", "W", "V", "U", "T", "S", "R",
    "Q", "P", "O", "N", "M", "L", "K", "J", "I",
    "H", "G", "F", "E", "D", "C", "B", "A"
];
type Evil = {
    A: Tuple<1>,
    B: Tuple<2>,
    C: Tuple<3>,
    D: Tuple<4>,
    E: Tuple<5>,
    F: Tuple<6>,
    G: Tuple<7>,
    H: Tuple<8>,
    I: Tuple<9>,
    J: Tuple<10>,
    K: Tuple<11>,
    L: Tuple<12>,
    M: Tuple<13>,
    N: Tuple<14>,
    O: Tuple<15>,
    P: Tuple<16>,
    Q: Tuple<17>,
    R: Tuple<18>,
    S: Tuple<19>,
    T: Tuple<20>,
    U: Tuple<21>,
    V: Tuple<22>,
    W: Tuple<23>,
    X: Tuple<24>,
    Y: Tuple<25>,
    Z: Tuple<26>,
}

type ToExcel<T extends void[]> = ToExcel1<[...T], Keys, []>;
type ToExcel1<T extends void[], L extends (keyof Evil)[], R extends void[]> =
    L extends [infer K extends keyof Evil, ...infer LC extends (keyof Evil)[]]
        ? T extends [...Evil[K], ...infer Over extends void[]]
            ? Over extends [] ? `${ToExcel1<R, Keys, []>}${K}`: ToExcel1<Over, Keys, [...R, void]>
            : ToExcel1<T, LC, R>
        : "";

type m = ToExcel<Tuple<560>>