if-else.ts

if-else.ts

import { curry } from "lodash/fp";

type Predicate<T, U extends T> = (value: T) => value is U;
type Transform<T> = <R = unknown>(value: T) => R;
type BranchReturn<
  T,
  U extends T,
  TBranch extends Transform<U>,
  FBranch extends Transform<T>
> = T extends U ? ReturnType<TBranch> : ReturnType<FBranch>;

export interface IfElse {
  // (predicate, onTrue, onFalse, data)
  <T, U extends T, TBranch extends Transform<U>, FBranch extends Transform<T>>(
    predicate: Predicate<T, U>,
    onTrue: TBranch,
    onFalse: FBranch,
    data: T
  ): BranchReturn<T, U, TBranch, FBranch>;

  // (predicate) => (onTrue, onFalse, data)
  <T, U extends T>(predicate: Predicate<T, U>): <
    TBranch extends Transform<U>,
    FBranch extends Transform<T>
  >(
    onTrue: TBranch,
    onFalse: FBranch,
    data: T
  ) => BranchReturn<T, U, TBranch, FBranch>;

  // (predicate, onTrue) => (onFalse, data)
  <T, U extends T, TBranch extends Transform<U>>(
    predicate: Predicate<T, U>,
    onTrue: TBranch
  ): <FBranch extends Transform<T>>(
    onFalse: FBranch,
    data: T
  ) => BranchReturn<T, U, TBranch, FBranch>;

  // (predicate, onTrue, onFalse) => (data)
  <T, U extends T, TBranch extends Transform<U>, FBranch extends Transform<T>>(
    predicate: Predicate<T, U>,
    onTrue: TBranch,
    onFalse: FBranch
  ): (data: T) => BranchReturn<T, U, TBranch, FBranch>;

  // (predicate) => (onTrue) => (onFalse, data)
  <T, U extends T>(predicate: Predicate<T, U>): <TBranch extends Transform<U>>(
    onTrue: TBranch
  ) => <FBranch extends Transform<T>>(
    onFalse: FBranch,
    data: T
  ) => BranchReturn<T, U, TBranch, FBranch>;

  // (predicate) => (onTrue, onFalse) => (data)
  <T, U extends T>(predicate: Predicate<T, U>): <
    TBranch extends Transform<U>,
    FBranch extends Transform<T>
  >(
    onTrue: TBranch,
    onFalse: FBranch
  ) => (data: T) => BranchReturn<T, U, TBranch, FBranch>;

  // (predicate, onTrue) => (onFalse) => (data)
  <T, U extends T, TBranch extends Transform<U>>(
    predicate: Predicate<T, U>,
    onTrue: TBranch
  ): <FBranch extends Transform<T>>(
    onFalse: FBranch
  ) => (data: T) => BranchReturn<T, U, TBranch, FBranch>;

  // (predicate) => (onTrue) => (onFalse) => (data)
  <T, U extends T>(predicate: Predicate<T, U>): <TBranch extends Transform<U>>(
    onTrue: TBranch
  ) => <FBranch extends Transform<T>>(
    onFalse: FBranch
  ) => (data: T) => BranchReturn<T, U, TBranch, FBranch>;
}

const ifElse = curry(function ifElse<
  T,
  U extends T,
  TBranch extends Transform<U>,
  FBranch extends Transform<T>
>(predicate: Predicate<T, U>, onTrue: TBranch, onFalse: FBranch, data: T) {
  return predicate(data) ? onTrue(data) : onFalse(data);
}) as IfElse;

export default ifElse;