transform schema to be client conform nextjs

to-client-schema.ts

import {
  z,
  ZodType,
  ZodObject,
  ZodArray,
  ZodOptional,
  ZodNullable,
  ZodDate,
  ZodCustom,
  ZodPipe,
  ZodTransform
} from 'zod/v4'
import { ObjectId } from 'mongodb'

export type ToClientZodType<T extends ZodType> = T extends ZodDate
  ? ZodPipe<ZodDate, ZodTransform<string, Date>>
  : T extends ZodCustom<ObjectId, ObjectId>
    ? ZodPipe<ZodCustom<ObjectId, ObjectId>, ZodTransform<string, ObjectId>>
    : T extends ZodOptional<infer Inner>
      ? ZodOptional<ToClientZodType<Inner extends ZodType ? Inner : never>>
      : T extends ZodNullable<infer Inner>
        ? ZodNullable<ToClientZodType<Inner extends ZodType ? Inner : never>>
        : T extends ZodArray<infer Element>
          ? ZodArray<ToClientZodType<Element extends ZodType ? Element : never>>
          : T extends ZodObject<infer Shape>
            ? ZodObject<{ [K in keyof Shape]: Shape[K] extends ZodType ? ToClientZodType<Shape[K]> : Shape[K] }>
            : T

export function toClientSchema<T extends ZodType>(schema: T): ToClientZodType<T> {
  // Base case: Handle Date transformation
  if (schema instanceof ZodDate) {
    const zodDate = schema as ZodDate
    return zodDate.transform(date => date.toISOString()) as unknown as ToClientZodType<T>
  }

  // Base case: Handle ObjectId transformation by checking metadata
  if (schema instanceof ZodCustom && schema.meta()?.bsonType === 'objectId') {
    const zodCustom = schema as ZodCustom<ObjectId, ObjectId>
    return zodCustom.transform(id => id.toString()) as unknown as ToClientZodType<T>
  }

  // --- Recursive cases for unwrapping and re-wrapping schemas ---
  if (schema instanceof ZodOptional) {
    const zodOptional = schema as unknown as ZodOptional<any>
    return toClientSchema(zodOptional.unwrap()).optional() as unknown as ToClientZodType<T>
  }
  if (schema instanceof ZodNullable) {
    const zodNullable = schema as unknown as ZodNullable<T>
    return toClientSchema(zodNullable.unwrap()).nullable() as unknown as ToClientZodType<T>
  }
  if (schema instanceof ZodArray) {
    const zodArray = schema as ZodArray<any>
    return z.array(toClientSchema(zodArray.element)) as unknown as ToClientZodType<T>
  }
  if (schema instanceof ZodObject) {
    const newShape: { [k: string]: ZodType } = {}
    for (const key in schema.shape) {
      newShape[key] = toClientSchema(schema.shape[key])
    }
    return z.object(newShape) as unknown as ToClientZodType<T>
  }

  // Return the original schema if no transformation is needed
  return schema as unknown as ToClientZodType<T>
}