"""
Email Service
Handles email fetching from IMAP or Microsoft Graph API
Based on OmniSync architecture - READ-ONLY mode for safety
"""

import logging
import imaplib
import email
from email.header import decode_header
from typing import List, Dict, Optional, Tuple
from datetime import datetime
import json
import asyncio
from aiohttp import ClientSession, BasicAuth
import msal

from app.core.config import settings
from app.core.database import execute_query, execute_insert

logger = logging.getLogger(__name__)


class EmailService:
    """Email fetching service with IMAP and Graph API support"""
    
    def __init__(self):
        self.use_graph = settings.USE_GRAPH_API
        self.imap_config = {
            'server': settings.IMAP_SERVER,
            'port': settings.IMAP_PORT,
            'username': settings.IMAP_USERNAME,
            'password': settings.IMAP_PASSWORD,
            'use_ssl': settings.IMAP_USE_SSL,
            'folder': settings.IMAP_FOLDER,
            'readonly': settings.IMAP_READ_ONLY
        }
        self.graph_config = {
            'tenant_id': settings.GRAPH_TENANT_ID,
            'client_id': settings.GRAPH_CLIENT_ID,
            'client_secret': settings.GRAPH_CLIENT_SECRET,
            'user_email': settings.GRAPH_USER_EMAIL
        }
    
    async def fetch_new_emails(self, limit: int = 50) -> List[Dict]:
        """
        Fetch new emails from configured source (IMAP or Graph API)
        Returns list of parsed email dictionaries
        """
        if self.use_graph and self.graph_config['client_id']:
            logger.info("📥 Fetching emails via Microsoft Graph API")
            return await self._fetch_via_graph(limit)
        elif self.imap_config['username']:
            logger.info("📥 Fetching emails via IMAP")
            return await self._fetch_via_imap(limit)
        else:
            logger.warning("⚠️ No email source configured (IMAP or Graph API)")
            return []
    
    async def _fetch_via_imap(self, limit: int) -> List[Dict]:
        """Fetch emails using IMAP protocol (READ-ONLY mode)"""
        emails = []
        
        try:
            # Connect to IMAP server
            if self.imap_config['use_ssl']:
                mail = imaplib.IMAP4_SSL(self.imap_config['server'], self.imap_config['port'])
            else:
                mail = imaplib.IMAP4(self.imap_config['server'], self.imap_config['port'])
            
            # Login
            mail.login(self.imap_config['username'], self.imap_config['password'])
            
            # Select folder in READ-ONLY mode (critical for safety)
            folder = self.imap_config['folder']
            readonly = self.imap_config['readonly']
            mail.select(folder, readonly=readonly)
            
            if readonly:
                logger.info(f"🔒 Connected to {folder} in READ-ONLY mode (emails will NOT be marked as read)")
            
            # Search for all emails
            status, messages = mail.search(None, 'ALL')
            
            if status != 'OK':
                logger.error(f"❌ IMAP search failed: {status}")
                return emails
            
            email_ids = messages[0].split()
            total_emails = len(email_ids)
            
            logger.info(f"📊 Found {total_emails} emails in {folder}")
            
            # Get most recent emails (reverse order, limit)
            email_ids_to_fetch = email_ids[-limit:] if len(email_ids) > limit else email_ids
            email_ids_to_fetch.reverse()  # Newest first
            
            for email_id in email_ids_to_fetch:
                try:
                    # Fetch email using BODY.PEEK to avoid marking as read
                    status, msg_data = mail.fetch(email_id, '(BODY.PEEK[])')
                    
                    if status != 'OK':
                        logger.warning(f"⚠️ Failed to fetch email {email_id}: {status}")
                        continue
                    
                    # Parse email
                    raw_email = msg_data[0][1]
                    msg = email.message_from_bytes(raw_email)
                    
                    # Extract fields
                    parsed_email = self._parse_email(msg, email_id.decode())
                    
                    # Check if already exists in database
                    if not self._email_exists(parsed_email['message_id']):
                        emails.append(parsed_email)
                        logger.info(f"✅ New email: {parsed_email['subject'][:50]}... from {parsed_email['sender_email']}")
                    else:
                        logger.debug(f"⏭️ Email already exists: {parsed_email['message_id']}")
                
                except Exception as e:
                    logger.error(f"❌ Error parsing email {email_id}: {e}")
                    continue
            
            # Logout
            mail.logout()
            
            logger.info(f"📥 Fetched {len(emails)} new emails via IMAP")
            return emails
        
        except imaplib.IMAP4.error as e:
            logger.error(f"❌ IMAP error: {e}")
            return []
        except Exception as e:
            logger.error(f"❌ Unexpected error fetching via IMAP: {e}")
            return []
    
    async def _fetch_via_graph(self, limit: int) -> List[Dict]:
        """Fetch emails using Microsoft Graph API (OAuth2)"""
        emails = []
        
        try:
            # Get access token using MSAL
            access_token = await self._get_graph_access_token()
            
            if not access_token:
                logger.error("❌ Failed to get Graph API access token")
                return []
            
            # Build Graph API request
            user_email = self.graph_config['user_email']
            folder = self.imap_config['folder']  # Use same folder name
            
            # Graph API endpoint for messages
            url = f"https://graph.microsoft.com/v1.0/users/{user_email}/mailFolders/{folder}/messages"
            params = {
                '$top': limit,
                '$orderby': 'receivedDateTime desc',
                '$select': 'id,subject,from,toRecipients,ccRecipients,receivedDateTime,bodyPreview,body,hasAttachments,internetMessageId'
            }
            
            headers = {
                'Authorization': f'Bearer {access_token}',
                'Content-Type': 'application/json'
            }
            
            async with ClientSession() as session:
                async with session.get(url, params=params, headers=headers) as response:
                    if response.status != 200:
                        error_text = await response.text()
                        logger.error(f"❌ Graph API error: {response.status} - {error_text}")
                        return []
                    
                    data = await response.json()
                    messages = data.get('value', [])
                    
                    logger.info(f"📊 Found {len(messages)} emails via Graph API")
                    
                    for msg in messages:
                        try:
                            parsed_email = self._parse_graph_message(msg)
                            
                            # Check if already exists
                            if not self._email_exists(parsed_email['message_id']):
                                emails.append(parsed_email)
                                logger.info(f"✅ New email: {parsed_email['subject'][:50]}... from {parsed_email['sender_email']}")
                            else:
                                logger.debug(f"⏭️ Email already exists: {parsed_email['message_id']}")
                        
                        except Exception as e:
                            logger.error(f"❌ Error parsing Graph message: {e}")
                            continue
            
            logger.info(f"📥 Fetched {len(emails)} new emails via Graph API")
            return emails
        
        except Exception as e:
            logger.error(f"❌ Unexpected error fetching via Graph API: {e}")
            return []
    
    async def _get_graph_access_token(self) -> Optional[str]:
        """Get OAuth2 access token for Microsoft Graph API using MSAL"""
        try:
            authority = f"https://login.microsoftonline.com/{self.graph_config['tenant_id']}"
            
            app = msal.ConfidentialClientApplication(
                self.graph_config['client_id'],
                authority=authority,
                client_credential=self.graph_config['client_secret']
            )
            
            # Request token with Mail.Read scope (Application permission)
            scopes = ["https://graph.microsoft.com/.default"]
            result = app.acquire_token_for_client(scopes=scopes)
            
            if "access_token" in result:
                logger.info("✅ Successfully obtained Graph API access token")
                return result["access_token"]
            else:
                error = result.get("error_description", result.get("error", "Unknown error"))
                logger.error(f"❌ Failed to obtain access token: {error}")
                return None
        
        except Exception as e:
            logger.error(f"❌ Error getting Graph access token: {e}")
            return None
    
    def _parse_email(self, msg: email.message.Message, email_id: str) -> Dict:
        """Parse IMAP email message into dictionary"""
        
        # Decode subject
        subject = self._decode_header(msg.get('Subject', ''))
        
        # Decode sender
        from_header = self._decode_header(msg.get('From', ''))
        sender_name, sender_email = self._parse_email_address(from_header)
        
        # Decode recipient
        to_header = self._decode_header(msg.get('To', ''))
        recipient_name, recipient_email = self._parse_email_address(to_header)
        
        # Decode CC
        cc_header = self._decode_header(msg.get('Cc', ''))
        
        # Get message ID
        message_id = msg.get('Message-ID', f"imap-{email_id}")
        
        # Get date
        date_str = msg.get('Date', '')
        received_date = self._parse_email_date(date_str)
        
        # Get body
        body_text = ""
        body_html = ""
        
        if msg.is_multipart():
            for part in msg.walk():
                content_type = part.get_content_type()
                
                if content_type == "text/plain":
                    try:
                        body_text = part.get_payload(decode=True).decode('utf-8', errors='ignore')
                    except Exception:
                        pass
                
                elif content_type == "text/html":
                    try:
                        body_html = part.get_payload(decode=True).decode('utf-8', errors='ignore')
                    except Exception:
                        pass
        else:
            try:
                body_text = msg.get_payload(decode=True).decode('utf-8', errors='ignore')
            except Exception:
                body_text = str(msg.get_payload())
        
        # Check for attachments
        has_attachments = False
        attachment_count = 0
        
        if msg.is_multipart():
            for part in msg.walk():
                if part.get_content_maintype() == 'multipart':
                    continue
                if part.get('Content-Disposition') is not None:
                    has_attachments = True
                    attachment_count += 1
        
        return {
            'message_id': message_id,
            'subject': subject,
            'sender_name': sender_name,
            'sender_email': sender_email,
            'recipient_email': recipient_email,
            'cc': cc_header,
            'body_text': body_text,
            'body_html': body_html,
            'received_date': received_date,
            'folder': self.imap_config['folder'],
            'has_attachments': has_attachments,
            'attachment_count': attachment_count
        }
    
    def _parse_graph_message(self, msg: Dict) -> Dict:
        """Parse Microsoft Graph API message into dictionary"""
        
        # Extract sender
        from_data = msg.get('from', {}).get('emailAddress', {})
        sender_name = from_data.get('name', '')
        sender_email = from_data.get('address', '')
        
        # Extract recipient (first TO recipient)
        to_recipients = msg.get('toRecipients', [])
        recipient_email = to_recipients[0]['emailAddress']['address'] if to_recipients else ''
        
        # Extract CC recipients
        cc_recipients = msg.get('ccRecipients', [])
        cc = ', '.join([r['emailAddress']['address'] for r in cc_recipients])
        
        # Get body
        body_data = msg.get('body', {})
        body_content = body_data.get('content', '')
        body_type = body_data.get('contentType', 'text')
        
        body_text = body_content if body_type == 'text' else ''
        body_html = body_content if body_type == 'html' else ''
        
        # Parse date
        received_date_str = msg.get('receivedDateTime', '')
        received_date = datetime.fromisoformat(received_date_str.replace('Z', '+00:00')) if received_date_str else datetime.now()
        
        return {
            'message_id': msg.get('internetMessageId', msg.get('id', '')),
            'subject': msg.get('subject', ''),
            'sender_name': sender_name,
            'sender_email': sender_email,
            'recipient_email': recipient_email,
            'cc': cc,
            'body_text': body_text,
            'body_html': body_html,
            'received_date': received_date,
            'folder': self.imap_config['folder'],
            'has_attachments': msg.get('hasAttachments', False),
            'attachment_count': 0  # TODO: Fetch attachment count from Graph API if needed
        }
    
    def _decode_header(self, header: str) -> str:
        """Decode email header (handles MIME encoding)"""
        if not header:
            return ""
        
        decoded_parts = decode_header(header)
        decoded_string = ""
        
        for content, encoding in decoded_parts:
            if isinstance(content, bytes):
                try:
                    decoded_string += content.decode(encoding or 'utf-8', errors='ignore')
                except Exception:
                    decoded_string += content.decode('utf-8', errors='ignore')
            else:
                decoded_string += str(content)
        
        return decoded_string.strip()
    
    def _parse_email_address(self, header: str) -> Tuple[str, str]:
        """Parse 'Name <email@domain.com>' into (name, email)"""
        if not header:
            return ("", "")
        
        if '<' in header and '>' in header:
            # Format: "Name <email@domain.com>"
            parts = header.split('<')
            name = parts[0].strip().strip('"')
            email_addr = parts[1].strip('>').strip()
            return (name, email_addr)
        else:
            # Just email address
            return ("", header.strip())
    
    def _parse_email_date(self, date_str: str) -> datetime:
        """Parse email date header into datetime object"""
        if not date_str:
            return datetime.now()
        
        try:
            # Use email.utils to parse RFC 2822 date
            from email.utils import parsedate_to_datetime
            return parsedate_to_datetime(date_str)
        except Exception:
            logger.warning(f"⚠️ Failed to parse date: {date_str}")
            return datetime.now()
    
    def _email_exists(self, message_id: str) -> bool:
        """Check if email already exists in database"""
        query = "SELECT id FROM email_messages WHERE message_id = %s AND deleted_at IS NULL"
        result = execute_query(query, (message_id,))
        return len(result) > 0
    
    async def save_email(self, email_data: Dict) -> Optional[int]:
        """Save email to database"""
        try:
            query = """
                INSERT INTO email_messages 
                (message_id, subject, sender_email, sender_name, recipient_email, cc, 
                 body_text, body_html, received_date, folder, has_attachments, attachment_count,
                 status, is_read)
                VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, 'new', false)
                RETURNING id
            """
            
            email_id = execute_insert(query, (
                email_data['message_id'],
                email_data['subject'],
                email_data['sender_email'],
                email_data['sender_name'],
                email_data['recipient_email'],
                email_data['cc'],
                email_data['body_text'],
                email_data['body_html'],
                email_data['received_date'],
                email_data['folder'],
                email_data['has_attachments'],
                email_data['attachment_count']
            ))
            
            logger.info(f"✅ Saved email {email_id}: {email_data['subject'][:50]}...")
            return email_id
        
        except Exception as e:
            logger.error(f"❌ Error saving email to database: {e}")
            return None
    
    async def get_unprocessed_emails(self, limit: int = 100) -> List[Dict]:
        """Get emails from database that haven't been processed yet"""
        query = """
            SELECT * FROM email_messages 
            WHERE status = 'new' AND deleted_at IS NULL
            ORDER BY received_date DESC
            LIMIT %s
        """
        result = execute_query(query, (limit,))
        return result
    
    async def update_email_status(self, email_id: int, status: str):
        """Update email processing status"""
        query = "UPDATE email_messages SET status = %s, updated_at = CURRENT_TIMESTAMP WHERE id = %s"
        execute_query(query, (status, email_id))
        logger.info(f"✅ Updated email {email_id} status to: {status}")