// 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))
}