heal-cli 0.1.0

//! Hotspot composite metric: technical debt priority scored as the
//! product of churn (commit count) and complexity (per-file CCN sum),
//! optionally re-weighted via `metrics.hotspot.weight_*`.
//!
//! The arithmetic is intentionally simple — `(weight_complexity *
//! ccn_sum) * (weight_churn * commits)` — matching the bash proof of
//! concept in
//! KNOWLEDGE.md § 10. Files that lack a churn or complexity contribution
//! get a score of 0 and are dropped from the report.
//!
//! `compose` is a pure function over already-computed reports so the
//! `status` command path can reuse the work the Churn/Complexity
//! observers already did. `Observer::observe` re-runs both observers from
//! the project root for callers (e.g. future history-snapshot writers)
//! that don't have reports on hand.

use std::collections::BTreeMap;
use std::path::{Path, PathBuf};

use serde::{Deserialize, Serialize};

use crate::core::config::Config;

use crate::observer::churn::{ChurnObserver, ChurnReport, FileChurn};
use crate::observer::complexity::{ComplexityObserver, ComplexityReport, FileComplexity};
use crate::observer::{ObservationMeta, Observer};

#[derive(Debug, Clone, Copy, PartialEq)]
pub struct HotspotWeights {
    pub churn: f64,
    pub complexity: f64,
}

impl Default for HotspotWeights {
    fn default() -> Self {
        Self {
            churn: 1.0,
            complexity: 1.0,
        }
    }
}

#[derive(Debug, Clone, Default)]
pub struct HotspotObserver {
    pub enabled: bool,
    pub weights: HotspotWeights,
    /// Used by `Observer::observe` to scan the project end-to-end. When
    /// composing externally via `compose`, the caller supplies pre-computed
    /// reports and these fields are unused.
    pub churn: ChurnObserver,
    pub complexity: ComplexityObserver,
}

impl HotspotObserver {
    #[must_use]
    pub fn from_config(cfg: &Config) -> Self {
        Self {
            enabled: cfg.metrics.hotspot.enabled,
            weights: HotspotWeights {
                churn: cfg.metrics.hotspot.weight_churn,
                complexity: cfg.metrics.hotspot.weight_complexity,
            },
            churn: ChurnObserver::from_config(cfg),
            complexity: ComplexityObserver::from_config(cfg),
        }
    }

    #[must_use]
    pub fn scan(&self, root: &Path) -> HotspotReport {
        if !self.enabled {
            return HotspotReport::default();
        }
        let churn = self.churn.scan(root);
        let complexity = self.complexity.scan(root);
        compose(&churn, &complexity, self.weights)
    }
}

/// Pure composer: zip a `ChurnReport` and `ComplexityReport` by file path
/// and emit a per-file score. Files appearing in only one of the two
/// inputs get a score of 0 and are filtered out.
#[must_use]
pub fn compose(
    churn: &ChurnReport,
    complexity: &ComplexityReport,
    weights: HotspotWeights,
) -> HotspotReport {
    let mut churn_by_path: BTreeMap<PathBuf, &FileChurn> = BTreeMap::new();
    for f in &churn.files {
        churn_by_path.insert(f.path.clone(), f);
    }
    let mut complexity_by_path: BTreeMap<PathBuf, &FileComplexity> = BTreeMap::new();
    for f in &complexity.files {
        complexity_by_path.insert(f.path.clone(), f);
    }

    let mut entries: Vec<HotspotEntry> = Vec::new();
    for (path, complexity_file) in &complexity_by_path {
        let Some(churn_file) = churn_by_path.get(path) else {
            continue;
        };
        let ccn_sum: u32 = complexity_file.functions.iter().map(|f| f.ccn).sum::<u32>();
        let commits = churn_file.commits;
        if ccn_sum == 0 || commits == 0 {
            continue;
        }
        let score = weighted_score(commits, ccn_sum, weights);
        entries.push(HotspotEntry {
            path: path.clone(),
            ccn_sum,
            churn_commits: commits,
            score,
        });
    }

    entries.sort_by(|a, b| {
        b.score
            .partial_cmp(&a.score)
            .unwrap_or(std::cmp::Ordering::Equal)
            .then_with(|| a.path.cmp(&b.path))
    });

    let max_score = entries.first().map_or(0.0, |e| e.score);
    let totals = HotspotTotals {
        files: entries.len(),
        max_score,
    };
    HotspotReport { entries, totals }
}

fn weighted_score(commits: u32, ccn_sum: u32, weights: HotspotWeights) -> f64 {
    let churn_term = weights.churn * f64::from(commits);
    let cmp_term = weights.complexity * f64::from(ccn_sum);
    churn_term * cmp_term
}

#[derive(Debug, Clone, Default, Serialize, Deserialize, PartialEq)]
pub struct HotspotReport {
    pub entries: Vec<HotspotEntry>,
    pub totals: HotspotTotals,
}

impl HotspotReport {
    #[must_use]
    pub fn worst_n(&self, n: usize) -> Vec<HotspotEntry> {
        let mut top = self.entries.clone();
        top.truncate(n);
        top
    }
}

#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub struct HotspotEntry {
    pub path: PathBuf,
    pub ccn_sum: u32,
    pub churn_commits: u32,
    pub score: f64,
}

#[derive(Debug, Clone, Default, Serialize, Deserialize, PartialEq)]
pub struct HotspotTotals {
    pub files: usize,
    pub max_score: f64,
}

impl Observer for HotspotObserver {
    type Output = HotspotReport;

    fn meta(&self) -> ObservationMeta {
        ObservationMeta {
            name: "hotspot",
            version: 1,
        }
    }

    fn observe(&self, project_root: &Path) -> anyhow::Result<Self::Output> {
        Ok(self.scan(project_root))
    }
}