/**
 * Encryption utilities for securing sensitive user data
 * Uses Web Crypto API with AES-GCM for authenticated encryption
 */

// Generate a key from a password using PBKDF2
async function deriveKey(password: string, salt: BufferSource): Promise<CryptoKey> {
  const encoder = new TextEncoder();
  const keyMaterial = await crypto.subtle.importKey(
    "raw",
    encoder.encode(password),
    "PBKDF2",
    false,
    ["deriveBits", "deriveKey"]
  );

  return crypto.subtle.deriveKey(
    {
      name: "PBKDF2",
      salt: salt,
      iterations: 100000,
      hash: "SHA-256",
    },
    keyMaterial,
    { name: "AES-GCM", length: 256 },
    false,
    ["encrypt", "decrypt"]
  );
}

// Get or create encryption key from localStorage
async function getEncryptionKey(): Promise<CryptoKey> {
  const STORAGE_KEY = "encryption_salt";
  const PASSWORD_KEY = "encryption_password";
  
  // Generate a unique password based on user's browser fingerprint
  // This creates a consistent key per browser/device
  const getBrowserFingerprint = (): string => {
    try {
      const canvas = document.createElement("canvas");
      const ctx = canvas.getContext("2d");
      if (ctx) {
        ctx.textBaseline = "top";
        ctx.font = "14px 'Arial'";
        ctx.textBaseline = "alphabetic";
        ctx.fillStyle = "#f60";
        ctx.fillRect(125, 1, 62, 20);
        ctx.fillStyle = "#069";
        ctx.fillText("Browser fingerprint", 2, 15);
        ctx.fillStyle = "rgba(102, 204, 0, 0.7)";
        ctx.fillText("Browser fingerprint", 4, 17);
      }
      const fingerprint = (canvas.toDataURL() || "") + 
        (navigator.userAgent || "") + 
        (navigator.language || "") + 
        (screen.width || 0) + 
        (screen.height || 0) + 
        (new Date().getTimezoneOffset() || 0);
      return fingerprint;
    } catch (error) {
      // Fallback if canvas fingerprinting fails
      return (navigator.userAgent || "") + 
        (navigator.language || "") + 
        (screen.width || 0) + 
        (screen.height || 0);
    }
  };

  let salt = localStorage.getItem(STORAGE_KEY);
  let password = localStorage.getItem(PASSWORD_KEY);

  if (!salt || !password) {
    // Generate new salt and password
    const saltBytes = crypto.getRandomValues(new Uint8Array(16));
    salt = Array.from(saltBytes)
      .map(b => b.toString(16).padStart(2, "0"))
      .join("");
    
    password = getBrowserFingerprint();
    
    localStorage.setItem(STORAGE_KEY, salt);
    localStorage.setItem(PASSWORD_KEY, password);
  }

  // Convert hex string back to Uint8Array
  const saltBytes = salt.match(/.{1,2}/g)?.map(byte => parseInt(byte, 16)) || [];
  const saltArray = new Uint8Array(saltBytes);

  return deriveKey(password, saltArray);
}

// Encrypt a string value
export async function encryptValue(value: string): Promise<string> {
  if (!value || typeof window === "undefined") return value;
  
  try {
    const key = await getEncryptionKey();
    const encoder = new TextEncoder();
    const data = encoder.encode(value);
    
    // Generate a random IV for each encryption
    const iv = crypto.getRandomValues(new Uint8Array(12));
    
    const encrypted = await crypto.subtle.encrypt(
      {
        name: "AES-GCM",
        iv: iv,
      },
      key,
      data
    );

    // Combine IV and encrypted data
    const combined = new Uint8Array(iv.length + encrypted.byteLength);
    combined.set(iv);
    combined.set(new Uint8Array(encrypted), iv.length);

    // Convert to base64 for storage
    const binaryString = String.fromCharCode(...combined);
    return btoa(binaryString);
  } catch (error) {
    // If encryption fails, return original value (graceful degradation)
    return value;
  }
}

// Decrypt a string value
export async function decryptValue(encryptedValue: string): Promise<string> {
  if (!encryptedValue || typeof window === "undefined") return encryptedValue;
  
  try {
    const key = await getEncryptionKey();
    
    // Decode from base64
    const binaryString = atob(encryptedValue);
    const combined = Uint8Array.from(binaryString, c => c.charCodeAt(0));
    
    // Extract IV and encrypted data
    const iv = combined.slice(0, 12);
    const encrypted = combined.slice(12);
    
    const decrypted = await crypto.subtle.decrypt(
      {
        name: "AES-GCM",
        iv: iv,
      },
      key,
      encrypted
    );

    const decoder = new TextDecoder();
    return decoder.decode(decrypted);
  } catch (error) {
    // If decryption fails, try to return as-is (might be unencrypted legacy data)
    return encryptedValue;
  }
}

// Encrypt sensitive fields in a user object
export async function encryptUserData(user: any): Promise<any> {
  if (!user || typeof window === "undefined") return user;
  
  const encrypted = { ...user };
  
  // Encrypt sensitive fields
  const sensitiveFields = ["first_name", "last_name", "phone_number", "email"];
  
  for (const field of sensitiveFields) {
    if (encrypted[field]) {
      encrypted[field] = await encryptValue(String(encrypted[field]));
    }
  }
  
  return encrypted;
}

// Decrypt sensitive fields in a user object
export async function decryptUserData(user: any): Promise<any> {
  if (!user || typeof window === "undefined") return user;
  
  const decrypted = { ...user };
  
  // Decrypt sensitive fields
  const sensitiveFields = ["first_name", "last_name", "phone_number", "email"];
  
  for (const field of sensitiveFields) {
    if (decrypted[field]) {
      try {
        decrypted[field] = await decryptValue(String(decrypted[field]));
      } catch (error) {
        // If decryption fails, keep original value (might be unencrypted)
      }
    }
  }
  
  return decrypted;
}

// Check if a value is encrypted (heuristic check)
function isEncrypted(value: string): boolean {
  // Encrypted values are base64 encoded and have a specific structure
  // This is a simple heuristic - encrypted values will be longer and base64-like
  if (!value || value.length < 20) return false;
  
  try {
    // Try to decode as base64
    atob(value);
    // If it decodes successfully and is long enough, it's likely encrypted
    return value.length > 30;
  } catch {
    return false;
  }
}

// Smart encrypt/decrypt that handles both encrypted and unencrypted data
export async function smartDecryptUserData(user: any): Promise<any> {
  if (!user || typeof window === "undefined") return user;
  
  const decrypted = { ...user };
  const sensitiveFields = ["first_name", "last_name", "phone_number", "email"];
  
  for (const field of sensitiveFields) {
    if (decrypted[field] && typeof decrypted[field] === "string") {
      if (isEncrypted(decrypted[field])) {
        try {
          decrypted[field] = await decryptValue(decrypted[field]);
        } catch (error) {
          // Failed to decrypt field, keep original value
        }
      }
      // If not encrypted, keep as-is (backward compatibility)
    }
  }
  
  return decrypted;
}