/**
 * Crypto utilities for stateless peer authentication
 * Uses Web Crypto API for compatibility with both Node.js and Cloudflare Workers
 * Uses @noble/ed25519 for Ed25519 signature verification
 */

import * as ed25519 from '@noble/ed25519';

// Set SHA-512 hash function for ed25519 (required in @noble/ed25519 v3+)
// Uses Web Crypto API (compatible with both Node.js and Cloudflare Workers)
ed25519.hashes.sha512Async = async (message: Uint8Array) => {
  return new Uint8Array(await crypto.subtle.digest('SHA-512', message as BufferSource));
};

const ALGORITHM = 'AES-GCM';
const IV_LENGTH = 12; // 96 bits for GCM
const KEY_LENGTH = 32; // 256 bits

// Username validation
const USERNAME_REGEX = /^[a-z0-9][a-z0-9-]*[a-z0-9]$/;
const USERNAME_MIN_LENGTH = 3;
const USERNAME_MAX_LENGTH = 32;

// Timestamp validation (5 minutes tolerance)
const TIMESTAMP_TOLERANCE_MS = 5 * 60 * 1000;

/**
 * Generates a random peer ID (16 bytes = 32 hex chars)
 */
export function generatePeerId(): string {
  const bytes = crypto.getRandomValues(new Uint8Array(16));
  return Array.from(bytes).map(b => b.toString(16).padStart(2, '0')).join('');
}

/**
 * Generates a random secret key for encryption (32 bytes = 64 hex chars)
 */
export function generateSecretKey(): string {
  const bytes = crypto.getRandomValues(new Uint8Array(KEY_LENGTH));
  return Array.from(bytes).map(b => b.toString(16).padStart(2, '0')).join('');
}

/**
 * Convert hex string to Uint8Array
 */
function hexToBytes(hex: string): Uint8Array {
  const bytes = new Uint8Array(hex.length / 2);
  for (let i = 0; i < hex.length; i += 2) {
    bytes[i / 2] = parseInt(hex.substring(i, i + 2), 16);
  }
  return bytes;
}

/**
 * Convert Uint8Array to base64 string
 */
function bytesToBase64(bytes: Uint8Array): string {
  const binString = Array.from(bytes, (byte) =>
    String.fromCodePoint(byte)
  ).join('');
  return btoa(binString);
}

/**
 * Convert base64 string to Uint8Array
 */
function base64ToBytes(base64: string): Uint8Array {
  const binString = atob(base64);
  return Uint8Array.from(binString, (char) => char.codePointAt(0)!);
}

/**
 * Encrypts a peer ID using the server secret key
 * Returns base64-encoded encrypted data (IV + ciphertext)
 */
export async function encryptPeerId(peerId: string, secretKeyHex: string): Promise<string> {
  const keyBytes = hexToBytes(secretKeyHex);

  if (keyBytes.length !== KEY_LENGTH) {
    throw new Error(`Secret key must be ${KEY_LENGTH * 2} hex characters (${KEY_LENGTH} bytes)`);
  }

  // Import key
  const key = await crypto.subtle.importKey(
    'raw',
    keyBytes,
    { name: ALGORITHM, length: 256 },
    false,
    ['encrypt']
  );

  // Generate random IV
  const iv = crypto.getRandomValues(new Uint8Array(IV_LENGTH));

  // Encrypt peer ID
  const encoder = new TextEncoder();
  const data = encoder.encode(peerId);

  const encrypted = await crypto.subtle.encrypt(
    { name: ALGORITHM, iv },
    key,
    data
  );

  // Combine IV + ciphertext and encode as base64
  const combined = new Uint8Array(iv.length + encrypted.byteLength);
  combined.set(iv, 0);
  combined.set(new Uint8Array(encrypted), iv.length);

  return bytesToBase64(combined);
}

/**
 * Decrypts an encrypted peer ID secret
 * Returns the plaintext peer ID or throws if decryption fails
 */
export async function decryptPeerId(encryptedSecret: string, secretKeyHex: string): Promise<string> {
  try {
    const keyBytes = hexToBytes(secretKeyHex);

    if (keyBytes.length !== KEY_LENGTH) {
      throw new Error(`Secret key must be ${KEY_LENGTH * 2} hex characters (${KEY_LENGTH} bytes)`);
    }

    // Decode base64
    const combined = base64ToBytes(encryptedSecret);

    // Extract IV and ciphertext
    const iv = combined.slice(0, IV_LENGTH);
    const ciphertext = combined.slice(IV_LENGTH);

    // Import key
    const key = await crypto.subtle.importKey(
      'raw',
      keyBytes,
      { name: ALGORITHM, length: 256 },
      false,
      ['decrypt']
    );

    // Decrypt
    const decrypted = await crypto.subtle.decrypt(
      { name: ALGORITHM, iv },
      key,
      ciphertext
    );

    const decoder = new TextDecoder();
    return decoder.decode(decrypted);
  } catch (err) {
    throw new Error('Failed to decrypt peer ID: invalid secret or secret key');
  }
}

/**
 * Validates that a peer ID and secret match
 * Returns true if valid, false otherwise
 */
export async function validateCredentials(peerId: string, encryptedSecret: string, secretKey: string): Promise<boolean> {
  try {
    const decryptedPeerId = await decryptPeerId(encryptedSecret, secretKey);
    return decryptedPeerId === peerId;
  } catch {
    return false;
  }
}

// ===== Username and Ed25519 Signature Utilities =====

/**
 * Validates username format
 * Rules: 3-32 chars, lowercase alphanumeric + dash, must start/end with alphanumeric
 */
export function validateUsername(username: string): { valid: boolean; error?: string } {
  if (typeof username !== 'string') {
    return { valid: false, error: 'Username must be a string' };
  }

  if (username.length < USERNAME_MIN_LENGTH) {
    return { valid: false, error: `Username must be at least ${USERNAME_MIN_LENGTH} characters` };
  }

  if (username.length > USERNAME_MAX_LENGTH) {
    return { valid: false, error: `Username must be at most ${USERNAME_MAX_LENGTH} characters` };
  }

  if (!USERNAME_REGEX.test(username)) {
    return { valid: false, error: 'Username must be lowercase alphanumeric with optional dashes, and start/end with alphanumeric' };
  }

  return { valid: true };
}

/**
 * Validates service FQN format (service:version@username or service:version)
 * Service name: lowercase alphanumeric with dots/dashes (e.g., chat, file-share, com.example.chat)
 * Version: semantic versioning (1.0.0, 2.1.3-beta, etc.)
 * Username: optional, lowercase alphanumeric with dashes
 */
export function validateServiceFqn(fqn: string): { valid: boolean; error?: string } {
  if (typeof fqn !== 'string') {
    return { valid: false, error: 'Service FQN must be a string' };
  }

  // Parse the FQN
  const parsed = parseServiceFqn(fqn);
  if (!parsed) {
    return { valid: false, error: 'Service FQN must be in format: service:version[@username]' };
  }

  const { serviceName, version, username } = parsed;

  // Validate service name (alphanumeric with dots/dashes)
  const serviceNameRegex = /^[a-z0-9]([a-z0-9.-]*[a-z0-9])?$/;
  if (!serviceNameRegex.test(serviceName)) {
    return { valid: false, error: 'Service name must be lowercase alphanumeric with optional dots/dashes' };
  }

  if (serviceName.length < 1 || serviceName.length > 128) {
    return { valid: false, error: 'Service name must be 1-128 characters' };
  }

  // Validate version (semantic versioning)
  const versionRegex = /^[0-9]+\.[0-9]+\.[0-9]+(-[a-z0-9.-]+)?$/;
  if (!versionRegex.test(version)) {
    return { valid: false, error: 'Version must be semantic versioning (e.g., 1.0.0, 2.1.3-beta)' };
  }

  // Validate username if present
  if (username) {
    const usernameCheck = validateUsername(username);
    if (!usernameCheck.valid) {
      return usernameCheck;
    }
  }

  return { valid: true };
}

/**
 * Parse semantic version string into components
 */
export function parseVersion(version: string): { major: number; minor: number; patch: number; prerelease?: string } | null {
  const match = version.match(/^([0-9]+)\.([0-9]+)\.([0-9]+)(-[a-z0-9.-]+)?$/);
  if (!match) return null;

  return {
    major: parseInt(match[1], 10),
    minor: parseInt(match[2], 10),
    patch: parseInt(match[3], 10),
    prerelease: match[4]?.substring(1), // Remove leading dash
  };
}

/**
 * Check if two versions are compatible (same major version)
 * Following semver rules: ^1.0.0 matches 1.x.x but not 2.x.x
 */
export function isVersionCompatible(requested: string, available: string): boolean {
  const req = parseVersion(requested);
  const avail = parseVersion(available);

  if (!req || !avail) return false;

  // Major version must match
  if (req.major !== avail.major) return false;

  // If major is 0, minor must also match (0.x.y is unstable)
  if (req.major === 0 && req.minor !== avail.minor) return false;

  // Available version must be >= requested version
  if (avail.minor < req.minor) return false;
  if (avail.minor === req.minor && avail.patch < req.patch) return false;

  // Prerelease versions are only compatible with exact matches
  if (req.prerelease && req.prerelease !== avail.prerelease) return false;

  return true;
}

/**
 * Parse service FQN into components
 * Formats supported:
 * - service:version@username (e.g., "chat:1.0.0@alice")
 * - service:version (e.g., "chat:1.0.0") for discovery
 */
export function parseServiceFqn(fqn: string): { serviceName: string; version: string; username: string | null } | null {
  if (!fqn || typeof fqn !== 'string') return null;

  // Check if username is present
  const atIndex = fqn.lastIndexOf('@');
  let serviceVersion: string;
  let username: string | null = null;

  if (atIndex > 0) {
    // Format: service:version@username
    serviceVersion = fqn.substring(0, atIndex);
    username = fqn.substring(atIndex + 1);
  } else {
    // Format: service:version (no username)
    serviceVersion = fqn;
  }

  // Split service:version
  const colonIndex = serviceVersion.indexOf(':');
  if (colonIndex <= 0) return null; // No colon or colon at start

  const serviceName = serviceVersion.substring(0, colonIndex);
  const version = serviceVersion.substring(colonIndex + 1);

  if (!serviceName || !version) return null;

  return {
    serviceName,
    version,
    username,
  };
}

/**
 * Validates timestamp is within acceptable range (prevents replay attacks)
 */
export function validateTimestamp(timestamp: number): { valid: boolean; error?: string } {
  if (typeof timestamp !== 'number' || !Number.isFinite(timestamp)) {
    return { valid: false, error: 'Timestamp must be a finite number' };
  }

  const now = Date.now();
  const diff = Math.abs(now - timestamp);

  if (diff > TIMESTAMP_TOLERANCE_MS) {
    return { valid: false, error: `Timestamp too old or too far in future (tolerance: ${TIMESTAMP_TOLERANCE_MS / 1000}s)` };
  }

  return { valid: true };
}

/**
 * Verifies Ed25519 signature
 * @param publicKey Base64-encoded Ed25519 public key (32 bytes)
 * @param signature Base64-encoded Ed25519 signature (64 bytes)
 * @param message Message that was signed (UTF-8 string)
 * @returns true if signature is valid, false otherwise
 */
export async function verifyEd25519Signature(
  publicKey: string,
  signature: string,
  message: string
): Promise<boolean> {
  try {
    // Decode base64 to bytes
    const publicKeyBytes = base64ToBytes(publicKey);
    const signatureBytes = base64ToBytes(signature);

    // Encode message as UTF-8
    const encoder = new TextEncoder();
    const messageBytes = encoder.encode(message);

    // Verify signature using @noble/ed25519 (async version)
    const isValid = await ed25519.verifyAsync(signatureBytes, messageBytes, publicKeyBytes);
    return isValid;
  } catch (err) {
    console.error('Ed25519 signature verification failed:', err);
    return false;
  }
}

/**
 * Validates a username claim request
 * Verifies format, timestamp, and signature
 */
export async function validateUsernameClaim(
  username: string,
  publicKey: string,
  signature: string,
  message: string
): Promise<{ valid: boolean; error?: string }> {
  // Validate username format
  const usernameCheck = validateUsername(username);
  if (!usernameCheck.valid) {
    return usernameCheck;
  }

  // Parse message format: "claim:{username}:{timestamp}"
  const parts = message.split(':');
  if (parts.length !== 3 || parts[0] !== 'claim' || parts[1] !== username) {
    return { valid: false, error: 'Invalid message format (expected: claim:{username}:{timestamp})' };
  }

  const timestamp = parseInt(parts[2], 10);
  if (isNaN(timestamp)) {
    return { valid: false, error: 'Invalid timestamp in message' };
  }

  // Validate timestamp
  const timestampCheck = validateTimestamp(timestamp);
  if (!timestampCheck.valid) {
    return timestampCheck;
  }

  // Verify signature
  const signatureValid = await verifyEd25519Signature(publicKey, signature, message);
  if (!signatureValid) {
    return { valid: false, error: 'Invalid signature' };
  }

  return { valid: true };
}

/**
 * Validates a service publish signature
 * Message format: publish:{username}:{serviceFqn}:{timestamp}
 */
export async function validateServicePublish(
  username: string,
  serviceFqn: string,
  publicKey: string,
  signature: string,
  message: string
): Promise<{ valid: boolean; error?: string }> {
  // Validate username format
  const usernameCheck = validateUsername(username);
  if (!usernameCheck.valid) {
    return usernameCheck;
  }

  // Parse message format: "publish:{username}:{serviceFqn}:{timestamp}"
  const parts = message.split(':');
  if (parts.length !== 4 || parts[0] !== 'publish' || parts[1] !== username || parts[2] !== serviceFqn) {
    return { valid: false, error: 'Invalid message format (expected: publish:{username}:{serviceFqn}:{timestamp})' };
  }

  const timestamp = parseInt(parts[3], 10);
  if (isNaN(timestamp)) {
    return { valid: false, error: 'Invalid timestamp in message' };
  }

  // Validate timestamp
  const timestampCheck = validateTimestamp(timestamp);
  if (!timestampCheck.valid) {
    return timestampCheck;
  }

  // Verify signature
  const signatureValid = await verifyEd25519Signature(publicKey, signature, message);
  if (!signatureValid) {
    return { valid: false, error: 'Invalid signature' };
  }

  return { valid: true };
}