sva-engine 0.7.4

// Concern: writes a render's lookups as log lines, per second of output and per node | Non-concern: counting them (stats.rs), where the lines go or when | IO: (CacheStats, rate) -> text

use std::collections::BTreeMap;
use std::fmt::Write;

use super::{CacheStats, Lookup, Outcome};

#[derive(Default)]
struct Tally {
    hit: usize,
    miss: usize,
    prefix: usize,
    new: usize,
    store_hit: usize,
    store_miss: usize,
}

impl Tally {
    fn of<'l>(lookups: impl IntoIterator<Item = &'l Lookup>) -> Tally {
        let mut tally = Tally::default();
        for lookup in lookups {
            tally.add(lookup);
        }
        tally
    }

    /// An extended run was found short and written again, so it is both a miss and new.
    fn add(&mut self, lookup: &Lookup) {
        let outcome = lookup.outcome;
        match lookup.store {
            Some(true) => self.store_hit += 1,
            Some(false) => self.store_miss += 1,
            None => {}
        }
        match outcome {
            Outcome::Hit => self.hit += 1,
            Outcome::Prefix => self.prefix += 1,
            _ => self.miss += 1,
        }
        if matches!(
            outcome,
            Outcome::ComputedStored | Outcome::ComputedReplaced | Outcome::Extended
        ) {
            self.new += 1;
        }
    }

    fn looked(&self) -> usize {
        self.hit + self.miss + self.prefix
    }
}

impl std::fmt::Display for Tally {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "hit={} miss={} prefix={} new={} store-hit={} store-miss={}",
            self.hit, self.miss, self.prefix, self.new, self.store_hit, self.store_miss
        )
    }
}

fn percent(part: usize, whole: usize) -> f64 {
    match whole {
        0 => 0.0,
        _ => 100.0 * part as f64 / whole as f64,
    }
}

/// Read once the render ends, so each lookup is counted as it finally settled: a run is stored
/// only when its node ends. `pass` is what the render looked up before its first block.
pub fn cache_log(stats: &CacheStats, rate: u32) -> String {
    let (lookups, reached) = (&stats.lookups, &stats.reached);
    let mut out = String::new();
    let mut cuts: Vec<(String, usize)> = Vec::new();
    let mut second = None;
    for (k, &(at, made)) in reached.iter().enumerate() {
        let whole = at.div_euclid(i64::from(rate));
        match second {
            None => cuts.push(("pass".to_string(), made)),
            Some(last) if whole > last || k + 1 == reached.len() => {
                cuts.push((format!("t={:.3}s", at as f64 / f64::from(rate)), made));
            }
            Some(_) => continue,
        }
        second = Some(whole);
    }
    if cuts.last().is_none_or(|(_, made)| *made < lookups.len()) {
        cuts.push(("end".to_string(), lookups.len()));
    }
    let (mut from, mut hits) = (0, 0);
    for (label, to) in cuts {
        let tally = Tally::of(&lookups[from..to]);
        hits += tally.hit;
        let cum = percent(hits, to);
        let _ = writeln!(out, "sva-cache {label} {tally} cum-hit={cum:.1}%");
        from = to;
    }
    let mut nodes: BTreeMap<&str, Tally> = BTreeMap::new();
    for lookup in lookups {
        nodes.entry(&lookup.node).or_default().add(lookup);
    }
    for (node, tally) in &nodes {
        let _ = writeln!(out, "sva-cache node {tally} {node}");
    }
    let total = Tally::of(lookups);
    let _ = writeln!(
        out,
        "sva-cache total {total} hit-rate={:.1}% nodes={} entries={} bytes={}",
        percent(total.hit, total.looked()),
        nodes.len(),
        stats.entries,
        stats.bytes
    );
    out
}