import os
import time
import logging
from threading import Thread
import smtplib
from email.mime.text import MIMEText
from flask import Flask, render_template, request, jsonify, g
from flask_limiter import Limiter
from flask_limiter.util import get_remote_address
from dotenv import load_dotenv
from database import init_db, get_connection, return_connection, add_email, remove_email

load_dotenv()

SMTP_SERVER   = os.getenv('SMTP_SERVER')
SMTP_PORT     = int(os.getenv('SMTP_PORT', 465))
SMTP_USER     = os.getenv('SMTP_USER')
SMTP_PASSWORD = os.getenv('SMTP_PASSWORD')

app = Flask(__name__)

# Rate limiting setup
limiter = Limiter(
    key_func=get_remote_address,
    app=app,
    default_limits=["1000 per hour", "100 per minute"],
    storage_uri="memory://"
)

# Configure logging
logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s %(levelname)s [%(name)s] %(message)s'
)

# Cache configuration
_newsletter_cache = {}
_cache_timestamp = {}
CACHE_DURATION = 300

def get_newsletters_cached():
    """Get newsletters with caching to reduce database hits"""
    current_time = time.time()
    
    if ('newsletters' in _newsletter_cache and 
        current_time - _cache_timestamp.get('newsletters', 0) < CACHE_DURATION):
        return _newsletter_cache['newsletters']
    
    conn = None
    try:
        conn = get_connection()
        cursor = conn.cursor()
        cursor.execute(
            "SELECT id, subject, body, sent_at "
            "FROM newsletters ORDER BY sent_at DESC LIMIT 100"
        )
        rows = cursor.fetchall()
        cursor.close()
        
        newsletters = [
            {"id": r[0], "subject": r[1], "body": r[2], "sent_at": r[3]}
            for r in rows
        ]
        
        _newsletter_cache['newsletters'] = newsletters
        _cache_timestamp['newsletters'] = current_time
        
        return newsletters
    except Exception as e:
        app.logger.error(f"Database error in get_newsletters_cached: {e}")
        return []
    finally:
        if conn:
            return_connection(conn)

def get_newsletter_by_id_cached(newsletter_id):
    """Get single newsletter with caching"""
    cache_key = f'newsletter_{newsletter_id}'
    current_time = time.time()
    
    if (cache_key in _newsletter_cache and 
        current_time - _cache_timestamp.get(cache_key, 0) < CACHE_DURATION):
        return _newsletter_cache[cache_key]
    
    conn = None
    try:
        conn = get_connection()
        cursor = conn.cursor()
        cursor.execute(
            "SELECT id, subject, body, sent_at "
            "FROM newsletters WHERE id = %s",
            (newsletter_id,)
        )
        row = cursor.fetchone()
        cursor.close()
        
        if not row:
            return None
            
        newsletter = {
            "id": row[0],
            "subject": row[1],
            "body": row[2],
            "sent_at": row[3]
        }
        
        _newsletter_cache[cache_key] = newsletter
        _cache_timestamp[cache_key] = current_time
        
        return newsletter
    except Exception as e:
        app.logger.error(f"Database error in get_newsletter_by_id_cached: {e}")
        return None
    finally:
        if conn:
            return_connection(conn)

def clear_newsletter_cache():
    """Clear newsletter cache when data is updated"""
    global _newsletter_cache, _cache_timestamp
    keys_to_remove = [k for k in _newsletter_cache.keys() 
                      if k.startswith('newsletter')]
    for key in keys_to_remove:
        _newsletter_cache.pop(key, None)
        _cache_timestamp.pop(key, None)

@app.before_request
def before_request():
    """Start timing the request and set up request context"""
    g.start_time = time.time()

@app.after_request
def after_request(response):
    """Log request timing and performance metrics"""
    total_time = time.time() - g.start_time
    
    # Log slow requests
    if total_time > 1.0:
        app.logger.warning(f"Slow request: {request.method} {request.path} took {total_time:.3f}s")
    elif total_time > 0.5:
        app.logger.info(f"Request: {request.method} {request.path} took {total_time:.3f}s")
    
    # Add performance headers for debugging
    response.headers['X-Response-Time'] = f"{total_time:.3f}s"
    
    return response

def send_confirmation_email(to_address: str, html_body: str):
    """
    Sends the HTML confirmation email to `to_address`.
    html_body is pre-rendered to avoid Flask context issues.
    """
    try:
        subject = "Thanks for subscribing!"

        msg = MIMEText(html_body, "html", "utf-8")
        msg["Subject"] = subject
        msg["From"] = SMTP_USER
        msg["To"] = to_address

        with smtplib.SMTP_SSL(SMTP_SERVER, SMTP_PORT, timeout=10) as server:
            server.login(SMTP_USER, SMTP_PASSWORD)
            server.sendmail(SMTP_USER, [to_address], msg.as_string())
            
        app.logger.info(f"Confirmation email sent successfully to {to_address}")
        
    except Exception as e:
        app.logger.error(f"Failed to send email to {to_address}: {e}")

def send_confirmation_async(email, html_body):
    """
    Wrapper for threading.Thread target.
    """
    send_confirmation_email(email, html_body)

@app.route("/", methods=["GET"])
def index():
    """Home page - no database access needed"""
    return render_template("index.html", is_home=True)

@app.route("/subscribe", methods=["POST"])
@limiter.limit("5 per minute")  # Strict rate limit for subscriptions
def subscribe():
    """Subscribe endpoint with optimized database handling"""
    data = request.get_json() or {}
    email = data.get("email")
    
    if not email:
        return jsonify(error="No email provided"), 400

    # Validate email format (basic check)
    if "@" not in email or "." not in email.split("@")[-1]:
        return jsonify(error="Invalid email format"), 400
    
    try:
        if add_email(email):
            # Render the template in the main thread (with Flask context)
            unsubscribe_link = f"{request.url_root}unsubscribe?email={email}"
            html_body = render_template(
                "confirmation_email.html",
                unsubscribe_link=unsubscribe_link
            )

            # Start email sending in background thread with pre-rendered HTML
            Thread(
                target=send_confirmation_async,
                args=(email, html_body),
                daemon=True
            ).start()

            return jsonify(message="Email has been added"), 201
        else:
            return jsonify(error="Email already exists"), 400
            
    except Exception as e:
        app.logger.error(f"Error in subscribe endpoint: {e}")
        return jsonify(error="Internal server error"), 500

@app.route("/unsubscribe", methods=["GET"])
@limiter.limit("10 per minute")
def unsubscribe():
    """Unsubscribe endpoint with optimized database handling"""
    email = request.args.get("email")
    
    if not email:
        return "No email specified.", 400

    try:
        if remove_email(email):
            return f"The email {email} has been unsubscribed.", 200
        else:
            return f"Email {email} was not found or has already been unsubscribed.", 400
            
    except Exception as e:
        app.logger.error(f"Error in unsubscribe endpoint: {e}")
        return "Internal server error", 500

@app.route("/newsletters", methods=["GET"])
@limiter.limit("30 per minute")
def newsletters():
    """
    List all newsletters (newest first) with caching for better performance.
    """
    try:
        newsletters = get_newsletters_cached()
        return render_template("newsletters.html", newsletters=newsletters, is_home=False)
    except Exception as e:
        app.logger.error(f"Error in newsletters endpoint: {e}")
        return "Internal server error", 500

@app.route("/newsletter/<int:newsletter_id>", methods=["GET"])
@limiter.limit("60 per minute")
def newsletter_detail(newsletter_id):
    """
    Show a single newsletter by its ID with caching.
    """
    try:
        newsletter = get_newsletter_by_id_cached(newsletter_id)
        
        if not newsletter:
            return "Newsletter not found.", 404

        return render_template("newsletter_detail.html", newsletter=newsletter, is_home=False)
    except Exception as e:
        app.logger.error(f"Error in newsletter_detail endpoint: {e}")
        return "Internal server error", 500

@app.route("/admin/clear-cache", methods=["POST"])
@limiter.limit("5 per minute")
def clear_cache():
    """Admin endpoint to clear newsletter cache"""
    try:
        clear_newsletter_cache()
        return jsonify(message="Cache cleared successfully"), 200
    except Exception as e:
        app.logger.error(f"Error clearing cache: {e}")
        return jsonify(error="Failed to clear cache"), 500

@app.route("/health", methods=["GET"])
@limiter.limit("120 per minute")
def health_check():
    """Health check endpoint for monitoring"""
    return jsonify(status="healthy", timestamp=time.time()), 200

# Rate limit error handler
@app.errorhandler(429)
def ratelimit_handler(e):
    return jsonify(error="Rate limit exceeded. Please try again later."), 429

# Error handlers
@app.errorhandler(404)
def not_found(error):
    return jsonify(error="Not found"), 404

@app.errorhandler(500)
def internal_error(error):
    return jsonify(error="Internal server error"), 500

# Initialize database at startup
try:
    init_db()
    app.logger.info("Database initialized successfully")
except Exception as e:
    app.logger.error(f"Failed to initialize database: {e}")
    raise

if __name__ == "__main__":
    app.run(host="0.0.0.0", debug=True)