feat: add stats helper service

Periodically snapshots Gitea instance metrics from a read-only MySQL
user and writes stats.json into Gitea custom/public/assets for the
home page to fetch same-origin. Config via env vars only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

stats/main.go

@@ -0,0 +1,144 @@
+// git-kc-stats — periodically snapshots Gitea instance metrics from the
+// (read-only) MySQL user and drops a static JSON into Gitea's custom/public
+// assets dir, which Gitea serves same-origin at /assets/stats.json.
+//
+// No HTTP endpoint is exposed to browsers; output is a shared file. A tiny
+// /healthz is bound locally only, for ops/debugging.
+package main
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"log"
+	"net/http"
+	"os"
+	"path/filepath"
+	"sync"
+	"time"
+
+	_ "github.com/go-sql-driver/mysql"
+)
+
+type Stats struct {
+	Repos       int64  `json:"repos"`
+	Agents      int64  `json:"agents"`
+	Commits7d   int64  `json:"commits_7d"`
+	PRs         int64  `json:"prs"`
+	Merged      int64  `json:"merged"`
+	GeneratedAt string `json:"generated_at"`
+	IntervalH   int    `json:"interval_hours"`
+}
+
+var (
+	mu   sync.RWMutex
+	last *Stats
+)
+
+func env(k, d string) string {
+	if v := os.Getenv(k); v != "" {
+		return v
+	}
+	return d
+}
+
+func collect(dsn string, interval time.Duration) (*Stats, error) {
+	db, err := sql.Open("mysql", dsn)
+	if err != nil {
+		return nil, err
+	}
+	defer db.Close()
+	db.SetConnMaxLifetime(time.Minute)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+	defer cancel()
+
+	var s Stats
+	err = db.QueryRowContext(ctx, `
+SELECT
+ (SELECT COUNT(*) FROM repository),
+ (SELECT COUNT(*) FROM user WHERE type=0 AND is_admin=0),
+ (SELECT COALESCE(SUM(CASE WHEN JSON_VALID(content)
+        THEN COALESCE(JSON_LENGTH(content,'$.Commits'),0) ELSE 0 END),0)
+    FROM action
+   WHERE op_type=5 AND created_unix > UNIX_TIMESTAMP()-604800),
+ (SELECT COUNT(*) FROM pull_request),
+ (SELECT COUNT(*) FROM pull_request WHERE has_merged=1)
+`).Scan(&s.Repos, &s.Agents, &s.Commits7d, &s.PRs, &s.Merged)
+	if err != nil {
+		return nil, err
+	}
+	s.GeneratedAt = time.Now().UTC().Format(time.RFC3339)
+	s.IntervalH = int(interval / time.Hour)
+	return &s, nil
+}
+
+func writeAtomic(path string, s *Stats) error {
+	b, err := json.MarshalIndent(s, "", "  ")
+	if err != nil {
+		return err
+	}
+	b = append(b, '\n')
+	tmp := path + ".tmp"
+	if err := os.WriteFile(tmp, b, 0o644); err != nil {
+		return err
+	}
+	return os.Rename(tmp, path)
+}
+
+func refresh(dsn, out string, interval time.Duration) {
+	s, err := collect(dsn, interval)
+	if err != nil {
+		log.Printf("collect error: %v (keeping previous output)", err)
+		return
+	}
+	if err := writeAtomic(out, s); err != nil {
+		log.Printf("write error: %v", err)
+		return
+	}
+	mu.Lock()
+	last = s
+	mu.Unlock()
+	log.Printf("ok repos=%d agents=%d commits_7d=%d prs=%d merged=%d",
+		s.Repos, s.Agents, s.Commits7d, s.PRs, s.Merged)
+}
+
+func main() {
+	dsn := os.Getenv("STATS_DB_DSN")
+	if dsn == "" {
+		log.Fatal("STATS_DB_DSN required")
+	}
+	out := env("STATS_OUT", "/out/stats.json")
+	iv, err := time.ParseDuration(env("STATS_INTERVAL", "12h"))
+	if err != nil {
+		log.Fatalf("bad STATS_INTERVAL: %v", err)
+	}
+	if err := os.MkdirAll(filepath.Dir(out), 0o755); err != nil {
+		log.Printf("mkdir: %v", err)
+	}
+
+	refresh(dsn, out, iv) // immediate snapshot on start
+
+	go func() {
+		t := time.NewTicker(iv)
+		defer t.Stop()
+		for range t.C {
+			refresh(dsn, out, iv)
+		}
+	}()
+
+	http.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
+		mu.RLock()
+		l := last
+		mu.RUnlock()
+		if l == nil {
+			http.Error(w, `{"status":"no-data"}`, http.StatusServiceUnavailable)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(l)
+	})
+	addr := env("STATS_ADDR", ":8080")
+	log.Printf("git-kc-stats up; out=%s interval=%s healthz=%s", out, iv, addr)
+	log.Fatal(http.ListenAndServe(addr, nil))
+}