/**
 * FullscreenDisplay
 *
 * Takes over the screen of an iOS device running Safari.
 * - Requests fullscreen / uses iOS standalone-mode tricks
 * - Creates a canvas sized to the true physical pixel resolution
 *   (CSS pixels × devicePixelRatio)
 * - Default state is solid black
 * - Acquires a Screen Wake Lock so the display never sleeps while active;
 *   automatically re-acquires the lock if the page is briefly hidden then
 *   shown again (iOS releases wake locks on page hide)
 * - display(image, ms) renders an HTMLImageElement for exactly `ms`
 *   milliseconds, then reverts to black, using requestAnimationFrame
 *   timestamps for sub-frame accuracy
 */

export class FullscreenDisplay {
  // ─── Public readonly state ───────────────────────────────────────────────

  /** The backing <canvas> element. */
  public readonly canvas: HTMLCanvasElement;

  /** Physical pixel width (CSS width × devicePixelRatio). */
  public readonly physicalWidth: number;

  /** Physical pixel height (CSS height × devicePixelRatio). */
  public readonly physicalHeight: number;

  /** Device pixel ratio detected at construction time. */
  public readonly devicePixelRatio: number;

  // ─── Private state ───────────────────────────────────────────────────────

  private readonly ctx: CanvasRenderingContext2D;

  /** Overlay <div> that acts as the fullscreen root. */
  private readonly overlay: HTMLDivElement;

  /** rAF handle so we can cancel an in-flight display call. */
  private rafHandle: number | null = null;

  /** Resolves the Promise returned by the active display() call. */
  private displayResolve: (() => void) | null = null;

  /**
   * Active Screen Wake Lock sentinel.
   * Typed loosely because lib.dom.d.ts only gained WakeLockSentinel
   * in TypeScript 4.4+; the cast below keeps older configs happy.
   */
  private wakeLock: WakeLockSentinel | null = null;

  // ─── Construction ─────────────────────────────────────────────────────────

  constructor() {
    // ── 1. Determine true screen density ──────────────────────────────────
    //
    // window.devicePixelRatio is the authoritative source on iOS Safari.
    // Common values: 2× (most iPhones / standard iPads), 3× (Pro iPhones).
    this.devicePixelRatio = window.devicePixelRatio ?? 1;

    // ── 2. Build fullscreen overlay ────────────────────────────────────────
    this.overlay = document.createElement("div");

    const overlayStyle = this.overlay.style;
    overlayStyle.position = "fixed";
    overlayStyle.inset = "0";               // top/right/bottom/left: 0
    overlayStyle.width = "100%";
    overlayStyle.height = "100%";
    overlayStyle.margin = "0";
    overlayStyle.padding = "0";
    overlayStyle.backgroundColor = "#000";
    overlayStyle.zIndex = "2147483647";     // max z-index
    // Prevent any rubber-band / scroll bleed-through on iOS
    overlayStyle.overflow = "hidden";
    overlayStyle.touchAction = "none";
    // GPU-composited layer – avoids repaint on canvas updates
    overlayStyle.transform = "translateZ(0)";
    overlayStyle.webkitTransform = "translateZ(0)";

    document.body.appendChild(this.overlay);

    // ── 3. Size the canvas to physical pixels ──────────────────────────────
    //
    // On iOS, window.innerWidth/Height gives the CSS pixel viewport after
    // the browser chrome has been accounted for.  Multiply by DPR to get
    // the true raster resolution.
    const cssWidth = window.innerWidth;
    const cssHeight = window.innerHeight;

    this.physicalWidth = Math.round(cssWidth * this.devicePixelRatio);
    this.physicalHeight = Math.round(cssHeight * this.devicePixelRatio);

    this.canvas = document.createElement("canvas");
    this.canvas.width = this.physicalWidth;
    this.canvas.height = this.physicalHeight;

    const canvasStyle = this.canvas.style;
    canvasStyle.display = "block";
    canvasStyle.width = `${cssWidth}px`;    // CSS size = viewport
    canvasStyle.height = `${cssHeight}px`;
    canvasStyle.backgroundColor = "#000";

    this.overlay.appendChild(this.canvas);

    // ── 4. Grab 2-D context with best quality hints ────────────────────────
    const ctx = this.canvas.getContext("2d", {
      alpha: false,                         // opaque → faster compositing
      desynchronized: false,                // keep in sync with display
    });

    if (ctx === null) {
      throw new Error("FullscreenDisplay: could not acquire 2D canvas context.");
    }

    this.ctx = ctx;

    // Scale once so every draw call works in physical pixels automatically.
    // (We do NOT use CSS transform scaling so image quality is always 1:1.)
    this.ctx.scale(this.devicePixelRatio, this.devicePixelRatio);

    // ── 5. Paint initial black frame ───────────────────────────────────────
    this.paintBlack();

    // ── 6. Attempt fullscreen (Web Fullscreen API) ─────────────────────────
    //
    // iOS 16.4+ supports Element.requestFullscreen() on Safari.
    // Older versions ignore it silently; the fixed overlay still covers
    // the screen, so we degrade gracefully.
    this.requestNativeFullscreen();

    // ── 7. Listen for resize (orientation change, split-view, etc.) ────────
    window.addEventListener("resize", this.handleResize);

    // ── 8. Acquire Screen Wake Lock ────────────────────────────────────────
    //
    // Prevents iOS from dimming or auto-locking the screen.
    // Supported in Safari 16.4+; silently no-ops on older versions.
    // The lock is automatically released by the browser whenever the page
    // is hidden (e.g. user switches apps), so we re-acquire it on
    // visibilitychange.
    this.acquireWakeLock();
    document.addEventListener("visibilitychange", this.handleVisibilityChange);
  }

  // ─── Public API ───────────────────────────────────────────────────────────

  /**
   * Display `image` for exactly `durationMs` milliseconds, then go back to
   * black.  Returns a Promise that resolves when the black frame is shown.
   *
   * If called while a previous display() is still running, the previous one
   * is cancelled immediately (image removed, black shown) before the new
   * one starts.
   *
   * @param image       A fully-loaded HTMLImageElement.
   * @param durationMs  How long (in milliseconds) to show the image.
   */
  public display(image: HTMLImageElement, durationMs: number): Promise<void> {
    // Cancel any in-flight display.
    this.cancelCurrentDisplay();

    return new Promise<void>((resolve) => {
      this.displayResolve = resolve;

      // We capture the rAF timestamp on the very first paint frame to use
      // as the precise start time, avoiding any lag between Promise
      // construction and actual screen output.
      let startTime: number | null = null;

      const frame = (timestamp: DOMHighResTimeStamp): void => {
        // ── First frame: record start, draw image ────────────────────────
        if (startTime === null) {
          startTime = timestamp;
          this.paintImage(image);
        }

        const elapsed = timestamp - startTime;

        if (elapsed < durationMs) {
          // Still within the window – schedule next check.
          this.rafHandle = requestAnimationFrame(frame);
        } else {
          // Duration expired – go back to black and resolve.
          this.paintBlack();
          this.rafHandle = null;
          this.displayResolve = null;
          resolve();
        }
      };

      this.rafHandle = requestAnimationFrame(frame);
    });
  }

  /**
   * Manually cancel any active display() and return to black immediately.
   */
  public cancelCurrentDisplay(): void {
    if (this.rafHandle !== null) {
      cancelAnimationFrame(this.rafHandle);
      this.rafHandle = null;
    }

    if (this.displayResolve !== null) {
      this.paintBlack();
      const resolve = this.displayResolve;
      this.displayResolve = null;
      resolve();
    }
  }

  /**
   * Tear down the overlay and release all resources.
   * Cancels any running display() first.
   */
  public destroy(): void {
    this.cancelCurrentDisplay();
    window.removeEventListener("resize", this.handleResize);
    document.removeEventListener("visibilitychange", this.handleVisibilityChange);

    this.releaseWakeLock();

    if (document.fullscreenElement === this.overlay) {
      document.exitFullscreen().catch(() => {/* ignore */});
    }

    this.overlay.remove();
  }

  // ─── Private helpers ──────────────────────────────────────────────────────

  /** Fill the entire canvas with solid black. */
  private paintBlack(): void {
    // Reset transform before raw pixel fill to avoid double-scaling.
    this.ctx.save();
    this.ctx.setTransform(1, 0, 0, 1, 0, 0);
    this.ctx.fillStyle = "#000000";
    this.ctx.fillRect(0, 0, this.physicalWidth, this.physicalHeight);
    this.ctx.restore();
  }

  /**
   * Draw `image` scaled to fill the canvas while preserving aspect ratio
   * (object-fit: contain semantics, centred, letterboxed with black).
   */
  private paintImage(image: HTMLImageElement): void {
    const cssWidth = window.innerWidth;
    const cssHeight = window.innerHeight;

    const imgW = image.naturalWidth || image.width;
    const imgH = image.naturalHeight || image.height;

    if (imgW === 0 || imgH === 0) {
      // Malformed image – just show black.
      this.paintBlack();
      return;
    }

    const scale = Math.min(cssWidth / imgW, cssHeight / imgH);
    const drawW = imgW * scale;
    const drawH = imgH * scale;
    const drawX = (cssWidth - drawW) / 2;
    const drawY = (cssHeight - drawH) / 2;

    // Background black (letterbox / pillarbox areas).
    this.paintBlack();

    // The canvas context was scaled by DPR at construction, so all
    // drawImage coordinates here are in CSS pixels – which is exactly
    // what we want.
    this.ctx.drawImage(image, drawX, drawY, drawW, drawH);
  }

  /** Attempt the Web Fullscreen API; silently no-op if unavailable. */
  private requestNativeFullscreen(): void {
    const el = this.overlay as HTMLDivElement & {
      webkitRequestFullscreen?: () => Promise<void>;
    };

    if (typeof el.requestFullscreen === "function") {
      el.requestFullscreen({ navigationUI: "hide" }).catch(() => {/* ok */});
    } else if (typeof el.webkitRequestFullscreen === "function") {
      // Older Safari / WebKit prefix
      el.webkitRequestFullscreen();
    }
  }

  // ─── Wake Lock helpers ────────────────────────────────────────────────────

  /**
   * Request a 'screen' wake lock via the Screen Wake Lock API.
   * Fails silently if the API is unavailable or the request is rejected
   * (e.g. Low Power Mode on iOS).
   */
  private acquireWakeLock(): void {
    if (!("wakeLock" in navigator)) return;

    (navigator.wakeLock as WakeLock)
      .request("screen")
      .then((sentinel: WakeLockSentinel) => {
        this.wakeLock = sentinel;

        // If the sentinel is released externally (browser-initiated),
        // clear our reference so we know to re-acquire on next
        // visibilitychange.
        sentinel.addEventListener("release", () => {
          if (this.wakeLock === sentinel) {
            this.wakeLock = null;
          }
        });
      })
      .catch(() => {
        // Permission denied, Low Power Mode, or API unavailable – no-op.
      });
  }

  /** Release the active wake lock, if any. */
  private releaseWakeLock(): void {
    if (this.wakeLock !== null) {
      this.wakeLock.release().catch(() => {/* ignore */});
      this.wakeLock = null;
    }
  }

  /**
   * Re-acquire the wake lock when the page returns to the foreground.
   * iOS releases all wake locks the moment the page is hidden, so this
   * is required to keep the screen alive after the user briefly switches
   * away and comes back.
   *
   * Arrow function so `this` is correctly bound as an event listener.
   */
  private readonly handleVisibilityChange = (): void => {
    if (document.visibilityState === "visible") {
      this.acquireWakeLock();
    }
  };

  // ─── Resize helper ────────────────────────────────────────────────────────
  
  /**
   * Resizes the canvas backing store and repaints black.
   *
   * Arrow function so `this` is always bound correctly as an event listener.
   */
  private readonly handleResize = (): void => {
    const cssWidth = window.innerWidth;
    const cssHeight = window.innerHeight;
    const dpr = window.devicePixelRatio ?? 1;

    const newPhysW = Math.round(cssWidth * dpr);
    const newPhysH = Math.round(cssHeight * dpr);

    // Mutating readonly at runtime – use type assertion.
    (this as { physicalWidth: number }).physicalWidth = newPhysW;
    (this as { physicalHeight: number }).physicalHeight = newPhysH;

    this.canvas.width = newPhysW;
    this.canvas.height = newPhysH;
    this.canvas.style.width = `${cssWidth}px`;
    this.canvas.style.height = `${cssHeight}px`;

    // Re-apply the DPR scale after canvas resize (resizing resets transform).
    this.ctx.setTransform(1, 0, 0, 1, 0, 0);
    this.ctx.scale(dpr, dpr);

    this.paintBlack();
  };
}