cm-dashboard/agent/src/collectors/memory.rs

use async_trait::async_trait;
use cm_dashboard_shared::{AgentData, TmpfsData, HysteresisThresholds, Status};

use tracing::debug;

use super::{utils, Collector, CollectorError};
use crate::config::MemoryConfig;

/// Extremely efficient memory metrics collector
///
/// EFFICIENCY OPTIMIZATIONS:
/// - Single /proc/meminfo read for all memory metrics
/// - Minimal string allocations
/// - No process spawning for basic metrics
/// - <0.5ms collection time target
pub struct MemoryCollector {
    usage_thresholds: HysteresisThresholds,
}

impl MemoryCollector {
    pub fn new(config: MemoryConfig) -> Self {
        // Create hysteresis thresholds with 10% gap for recovery
        let usage_thresholds = HysteresisThresholds::new(
            config.usage_warning_percent,
            config.usage_critical_percent,
        );
        
        Self {
            usage_thresholds,
        }
    }

    /// Parse /proc/meminfo efficiently
    /// Format: "MemTotal:       16384000 kB"
    async fn parse_meminfo(&self) -> Result<MemoryInfo, CollectorError> {
        let content = utils::read_proc_file("/proc/meminfo")?;
        let mut info = MemoryInfo::default();

        // Parse each line efficiently - only extract what we need
        for line in content.lines() {
            if let Some(colon_pos) = line.find(':') {
                let key = &line[..colon_pos];
                let value_part = &line[colon_pos + 1..];

                // Extract number from value part (format: "    12345 kB")
                if let Some(number_str) = value_part.split_whitespace().next() {
                    if let Ok(value_kb) = utils::parse_u64(number_str) {
                        match key {
                            "MemTotal" => info.total_kb = value_kb,
                            "MemAvailable" => info.available_kb = value_kb,
                            "MemFree" => info.free_kb = value_kb,
                            "Buffers" => info.buffers_kb = value_kb,
                            "Cached" => info.cached_kb = value_kb,
                            "SwapTotal" => info.swap_total_kb = value_kb,
                            "SwapFree" => info.swap_free_kb = value_kb,
                            _ => {} // Skip other fields for efficiency
                        }
                    }
                }
            }
        }

        // Validate that we got essential fields
        if info.total_kb == 0 {
            return Err(CollectorError::Parse {
                value: "MemTotal".to_string(),
                error: "MemTotal not found or zero in /proc/meminfo".to_string(),
            });
        }

        // If MemAvailable is not available (older kernels), calculate it
        if info.available_kb == 0 {
            info.available_kb = info.free_kb + info.buffers_kb + info.cached_kb;
        }

        Ok(info)
    }

    /// Populate memory data directly into AgentData
    async fn populate_memory_data(&self, info: &MemoryInfo, agent_data: &mut AgentData) -> Result<(), CollectorError> {
        // Calculate derived values
        let available = info.available_kb;
        let used = info.total_kb - available;
        let usage_percent = (used as f32 / info.total_kb as f32) * 100.0;

        // Populate basic memory fields
        agent_data.system.memory.usage_percent = usage_percent;
        agent_data.system.memory.total_gb = info.total_kb as f32 / (1024.0 * 1024.0);
        agent_data.system.memory.used_gb = used as f32 / (1024.0 * 1024.0);

        // Populate swap data if available
        agent_data.system.memory.swap_total_gb = info.swap_total_kb as f32 / (1024.0 * 1024.0);
        agent_data.system.memory.swap_used_gb = (info.swap_total_kb - info.swap_free_kb) as f32 / (1024.0 * 1024.0);

        Ok(())
    }

    /// Populate tmpfs data into AgentData using statvfs syscall
    async fn populate_tmpfs_data(&self, agent_data: &mut AgentData) -> Result<(), CollectorError> {
        use nix::sys::statvfs::statvfs;

        // Discover all tmpfs mount points
        let tmpfs_mounts = self.discover_tmpfs_mounts()?;

        if tmpfs_mounts.is_empty() {
            debug!("No tmpfs mounts found to monitor");
            return Ok(());
        }

        // Get usage data for each tmpfs mount using statvfs syscall
        for mount_point in tmpfs_mounts {
            match statvfs(mount_point.as_str()) {
                Ok(stat) => {
                    let block_size = stat.fragment_size() as u64;
                    let total_bytes = stat.blocks() as u64 * block_size;
                    let available_bytes = stat.blocks_available() as u64 * block_size;
                    let used_bytes = total_bytes - available_bytes;

                    if total_bytes == 0 {
                        continue;
                    }

                    let total_gb = total_bytes as f32 / (1024.0 * 1024.0 * 1024.0);
                    let used_gb = used_bytes as f32 / (1024.0 * 1024.0 * 1024.0);
                    let usage_percent = (used_bytes as f32 / total_bytes as f32) * 100.0;

                    // Add to tmpfs list
                    agent_data.system.memory.tmpfs.push(TmpfsData {
                        mount: mount_point.clone(),
                        usage_percent,
                        used_gb,
                        total_gb,
                    });
                }
                Err(e) => {
                    debug!("Failed to get stats for tmpfs mount {}: {}", mount_point, e);
                }
            }
        }

        // Sort tmpfs mounts by mount point for consistent display order
        agent_data.system.memory.tmpfs.sort_by(|a, b| a.mount.cmp(&b.mount));

        Ok(())
    }

    /// Discover all tmpfs mount points from /proc/mounts
    fn discover_tmpfs_mounts(&self) -> Result<Vec<String>, CollectorError> {
        let content = utils::read_proc_file("/proc/mounts")?;
        let mut tmpfs_mounts = Vec::new();

        for line in content.lines() {
            let fields: Vec<&str> = line.split_whitespace().collect();
            if fields.len() >= 3 && fields[2] == "tmpfs" {
                let mount_point = fields[1];
                
                // Filter out system/internal tmpfs mounts that aren't useful for monitoring
                if self.should_monitor_tmpfs(mount_point) {
                    tmpfs_mounts.push(mount_point.to_string());
                }
            }
        }

        debug!("Discovered {} tmpfs mounts: {:?}", tmpfs_mounts.len(), tmpfs_mounts);
        Ok(tmpfs_mounts)
    }

    /// Determine if a tmpfs mount point should be monitored
    fn should_monitor_tmpfs(&self, mount_point: &str) -> bool {
        // Include commonly useful tmpfs mounts
        matches!(mount_point, 
            "/tmp" | "/var/tmp" | "/dev/shm" | "/run" | "/var/log"
        ) || mount_point.starts_with("/run/user/") // User session tmpfs
    }

    /// Calculate memory usage status based on thresholds
    fn calculate_memory_status(&self, usage_percent: f32) -> Status {
        self.usage_thresholds.evaluate(usage_percent)
    }
}

#[async_trait]
impl Collector for MemoryCollector {
    async fn collect_structured(&self, agent_data: &mut AgentData) -> Result<(), CollectorError> {
        debug!("Collecting memory metrics");
        let start = std::time::Instant::now();

        // Parse memory info from /proc/meminfo
        let info = self.parse_meminfo().await?;

        // Populate memory data directly
        self.populate_memory_data(&info, agent_data).await?;

        // Collect tmpfs data  
        self.populate_tmpfs_data(agent_data).await?;

        let duration = start.elapsed();
        debug!("Memory collection completed in {:?}", duration);

        // Efficiency check: warn if collection takes too long
        if duration.as_millis() > 1 {
            debug!(
                "Memory collection took {}ms - consider optimization",
                duration.as_millis()
            );
        }

        // Calculate status using thresholds
        agent_data.system.memory.usage_status = self.calculate_memory_status(agent_data.system.memory.usage_percent);

        Ok(())
    }
}

/// Internal structure for parsing /proc/meminfo
#[derive(Default)]
struct MemoryInfo {
    total_kb: u64,
    available_kb: u64,
    free_kb: u64,
    buffers_kb: u64,
    cached_kb: u64,
    swap_total_kb: u64,
    swap_free_kb: u64,
}