use anyhow::Result;
use async_trait::async_trait;
use cm_dashboard_shared::{Metric, MetricValue, Status, StatusTracker};
use std::process::Command;
use std::sync::RwLock;
use std::time::Instant;
use tracing::debug;

use super::{Collector, CollectorError};
use crate::config::SystemdConfig;

/// Systemd collector for monitoring systemd services
pub struct SystemdCollector {
    /// Cached state with thread-safe interior mutability
    state: RwLock<ServiceCacheState>,
    /// Configuration for service monitoring
    config: SystemdConfig,
}

/// Internal state for service caching
#[derive(Debug)]
struct ServiceCacheState {
    /// Interesting services to monitor (cached after discovery)
    monitored_services: Vec<String>,
    /// Cached service status information from discovery
    service_status_cache: std::collections::HashMap<String, ServiceStatusInfo>,
    /// Last time services were discovered
    last_discovery_time: Option<Instant>,
    /// How often to rediscover services (5 minutes)
    discovery_interval_seconds: u64,
    /// Cached nginx site latency metrics
    nginx_site_metrics: Vec<Metric>,
    /// Last time nginx sites were checked
    last_nginx_check_time: Option<Instant>,
    /// How often to check nginx site latency (configurable)
    nginx_check_interval_seconds: u64,
}

/// Cached service status information from systemctl list-units
#[derive(Debug, Clone)]
struct ServiceStatusInfo {
    load_state: String,
    active_state: String,
    sub_state: String,
}

impl SystemdCollector {
    pub fn new(config: SystemdConfig) -> Self {
        Self {
            state: RwLock::new(ServiceCacheState {
                monitored_services: Vec::new(),
                service_status_cache: std::collections::HashMap::new(),
                last_discovery_time: None,
                discovery_interval_seconds: config.interval_seconds,
                nginx_site_metrics: Vec::new(),
                last_nginx_check_time: None,
                nginx_check_interval_seconds: config.nginx_check_interval_seconds,
            }),
            config,
        }
    }

    /// Get monitored services, discovering them if needed or cache is expired
    fn get_monitored_services(&self) -> Result<Vec<String>> {
        // Check if we need discovery without holding the lock
        let needs_discovery = {
            let state = self.state.read().unwrap();
            match state.last_discovery_time {
                None => true, // First time
                Some(last_time) => {
                    let elapsed = last_time.elapsed().as_secs();
                    elapsed >= state.discovery_interval_seconds
                }
            }
        };

        if needs_discovery {
            debug!("Discovering systemd services (cache expired or first run)");
            // Call discover_services_internal which doesn't update state
            match self.discover_services_internal() {
                Ok((services, status_cache)) => {
                    // Update state with discovered services in a separate scope
                    if let Ok(mut state) = self.state.write() {
                        state.monitored_services = services.clone();
                        state.service_status_cache = status_cache;
                        state.last_discovery_time = Some(Instant::now());
                        debug!(
                            "Auto-discovered {} services to monitor: {:?}",
                            state.monitored_services.len(),
                            state.monitored_services
                        );
                        return Ok(services);
                    }
                }
                Err(e) => {
                    debug!("Failed to discover services, using cached list: {}", e);
                    // Continue with existing cached services if discovery fails
                }
            }
        }

        // Return cached services
        let state = self.state.read().unwrap();
        Ok(state.monitored_services.clone())
    }

    /// Get nginx site metrics, checking them if cache is expired
    fn get_nginx_site_metrics(&self) -> Vec<Metric> {
        let mut state = self.state.write().unwrap();

        // Check if we need to refresh nginx site metrics
        let needs_refresh = match state.last_nginx_check_time {
            None => true, // First time
            Some(last_time) => {
                let elapsed = last_time.elapsed().as_secs();
                elapsed >= state.nginx_check_interval_seconds
            }
        };

        if needs_refresh {
            // Only check nginx sites if nginx service is active
            if state.monitored_services.iter().any(|s| s.contains("nginx")) {
                debug!(
                    "Refreshing nginx site latency metrics (interval: {}s)",
                    state.nginx_check_interval_seconds
                );
                let fresh_metrics = self.get_nginx_sites();
                state.nginx_site_metrics = fresh_metrics;
                state.last_nginx_check_time = Some(Instant::now());
            }
        }

        state.nginx_site_metrics.clone()
    }

    /// Auto-discover interesting services to monitor (internal version that doesn't update state)
    fn discover_services_internal(&self) -> Result<(Vec<String>, std::collections::HashMap<String, ServiceStatusInfo>)> {
        debug!("Starting systemd service discovery with status caching");
        
        // First: Get all service unit files (includes services that have never been started)
        let unit_files_output = Command::new("systemctl")
            .arg("list-unit-files")
            .arg("--type=service")
            .arg("--no-pager")
            .arg("--plain")
            .output()?;

        if !unit_files_output.status.success() {
            return Err(anyhow::anyhow!("systemctl list-unit-files command failed"));
        }

        // Second: Get runtime status of all units
        let units_status_output = Command::new("systemctl")
            .arg("list-units")
            .arg("--type=service")
            .arg("--all")
            .arg("--no-pager")
            .arg("--plain")
            .output()?;

        if !units_status_output.status.success() {
            return Err(anyhow::anyhow!("systemctl list-units command failed"));
        }

        let unit_files_str = String::from_utf8(unit_files_output.stdout)?;
        let units_status_str = String::from_utf8(units_status_output.stdout)?;
        let mut services = Vec::new();

        // Use configuration instead of hardcoded values
        let excluded_services = &self.config.excluded_services;
        let service_name_filters = &self.config.service_name_filters;

        // Parse all service unit files to get complete service list
        let mut all_service_names = std::collections::HashSet::new();
        
        for line in unit_files_str.lines() {
            let fields: Vec<&str> = line.split_whitespace().collect();
            if fields.len() >= 2 && fields[0].ends_with(".service") {
                let service_name = fields[0].trim_end_matches(".service");
                all_service_names.insert(service_name.to_string());
                debug!("Found service unit file: {}", service_name);
            }
        }

        // Parse runtime status for all units
        let mut status_cache = std::collections::HashMap::new();
        for line in units_status_str.lines() {
            let fields: Vec<&str> = line.split_whitespace().collect();
            if fields.len() >= 4 && fields[0].ends_with(".service") {
                let service_name = fields[0].trim_end_matches(".service");
                
                // Extract status information from systemctl list-units output
                let load_state = fields.get(1).unwrap_or(&"unknown").to_string();
                let active_state = fields.get(2).unwrap_or(&"unknown").to_string();
                let sub_state = fields.get(3).unwrap_or(&"unknown").to_string();

                // Cache the status information
                status_cache.insert(service_name.to_string(), ServiceStatusInfo {
                    load_state: load_state.clone(),
                    active_state: active_state.clone(),
                    sub_state: sub_state.clone(),
                });

                debug!("Got runtime status for service: {} (load:{}, active:{}, sub:{})", service_name, load_state, active_state, sub_state);
            }
        }

        // For services found in unit files but not in runtime status, set default inactive status
        for service_name in &all_service_names {
            if !status_cache.contains_key(service_name) {
                status_cache.insert(service_name.to_string(), ServiceStatusInfo {
                    load_state: "not-loaded".to_string(),
                    active_state: "inactive".to_string(),
                    sub_state: "dead".to_string(),
                });
                debug!("Service {} found in unit files but not runtime - marked as inactive", service_name);
            }
        }


        // Now process all discovered services
        for service_name in &all_service_names {
                debug!("Processing service: '{}'", service_name);

                // Skip excluded services first
                let mut is_excluded = false;
                for excluded in excluded_services {
                    if service_name.contains(excluded) {
                        debug!(
                            "EXCLUDING service '{}' because it matches pattern '{}'",
                            service_name, excluded
                        );
                        is_excluded = true;
                        break;
                    }
                }

                if is_excluded {
                    debug!("Skipping excluded service: '{}'", service_name);
                    continue;
                }

                // Check if this service matches our filter patterns (supports wildcards)
                for pattern in service_name_filters {
                    if self.matches_pattern(service_name, pattern) {
                        debug!(
                            "INCLUDING service '{}' because it matches pattern '{}'",
                            service_name, pattern
                        );
                        services.push(service_name.to_string());
                        break;
                    }
                }
        }

        debug!("Service discovery completed: found {} matching services: {:?}", services.len(), services);
        if services.is_empty() {
            debug!("No services found matching the configured filters - this may indicate a parsing issue");
        }

        Ok((services, status_cache))
    }

    /// Check if service name matches pattern (supports wildcards like nginx*)
    fn matches_pattern(&self, service_name: &str, pattern: &str) -> bool {
        if pattern.contains('*') {
            // Wildcard pattern matching
            if pattern.ends_with('*') {
                // Pattern like "nginx*" - match if service starts with "nginx"
                let prefix = &pattern[..pattern.len() - 1];
                service_name.starts_with(prefix)
            } else if pattern.starts_with('*') {
                // Pattern like "*backup" - match if service ends with "backup"
                let suffix = &pattern[1..];
                service_name.ends_with(suffix)
            } else {
                // Pattern like "nginx*backup" - simple glob matching
                self.simple_glob_match(service_name, pattern)
            }
        } else {
            // Exact match (existing behavior)
            service_name == pattern
        }
    }

    /// Simple glob pattern matching for patterns with * in middle
    fn simple_glob_match(&self, text: &str, pattern: &str) -> bool {
        let parts: Vec<&str> = pattern.split('*').collect();
        if parts.is_empty() {
            return false;
        }

        let mut pos = 0;
        for (i, part) in parts.iter().enumerate() {
            if part.is_empty() {
                continue;
            }

            if i == 0 {
                // First part must match at start
                if !text[pos..].starts_with(part) {
                    return false;
                }
                pos += part.len();
            } else if i == parts.len() - 1 {
                // Last part must match at end
                return text[pos..].ends_with(part);
            } else {
                // Middle part must be found somewhere
                if let Some(found_pos) = text[pos..].find(part) {
                    pos += found_pos + part.len();
                } else {
                    return false;
                }
            }
        }
        true
    }

    /// Get service status from cache (if available) or fallback to systemctl
    fn get_service_status(&self, service: &str) -> Result<(String, String)> {
        // Try to get status from cache first
        if let Ok(state) = self.state.read() {
            if let Some(cached_info) = state.service_status_cache.get(service) {
                let active_status = cached_info.active_state.clone();
                let detailed_info = format!(
                    "LoadState={}\nActiveState={}\nSubState={}",
                    cached_info.load_state,
                    cached_info.active_state,
                    cached_info.sub_state
                );
                return Ok((active_status, detailed_info));
            }
        }

        // Fallback to systemctl if not in cache (shouldn't happen during normal operation)
        debug!("Service '{}' not found in cache, falling back to systemctl", service);
        let output = Command::new("systemctl")
            .arg("is-active")
            .arg(format!("{}.service", service))
            .output()?;

        let active_status = String::from_utf8(output.stdout)?.trim().to_string();

        // Get more detailed info
        let output = Command::new("systemctl")
        .arg("show")
        .arg(format!("{}.service", service))
        .arg("--property=LoadState,ActiveState,SubState")
        .output()?;

        let detailed_info = String::from_utf8(output.stdout)?;
        Ok((active_status, detailed_info))
    }

    /// Calculate service status, taking user-stopped services into account
    fn calculate_service_status(&self, service_name: &str, active_status: &str) -> Status {
        match active_status.to_lowercase().as_str() {
            "active" => Status::Ok,
            "inactive" | "dead" => {
                debug!("Service '{}' is inactive - treating as Inactive status", service_name);
                Status::Inactive
            },
            "failed" | "error" => Status::Critical,
            "activating" | "deactivating" | "reloading" | "start" | "stop" | "restart" => {
                debug!("Service '{}' is transitioning - treating as Pending", service_name);
                Status::Pending
            },
            _ => Status::Unknown,
        }
    }

    /// Get service memory usage (if available)
    fn get_service_memory(&self, service: &str) -> Option<f32> {
        let output = Command::new("systemctl")
            .arg("show")
            .arg(format!("{}.service", service))
            .arg("--property=MemoryCurrent")
            .output()
            .ok()?;

        let output_str = String::from_utf8(output.stdout).ok()?;
        for line in output_str.lines() {
            if line.starts_with("MemoryCurrent=") {
                let memory_str = line.trim_start_matches("MemoryCurrent=");
                if let Ok(memory_bytes) = memory_str.parse::<u64>() {
                    return Some(memory_bytes as f32 / (1024.0 * 1024.0)); // Convert to MB
                }
            }
        }
        None
    }


    /// Get directory size in GB with permission-aware logging
    fn get_directory_size(&self, dir: &str) -> Option<f32> {
        let output = Command::new("sudo").arg("du").arg("-sb").arg(dir).output().ok()?;

        if !output.status.success() {
            // Log permission errors for debugging but don't spam logs
            let stderr = String::from_utf8_lossy(&output.stderr);
            if stderr.contains("Permission denied") {
                debug!("Permission denied accessing directory: {}", dir);
            } else {
                debug!("Failed to get size for directory {}: {}", dir, stderr);
            }
            return None;
        }

        let output_str = String::from_utf8(output.stdout).ok()?;
        let size_str = output_str.split_whitespace().next()?;
        if let Ok(size_bytes) = size_str.parse::<u64>() {
            let size_gb = size_bytes as f32 / (1024.0 * 1024.0 * 1024.0);
            // Return size even if very small (minimum 0.001 GB = 1MB for visibility)
            if size_gb > 0.0 {
                Some(size_gb.max(0.001))
            } else {
                None
            }
        } else {
            None
        }
    }

    /// Get service disk usage - simplified and configuration-driven
    fn get_service_disk_usage(&self, service: &str) -> Option<f32> {
        // 1. Check if service has configured directories (exact match only)
        if let Some(dirs) = self.config.service_directories.get(service) {
            // Service has configured paths - use the first accessible one
            for dir in dirs {
                if let Some(size) = self.get_directory_size(dir) {
                    return Some(size);
                }
            }
            // If configured paths failed, return None (shows as 0)
            return Some(0.0);
        }

        // 2. No configured path - use systemctl WorkingDirectory
        let output = Command::new("systemctl")
            .arg("show")
            .arg(format!("{}.service", service))
            .arg("--property=WorkingDirectory")
            .output()
            .ok()?;

        let output_str = String::from_utf8(output.stdout).ok()?;
        for line in output_str.lines() {
            if line.starts_with("WorkingDirectory=") && !line.contains("[not set]") {
                let dir = line.trim_start_matches("WorkingDirectory=");
                if !dir.is_empty() && dir != "/" {
                    return self.get_directory_size(dir);
                }
            }
        }

        None
    }






}

#[async_trait]
impl Collector for SystemdCollector {

    async fn collect(&self, _status_tracker: &mut StatusTracker) -> Result<Vec<Metric>, CollectorError> {
        let start_time = Instant::now();
        debug!("Collecting systemd services metrics");

        let mut metrics = Vec::new();

        // Get cached services (discovery only happens when needed)
        let monitored_services = match self.get_monitored_services() {
            Ok(services) => services,
            Err(e) => {
                debug!("Failed to get monitored services: {}", e);
                return Ok(metrics);
            }
        };

        // Collect individual metrics for each monitored service (status, memory, disk only)
        for service in &monitored_services {
            match self.get_service_status(service) {
                Ok((active_status, _detailed_info)) => {
                    let status = self.calculate_service_status(service, &active_status);

                    // Individual service status metric
                    metrics.push(Metric {
                        name: format!("service_{}_status", service),
                        value: MetricValue::String(active_status.clone()),
                        unit: None,
                        description: Some(format!("Service {} status", service)),
                        status,
                        timestamp: chrono::Utc::now().timestamp() as u64,
                    });

                    // Service memory usage (if available)
                    if let Some(memory_mb) = self.get_service_memory(service) {
                        metrics.push(Metric {
                            name: format!("service_{}_memory_mb", service),
                            value: MetricValue::Float(memory_mb),
                            unit: Some("MB".to_string()),
                            description: Some(format!("Service {} memory usage", service)),
                            status: Status::Ok,
                            timestamp: chrono::Utc::now().timestamp() as u64,
                        });
                    }

                    // Service disk usage (comprehensive detection)
                    if let Some(disk_gb) = self.get_service_disk_usage(service) {
                        metrics.push(Metric {
                            name: format!("service_{}_disk_gb", service),
                            value: MetricValue::Float(disk_gb),
                            unit: Some("GB".to_string()),
                            description: Some(format!("Service {} disk usage", service)),
                            status: Status::Ok,
                            timestamp: chrono::Utc::now().timestamp() as u64,
                        });
                    }

                    // Sub-service metrics for specific services
                    if service.contains("nginx") && active_status == "active" {
                        metrics.extend(self.get_nginx_site_metrics());
                    }

                    if service.contains("docker") && active_status == "active" {
                        metrics.extend(self.get_docker_containers());
                    }
                }
                Err(e) => {
                    debug!("Failed to get status for service {}: {}", service, e);
                }
            }
        }

        let collection_time = start_time.elapsed();
        debug!(
            "Systemd collection completed in {:?} with {} individual service metrics",
            collection_time,
            metrics.len()
        );

        Ok(metrics)
    }

}

impl SystemdCollector {
    /// Get nginx sites with latency checks
    fn get_nginx_sites(&self) -> Vec<Metric> {
        let mut metrics = Vec::new();
        let timestamp = chrono::Utc::now().timestamp() as u64;

        // Discover nginx sites from configuration
        let sites = self.discover_nginx_sites();

        for (site_name, url) in &sites {
            match self.check_site_latency(url) {
                Ok(latency_ms) => {
                    let status = if latency_ms < self.config.nginx_latency_critical_ms {
                        Status::Ok
                    } else {
                        Status::Critical
                    };

                    metrics.push(Metric {
                        name: format!("service_nginx_{}_latency_ms", site_name),
                        value: MetricValue::Float(latency_ms),
                        unit: Some("ms".to_string()),
                        description: Some(format!("Response time for {}", url)),
                        status,
                        timestamp,
                    });
                }
                Err(_) => {
                    // Site is unreachable
                    metrics.push(Metric {
                        name: format!("service_nginx_{}_latency_ms", site_name),
                        value: MetricValue::Float(-1.0), // Use -1 to indicate error
                        unit: Some("ms".to_string()),
                        description: Some(format!("Response time for {} (unreachable)", url)),
                        status: Status::Critical,
                        timestamp,
                    });
                }
            }
        }

        metrics
    }

    /// Get docker containers as sub-services
    fn get_docker_containers(&self) -> Vec<Metric> {
        let mut metrics = Vec::new();
        let timestamp = chrono::Utc::now().timestamp() as u64;

        // Check if docker is available
        let output = Command::new("docker")
            .arg("ps")
            .arg("--format")
            .arg("{{.Names}},{{.Status}}")
            .output();

        let output = match output {
            Ok(out) if out.status.success() => out,
            _ => return metrics, // Docker not available or failed
        };

        let output_str = match String::from_utf8(output.stdout) {
            Ok(s) => s,
            Err(_) => return metrics,
        };

        for line in output_str.lines() {
            if line.trim().is_empty() {
                continue;
            }

            let parts: Vec<&str> = line.split(',').collect();
            if parts.len() >= 2 {
                let container_name = parts[0].trim();
                let status_str = parts[1].trim();

                let status = if status_str.contains("Up") {
                    Status::Ok
                } else if status_str.contains("Exited") {
                    Status::Warning
                } else {
                    Status::Critical
                };

                metrics.push(Metric {
                    name: format!("service_docker_{}_status", container_name),
                    value: MetricValue::String(status_str.to_string()),
                    unit: None,
                    description: Some(format!("Docker container {} status", container_name)),
                    status,
                    timestamp,
                });
            }
        }

        metrics
    }

    /// Check site latency using HTTP GET requests
    fn check_site_latency(&self, url: &str) -> Result<f32, Box<dyn std::error::Error>> {
        use std::time::Duration;
        use std::time::Instant;

        let start = Instant::now();

        // Create HTTP client with timeouts from configuration
        let client = reqwest::blocking::Client::builder()
            .timeout(Duration::from_secs(self.config.http_timeout_seconds))
            .connect_timeout(Duration::from_secs(self.config.http_connect_timeout_seconds))
            .redirect(reqwest::redirect::Policy::limited(10))
            .build()?;

        // Make GET request and measure latency
        let response = client.get(url).send()?;
        let latency = start.elapsed().as_millis() as f32;

        // Check if response is successful (2xx or 3xx status codes)
        if response.status().is_success() || response.status().is_redirection() {
            Ok(latency)
        } else {
            Err(format!(
                "HTTP request failed for {} with status: {}",
                url,
                response.status()
            )
            .into())
        }
    }

    /// Discover nginx sites from configuration files (like the old working implementation)
    fn discover_nginx_sites(&self) -> Vec<(String, String)> {
        use tracing::debug;

        // Use the same approach as the old working agent: get nginx config from systemd
        let config_content = match self.get_nginx_config_from_systemd() {
            Some(content) => content,
            None => {
                debug!("Could not get nginx config from systemd, trying nginx -T fallback");
                match self.get_nginx_config_via_command() {
                    Some(content) => content,
                    None => {
                        debug!("Could not get nginx config via any method");
                        return Vec::new();
                    }
                }
            }
        };

        // Parse the config content to extract sites
        self.parse_nginx_config_for_sites(&config_content)
    }

    /// Get nginx config from systemd service definition (NixOS compatible)
    fn get_nginx_config_from_systemd(&self) -> Option<String> {
        use tracing::debug;

        let output = std::process::Command::new("systemctl")
            .args(["show", "nginx", "--property=ExecStart", "--no-pager"])
            .output()
            .ok()?;

        if !output.status.success() {
            debug!("Failed to get nginx ExecStart from systemd");
            return None;
        }

        let stdout = String::from_utf8_lossy(&output.stdout);
        debug!("systemctl show nginx output: {}", stdout);

        // Parse ExecStart to extract -c config path
        for line in stdout.lines() {
            if line.starts_with("ExecStart=") {
                debug!("Found ExecStart line: {}", line);
                // Handle both traditional and NixOS systemd formats
                if let Some(config_path) = self.extract_config_path_from_exec_start(line) {
                    debug!("Extracted config path: {}", config_path);
                    // Read the config file
                    return std::fs::read_to_string(&config_path)
                        .map_err(|e| debug!("Failed to read config file {}: {}", config_path, e))
                        .ok();
                }
            }
        }

        None
    }

    /// Extract config path from ExecStart line
    fn extract_config_path_from_exec_start(&self, exec_start: &str) -> Option<String> {
        use tracing::debug;

        // Remove ExecStart= prefix
        let exec_part = exec_start.strip_prefix("ExecStart=")?;
        debug!("Parsing exec part: {}", exec_part);

        // Handle NixOS format: ExecStart={ path=...; argv[]=...nginx -c /config; ... }
        if exec_part.contains("argv[]=") {
            // Extract the part after argv[]=
            let argv_start = exec_part.find("argv[]=")?;
            let argv_part = &exec_part[argv_start + 7..]; // Skip "argv[]="
            debug!("Found NixOS argv part: {}", argv_part);

            // Look for -c flag followed by config path
            if let Some(c_pos) = argv_part.find(" -c ") {
                let after_c = &argv_part[c_pos + 4..];
                // Find the config path (until next space or semicolon)
                let config_path = after_c.split([' ', ';']).next()?;
                return Some(config_path.to_string());
            }
        } else {
            // Handle traditional format: ExecStart=/path/nginx -c /config
            debug!("Parsing traditional format");
            if let Some(c_pos) = exec_part.find(" -c ") {
                let after_c = &exec_part[c_pos + 4..];
                let config_path = after_c.split_whitespace().next()?;
                return Some(config_path.to_string());
            }
        }

        None
    }

    /// Fallback: get nginx config via nginx -T command
    fn get_nginx_config_via_command(&self) -> Option<String> {
        use tracing::debug;

        let output = std::process::Command::new("nginx")
            .args(["-T"])
            .output()
            .ok()?;

        if !output.status.success() {
            debug!("nginx -T failed");
            return None;
        }

        Some(String::from_utf8_lossy(&output.stdout).to_string())
    }

    /// Parse nginx config content to extract server names and build site list
    fn parse_nginx_config_for_sites(&self, config_content: &str) -> Vec<(String, String)> {
        use tracing::debug;
        let mut sites = Vec::new();
        let lines: Vec<&str> = config_content.lines().collect();
        let mut i = 0;

        debug!("Parsing nginx config with {} lines", lines.len());

        while i < lines.len() {
            let line = lines[i].trim();
            if line.starts_with("server") && line.contains("{") {
                if let Some(server_name) = self.parse_server_block(&lines, &mut i) {
                    let url = format!("https://{}", server_name);
                    sites.push((server_name.clone(), url));
                }
            }
            i += 1;
        }

        debug!("Discovered {} nginx sites total", sites.len());
        sites
    }

    /// Parse a server block to extract the primary server_name
    fn parse_server_block(&self, lines: &[&str], start_index: &mut usize) -> Option<String> {
        use tracing::debug;
        let mut server_names = Vec::new();
        let mut has_redirect = false;
        let mut i = *start_index + 1;
        let mut brace_count = 1;

        // Parse until we close the server block
        while i < lines.len() && brace_count > 0 {
            let trimmed = lines[i].trim();

            // Track braces
            brace_count += trimmed.matches('{').count();
            brace_count -= trimmed.matches('}').count();

            // Extract server_name
            if trimmed.starts_with("server_name") {
                if let Some(names_part) = trimmed.strip_prefix("server_name") {
                    let names_clean = names_part.trim().trim_end_matches(';');
                    for name in names_clean.split_whitespace() {
                        if name != "_"
                            && !name.is_empty()
                            && name.contains('.')
                            && !name.starts_with('$')
                        {
                            server_names.push(name.to_string());
                            debug!("Found server_name in block: {}", name);
                        }
                    }
                }
            }


            // Check for redirects (skip redirect-only servers)
            if trimmed.contains("return") && (trimmed.contains("301") || trimmed.contains("302")) {
                has_redirect = true;
            }

            i += 1;
        }

        *start_index = i - 1;

        if !server_names.is_empty() && !has_redirect {
            return Some(server_names[0].clone());
        }

        None
    }
}