import type { Cause } from '../options/instance.js'

/**
 * Single aggregate error
 */
export type AggregateErrorOption = unknown

/**
 * Aggregate `errors` array
 */
export type DefinedAggregateErrors = readonly AggregateErrorOption[]

/**
 * Optional aggregate `errors` array
 */
export type AggregateErrors = DefinedAggregateErrors | undefined

/**
 * Normalize each error in the `errors` option to `Error` instances
 */
type NormalizeAggregateError<ErrorArg extends AggregateErrorOption> =
  ErrorArg extends Error ? ErrorArg : Error

/**
 * Normalize all errors in the `errors` option to `Error` instances
 */
type NormalizeAggregateErrors<
  AggregateErrorsArg extends DefinedAggregateErrors,
> = AggregateErrorsArg extends never[]
  ? []
  : AggregateErrorsArg extends readonly [
        infer AggregateErrorArg extends AggregateErrorOption,
        ...infer Rest extends DefinedAggregateErrors,
      ]
    ? [
        NormalizeAggregateError<AggregateErrorArg>,
        ...NormalizeAggregateErrors<Rest>,
      ]
    : NormalizeAggregateError<AggregateErrorsArg[number]>[]

/**
 * Concatenate the `errors` option with `cause.errors`, if either is defined
 */
type ConcatAggregateErrors<
  AggregateErrorsArg extends AggregateErrors,
  CauseArg extends Cause,
> = [AggregateErrorsArg] extends [DefinedAggregateErrors]
  ? 'errors' extends keyof CauseArg
    ? CauseArg['errors'] extends DefinedAggregateErrors
      ? [...CauseArg['errors'], ...AggregateErrorsArg]
      : AggregateErrorsArg
    : AggregateErrorsArg
  : 'errors' extends keyof CauseArg
    ? CauseArg['errors'] extends DefinedAggregateErrors
      ? CauseArg['errors']
      : never
    : never

/**
 * Object with an `errors` property to set as `error.errors`
 */
export type AggregateErrorsProperty<
  AggregateErrorsArg extends AggregateErrors,
  CauseArg extends Cause,
> =
  ConcatAggregateErrors<AggregateErrorsArg, CauseArg> extends never
    ? { errors?: Error[] }
    : {
        errors: NormalizeAggregateErrors<
          ConcatAggregateErrors<AggregateErrorsArg, CauseArg>
        >
      }