/** Field's layout vocabulary is shared by every renderer. */
export const FIELD_LAYOUTS = ["stacked", "inline"] as const;
export type FieldLayout = (typeof FIELD_LAYOUTS)[number];

/** Semantic Field props; class, children and id generation belong to adapters. */
export interface FieldContractProps {
  /** Visible label text. */
  label: string;
  /** Supporting text announced with the control. */
  help?: string;
  /** Current validation error, announced and associated with the control. */
  error?: string;
  /** Makes the requirement visible and native. */
  required?: boolean;
  /** Explicit control id; otherwise the renderer supplies a stable generated one. */
  id?: string;
  /** Label placement: stacked above the control, or inline beside a binary choice. */
  layout?: FieldLayout;
}

/** The framework-neutral association passed by Field to its control. */
export interface FieldControlProps {
  /** The id the label targets. */
  id: string;
  /** Native required semantics, when the Field declares them. */
  required?: true;
  /** Space-separated help and error ids. */
  "aria-describedby"?: string;
  /** Present only while the Field has an error. */
  "aria-invalid"?: "true";
  /** The Field's current error id. */
  "aria-errormessage"?: string;
}

export interface FieldAssociationOptions {
  /** Framework-generated or application-supplied stable control id. */
  id: string;
  /** Supporting text, if present. */
  help?: string;
  /** Validation error, if present. */
  error?: string;
  /** Whether the native control is required. */
  required?: boolean;
}

/** Pure association logic; frameworks own id generation and reactive updates. */
export function fieldAssociation({ id, help, error, required }: FieldAssociationOptions) {
  const helpId = `${id}-help`;
  const errorId = `${id}-error`;
  const control: FieldControlProps = {
    id, required: required || undefined,
    "aria-describedby": [help ? helpId : undefined, error ? errorId : undefined].filter(Boolean).join(" ") || undefined,
    "aria-invalid": error ? "true" : undefined,
    "aria-errormessage": error ? errorId : undefined,
  };
  return { control, helpId, errorId };
}