test: add nova-stats unit tests, wire to nix flake check

flake.nix

@@ -91,6 +91,7 @@
         {
           formatting = treefmt-eval.config.build.check self;
           build = self.packages.${pkgs.stdenv.hostPlatform.system}.default;
+          nova-stats = self.packages.${pkgs.stdenv.hostPlatform.system}.nova-stats;
         }
       );
 

stats-daemon/src/main.rs

@@ -8,9 +8,17 @@ struct Sample {
     total: u64,
 }
 
-fn read_stat() -> Vec<Sample> {
-    fs::read_to_string("/proc/stat")
-        .unwrap_or_default()
+struct MemInfo {
+    percent: u64,
+    used_gb: f64,
+    total_gb: f64,
+    avail_gb: f64,
+    cached_gb: f64,
+    buffers_gb: f64,
+}
+
+fn parse_stat(input: &str) -> Vec<Sample> {
+    input
         .lines()
         .filter(|l| l.starts_with("cpu"))
         .map(|l| {
@@ -26,6 +34,52 @@ fn read_stat() -> Vec<Sample> {
         .collect()
 }
 
+fn parse_meminfo(input: &str) -> Option<MemInfo> {
+    let mut total = 0u64;
+    let mut avail = 0u64;
+    let mut buffers = 0u64;
+    let mut cached = 0u64;
+    let mut sreclaimable = 0u64;
+
+    for line in input.lines() {
+        let mut parts = line.splitn(2, ':');
+        let key = parts.next().unwrap_or("").trim();
+        let val: u64 = parts
+            .next()
+            .unwrap_or("")
+            .split_whitespace()
+            .next()
+            .unwrap_or("")
+            .parse()
+            .unwrap_or(0);
+        match key {
+            "MemTotal" => total = val,
+            "MemAvailable" => avail = val,
+            "Buffers" => buffers = val,
+            "Cached" => cached = val,
+            "SReclaimable" => sreclaimable = val,
+            _ => {}
+        }
+    }
+
+    if total == 0 {
+        return None;
+    }
+
+    let used = total.saturating_sub(avail);
+    let cached_total = cached + sreclaimable;
+    let gb = |kb: u64| kb as f64 / 1_048_576.0;
+
+    Some(MemInfo {
+        percent: used * 100 / total,
+        used_gb: gb(used),
+        total_gb: gb(total),
+        avail_gb: gb(avail),
+        cached_gb: gb(cached_total),
+        buffers_gb: gb(buffers),
+    })
+}
+
 fn pct(prev: &Sample, curr: &Sample) -> u32 {
     let dt = curr.total.saturating_sub(prev.total);
     let di = curr.idle.saturating_sub(prev.idle);
@@ -35,6 +89,10 @@ fn pct(prev: &Sample, curr: &Sample) -> u32 {
     (dt.saturating_sub(di) * 100 / dt) as u32
 }
 
+fn read_stat() -> Vec<Sample> {
+    parse_stat(&fs::read_to_string("/proc/stat").unwrap_or_default())
+}
+
 fn read_core_freqs() -> Vec<f64> {
     let mut freqs = Vec::new();
     for i in 0.. {
@@ -96,52 +154,14 @@ fn emit_cpu(out: &mut impl Write, prev: &[Sample], curr: &[Sample], freqs: &[f64
 
 fn emit_mem(out: &mut impl Write) {
     let content = fs::read_to_string("/proc/meminfo").unwrap_or_default();
-    let mut total = 0u64;
-    let mut avail = 0u64;
-    let mut buffers = 0u64;
-    let mut cached = 0u64;
-    let mut sreclaimable = 0u64;
-
-    for line in content.lines() {
-        let mut parts = line.splitn(2, ':');
-        let key = parts.next().unwrap_or("").trim();
-        let val: u64 = parts
-            .next()
-            .unwrap_or("")
-            .split_whitespace()
-            .next()
-            .unwrap_or("")
-            .parse()
-            .unwrap_or(0);
-        match key {
-            "MemTotal" => total = val,
-            "MemAvailable" => avail = val,
-            "Buffers" => buffers = val,
-            "Cached" => cached = val,
-            "SReclaimable" => sreclaimable = val,
-            _ => {}
-        }
-    }
-
-    if total == 0 {
-        return;
-    }
-
-    let used = total.saturating_sub(avail);
-    let cached_total = cached + sreclaimable;
-    let percent = used * 100 / total;
-    let gb = |kb: u64| kb as f64 / 1_048_576.0;
-
+    if let Some(m) = parse_meminfo(&content) {
         let _ = writeln!(
             out,
-        "{{\"type\":\"mem\",\"percent\":{percent},\"used_gb\":{:.3},\"total_gb\":{:.3},\"avail_gb\":{:.3},\"cached_gb\":{:.3},\"buffers_gb\":{:.3}}}",
-        gb(used),
-        gb(total),
-        gb(avail),
-        gb(cached_total),
-        gb(buffers),
+            "{{\"type\":\"mem\",\"percent\":{},\"used_gb\":{:.3},\"total_gb\":{:.3},\"avail_gb\":{:.3},\"cached_gb\":{:.3},\"buffers_gb\":{:.3}}}",
+            m.percent, m.used_gb, m.total_gb, m.avail_gb, m.cached_gb, m.buffers_gb,
         );
     }
+}
 
 fn main() {
     let stdout = io::stdout();
@@ -170,3 +190,233 @@ fn main() {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // ── pct ──────────────────────────────────────────────────────────────
+
+    #[test]
+    fn pct_zero_delta_returns_zero() {
+        let s = Sample {
+            idle: 100,
+            total: 400,
+        };
+        assert_eq!(pct(&s, &s), 0);
+    }
+
+    #[test]
+    fn pct_all_idle() {
+        let prev = Sample {
+            idle: 0,
+            total: 100,
+        };
+        let curr = Sample {
+            idle: 100,
+            total: 200,
+        };
+        assert_eq!(pct(&prev, &curr), 0);
+    }
+
+    #[test]
+    fn pct_fully_busy() {
+        let prev = Sample {
+            idle: 100,
+            total: 200,
+        };
+        let curr = Sample {
+            idle: 100,
+            total: 300,
+        };
+        assert_eq!(pct(&prev, &curr), 100);
+    }
+
+    #[test]
+    fn pct_half_busy() {
+        let prev = Sample { idle: 0, total: 0 };
+        let curr = Sample {
+            idle: 50,
+            total: 100,
+        };
+        assert_eq!(pct(&prev, &curr), 50);
+    }
+
+    #[test]
+    fn pct_no_underflow_on_backwards_clock() {
+        let prev = Sample {
+            idle: 200,
+            total: 400,
+        };
+        let curr = Sample {
+            idle: 100,
+            total: 300,
+        }; // idle went backwards
+        // dt=saturating 0, di=saturating 0 → returns 0
+        assert_eq!(pct(&prev, &curr), 0);
+    }
+
+    // ── parse_stat ───────────────────────────────────────────────────────
+
+    const STAT_SAMPLE: &str = "\
+cpu  100 10 50 700 40 0 0 0 0 0
+cpu0 50  5  25 350 20 0 0 0 0 0
+cpu1 50  5  25 350 20 0 0 0 0 0";
+
+    #[test]
+    fn parse_stat_count() {
+        // aggregate line + 2 cores = 3 samples
+        let samples = parse_stat(STAT_SAMPLE);
+        assert_eq!(samples.len(), 3);
+    }
+
+    #[test]
+    fn parse_stat_aggregate_idle() {
+        // idle=field[3], iowait=field[4] → 700+40=740
+        let samples = parse_stat(STAT_SAMPLE);
+        assert_eq!(samples[0].idle, 740);
+    }
+
+    #[test]
+    fn parse_stat_aggregate_total() {
+        // sum of all fields: 100+10+50+700+40 = 900
+        let samples = parse_stat(STAT_SAMPLE);
+        assert_eq!(samples[0].total, 900);
+    }
+
+    #[test]
+    fn parse_stat_per_core_idle() {
+        let samples = parse_stat(STAT_SAMPLE);
+        assert_eq!(samples[1].idle, 370); // 350+20
+        assert_eq!(samples[2].idle, 370);
+    }
+
+    #[test]
+    fn parse_stat_ignores_non_cpu_lines() {
+        let input = "intr 12345\ncpu 1 2 3 4 5 0 0 0 0 0\npage 0 0";
+        let samples = parse_stat(input);
+        assert_eq!(samples.len(), 1);
+    }
+
+    // ── parse_meminfo ────────────────────────────────────────────────────
+
+    const MEMINFO_SAMPLE: &str = "\
+MemTotal:       16384000 kB
+MemFree:         2048000 kB
+MemAvailable:    4096000 kB
+Buffers:          512000 kB
+Cached:          3072000 kB
+SReclaimable:     512000 kB
+SwapTotal:       8192000 kB
+SwapFree:        8192000 kB";
+
+    #[test]
+    fn parse_meminfo_percent() {
+        let m = parse_meminfo(MEMINFO_SAMPLE).unwrap();
+        // used = total - avail = 16384000 - 4096000 = 12288000
+        // percent = 12288000 * 100 / 16384000 = 75
+        assert_eq!(m.percent, 75);
+    }
+
+    #[test]
+    fn parse_meminfo_total_gb() {
+        let m = parse_meminfo(MEMINFO_SAMPLE).unwrap();
+        // 16384000 kB / 1048576 ≈ 15.625 GB
+        assert!((m.total_gb - 15.625).abs() < 0.001);
+    }
+
+    #[test]
+    fn parse_meminfo_cached_includes_sreclaimable() {
+        let m = parse_meminfo(MEMINFO_SAMPLE).unwrap();
+        // cached = 3072000 + 512000 = 3584000 kB
+        let expected = 3_584_000.0 / 1_048_576.0;
+        assert!((m.cached_gb - expected).abs() < 0.001);
+    }
+
+    #[test]
+    fn parse_meminfo_zero_total_returns_none() {
+        assert!(parse_meminfo("MemFree: 1000 kB\n").is_none());
+    }
+
+    #[test]
+    fn parse_meminfo_empty_returns_none() {
+        assert!(parse_meminfo("").is_none());
+    }
+
+    // ── emit_cpu ─────────────────────────────────────────────────────────
+
+    fn sample(idle: u64, total: u64) -> Sample {
+        Sample { idle, total }
+    }
+
+    #[test]
+    fn emit_cpu_valid_json_structure() {
+        let prev = vec![sample(0, 0), sample(0, 0)];
+        let curr = vec![sample(50, 100), sample(25, 100)];
+        let freqs = vec![3.2, 3.1];
+        let mut buf = Vec::new();
+        emit_cpu(&mut buf, &prev, &curr, &freqs);
+        let s = String::from_utf8(buf).unwrap();
+        assert!(s.contains("\"type\":\"cpu\""));
+        assert!(s.contains("\"usage\":"));
+        assert!(s.contains("\"freq_ghz\":"));
+        assert!(s.contains("\"core_usage\":"));
+        assert!(s.contains("\"core_freq_ghz\":"));
+        assert!(s.trim().ends_with('}'));
+    }
+
+    #[test]
+    fn emit_cpu_correct_usage() {
+        // prev aggregate: idle=0, total=0 → curr: idle=50, total=100 → 50% busy
+        let prev = vec![sample(0, 0), sample(0, 0)];
+        let curr = vec![sample(50, 100), sample(0, 0)];
+        let mut buf = Vec::new();
+        emit_cpu(&mut buf, &prev, &curr, &[]);
+        let s = String::from_utf8(buf).unwrap();
+        assert!(s.contains("\"usage\":50"), "got: {s}");
+    }
+
+    #[test]
+    fn emit_cpu_no_prev_gives_zero_usage() {
+        let curr = vec![sample(50, 100)];
+        let mut buf = Vec::new();
+        emit_cpu(&mut buf, &[], &curr, &[]);
+        let s = String::from_utf8(buf).unwrap();
+        assert!(s.contains("\"usage\":0"), "got: {s}");
+    }
+
+    #[test]
+    fn emit_cpu_empty_curr_produces_no_output() {
+        let mut buf = Vec::new();
+        emit_cpu(&mut buf, &[], &[], &[]);
+        assert!(buf.is_empty());
+    }
+
+    #[test]
+    fn emit_cpu_core_freqs_in_output() {
+        let curr = vec![sample(0, 100)];
+        let freqs = vec![3.200, 2.900];
+        let mut buf = Vec::new();
+        emit_cpu(&mut buf, &curr, &curr, &freqs);
+        let s = String::from_utf8(buf).unwrap();
+        assert!(s.contains("3.200"), "got: {s}");
+        assert!(s.contains("2.900"), "got: {s}");
+    }
+
+    // ── emit_mem (via parse_meminfo) ─────────────────────────────────────
+
+    #[test]
+    fn emit_mem_valid_json_structure() {
+        let m = parse_meminfo(MEMINFO_SAMPLE).unwrap();
+        let mut buf = Vec::new();
+        let _ = writeln!(
+            &mut buf,
+            "{{\"type\":\"mem\",\"percent\":{},\"used_gb\":{:.3},\"total_gb\":{:.3},\"avail_gb\":{:.3},\"cached_gb\":{:.3},\"buffers_gb\":{:.3}}}",
+            m.percent, m.used_gb, m.total_gb, m.avail_gb, m.cached_gb, m.buffers_gb,
+        );
+        let s = String::from_utf8(buf).unwrap();
+        assert!(s.contains("\"type\":\"mem\""));
+        assert!(s.contains("\"percent\":75"));
+        assert!(s.trim().ends_with('}'));
+    }
+}