status-monitor/agent/src/cpu.rs

use std::collections::HashMap;
use common::metrics::CpuBreakdown;

#[derive(Debug, Clone, Copy)]
struct CpuValues {
    pub user: u64,
    pub nice: u64,
    pub system: u64,
    pub idle: u64,
    pub iowait: u64,
    pub irq: u64,
    pub softirq: u64,
    pub steal: u64,
    pub guest: u64,
    pub guest_nice: u64,
}

impl CpuValues {
    pub fn total(&self) -> u64 {
        self.user + self.nice + self.system + self.idle + self.iowait +
        self.irq + self.softirq + self.steal + self.guest + self.guest_nice
    }
}

pub struct CpuStatReader {
    previous_stats: HashMap<String, CpuValues>,
}

impl CpuStatReader {
    pub fn new() -> Self {
        Self { previous_stats: HashMap::new() }
    }

    pub fn read_global_cpu_stats(&mut self) -> anyhow::Result<CpuBreakdown> {
        let content = std::fs::read_to_string("/proc/stat").unwrap();

        let cpu_line = content
            .lines()
            .find(|line| line.starts_with("cpu "))
            .unwrap();

        self.parse_cpu_line(cpu_line)
    }

    fn parse_cpu_line(&mut self, line: &str) -> anyhow::Result<CpuBreakdown> {
        let parts: Vec<&str> = line.split_whitespace().collect();

        let cpu_name = parts[0].to_string();

        let parse = |num: usize| -> u64 {
            parts[num].parse().ok().unwrap()
        };

        let values = CpuValues {
            user: parse(1),
            nice: parse(2),
            system: parse(3),
            idle: parse(4),
            iowait: parse(5),
            irq: parse(6),
            softirq: parse(7),
            steal: parse(8),
            guest: parse(9),
            guest_nice: parse(10),
        };

        let previous = self.previous_stats.get(&cpu_name).copied();
        let percentages = self.calculate_percentages(&values, previous);

        self.previous_stats.insert(cpu_name, values);

        Ok(percentages)
    }

    fn calculate_percentages(&self, current: &CpuValues, previous: Option<CpuValues>) -> CpuBreakdown {
        let Some(prev) = previous else {
            return CpuBreakdown::default();
        };

        let total_delta = current.total().saturating_sub(prev.total()) as f32;
        if total_delta <= 0.0 {
            return CpuBreakdown::default();
        }

        let calculate_pct = |current: u64, prev: u64| {
            (current.saturating_sub(prev) as f32 / total_delta) * 100.0
        };

        CpuBreakdown {
            system: calculate_pct(current.system, prev.system),
            user: calculate_pct(current.user, prev.user),
            idle: calculate_pct(current.idle, prev.idle),
            steal: calculate_pct(current.steal, prev.steal),
            iowait: calculate_pct(current.iowait, prev.iowait),
        }
    }
}