import type { Renderer, ViewerSource } from "./types.ts";

/**
 * What an action can see when it is offered and when it runs. `content` is the
 * element the renderer drew into, so an action can read or print what is on
 * screen rather than re-fetching the file.
 */
export interface ViewerActionContext {
  host: HTMLElement;
  content: HTMLElement;
  source: ViewerSource;
  /** Absent while the preview is still resolving, or when nothing could render. */
  renderer?: Renderer;
  kind?: string;
}

export interface ViewerAction {
  /** Stable identifier; registering the same id again replaces the earlier one. */
  id: string;
  label: string;
  /** Name from the built-in icon set. Falls back to one derived from the label. */
  icon?: string;
  /** Toolbar side: alongside the renderer's own controls, or with download. */
  placement?: "controls" | "actions";
  /** Offered only when this returns true. Defaults to always. */
  when?: (context: ViewerActionContext) => boolean;
  run: (context: ViewerActionContext) => void | Promise<void>;
}

const registered = new Map<string, ViewerAction>();

/**
 * Adds a toolbar action to every viewer in the page. Returns an unregister
 * function, so a component can add one for as long as it is mounted.
 *
 * ```ts
 * registerViewerAction({
 *   id: "open-in-tab",
 *   label: "Open in new tab",
 *   when: ({ source }) => Boolean(source.src),
 *   run: ({ source }) => window.open(source.src, "_blank", "noopener"),
 * });
 * ```
 */
export function registerViewerAction(action: ViewerAction): () => void {
  registered.set(action.id, action);
  return () => {
    if (registered.get(action.id) === action) registered.delete(action.id);
  };
}

/** Globally registered actions, in registration order. */
export function viewerActions(): ViewerAction[] {
  return [...registered.values()];
}

/** Testing helper: drops every globally registered action. */
export function clearViewerActions(): void {
  registered.clear();
}