/**
 * Where a mounted module UI is in the Dashboard, and how it moves (ADR 0063).
 *
 * A **host capability**, not a router. The host owns the address bar, the sidebar, and every
 * platform route; a module owns the pages beneath its own root. So a module never touches
 * `window.location` or `window.history`, never spells a platform route, and never builds another
 * module's address: it names paths **relative to its own root**, and the host maps them to real,
 * refreshable, bookmarkable Dashboard addresses — or refuses them.
 *
 * Paths:
 *
 * - `""` is the module's root, its landing view.
 * - `"timelines"` is a declared page; `"media/sermons/123"` is a route **beneath** the declared page
 *   `media`, which a module may use for detail views without listing every record in its manifest.
 * - A leading `/` means the same thing as none: `"/timelines"` is still this module's `timelines`.
 *   There is no way to name anything outside this module.
 * - Segments are unreserved URL characters only (letters, digits, `-`, `.`, `_`, `~`), never `.` or
 *   `..`, never empty; no query, fragment, scheme, or percent-encoding.
 *
 * A path the host would not open — malformed, or outside the module's root and its declared pages —
 * is refused with a {@link ModuleUiNavigationError} rather than silently opening something else.
 */
export interface ModuleUiNavigation {
  /** Where this module is now. */
  location(): ModuleUiLocation;
  /** Notifies after the location changes — a link, Back or Forward, or a refresh of the sidebar.
   * Returns an unsubscribe. The module stays mounted while it moves between its own pages. */
  subscribe(listener: () => void): () => void;
  /**
   * Opens one of this module's own routes. `replace` corrects the current history entry instead of
   * adding one — for a route the module just respelled, not for ordinary navigation.
   *
   * @throws {ModuleUiNavigationError} for a path this module may not open.
   */
  navigate(path: string, options?: ModuleUiNavigateOptions): void;
  /**
   * A link to one of this module's own routes, for a real `<a>`: `href` is the host's address for it,
   * so the link can be opened in a new tab, copied, or bookmarked, and `onClick` opens it in place on
   * an ordinary click while leaving a modified or middle click to the browser.
   *
   * @throws {ModuleUiNavigationError} for a path this module may not open.
   */
  link(path: string): ModuleUiLink;
  /**
   * This module's page in the Dashboard's centralized Settings, or `undefined` when there is none for
   * this viewer — the module declares no configuration, or the viewer may not change it. A
   * presentation hint like {@link ModuleUiPermissions}: Settings enforces its own authority.
   *
   * Opening it carries the module's current location as the place to come back to, so Settings'
   * Back returns exactly here. The host validates that destination; the module neither builds nor
   * checks it.
   */
  readonly settings: ModuleUiSettingsLocation | undefined;
}

export interface ModuleUiLocation {
  /** This module's route, relative to its root: `""`, `"timelines"`, `"media/sermons/123"`. Never a
   * leading or trailing `/`. */
  readonly path: string;
  /** The declared page that route is, or lies beneath; `undefined` at the module's root. */
  readonly page: string | undefined;
}

export interface ModuleUiNavigateOptions {
  readonly replace?: boolean;
}

/** What a link's click handler reads: satisfied by a DOM `MouseEvent` and by React's synthetic one. */
export interface ModuleUiLinkClickEvent {
  readonly button: number;
  readonly metaKey: boolean;
  readonly ctrlKey: boolean;
  readonly shiftKey: boolean;
  readonly altKey: boolean;
  readonly defaultPrevented: boolean;
  preventDefault(): void;
}

export interface ModuleUiLink {
  readonly href: string;
  onClick(event: ModuleUiLinkClickEvent): void;
}

export interface ModuleUiSettingsLocation {
  /** Opens this module's Settings page, remembering where the module was. */
  open(): void;
  /** The same, as a link: its `href` includes the place to return to, so it also works in a new tab. */
  link(): ModuleUiLink;
}

export type ModuleUiNavigationErrorCode =
  /** Not a path this contract can express: absolute, traversing, malformed, or out of bounds. */
  | "MODULE_NAVIGATION_PATH_INVALID"
  /** A well-formed path that is neither the module's root nor a declared page or beneath one. */
  | "MODULE_NAVIGATION_PATH_UNKNOWN";

const navigationErrorMessages: Readonly<Record<ModuleUiNavigationErrorCode, string>> =
  Object.freeze({
    MODULE_NAVIGATION_PATH_INVALID: "A module asked to open a path outside its own routes.",
    MODULE_NAVIGATION_PATH_UNKNOWN: "A module asked to open a page it does not declare.",
  });

/** Carries a stable code and a fixed message — never the path the module asked for. */
export class ModuleUiNavigationError extends Error {
  readonly code: ModuleUiNavigationErrorCode;

  constructor(code: ModuleUiNavigationErrorCode) {
    super(navigationErrorMessages[code]);
    this.name = "ModuleUiNavigationError";
    this.code = code;
    this.stack = `${this.name}: ${this.message}`;
  }
}