"""
ICANN CZDS (Centralized Zone Data Service) Client
==================================================
Downloads zone files from ICANN CZDS, parses them, and detects dropped domains.

Authentication: OAuth2 with username/password
Zone Format: Standard DNS zone file format (.txt.gz)

Usage:
    client = CZDSClient(username, password)
    await client.sync_all_zones(db)
"""

import asyncio
import gzip
import hashlib
import logging
import os
import re
import shutil
from datetime import datetime, timedelta
from pathlib import Path
from typing import Optional

import httpx
from sqlalchemy import select, func, text
from sqlalchemy.ext.asyncio import AsyncSession

from app.config import get_settings
from app.models.zone_file import ZoneSnapshot, DroppedDomain

logger = logging.getLogger(__name__)
settings = get_settings()

# ============================================================================
# CONSTANTS
# ============================================================================

CZDS_AUTH_URL = "https://account-api.icann.org/api/authenticate"
CZDS_ZONES_URL = "https://czds-api.icann.org/czds/downloads/links"
CZDS_DOWNLOAD_BASE = "https://czds-download.icann.org"

# TLDs we have approved access to
APPROVED_TLDS = ["xyz", "org", "online", "info", "dev", "app"]

# Regex to extract domain names from zone file NS records
# Format: example.tld.    IN    NS    ns1.example.com.
NS_RECORD_PATTERN = re.compile(r'^([a-z0-9][-a-z0-9]*)\.[a-z]+\.\s+\d*\s*IN\s+NS\s+', re.IGNORECASE)


# ============================================================================
# CZDS CLIENT
# ============================================================================

class CZDSClient:
    """Client for ICANN CZDS zone file downloads."""
    
    def __init__(
        self, 
        username: Optional[str] = None, 
        password: Optional[str] = None,
        data_dir: Optional[Path] = None
    ):
        self.username = username or os.getenv("CZDS_USERNAME") or settings.czds_username
        self.password = password or os.getenv("CZDS_PASSWORD") or settings.czds_password
        self.data_dir = data_dir or Path(os.getenv("CZDS_DATA_DIR", "/tmp/pounce_czds"))
        self.data_dir.mkdir(parents=True, exist_ok=True)
        
        self._token: Optional[str] = None
        self._token_expires: Optional[datetime] = None
    
    async def _authenticate(self) -> str:
        """Authenticate with ICANN and get access token."""
        if self._token and self._token_expires and datetime.utcnow() < self._token_expires:
            return self._token
        
        if not self.username or not self.password:
            raise ValueError("CZDS credentials not configured. Set CZDS_USERNAME and CZDS_PASSWORD.")
        
        logger.info("Authenticating with ICANN CZDS...")
        
        async with httpx.AsyncClient(timeout=30) as client:
            response = await client.post(
                CZDS_AUTH_URL,
                json={"username": self.username, "password": self.password},
                headers={"Content-Type": "application/json"}
            )
            
            if response.status_code != 200:
                logger.error(f"CZDS authentication failed: {response.status_code} {response.text}")
                raise RuntimeError(f"CZDS authentication failed: {response.status_code}")
            
            data = response.json()
            self._token = data.get("accessToken")
            
            # Token expires in 24 hours, refresh after 23 hours
            self._token_expires = datetime.utcnow() + timedelta(hours=23)
            
            logger.info("CZDS authentication successful")
            return self._token
    
    async def get_available_zones(self) -> list[str]:
        """Get list of zone files available for download."""
        token = await self._authenticate()
        
        async with httpx.AsyncClient(timeout=60) as client:
            response = await client.get(
                CZDS_ZONES_URL,
                headers={"Authorization": f"Bearer {token}"}
            )
            
            if response.status_code != 200:
                logger.error(f"Failed to get zone list: {response.status_code}")
                return []
            
            # Response is a list of download URLs
            urls = response.json()
            
            # Extract TLDs from URLs
            tlds = []
            for url in urls:
                # URL format: https://czds-download.icann.org/czds/downloads/xyz.zone
                match = re.search(r'/([a-z0-9-]+)\.zone$', url, re.IGNORECASE)
                if match:
                    tlds.append(match.group(1).lower())
            
            logger.info(f"Available zones: {tlds}")
            return tlds
    
    async def download_zone(self, tld: str) -> Optional[Path]:
        """Download a zone file for a specific TLD."""
        token = await self._authenticate()
        
        download_url = f"{CZDS_DOWNLOAD_BASE}/czds/downloads/{tld}.zone"
        output_path = self.data_dir / f"{tld}.zone.txt.gz"
        
        logger.info(f"Downloading zone file for .{tld}...")
        
        async with httpx.AsyncClient(timeout=600, follow_redirects=True) as client:
            try:
                async with client.stream(
                    "GET",
                    download_url,
                    headers={"Authorization": f"Bearer {token}"}
                ) as response:
                    if response.status_code != 200:
                        logger.error(f"Failed to download .{tld}: {response.status_code}")
                        return None
                    
                    # Stream to file
                    with open(output_path, "wb") as f:
                        async for chunk in response.aiter_bytes(chunk_size=1024 * 1024):
                            f.write(chunk)
                
                file_size = output_path.stat().st_size / (1024 * 1024)
                logger.info(f"Downloaded .{tld} zone file: {file_size:.1f} MB")
                return output_path
                
            except Exception as e:
                logger.error(f"Error downloading .{tld}: {e}")
                return None
    
    def extract_zone_file(self, gz_path: Path) -> Path:
        """Extract gzipped zone file."""
        output_path = gz_path.with_suffix('')  # Remove .gz
        
        logger.info(f"Extracting {gz_path.name}...")
        
        with gzip.open(gz_path, 'rb') as f_in:
            with open(output_path, 'wb') as f_out:
                shutil.copyfileobj(f_in, f_out)
        
        # Remove gz file to save space
        gz_path.unlink()
        
        return output_path
    
    def parse_zone_file(self, zone_path: Path, tld: str) -> set[str]:
        """
        Parse zone file and extract unique domain names.
        
        Zone files contain various record types. We extract domains from:
        - NS records (most reliable indicator of active domain)
        - A/AAAA records
        
        Returns set of domain names (without TLD suffix).
        """
        logger.info(f"Parsing zone file for .{tld}...")
        
        domains = set()
        line_count = 0
        
        with open(zone_path, 'r', encoding='utf-8', errors='ignore') as f:
            for line in f:
                line_count += 1
                
                # Skip comments and empty lines
                if line.startswith(';') or not line.strip():
                    continue
                
                # Look for NS records which indicate delegated domains
                # Format: example.tld.    86400    IN    NS    ns1.registrar.com.
                parts = line.split()
                if len(parts) >= 4:
                    # First column is the domain name
                    name = parts[0].rstrip('.')
                    
                    # Must end with our TLD
                    if name.lower().endswith(f'.{tld}'):
                        # Extract just the domain name part
                        domain_name = name[:-(len(tld) + 1)]
                        
                        # Skip the TLD itself and subdomains
                        if domain_name and '.' not in domain_name:
                            domains.add(domain_name.lower())
        
        logger.info(f"Parsed .{tld}: {len(domains):,} unique domains from {line_count:,} lines")
        return domains
    
    def compute_checksum(self, domains: set[str]) -> str:
        """Compute SHA256 checksum of sorted domain list."""
        sorted_domains = "\n".join(sorted(domains))
        return hashlib.sha256(sorted_domains.encode()).hexdigest()
    
    async def get_previous_domains(self, tld: str) -> Optional[set[str]]:
        """Load previous day's domain set from cache file."""
        cache_file = self.data_dir / f"{tld}_domains.txt"
        
        if cache_file.exists():
            try:
                content = cache_file.read_text()
                return set(line.strip() for line in content.splitlines() if line.strip())
            except Exception as e:
                logger.warning(f"Failed to load cache for .{tld}: {e}")
        
        return None
    
    async def save_domains(self, tld: str, domains: set[str]):
        """Save current domains to cache file."""
        cache_file = self.data_dir / f"{tld}_domains.txt"
        cache_file.write_text("\n".join(sorted(domains)))
        logger.info(f"Saved {len(domains):,} domains for .{tld}")
    
    async def process_drops(
        self, 
        db: AsyncSession, 
        tld: str, 
        previous: set[str], 
        current: set[str]
    ) -> list[dict]:
        """Find and store dropped domains."""
        dropped = previous - current
        
        if not dropped:
            logger.info(f"No dropped domains found for .{tld}")
            return []
        
        logger.info(f"Found {len(dropped):,} dropped domains for .{tld}")
        
        today = datetime.utcnow().replace(hour=0, minute=0, second=0, microsecond=0)
        
        # Batch insert for performance
        dropped_records = []
        batch_size = 1000
        batch = []
        
        for name in dropped:
            record = DroppedDomain(
                domain=f"{name}.{tld}",
                tld=tld,
                dropped_date=today,
                length=len(name),
                is_numeric=name.isdigit(),
                has_hyphen='-' in name
            )
            batch.append(record)
            dropped_records.append({
                "domain": f"{name}.{tld}",
                "length": len(name),
                "is_numeric": name.isdigit(),
                "has_hyphen": '-' in name
            })
            
            if len(batch) >= batch_size:
                db.add_all(batch)
                await db.flush()
                batch = []
        
        # Add remaining
        if batch:
            db.add_all(batch)
        
        await db.commit()
        
        return dropped_records
    
    async def sync_zone(self, db: AsyncSession, tld: str) -> dict:
        """
        Sync a single zone file:
        1. Download zone file
        2. Extract and parse
        3. Compare with previous snapshot
        4. Store dropped domains
        5. Save new snapshot
        """
        logger.info(f"Starting sync for .{tld}")
        
        result = {
            "tld": tld,
            "status": "pending",
            "current_count": 0,
            "previous_count": 0,
            "dropped_count": 0,
            "new_count": 0,
            "error": None
        }
        
        try:
            # Download zone file
            gz_path = await self.download_zone(tld)
            if not gz_path:
                result["status"] = "download_failed"
                result["error"] = "Failed to download zone file"
                return result
            
            # Extract
            zone_path = self.extract_zone_file(gz_path)
            
            # Parse
            current_domains = self.parse_zone_file(zone_path, tld)
            result["current_count"] = len(current_domains)
            
            # Clean up zone file (can be very large)
            zone_path.unlink()
            
            # Get previous snapshot
            previous_domains = await self.get_previous_domains(tld)
            
            if previous_domains:
                result["previous_count"] = len(previous_domains)
                
                # Find dropped domains
                dropped = await self.process_drops(db, tld, previous_domains, current_domains)
                result["dropped_count"] = len(dropped)
                result["new_count"] = len(current_domains - previous_domains)
            
            # Save current snapshot
            await self.save_domains(tld, current_domains)
            
            # Save snapshot metadata
            checksum = self.compute_checksum(current_domains)
            snapshot = ZoneSnapshot(
                tld=tld,
                snapshot_date=datetime.utcnow(),
                domain_count=len(current_domains),
                checksum=checksum
            )
            db.add(snapshot)
            await db.commit()
            
            result["status"] = "success"
            logger.info(
                f"Sync complete for .{tld}: "
                f"{result['current_count']:,} domains, "
                f"{result['dropped_count']:,} dropped, "
                f"{result['new_count']:,} new"
            )
            
        except Exception as e:
            logger.exception(f"Error syncing .{tld}: {e}")
            result["status"] = "error"
            result["error"] = str(e)
        
        return result
    
    async def sync_all_zones(
        self, 
        db: AsyncSession, 
        tlds: Optional[list[str]] = None
    ) -> list[dict]:
        """
        Sync all approved zone files.
        
        Args:
            db: Database session
            tlds: Optional list of TLDs to sync. Defaults to APPROVED_TLDS.
        
        Returns:
            List of sync results for each TLD.
        """
        tlds = tlds or APPROVED_TLDS
        
        logger.info(f"Starting CZDS sync for {len(tlds)} zones: {tlds}")
        
        results = []
        for tld in tlds:
            result = await self.sync_zone(db, tld)
            results.append(result)
            
            # Small delay between zones to be nice to ICANN servers
            await asyncio.sleep(2)
        
        # Summary
        success_count = sum(1 for r in results if r["status"] == "success")
        total_dropped = sum(r["dropped_count"] for r in results)
        
        logger.info(
            f"CZDS sync complete: "
            f"{success_count}/{len(tlds)} zones successful, "
            f"{total_dropped:,} total dropped domains"
        )
        
        return results


# ============================================================================
# STANDALONE SCRIPT
# ============================================================================

async def main():
    """Standalone script to run CZDS sync."""
    import sys
    from app.database import AsyncSessionLocal, init_db
    
    # Initialize database
    await init_db()
    
    # Parse arguments
    tlds = sys.argv[1:] if len(sys.argv) > 1 else APPROVED_TLDS
    
    print(f"🌐 CZDS Zone File Sync")
    print(f"📂 TLDs: {', '.join(tlds)}")
    print("-" * 50)
    
    client = CZDSClient()
    
    async with AsyncSessionLocal() as db:
        results = await client.sync_all_zones(db, tlds)
    
    print("\n" + "=" * 50)
    print("📊 RESULTS")
    print("=" * 50)
    
    for r in results:
        status_icon = "✅" if r["status"] == "success" else "❌"
        print(f"{status_icon} .{r['tld']}: {r['current_count']:,} domains, "
              f"{r['dropped_count']:,} dropped, {r['new_count']:,} new")
        if r["error"]:
            print(f"   ⚠️ Error: {r['error']}")
    
    total_dropped = sum(r["dropped_count"] for r in results)
    print(f"\n🎯 Total dropped domains: {total_dropped:,}")


if __name__ == "__main__":
    asyncio.run(main())