import { NextRequest } from 'next/server';
import crypto from 'crypto';

const DEFAULT_INSECURE_ADMIN = 'admin:default_password_change_me';
const SESSION_DURATION_MS = 2 * 60 * 60 * 1000; // 2 hours

function base64UrlEncode(input: string | Buffer): string {
  const buf = typeof input === 'string' ? Buffer.from(input, 'utf8') : input;
  return buf.toString('base64').replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/g, '');
}

function base64UrlDecodeToString(input: string): string {
  const normalized = input.replace(/-/g, '+').replace(/_/g, '/');
  const pad = normalized.length % 4 === 0 ? '' : '='.repeat(4 - (normalized.length % 4));
  return Buffer.from(normalized + pad, 'base64').toString('utf8');
}

function base64UrlDecodeToBuffer(input: string): Buffer {
  const normalized = input.replace(/-/g, '+').replace(/_/g, '/');
  const pad = normalized.length % 4 === 0 ? '' : '='.repeat(4 - (normalized.length % 4));
  return Buffer.from(normalized + pad, 'base64');
}

export function getClientIp(request: NextRequest): string {
  const xff = request.headers.get('x-forwarded-for');
  if (xff) {
    // x-forwarded-for can be a list: client, proxy1, proxy2
    return xff.split(',')[0]?.trim() || 'unknown';
  }
  return request.headers.get('x-real-ip') || 'unknown';
}

function getAdminCredentials(): { username: string; password: string } | null {
  const raw = process.env.ADMIN_BASIC_AUTH;
  if (!raw || raw.trim() === '' || raw === DEFAULT_INSECURE_ADMIN) return null;
  const idx = raw.indexOf(':');
  if (idx <= 0 || idx === raw.length - 1) return null;
  return { username: raw.slice(0, idx), password: raw.slice(idx + 1) };
}

function getSessionSecret(): string | null {
  const secret = process.env.ADMIN_SESSION_SECRET;
  if (!secret || secret.trim().length < 32) return null; // require a reasonably strong secret
  return secret;
}

type SessionPayload = {
  v: 1;
  iat: number;
  rnd: string;
  ip: string;
  ua: string;
};

export function createSessionToken(request: NextRequest): string | null {
  const secret = getSessionSecret();
  if (!secret) return null;

  const payload: SessionPayload = {
    v: 1,
    iat: Date.now(),
    rnd: crypto.randomBytes(32).toString('hex'),
    ip: getClientIp(request),
    ua: request.headers.get('user-agent') || 'unknown',
  };

  const payloadB64 = base64UrlEncode(JSON.stringify(payload));
  const sig = crypto.createHmac('sha256', secret).update(payloadB64).digest();
  const sigB64 = base64UrlEncode(sig);
  return `${payloadB64}.${sigB64}`;
}

export function verifySessionToken(request: NextRequest, token: string): boolean {
  const secret = getSessionSecret();
  if (!secret) return false;

  const parts = token.split('.');
  if (parts.length !== 2) return false;
  const [payloadB64, sigB64] = parts;
  if (!payloadB64 || !sigB64) return false;

  let providedSigBytes: Buffer;
  try {
    providedSigBytes = base64UrlDecodeToBuffer(sigB64);
  } catch {
    return false;
  }

  const expectedSigBytes = crypto.createHmac('sha256', secret).update(payloadB64).digest();
  if (providedSigBytes.length !== expectedSigBytes.length) return false;
  if (!crypto.timingSafeEqual(providedSigBytes, expectedSigBytes)) return false;

  let payload: SessionPayload;
  try {
    payload = JSON.parse(base64UrlDecodeToString(payloadB64)) as SessionPayload;
  } catch {
    return false;
  }

  if (!payload || payload.v !== 1 || typeof payload.iat !== 'number' || typeof payload.rnd !== 'string') {
    return false;
  }

  const now = Date.now();
  if (now - payload.iat > SESSION_DURATION_MS) return false;

  // Bind token to client IP + UA (best-effort; "unknown" should not hard-fail)
  const currentIp = getClientIp(request);
  const currentUa = request.headers.get('user-agent') || 'unknown';
  if (payload.ip !== 'unknown' && currentIp !== 'unknown' && payload.ip !== currentIp) return false;
  if (payload.ua !== 'unknown' && currentUa !== 'unknown' && payload.ua !== currentUa) return false;

  return true;
}

// Server-side authentication utilities
export function verifyAdminAuth(request: NextRequest): boolean {
  // Check for basic auth header
  const authHeader = request.headers.get('authorization');
  
  if (!authHeader || !authHeader.startsWith('Basic ')) {
    return false;
  }

  try {
    const base64Credentials = authHeader.split(' ')[1];
    const credentials = Buffer.from(base64Credentials, 'base64').toString('utf8');
    const [username, password] = credentials.split(':');
    
    // Get admin credentials from environment
    const creds = getAdminCredentials();
    if (!creds) return false;
    
    return username === creds.username && password === creds.password;
  } catch {
    return false;
  }
}

export function requireAdminAuth(request: NextRequest): Response | null {
  if (!verifyAdminAuth(request)) {
    return new Response(
      JSON.stringify({ error: 'Unauthorized' }), 
      { 
        status: 401, 
        headers: { 
          'Content-Type': 'application/json'
        } 
      }
    );
  }
  return null;
}

// Session-based authentication (no browser popup)
export function verifySessionAuth(request: NextRequest): boolean {
  // Check for session token in headers
  const sessionToken = request.headers.get('x-session-token');
  if (!sessionToken) return false;

  try {
    return verifySessionToken(request, sessionToken);
  } catch {
    return false;
  }
}

export function requireSessionAuth(request: NextRequest): Response | null {
  if (!verifySessionAuth(request)) {
    return new Response(
      JSON.stringify({ error: 'Session expired or invalid' }), 
      { 
        status: 401, 
        headers: { 
          'Content-Type': 'application/json'
        } 
      }
    );
  }
  return null;
}

// Rate limiting for admin endpoints
const rateLimitMap = new Map<string, { count: number; resetTime: number }>();

// Clear rate limit cache on startup
if (typeof window === 'undefined') {
  // Server-side: clear cache periodically
  setInterval(() => {
    const now = Date.now();
    for (const [key, value] of rateLimitMap.entries()) {
      if (now > value.resetTime) {
        rateLimitMap.delete(key);
      }
    }
  }, 60000); // Clear every minute
}

export function checkRateLimit(ip: string, maxRequests: number = 10, windowMs: number = 60000): boolean {
  const now = Date.now();
  const key = `admin_${ip}`;
  
  const current = rateLimitMap.get(key);
  
  if (!current || now > current.resetTime) {
    rateLimitMap.set(key, { count: 1, resetTime: now + windowMs });
    return true;
  }
  
  if (current.count >= maxRequests) {
    return false;
  }
  
  current.count++;
  return true;
}

export function getRateLimitHeaders(ip: string, maxRequests: number = 10, windowMs: number = 60000): Record<string, string> {
  const current = rateLimitMap.get(`admin_${ip}`);
  const remaining = current ? Math.max(0, maxRequests - current.count) : maxRequests;
  
  return {
    'X-RateLimit-Limit': maxRequests.toString(),
    'X-RateLimit-Remaining': remaining.toString(),
    'X-RateLimit-Reset': current ? Math.ceil(current.resetTime / 1000).toString() : Math.ceil((Date.now() + windowMs) / 1000).toString()
  };
}