# Nginx Reverse Proxy Configuration for StemeDB
#
# This configuration provides:
# - TLS 1.3 termination with Let's Encrypt
# - HTTP → HTTPS redirect
# - Request size limits (2MB)
# - Rate limiting (100 req/sec per IP)
# - Security headers (HSTS, X-Frame-Options)
# - Health-checked upstream (single-node or cluster)
# - Admin endpoint restrictions (VPN-only)
# - Metrics endpoint restrictions (internal-only)
#
# Installation:
#   sudo cp stemedb.conf /etc/nginx/sites-available/
#   sudo ln -s /etc/nginx/sites-available/stemedb.conf /etc/nginx/sites-enabled/
#   sudo nginx -t
#   sudo systemctl reload nginx

# ┌───────────────────────────────────────────────────────────┐
# │  Rate Limiting Zones                                      │
# └───────────────────────────────────────────────────────────┘

# Zone for general API requests (100 req/sec per IP)
limit_req_zone $binary_remote_addr zone=api_limit:10m rate=100r/s;

# Zone for write-heavy endpoints (10 req/sec per IP)
limit_req_zone $binary_remote_addr zone=write_limit:10m rate=10r/s;

# Connection limit (max 10 concurrent per IP)
limit_conn_zone $binary_remote_addr zone=conn_limit:10m;

# ┌───────────────────────────────────────────────────────────┐
# │  Upstream Configuration                                   │
# └───────────────────────────────────────────────────────────┘

# Single-node configuration
upstream stemedb_backend {
    server localhost:18180;

    # Health check (requires nginx_upstream_check_module)
    # check interval=5000 rise=2 fall=3 timeout=3000;

    # Connection keepalive
    keepalive 32;
}

# Three-node cluster configuration (comment out single-node above)
# upstream stemedb_cluster {
#     # Round-robin (default)
#     server 10.0.1.51:18180 weight=1 max_fails=3 fail_timeout=30s;
#     server 10.0.1.52:18180 weight=1 max_fails=3 fail_timeout=30s;
#     server 10.0.1.53:18180 weight=1 max_fails=3 fail_timeout=30s;
#
#     # Connection keepalive
#     keepalive 32;
# }

# ┌───────────────────────────────────────────────────────────┐
# │  HTTP → HTTPS Redirect                                    │
# └───────────────────────────────────────────────────────────┘

server {
    listen 80;
    listen [::]:80;
    server_name stemedb.example.com;

    # Let's Encrypt ACME challenge
    location /.well-known/acme-challenge/ {
        root /var/www/certbot;
    }

    # Redirect all other traffic to HTTPS
    location / {
        return 301 https://$server_name$request_uri;
    }
}

# ┌───────────────────────────────────────────────────────────┐
# │  HTTPS Server (Main Configuration)                        │
# └───────────────────────────────────────────────────────────┘

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    server_name stemedb.example.com;

    # ─────────────────────────────────────────────────────────
    # TLS Configuration
    # ─────────────────────────────────────────────────────────

    # Let's Encrypt certificates (managed by certbot)
    ssl_certificate /etc/letsencrypt/live/stemedb.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/stemedb.example.com/privkey.pem;

    # TLS 1.3 only (most secure)
    ssl_protocols TLSv1.3;

    # Strong ciphers (TLS 1.3)
    ssl_prefer_server_ciphers on;
    ssl_ciphers 'TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256';

    # SSL session cache
    ssl_session_cache shared:SSL:10m;
    ssl_session_timeout 10m;
    ssl_session_tickets off;

    # OCSP Stapling
    ssl_stapling on;
    ssl_stapling_verify on;
    ssl_trusted_certificate /etc/letsencrypt/live/stemedb.example.com/chain.pem;
    resolver 8.8.8.8 8.8.4.4 valid=300s;
    resolver_timeout 5s;

    # ─────────────────────────────────────────────────────────
    # Security Headers
    # ─────────────────────────────────────────────────────────

    # HSTS (1 year, include subdomains)
    add_header Strict-Transport-Security "max-age=31536000; includeSubDomains; preload" always;

    # Prevent clickjacking
    add_header X-Frame-Options "SAMEORIGIN" always;

    # Content type sniffing
    add_header X-Content-Type-Options "nosniff" always;

    # XSS protection
    add_header X-XSS-Protection "1; mode=block" always;

    # Referrer policy
    add_header Referrer-Policy "strict-origin-when-cross-origin" always;

    # CSP (Content Security Policy)
    add_header Content-Security-Policy "default-src 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; font-src 'self'; connect-src 'self';" always;

    # ─────────────────────────────────────────────────────────
    # Logging
    # ─────────────────────────────────────────────────────────

    access_log /var/log/nginx/stemedb-access.log combined;
    error_log /var/log/nginx/stemedb-error.log warn;

    # ─────────────────────────────────────────────────────────
    # Global Limits
    # ─────────────────────────────────────────────────────────

    # Max request body size (2MB for assertions)
    client_max_body_size 2M;

    # Timeout settings
    proxy_connect_timeout 10s;
    proxy_send_timeout 30s;
    proxy_read_timeout 30s;

    # Connection limits
    limit_conn conn_limit 10;

    # ─────────────────────────────────────────────────────────
    # Health Check Endpoint (Public)
    # ─────────────────────────────────────────────────────────

    location = /v1/health {
        proxy_pass http://stemedb_backend;
        proxy_http_version 1.1;
        proxy_set_header Connection "";

        # No rate limiting on health checks
        limit_req off;

        # Fast timeout for health checks
        proxy_connect_timeout 3s;
        proxy_send_timeout 5s;
        proxy_read_timeout 5s;
    }

    # ─────────────────────────────────────────────────────────
    # Write Endpoints (Stricter Rate Limits)
    # ─────────────────────────────────────────────────────────

    location ~ ^/v1/(assert|retract)$ {
        # Apply write rate limit (10 req/sec, burst 20)
        limit_req zone=write_limit burst=20 nodelay;

        proxy_pass http://stemedb_backend;
        proxy_http_version 1.1;
        proxy_set_header Connection "";
        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;

        # Don't retry writes (not idempotent)
        proxy_next_upstream off;
    }

    # ─────────────────────────────────────────────────────────
    # Query Endpoints (Standard Rate Limits)
    # ─────────────────────────────────────────────────────────

    location /v1/query {
        # Apply API rate limit (100 req/sec, burst 200)
        limit_req zone=api_limit burst=200 nodelay;

        proxy_pass http://stemedb_backend;
        proxy_http_version 1.1;
        proxy_set_header Connection "";
        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;

        # Retry on specific errors
        proxy_next_upstream error timeout http_502 http_503;
        proxy_next_upstream_tries 2;
        proxy_next_upstream_timeout 10s;
    }

    # ─────────────────────────────────────────────────────────
    # Admin Endpoints (Restricted to Internal Network)
    # ─────────────────────────────────────────────────────────

    location /v1/admin/ {
        # ⚠️ CRITICAL: Admin endpoints have NO authentication
        # Restrict to internal network only

        # Allow from internal network
        allow 10.0.0.0/8;
        allow 172.16.0.0/12;
        allow 192.168.0.0/16;

        # Or allow from specific VPN subnet
        # allow 10.8.0.0/24;

        # Deny all others
        deny all;

        proxy_pass http://stemedb_backend;
        proxy_http_version 1.1;
        proxy_set_header Connection "";
        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;
    }

    # ─────────────────────────────────────────────────────────
    # Metrics Endpoint (Restricted to Prometheus)
    # ─────────────────────────────────────────────────────────

    location /metrics {
        # Only allow from Prometheus server
        allow 10.0.1.100;  # Replace with your Prometheus IP

        # Deny all others
        deny all;

        proxy_pass http://stemedb_backend;
        proxy_http_version 1.1;
        proxy_set_header Connection "";

        # No rate limiting on metrics
        limit_req off;
    }

    # ─────────────────────────────────────────────────────────
    # Dashboard (Public with Rate Limiting)
    # ─────────────────────────────────────────────────────────

    location / {
        # Apply API rate limit
        limit_req zone=api_limit burst=200 nodelay;

        proxy_pass http://stemedb_backend;
        proxy_http_version 1.1;
        proxy_set_header Connection "";
        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;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";  # For WebSocket support
    }

    # ─────────────────────────────────────────────────────────
    # Static Files (Optional - for custom dashboard assets)
    # ─────────────────────────────────────────────────────────

    # location /static/ {
    #     alias /var/www/stemedb/static/;
    #     expires 1y;
    #     add_header Cache-Control "public, immutable";
    # }

    # ─────────────────────────────────────────────────────────
    # Error Pages
    # ─────────────────────────────────────────────────────────

    error_page 502 503 504 /50x.html;
    location = /50x.html {
        root /usr/share/nginx/html;
        internal;
    }

    # Custom 429 (rate limit) page
    error_page 429 /429.html;
    location = /429.html {
        root /usr/share/nginx/html;
        internal;
    }

    # Custom 403 (forbidden) page
    error_page 403 /403.html;
    location = /403.html {
        root /usr/share/nginx/html;
        internal;
    }
}

# ┌───────────────────────────────────────────────────────────┐
# │  Usage Instructions                                       │
# └───────────────────────────────────────────────────────────┘
#
# 1. Install certbot:
#    sudo apt install certbot python3-certbot-nginx
#
# 2. Obtain certificate:
#    sudo certbot --nginx -d stemedb.example.com
#
# 3. Copy config:
#    sudo cp stemedb.conf /etc/nginx/sites-available/
#
# 4. Update variables:
#    - Replace stemedb.example.com with your domain
#    - Update internal network ranges (10.0.0.0/8)
#    - Update Prometheus IP (10.0.1.100)
#
# 5. Enable site:
#    sudo ln -s /etc/nginx/sites-available/stemedb.conf /etc/nginx/sites-enabled/
#
# 6. Test config:
#    sudo nginx -t
#
# 7. Reload nginx:
#    sudo systemctl reload nginx
#
# 8. Test endpoints:
#    curl https://stemedb.example.com/v1/health
#
# 9. Set up auto-renewal:
#    sudo crontab -e
#    # Add: 0 3 * * * certbot renew --quiet && systemctl reload nginx

# ┌───────────────────────────────────────────────────────────┐
# │  Monitoring & Troubleshooting                             │
# └───────────────────────────────────────────────────────────┘
#
# View access logs:
#   sudo tail -f /var/log/nginx/stemedb-access.log
#
# View error logs:
#   sudo tail -f /var/log/nginx/stemedb-error.log
#
# Check rate limit status:
#   sudo grep "limiting requests" /var/log/nginx/stemedb-error.log
#
# Test rate limiting:
#   for i in {1..150}; do curl https://stemedb.example.com/v1/health; done
#   # Should see 429 after 100 requests
#
# Check TLS configuration:
#   openssl s_client -connect stemedb.example.com:443 -tls1_3
#
# Test security headers:
#   curl -I https://stemedb.example.com/v1/health

# ┌───────────────────────────────────────────────────────────┐
# │  Production Hardening Checklist                           │
# └───────────────────────────────────────────────────────────┘
#
# - [ ] Enable ModSecurity WAF (optional)
# - [ ] Set up fail2ban for DDoS protection
# - [ ] Configure log rotation (logrotate)
# - [ ] Set up centralized logging (ELK, Splunk)
# - [ ] Enable nginx status page (/nginx_status) for monitoring
# - [ ] Configure backup upstream servers
# - [ ] Set up nginx Prometheus exporter
# - [ ] Test certificate renewal process
# - [ ] Document rate limit thresholds
# - [ ] Create custom error pages (50x.html, 429.html)