/**
 * Utility for generating row / column headers
 */
import {Axis as VgAxis, SignalRef, Text} from 'vega';
import {FacetFieldDef} from '../../spec/facet.js';

export type HeaderChannel = 'row' | 'column';
export const HEADER_CHANNELS: HeaderChannel[] = ['row', 'column'];

export type HeaderType = 'header' | 'footer';
export const HEADER_TYPES: HeaderType[] = ['header', 'footer'];

export interface LayoutHeaderComponentIndex {
  row?: LayoutHeaderComponent;
  column?: LayoutHeaderComponent;
  facet?: LayoutHeaderComponent;
}

/**
 * A component that represents all header, footers and title of a Vega group with layout directive.
 */
export interface LayoutHeaderComponent {
  title?: Text | SignalRef;

  // TODO: concat can have multiple header / footer.
  // Need to redesign this part a bit.

  facetFieldDef?: FacetFieldDef<string, SignalRef>;

  /**
   * An array of header components for headers.
   * For facet, there should be only one header component, which is data-driven.
   * For concat, there can be multiple header components that explicitly list different axes.
   */
  header?: HeaderComponent[];

  /**
   * An array of header components for footers.
   * For facet, there should be only one header component, which is data-driven.
   * For concat, there can be multiple header components that explicitly list different axes.
   */
  footer?: HeaderComponent[];
}

/**
 * A component that represents one group of row/column-header/footer.
 */
export interface HeaderComponent {
  labels: boolean;

  sizeSignal: {signal: string};

  axes: VgAxis[];
}