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

export interface ImageValidationResult {
  valid: boolean;
  error?: string;
  mimeType?: "image/jpeg" | "image/png" | "image/webp";
  extension?: "jpg" | "png" | "webp";
  sanitizedBase64?: string;
  sizeBytes?: number;
}

/**
 * Known file signatures (magic bytes) for allowed image formats
 */
const MAGIC_SIGNATURES = {
  // JPEG: starts with FF D8 FF
  jpeg: [0xff, 0xd8, 0xff],
  // PNG: starts with 89 50 4E 47 0D 0A 1A 0A
  png: [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a],
  // WebP: starts with "RIFF" (52 49 46 46) and at offset 8 has "WEBP" (57 45 42 50)
  riff: [0x52, 0x49, 0x46, 0x46],
  webp: [0x57, 0x45, 0x42, 0x50],
};

/**
 * Dangerous executable & script signatures to explicitly detect and reject
 */
const DANGEROUS_SIGNATURES = [
  // Windows DOS/PE executable ('MZ' - 4D 5A)
  { name: "Windows Executable (PE/DOS)", bytes: [0x4d, 0x5a] },
  // Linux ELF binary (7F 45 4C 46)
  { name: "Linux ELF Binary", bytes: [0x7f, 0x45, 0x4c, 0x46] },
  // Mach-O binary (FE ED FA CE / FE ED FA CF / CE FA ED FE / CF FA ED FE)
  { name: "Mach-O Binary (32-bit)", bytes: [0xfe, 0xed, 0xfa, 0xce] },
  { name: "Mach-O Binary (64-bit)", bytes: [0xfe, 0xed, 0xfa, 0xcf] },
  { name: "Mach-O Binary (rev 32)", bytes: [0xce, 0xfa, 0xed, 0xfe] },
  { name: "Mach-O Binary (rev 64)", bytes: [0xcf, 0xfa, 0xed, 0xfe] },
  // Java class file (CA FE BA BE)
  { name: "Java Class File", bytes: [0xca, 0xfe, 0xba, 0xbe] },
  // Shell script shebang ('#!' - 23 21)
  { name: "Shell Script", bytes: [0x23, 0x21] },
];

/**
 * Matches bytes at specific offset
 */
function matchesBytes(buffer: Buffer, expected: number[], offset = 0): boolean {
  if (buffer.length < offset + expected.length) return false;
  for (let i = 0; i < expected.length; i++) {
    if (buffer[offset + i] !== expected[i]) return false;
  }
  return true;
}

/**
 * Validates a base64 string or data URL:
 * 1. Checks max size limits
 * 2. Decodes binary buffer
 * 3. Scans for known executable/script signatures
 * 4. Verifies genuine image magic bytes (JPEG, PNG, WebP)
 * 5. Rejects scripts / HTML / SVG content
 */
export function validateAndSanitizeImage(
  input: string,
  maxSizeBytes: number = 10 * 1024 * 1024
): ImageValidationResult {
  if (!input || typeof input !== "string") {
    return { valid: false, error: "Missing or invalid image payload" };
  }

  // Check approximate string size (base64 string is ~4/3 larger than binary)
  // 10MB binary ≈ 13.5MB base64 string
  const maxStringLen = Math.ceil(maxSizeBytes * 1.4) + 1024;
  if (input.length > maxStringLen) {
    return { valid: false, error: `Image exceeds maximum allowed size (${Math.round(maxSizeBytes / (1024 * 1024))}MB)` };
  }

  // Strip possible Data URL prefix
  const dataUrlMatch = input.match(/^data:([a-zA-Z0-9/+-]+);base64,(.+)$/);
  const rawBase64 = dataUrlMatch ? dataUrlMatch[2] : input.trim();

  // Basic Base64 character validation (safe regex pattern)
  if (!/^[A-Za-z0-9+/=]+$/.test(rawBase64)) {
    return { valid: false, error: "Invalid base64 encoding" };
  }

  let buffer: Buffer;
  try {
    buffer = Buffer.from(rawBase64, "base64");
  } catch {
    return { valid: false, error: "Failed to decode base64 payload" };
  }

  if (buffer.length === 0) {
    return { valid: false, error: "Empty image payload" };
  }

  if (buffer.length > maxSizeBytes) {
    return { valid: false, error: `Image binary size exceeds ${Math.round(maxSizeBytes / (1024 * 1024))}MB limit` };
  }

  // 1. Explicitly check for known executable or script signatures
  for (const sig of DANGEROUS_SIGNATURES) {
    if (matchesBytes(buffer, sig.bytes)) {
      return {
        valid: false,
        error: `Executable or script payload detected (${sig.name}). Upload rejected.`,
      };
    }
  }

  // 2. Check for script/text content (e.g. <?php, <script, <svg, <html>)
  const headerPreview = buffer.slice(0, Math.min(buffer.length, 512)).toString("utf8").toLowerCase();
  const dangerousPatterns = [
    "<?php",
    "<% ",
    "<script",
    "<html",
    "<body",
    "<svg",
    "#!/",
    "eval(",
    "system(",
    "exec(",
  ];
  for (const pattern of dangerousPatterns) {
    if (headerPreview.includes(pattern)) {
      return {
        valid: false,
        error: "Script or HTML content detected in image payload. Upload rejected.",
      };
    }
  }

  // 3. Verify legitimate image magic bytes
  let detectedType: "image/jpeg" | "image/png" | "image/webp" | null = null;
  let extension: "jpg" | "png" | "webp" = "jpg";

  if (matchesBytes(buffer, MAGIC_SIGNATURES.jpeg)) {
    detectedType = "image/jpeg";
    extension = "jpg";
  } else if (matchesBytes(buffer, MAGIC_SIGNATURES.png)) {
    detectedType = "image/png";
    extension = "png";
  } else if (
    matchesBytes(buffer, MAGIC_SIGNATURES.riff, 0) &&
    matchesBytes(buffer, MAGIC_SIGNATURES.webp, 8)
  ) {
    detectedType = "image/webp";
    extension = "webp";
  }

  if (!detectedType) {
    return {
      valid: false,
      error: "Unsupported or invalid image format. Only authentic JPEG, PNG, or WebP images are permitted.",
    };
  }

  return {
    valid: true,
    mimeType: detectedType,
    extension,
    sanitizedBase64: `data:${detectedType};base64,${buffer.toString("base64")}`,
    sizeBytes: buffer.length,
  };
}

/**
 * Extracts and normalizes the client IP address from request headers
 */
export function getClientIp(req: NextRequest): string {
  const forwardedFor = req.headers.get("x-forwarded-for");
  if (forwardedFor) {
    const firstIp = forwardedFor.split(",")[0].trim();
    if (firstIp) return firstIp;
  }

  const realIp = req.headers.get("x-real-ip");
  if (realIp && realIp.trim()) {
    return realIp.trim();
  }

  return "127.0.0.1";
}

/**
 * Constant-time string comparison using SHA-256 digests to prevent timing attacks
 */
export function constantTimeCompare(a: string, b: string): boolean {
  if (typeof a !== "string" || typeof b !== "string") return false;

  const hashA = crypto.createHash("sha256").update(a).digest();
  const hashB = crypto.createHash("sha256").update(b).digest();

  return crypto.timingSafeEqual(hashA, hashB);
}

/**
 * In-memory brute-force protection for sensitive endpoints (e.g. portal login)
 */
interface AuthAttemptRecord {
  failedAttempts: number;
  lockedUntil: number;
  firstAttemptAt: number;
}

const authAttemptsStore = new Map<string, AuthAttemptRecord>();

export function checkAuthRateLimit(
  ip: string,
  maxFailures: number = 5,
  lockoutMinutes: number = 15
): { allowed: boolean; remainingAttempts: number; lockoutSeconds: number } {
  const now = Date.now();
  const record = authAttemptsStore.get(ip);

  if (!record) {
    return { allowed: true, remainingAttempts: maxFailures, lockoutSeconds: 0 };
  }

  // If currently locked out
  if (record.lockedUntil > now) {
    const lockoutSeconds = Math.ceil((record.lockedUntil - now) / 1000);
    return { allowed: false, remainingAttempts: 0, lockoutSeconds };
  }

  // If lockout or window has expired (15 minutes), reset
  const windowMs = lockoutMinutes * 60 * 1000;
  if (now - record.firstAttemptAt > windowMs) {
    authAttemptsStore.delete(ip);
    return { allowed: true, remainingAttempts: maxFailures, lockoutSeconds: 0 };
  }

  const remainingAttempts = Math.max(0, maxFailures - record.failedAttempts);
  return {
    allowed: record.failedAttempts < maxFailures,
    remainingAttempts,
    lockoutSeconds: 0,
  };
}

export function recordAuthFailure(
  ip: string,
  maxFailures: number = 5,
  lockoutMinutes: number = 15
): void {
  const now = Date.now();
  const record = authAttemptsStore.get(ip);

  if (!record) {
    authAttemptsStore.set(ip, {
      failedAttempts: 1,
      lockedUntil: 0,
      firstAttemptAt: now,
    });
  } else {
    record.failedAttempts += 1;
    if (record.failedAttempts >= maxFailures) {
      record.lockedUntil = now + lockoutMinutes * 60 * 1000;
    }
  }
}

export function recordAuthSuccess(ip: string): void {
  authAttemptsStore.delete(ip);
}