// --- CIDR Calculation Core Engine ---

/**
 * Converts IP dotted decimal string to 32-bit unsigned integer.
 */
function ipToInt(ip) {
  return ip.split('.').reduce((acc, octet) => (acc << 8) + parseInt(octet, 10), 0) >>> 0;
}

/**
 * Converts 32-bit unsigned integer to IP dotted decimal string.
 */
function intToIp(int) {
  return [
    (int >>> 24) & 255,
    (int >>> 16) & 255,
    (int >>> 8) & 255,
    int & 255
  ].join('.');
}

/**
 * Checks if the IP is in private ranges:
 * - 10.0.0.0/8
 * - 172.16.0.0/12
 * - 192.168.0.0/16
 * - 127.0.0.0/8 (Loopback is technically not private in the RFC 1918 sense, but we can treat as private/internal)
 */
function checkPrivate(ipInt) {
  const o1 = (ipInt >>> 24) & 255;
  const o2 = (ipInt >>> 16) & 255;
  if (o1 === 10) return true;
  if (o1 === 172 && o2 >= 16 && o2 <= 31) return true;
  if (o1 === 192 && o2 === 168) return true;
  if (o1 === 127) return true;
  return false;
}

/**
 * Determines class of IP based on first octet.
 */
function getIpClass(ipInt) {
  const o1 = (ipInt >>> 24) & 255;
  if (o1 >= 0 && o1 <= 127) return 'Class A';
  if (o1 >= 128 && o1 <= 191) return 'Class B';
  if (o1 >= 192 && o1 <= 223) return 'Class C';
  if (o1 >= 224 && o1 <= 239) return 'Class D (Multicast)';
  return 'Class E (Experimental)';
}

/**
 * Parses and validates an IPv4 CIDR string.
 */
function parseCIDR(cidrStr) {
  const clean = cidrStr.trim();
  const parts = clean.split('/');
  
  if (parts.length > 2) return null;

  const ipPart = parts[0];
  const prefixPart = parts[1];

  // Validate IP format
  const ipRegex = /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/;
  const match = ipPart.match(ipRegex);
  if (!match) return null;

  for (let i = 1; i <= 4; i++) {
    const val = parseInt(match[i], 10);
    if (val < 0 || val > 255) return null;
    // Prevent leading zero issues like 192.168.01.1
    if (match[i].length > 1 && match[i].startsWith('0')) return null;
  }

  let prefix = 24;
  if (prefixPart !== undefined) {
    if (!/^\d+$/.test(prefixPart)) return null;
    prefix = parseInt(prefixPart, 10);
    if (prefix < 0 || prefix > 32) return null;
  }

  return { ip: ipPart, prefix };
}

/**
 * Runs calculations on valid input.
 */
function calculateCIDR(ip, prefix) {
  const ipVal = ipToInt(ip);
  const maskVal = (prefix === 0 ? 0 : (~0 << (32 - prefix))) >>> 0;
  const networkVal = (ipVal & maskVal) >>> 0;
  const broadcastVal = (networkVal | ~maskVal) >>> 0;

  let usableHosts = 0;
  let firstHostVal = 0;
  let lastHostVal = 0;

  if (prefix === 32) {
    usableHosts = 1;
    firstHostVal = networkVal;
    lastHostVal = networkVal;
  } else if (prefix === 31) {
    usableHosts = 2; // RFC 3021
    firstHostVal = networkVal;
    lastHostVal = broadcastVal;
  } else {
    usableHosts = Math.max(0, (broadcastVal - networkVal) - 1);
    firstHostVal = networkVal + 1;
    lastHostVal = broadcastVal - 1;
  }

  const wildcardVal = (~maskVal) >>> 0;

  return {
    cidrNotation: `${intToIp(networkVal)}/${prefix}`,
    networkAddress: intToIp(networkVal),
    broadcastAddress: intToIp(broadcastVal),
    subnetMask: intToIp(maskVal),
    wildcardMask: intToIp(wildcardVal),
    usableHosts: usableHosts.toLocaleString(),
    hostRange: usableHosts > 0 ? `${intToIp(firstHostVal)} – ${intToIp(lastHostVal)}` : 'N/A',
    ipClass: getIpClass(ipVal),
    isPrivate: checkPrivate(ipVal) ? 'Private (RFC 1918)' : 'Public'
  };
}


// --- UI and Controller Layer ---

document.addEventListener('DOMContentLoaded', () => {
  const cidrInput = document.getElementById('cidr-input');
  const prefixDropdown = document.getElementById('prefix-dropdown');
  const errorMsg = document.getElementById('error-msg');
  const resultsContainer = document.getElementById('results');

  // Value DOM fields
  const outCidr = document.getElementById('out-cidr');
  const outNetwork = document.getElementById('out-network');
  const outBroadcast = document.getElementById('out-broadcast');
  const outMask = document.getElementById('out-mask');
  const outRange = document.getElementById('out-range');
  const outHosts = document.getElementById('out-hosts');
  const outClass = document.getElementById('out-class');
  const outType = document.getElementById('out-type');

  // Setup dropdown options (0 to 32)
  for (let i = 0; i <= 32; i++) {
    const opt = document.createElement('option');
    opt.value = i;
    opt.textContent = `/${i}`;
    if (i === 24) opt.selected = true;
    prefixDropdown.appendChild(opt);
  }

  // Live calculation function
  function update() {
    let rawVal = cidrInput.value.trim();
    if (!rawVal) {
      clearResults();
      hideError();
      return;
    }

    // Auto-sync prefix dropdown if typed/pasted with a slash, then clean the input field to show only the IP
    if (rawVal.includes('/')) {
      const parts = rawVal.split('/');
      const ipPart = parts[0].trim();
      const prefixPart = parts[1].trim();
      if (/^\d+$/.test(prefixPart)) {
        const prefixVal = parseInt(prefixPart, 10);
        if (prefixVal >= 0 && prefixVal <= 32) {
          prefixDropdown.value = prefixVal;
        }
      }
      cidrInput.value = ipPart;
      rawVal = ipPart;
    }

    // Validate IP format
    const ipRegex = /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/;
    const match = rawVal.match(ipRegex);
    let isValidIp = true;
    if (!match) {
      isValidIp = false;
    } else {
      for (let i = 1; i <= 4; i++) {
        const val = parseInt(match[i], 10);
        if (val < 0 || val > 255) isValidIp = false;
        if (match[i].length > 1 && match[i].startsWith('0')) isValidIp = false;
      }
    }

    if (!isValidIp) {
      showError('Invalid IPv4 address. Use format: e.g. 192.168.0.1');
      clearResults();
      return;
    }

    hideError();

    const prefix = parseInt(prefixDropdown.value, 10);
    const results = calculateCIDR(rawVal, prefix);
    displayResults(results);
  }

  function displayResults(data) {
    outCidr.textContent = data.cidrNotation;
    outNetwork.textContent = data.networkAddress;
    outBroadcast.textContent = data.broadcastAddress;
    outMask.textContent = data.subnetMask;
    outRange.textContent = data.hostRange;
    outHosts.textContent = data.usableHosts;
    outClass.textContent = data.ipClass;
    outType.textContent = data.isPrivate;
    resultsContainer.classList.add('visible');
  }

  function clearResults() {
    resultsContainer.classList.remove('visible');
  }

  function showError(msg) {
    cidrInput.classList.add('input-error');
    errorMsg.textContent = msg;
    errorMsg.classList.add('visible');
  }

  function hideError() {
    cidrInput.classList.remove('input-error');
    errorMsg.classList.remove('visible');
  }

  // Listeners
  cidrInput.addEventListener('input', update);

  prefixDropdown.addEventListener('change', update);

  // Copy to Clipboard
  document.querySelectorAll('.copy-btn').forEach(btn => {
    btn.addEventListener('click', () => {
      const targetId = btn.getAttribute('data-target');
      const targetEl = document.getElementById(targetId);
      if (!targetEl) return;
      
      const text = targetEl.textContent;
      navigator.clipboard.writeText(text).then(() => {
        btn.classList.add('copied');
        setTimeout(() => {
          btn.classList.remove('copied');
        }, 1500);
      });
    });
  });

  // --- Theme Toggle FAB Controller ---
  const themeToggle = document.getElementById('theme-toggle');
  const themeIcon = document.getElementById('theme-icon');
  const themes = ['system', 'light', 'dark'];
  let currentThemeIndex = 0; // Default to 'system'

  function applyTheme(theme) {
    document.documentElement.removeAttribute('data-theme');
    
    if (theme === 'system') {
      const isDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
      document.documentElement.setAttribute('data-theme', isDark ? 'dark' : 'light');
      themeIcon.innerHTML = `<path d="M4 2h16a2 2 0 0 1 2 2v12a2 2 0 0 1-2 2H4a2 2 0 0 1-2-2V4a2 2 0 0 1 2-2zm0 2v10h16V4H4zm4 16h8v2H8v-2z" fill="currentColor"/>`; // Monitor icon
    } else if (theme === 'light') {
      document.documentElement.setAttribute('data-theme', 'light');
      themeIcon.innerHTML = `<circle cx="12" cy="12" r="5" fill="none" stroke="currentColor" stroke-width="2"/><path d="M12 1v2M12 21v2M4.22 4.22l1.42 1.42M18.36 18.36l1.42 1.42M1 12h2M21 12h2M4.22 19.78l1.42-1.42M18.36 5.64l1.42-1.42" stroke="currentColor" stroke-width="2" stroke-linecap="round"/>`; // Sun icon
    } else if (theme === 'dark') {
      document.documentElement.setAttribute('data-theme', 'dark');
      themeIcon.innerHTML = `<path d="M21 12.79A9 9 0 1 1 11.21 3 7 7 0 0 0 21 12.79z" fill="currentColor"/>`; // Moon icon
    }
  }

  // Handle system preference change dynamically if system theme is selected
  window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
    if (themes[currentThemeIndex] === 'system') {
      applyTheme('system');
    }
  });

  themeToggle.addEventListener('click', () => {
    currentThemeIndex = (currentThemeIndex + 1) % themes.length;
    applyTheme(themes[currentThemeIndex]);
  });

  // Init theme and calculation
  applyTheme('system');
  update();
});

// --- PWA Service Worker Registration ---
if ('serviceWorker' in navigator) {
  window.addEventListener('load', () => {
    navigator.serviceWorker.register('./sw.js')
      .then(reg => console.log('Service worker registered successfully', reg.scope))
      .catch(err => console.error('Service worker registration failed', err));
  });
}