buckets/frontend/src/lib/fieldErrors.ts

import { ApiError } from './api'

/** Per-field validation messages: a 422 body's `{ errors: { field: [msg] } }`. */
export type FieldErrors = Record<string, string[]>

function isStringArray(value: unknown): value is string[] {
  return Array.isArray(value) && value.every((item) => typeof item === 'string')
}

/**
 * Extract the `{ errors: { field: [...] } }` map from a 422 ApiError body.
 * Returns null for anything that isn't a well-formed 422 field-error response
 * (wrong status, non-ApiError, non-JSON body, or a malformed errors shape) so
 * the caller can fall back to a generic error message.
 */
export function parseFieldErrors(error: unknown): FieldErrors | null {
  if (!(error instanceof ApiError) || error.status !== 422) {
    return null
  }

  let parsed: unknown
  try {
    parsed = JSON.parse(error.body)
  } catch {
    return null
  }

  if (
    typeof parsed !== 'object' ||
    parsed === null ||
    !('errors' in parsed) ||
    typeof parsed.errors !== 'object' ||
    parsed.errors === null
  ) {
    return null
  }

  // Only accept the contract shape: every field maps to an array of strings.
  const entries = Object.entries(parsed.errors as Record<string, unknown>)
  if (!entries.every(([, messages]) => isStringArray(messages))) {
    return null
  }

  return parsed.errors as FieldErrors
}

function isViolation(
  value: unknown,
): value is { propertyPath: string; message: string } {
  return (
    typeof value === 'object' &&
    value !== null &&
    'propertyPath' in value &&
    typeof value.propertyPath === 'string' &&
    'message' in value &&
    typeof value.message === 'string'
  )
}

/**
 * Extract the API Platform `{ violations: [{ propertyPath, message }] }` list
 * from a 422 ApiError body, grouped into a per-field map keyed by propertyPath
 * (multiple messages for the same path are collected in order).
 *
 * This is the sibling of {@link parseFieldErrors}: API Platform resources emit
 * this violations shape, while the hand-rolled auth endpoints emit the
 * `{ errors: { field: [...] } }` shape. Returns null for anything that isn't a
 * well-formed 422 violations response — including the auth shape — so the
 * caller can fall back to a generic error message.
 */
export function parseViolations(error: unknown): FieldErrors | null {
  if (!(error instanceof ApiError) || error.status !== 422) {
    return null
  }

  let parsed: unknown
  try {
    parsed = JSON.parse(error.body)
  } catch {
    return null
  }

  if (
    typeof parsed !== 'object' ||
    parsed === null ||
    !('violations' in parsed) ||
    !Array.isArray(parsed.violations)
  ) {
    return null
  }

  // Only accept the contract shape: every entry has a string propertyPath and
  // message. A malformed entry rejects the whole body rather than dropping it.
  if (!parsed.violations.every(isViolation)) {
    return null
  }

  const fieldErrors: FieldErrors = {}
  for (const { propertyPath, message } of parsed.violations) {
    if (!fieldErrors[propertyPath]) {
      fieldErrors[propertyPath] = []
    }
    fieldErrors[propertyPath].push(message)
  }

  return fieldErrors
}