server {
    listen 80;
    server_name localhost;
    root /usr/share/nginx/html;
    index index.html;

    # Enable gzip compression
    gzip on;
    gzip_vary on;
    gzip_min_length 1024;
    gzip_types text/plain text/css text/xml text/javascript application/javascript application/xml+rss application/json;

    # Handle Vue.js SPA routing
    location / {
        try_files $uri $uri/ /index.html;
    }

    # API proxy to backend with service discovery
    location /api/ {
        # Use resolver for Docker DNS
        resolver 127.0.0.11 valid=30s;
        set $backend_endpoint http://backend:80;
        
        # Use HTTPS for backend if frontend is HTTPS
        if ($scheme = https) {
            set $backend_endpoint http://backend:80;
        }
        proxy_pass $backend_endpoint;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        
        # Error handling for backend service
        proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
        proxy_connect_timeout 5s;
        proxy_send_timeout 10s;
        proxy_read_timeout 10s;
        
        # Handle CORS headers
        add_header Access-Control-Allow-Origin "*" always;
        add_header Access-Control-Allow-Methods "GET, POST, PUT, DELETE, OPTIONS" always;
        add_header Access-Control-Allow-Headers "Content-Type, Authorization, X-Requested-With" always;
        
        # Handle preflight requests
        if ($request_method = 'OPTIONS') {
            add_header Access-Control-Allow-Origin "*";
            add_header Access-Control-Allow-Methods "GET, POST, PUT, DELETE, OPTIONS";
            add_header Access-Control-Allow-Headers "Content-Type, Authorization, X-Requested-With";
            add_header Content-Length 0;
            add_header Content-Type text/plain;
            return 204;
        }
    }

    # Cache static assets
    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg)$ {
        expires 1y;
        add_header Cache-Control "public, immutable";
    }

    # Security headers
    add_header X-Frame-Options "SAMEORIGIN" always;
    add_header X-Content-Type-Options "nosniff" always;
    add_header X-XSS-Protection "1; mode=block" always;
    add_header Referrer-Policy "strict-origin-when-cross-origin" always;

    # Error pages
    error_page 404 /index.html;
    error_page 500 502 503 504 /50x.html;
    location = /50x.html {
        root /usr/share/nginx/html;
    }
}