rivo/Num/internal/_Div10.d.ts

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import type { _StrToNum } from "./_StrToNum";
import type { Reverse } from "../../Str/Reverse";

/**
 * Divide integer `N` by 10^`Length<By>`.
 *
 * **⚠️ Warning:** length of `By` must be less than or equal to the number of digits in `N`.
 * @private
 *
 * @example
 * ```typescript
 * type R1 = _Div10<125, "_">;
 * //   ^?: 12.5
 * type R2 = _Div10<-12300, "__">;
 * //   ^?: -123
 * type R3 = _Div10<-12300, "___">;
 * //   ^?: -12.3
 * ```
 */
export type _Div10<N extends number, By extends string> = _StrToNum<
  __Div10<Reverse<`${N}`>, By, ""> extends infer R extends string ?
    R extends `.${infer R}` ?
      `0.${R}`
    : R
  : never
>;
type __Div10<A extends string, By extends string, B extends string> =
  By extends `${string}${infer RestBy}` ?
    A extends `${infer F}${infer R}` ?
      __Div10<R, RestBy, `${F}${B}`>
    : never
  : _RemoveTrailingFractional0s<`${Reverse<A>}.${B}`>;
type _RemoveTrailingFractional0s<S extends string> =
  S extends `${infer F}0` ? _RemoveTrailingFractional0s<F>
  : S extends `${infer F}.` ? F
  : S;