export interface OptionFromOptionalNullOr<S extends Constraint>
  extends decodeTo<Option<toType<S>>, optional<NullOr<S>>>
{
  readonly "Rebuild": OptionFromOptionalNullOr<S>
}

/**
 * Decodes an optional or `null` or `undefined` value `A` to a required `Option<A>`
 * value.
 *
 * **Details**
 *
 * Decoding maps a missing key, `undefined`, or `null` to `None`, and maps all
 * other values to `Some`. Encoding maps `Some` to its value. `None` is encoded
 * according to `options.onNoneEncoding`: `"omit"` encodes a missing key,
 * `null` encodes `null`, and `undefined` encodes `undefined`.
 *
 * @category Option
 * @since 4.0.0
 */
export function OptionFromOptionalNullOr<S extends Constraint>(
  schema: S,
  options?: {
    readonly onNoneEncoding: "omit" | null | undefined
  }
): OptionFromOptionalNullOr<S> {
  const onNoneEncoding = options === undefined ? "omit" : options.onNoneEncoding
  const noneValue = onNoneEncoding === null
    ? null as S["Type"] | null | undefined
    : undefined as S["Type"] | null | undefined
  return optional(NullOr(schema)).pipe(decodeTo(
    Option(toType(schema)),
    SchemaTransformation.transformOptional<Option_.Option<S["Type"]>, S["Type"] | null | undefined>({
      decode: (oe) => oe.pipe(Option_.filter(Predicate.isNotNullish), Option_.some),
      encode: onNoneEncoding === "omit"
        ? Option_.flatten
        : (ot) => Option_.some(Option_.getOrElse(Option_.flatten(ot), () => noneValue))
    })
  ))
}