/**
 * Per-tab session state.
 *
 * Extracted from BrowserManager to enable parallel tab execution in /batch.
 * Each TabSession holds the state that is scoped to a single browser tab:
 * page reference, element refs, snapshot baseline, and frame context.
 *
 *   BrowserManager (global)
 *     └── tabSessions: Map<number, TabSession>
 *           ├── TabSession(page1)  ←  refMap, lastSnapshot, frame
 *           ├── TabSession(page2)  ←  refMap, lastSnapshot, frame
 *           └── TabSession(page3)  ←  refMap, lastSnapshot, frame
 *
 * The /command path gets the active session via bm.getActiveSession().
 * The /batch path gets specific sessions via bm.getSession(tabId).
 * Both paths pass TabSession to the same handler functions.
 */

import type { Page, Locator, Frame } from 'playwright';

export interface RefEntry {
  locator: Locator;
  role: string;
  name: string;
}

export class TabSession {
  readonly page: Page;

  // ─── Ref Map (snapshot → @e1, @e2, @c1, @c2, ...) ────────
  private refMap: Map<string, RefEntry> = new Map();

  // ─── Snapshot Diffing ─────────────────────────────────────
  // NOT cleared on navigation — it's a text baseline for diffing
  private lastSnapshot: string | null = null;

  // ─── Frame context ─────────────────────────────────────────
  private activeFrame: Frame | null = null;

  constructor(page: Page) {
    this.page = page;
  }

  // ─── Page Access ───────────────────────────────────────────
  getPage(): Page {
    return this.page;
  }

  // ─── Ref Map ──────────────────────────────────────────────
  setRefMap(refs: Map<string, RefEntry>) {
    this.refMap = refs;
  }

  clearRefs() {
    this.refMap.clear();
  }

  /**
   * Resolve a selector that may be a @ref (e.g., "@e3", "@c1") or a CSS selector.
   * Returns { locator } for refs or { selector } for CSS selectors.
   */
  async resolveRef(selector: string): Promise<{ locator: Locator } | { selector: string }> {
    if (selector.startsWith('@e') || selector.startsWith('@c')) {
      const ref = selector.slice(1); // "e3" or "c1"
      const entry = this.refMap.get(ref);
      if (!entry) {
        throw new Error(
          `Ref ${selector} not found. Run 'snapshot' to get fresh refs.`
        );
      }
      const count = await entry.locator.count();
      if (count === 0) {
        throw new Error(
          `Ref ${selector} (${entry.role} "${entry.name}") is stale — element no longer exists. ` +
          `Run 'snapshot' for fresh refs.`
        );
      }
      return { locator: entry.locator };
    }
    return { selector };
  }

  /** Get the ARIA role for a ref selector, or null for CSS selectors / unknown refs. */
  getRefRole(selector: string): string | null {
    if (selector.startsWith('@e') || selector.startsWith('@c')) {
      const entry = this.refMap.get(selector.slice(1));
      return entry?.role ?? null;
    }
    return null;
  }

  getRefCount(): number {
    return this.refMap.size;
  }

  /** Get all ref entries for the /refs endpoint. */
  getRefEntries(): Array<{ ref: string; role: string; name: string }> {
    return Array.from(this.refMap.entries()).map(([ref, entry]) => ({
      ref, role: entry.role, name: entry.name,
    }));
  }

  // ─── Snapshot Diffing ─────────────────────────────────────
  setLastSnapshot(text: string | null) {
    this.lastSnapshot = text;
  }

  getLastSnapshot(): string | null {
    return this.lastSnapshot;
  }

  // ─── Frame context ─────────────────────────────────────────
  setFrame(frame: Frame | null): void {
    this.activeFrame = frame;
  }

  getFrame(): Frame | null {
    return this.activeFrame;
  }

  /**
   * Returns the active frame if set, otherwise the current page.
   * Use this for operations that work on both Page and Frame (locator, evaluate, etc.).
   */
  getActiveFrameOrPage(): Page | Frame {
    // Auto-recover from detached frames (iframe removed/navigated)
    if (this.activeFrame?.isDetached()) {
      this.activeFrame = null;
    }
    return this.activeFrame ?? this.page;
  }

  /**
   * Called on main-frame navigation to clear stale refs and frame context.
   */
  onMainFrameNavigated(): void {
    this.clearRefs();
    this.activeFrame = null;
  }
}