const video = document.getElementById('video');
const previewCanvas = document.getElementById('preview-canvas');
const previewImg = document.getElementById('preview-img');
const captureCanvas = document.getElementById('capture-canvas');
const cameraStatus = document.getElementById('camera-status');
const studentNumberInput = document.getElementById('student-number');
const inputError = document.getElementById('input-error');
const captureBtn = document.getElementById('capture-btn');
const downloadLink = document.getElementById('download-link');
const zoomControl = document.getElementById('zoom-control');
const zoomValue = document.getElementById('zoom-value');
const panXControl = document.getElementById('pan-x-control');
const panYControl = document.getElementById('pan-y-control');
const focusControls = document.getElementById('focus-controls');
const focusUnsupported = document.getElementById('focus-unsupported');
const focusAutoBtn = document.getElementById('focus-auto-btn');
const focusManualBtn = document.getElementById('focus-manual-btn');
const focusControl = document.getElementById('focus-control');

const OUTPUT_WIDTH = 145;
const OUTPUT_HEIGHT = 185;
const TARGET_RATIO = OUTPUT_WIDTH / OUTPUT_HEIGHT;
const PREVIEW_SCALE = 3;

let captured = false;
let previewLoopId = null;
let videoTrack = null;

function computeCropRect(videoWidth, videoHeight, zoom, panX, panY) {
  const videoRatio = videoWidth / videoHeight;
  let baseSw, baseSh;

  if (videoRatio > TARGET_RATIO) {
    baseSh = videoHeight;
    baseSw = baseSh * TARGET_RATIO;
  } else {
    baseSw = videoWidth;
    baseSh = baseSw / TARGET_RATIO;
  }

  const sw = baseSw / zoom;
  const sh = baseSh / zoom;
  const maxOffsetX = (videoWidth - sw) / 2;
  const maxOffsetY = (videoHeight - sh) / 2;

  const cx = videoWidth / 2 + panX * maxOffsetX;
  const cy = videoHeight / 2 + panY * maxOffsetY;

  return { sx: cx - sw / 2, sy: cy - sh / 2, sw, sh };
}

function currentCropRect() {
  return computeCropRect(
    video.videoWidth,
    video.videoHeight,
    parseFloat(zoomControl.value),
    parseFloat(panXControl.value),
    parseFloat(panYControl.value)
  );
}

function renderPreviewFrame() {
  if (!captured && video.videoWidth) {
    const { sx, sy, sw, sh } = currentCropRect();
    const ctx = previewCanvas.getContext('2d');
    ctx.save();
    ctx.translate(previewCanvas.width, 0);
    ctx.scale(-1, 1);
    ctx.drawImage(video, sx, sy, sw, sh, 0, 0, previewCanvas.width, previewCanvas.height);
    ctx.restore();
  }
  previewLoopId = requestAnimationFrame(renderPreviewFrame);
}

async function startCamera() {
  try {
    const stream = await navigator.mediaDevices.getUserMedia({ video: true, audio: false });
    video.srcObject = stream;
    videoTrack = stream.getVideoTracks()[0];

    await new Promise((resolve) => video.addEventListener('loadedmetadata', resolve, { once: true }));

    previewCanvas.width = OUTPUT_WIDTH * PREVIEW_SCALE;
    previewCanvas.height = OUTPUT_HEIGHT * PREVIEW_SCALE;

    cameraStatus.classList.add('hidden');
    captureBtn.disabled = false;
    renderPreviewFrame();
    setupFocusControls(videoTrack);
  } catch (err) {
    cameraStatus.textContent = 'Unable to access camera: ' + err.message;
  }
}

function setupFocusControls(track) {
  if (!track.getCapabilities) {
    focusUnsupported.classList.remove('hidden');
    return;
  }

  const capabilities = track.getCapabilities();
  if (!capabilities.focusDistance || !capabilities.focusMode) {
    focusUnsupported.classList.remove('hidden');
    return;
  }

  focusControls.classList.remove('hidden');
  focusControl.min = capabilities.focusDistance.min;
  focusControl.max = capabilities.focusDistance.max;
  focusControl.step = capabilities.focusDistance.step || 0.01;
  focusControl.value = capabilities.focusDistance.min;

  const supportsAuto = capabilities.focusMode.includes('continuous');
  focusAutoBtn.disabled = !supportsAuto;
  if (!supportsAuto) focusAutoBtn.classList.add('opacity-50', 'cursor-not-allowed');

  function setActiveButton(manual) {
    focusManualBtn.classList.toggle('bg-blue-600', manual);
    focusManualBtn.classList.toggle('text-white', manual);
    focusManualBtn.classList.toggle('bg-white', !manual);
    focusManualBtn.classList.toggle('dark:bg-gray-700', !manual);
    focusManualBtn.classList.toggle('text-gray-700', !manual);
    focusManualBtn.classList.toggle('dark:text-gray-200', !manual);

    focusAutoBtn.classList.toggle('bg-blue-600', !manual);
    focusAutoBtn.classList.toggle('text-white', !manual);
    focusAutoBtn.classList.toggle('bg-white', manual);
    focusAutoBtn.classList.toggle('dark:bg-gray-700', manual);
    focusAutoBtn.classList.toggle('text-gray-700', manual);
    focusAutoBtn.classList.toggle('dark:text-gray-200', manual);
  }

  focusAutoBtn.addEventListener('click', async () => {
    if (!supportsAuto) return;
    try {
      await track.applyConstraints({ advanced: [{ focusMode: 'continuous' }] });
      focusControl.classList.add('hidden');
      setActiveButton(false);
    } catch (err) {
      focusUnsupported.textContent = 'Unable to switch to autofocus: ' + err.message;
      focusUnsupported.classList.remove('hidden');
    }
  });

  focusManualBtn.addEventListener('click', async () => {
    try {
      await track.applyConstraints({ advanced: [{ focusMode: 'manual', focusDistance: parseFloat(focusControl.value) }] });
      focusControl.classList.remove('hidden');
      setActiveButton(true);
    } catch (err) {
      focusUnsupported.textContent = 'Unable to switch to manual focus: ' + err.message;
      focusUnsupported.classList.remove('hidden');
    }
  });

  focusControl.addEventListener('input', async () => {
    try {
      await track.applyConstraints({ advanced: [{ focusMode: 'manual', focusDistance: parseFloat(focusControl.value) }] });
    } catch (err) {
      /* ignore live-drag failures; the constraint is retried on the next input event */
    }
  });
}

function sanitizeFilename(name) {
  return name.trim().replace(/[^a-z0-9_-]+/gi, '_');
}

function showLiveView() {
  previewImg.classList.add('hidden');
  previewCanvas.classList.remove('hidden');
  downloadLink.classList.add('hidden');
  captureBtn.textContent = 'Capture Photo';
  captured = false;
}

function showCapturedView() {
  previewCanvas.classList.add('hidden');
  previewImg.classList.remove('hidden');
  captureBtn.textContent = 'Retake Photo';
  captured = true;
}

function capturePhoto() {
  if (captured) {
    showLiveView();
    return;
  }

  const studentNumber = studentNumberInput.value.trim();
  if (!studentNumber) {
    inputError.classList.remove('hidden');
    studentNumberInput.focus();
    return;
  }
  inputError.classList.add('hidden');

  const { sx, sy, sw, sh } = currentCropRect();

  captureCanvas.width = OUTPUT_WIDTH;
  captureCanvas.height = OUTPUT_HEIGHT;
  const ctx = captureCanvas.getContext('2d');
  ctx.drawImage(video, sx, sy, sw, sh, 0, 0, OUTPUT_WIDTH, OUTPUT_HEIGHT);

  const dataUrl = captureCanvas.toDataURL('image/png');
  const filename = `${sanitizeFilename(studentNumber)}.png`;

  previewImg.src = dataUrl;
  downloadLink.href = dataUrl;
  downloadLink.download = filename;
  downloadLink.classList.remove('hidden');

  showCapturedView();

  downloadLink.click();
}

zoomControl.addEventListener('input', () => {
  zoomValue.textContent = `${parseFloat(zoomControl.value).toFixed(2)}x`;
});

captureBtn.addEventListener('click', capturePhoto);

studentNumberInput.addEventListener('keydown', (event) => {
  if (event.key === 'Enter') {
    event.preventDefault();
    capturePhoto();
  }
});

startCamera();