/** 화면 캡처 영역 → 업로드용 PNG File */

export interface ScreenCaptureRect {
  left: number;
  top: number;
  width: number;
  height: number;
}

export function clientRectToVideoPixels(
  rect: ScreenCaptureRect,
  videoEl: HTMLVideoElement,
): ScreenCaptureRect | null {
  const bounds = videoEl.getBoundingClientRect();
  if (bounds.width <= 0 || bounds.height <= 0) return null;
  const vw = videoEl.videoWidth;
  const vh = videoEl.videoHeight;
  if (vw <= 0 || vh <= 0) return null;

  const toVidX = (cx: number) => ((cx - bounds.left) / bounds.width) * vw;
  const toVidY = (cy: number) => ((cy - bounds.top) / bounds.height) * vh;

  const x1 = Math.max(0, Math.min(vw, Math.round(toVidX(rect.left))));
  const y1 = Math.max(0, Math.min(vh, Math.round(toVidY(rect.top))));
  const x2 = Math.max(0, Math.min(vw, Math.round(toVidX(rect.left + rect.width))));
  const y2 = Math.max(0, Math.min(vh, Math.round(toVidY(rect.top + rect.height))));

  const width = x2 - x1;
  const height = y2 - y1;
  if (width < 2 || height < 2) return null;

  return { left: x1, top: y1, width, height };
}

export async function cropVideoFrameToFile(
  videoEl: HTMLVideoElement,
  rect: ScreenCaptureRect,
): Promise<File> {
  const canvas = document.createElement('canvas');
  canvas.width = rect.width;
  canvas.height = rect.height;
  const ctx = canvas.getContext('2d');
  if (!ctx) throw new Error('CANVAS_FAILED');

  ctx.drawImage(
    videoEl,
    rect.left,
    rect.top,
    rect.width,
    rect.height,
    0,
    0,
    rect.width,
    rect.height,
  );

  const blob = await new Promise<Blob | null>(resolve => {
    canvas.toBlob(resolve, 'image/png');
  });
  if (!blob) throw new Error('BLOB_FAILED');

  return new File([blob], `screen-capture-${Date.now()}.png`, {
    type: 'image/png',
    lastModified: Date.now(),
  });
}

export async function requestDisplayCaptureStream(): Promise<MediaStream> {
  if (!navigator.mediaDevices?.getDisplayMedia) {
    throw new Error('DISPLAY_CAPTURE_UNSUPPORTED');
  }
  return navigator.mediaDevices.getDisplayMedia({
    video: { displaySurface: 'browser' } as MediaTrackConstraints,
    audio: false,
  });
}

export function stopMediaStream(stream: MediaStream | null): void {
  stream?.getTracks().forEach(t => t.stop());
}

export function captureErrorMessage(e: unknown): string {
  if (e instanceof Error) {
    if (e.name === 'NotAllowedError' || e.message === 'DISPLAY_CAPTURE_UNSUPPORTED') {
      return '화면 캡처 권한이 거부되었거나 이 브라우저에서 지원하지 않습니다.';
    }
    if (e.message === 'REGION_TOO_SMALL') {
      return '선택 영역이 너무 작습니다. 다시 드래그해 주세요.';
    }
    if (e.message) return e.message;
  }
  return '화면 캡처에 실패했습니다.';
}