package main

import (
	"fmt"
	"log/slog"
	"sync"
)

// reconcileMu ensures only one reconcile runs at a time.
// TryLock is used so that concurrent triggers simply skip rather than queue.
var reconcileMu sync.Mutex

// Reconcile is the core reconciliation loop:
//  1. Fetches the active router list from Traefik (source of truth).
//  2. Pulls the DNS repository to ensure it is up to date.
//  3. Writes desired zone files for each managed zone.
//  4. Commits and pushes if anything changed.
//
// If Traefik is unreachable or git pull fails, the reconcile is aborted
// without modifying any DNS files (safe-fail behaviour).
func Reconcile(cfg *Config) {
	if !reconcileMu.TryLock() {
		slog.Info("reconcile already in progress, skipping")
		return
	}
	defer reconcileMu.Unlock()

	slog.Info("reconcile started")

	routers, err := FetchRouters(cfg)
	if err != nil {
		slog.Error("failed to fetch Traefik routers — skipping reconcile to avoid stale DNS removal",
			"error", err)
		return
	}
	slog.Info("fetched routers from Traefik", "count", len(routers))

	desired := FilterDomains(routers, cfg)

	if err := GitPull(cfg); err != nil {
		slog.Error("git pull failed — skipping reconcile", "error", err)
		return
	}

	var total RecordStats
	for zone, subdomains := range desired {
		path := ZoneFilePath(cfg, zone)

		current, err := ReadZoneFile(path)
		if err != nil {
			slog.Error("failed to read zone file", "zone", zone, "error", err)
			return
		}

		newZF := BuildZoneFile(subdomains, cfg)
		stats := DiffZoneFile(current, newZF)
		total.Added += stats.Added
		total.Removed += stats.Removed
		total.Changed += stats.Changed

		if err := WriteZoneFile(path, newZF); err != nil {
			slog.Error("failed to write zone file", "zone", zone, "error", err)
			return
		}

		if stats.Added+stats.Removed+stats.Changed > 0 {
			slog.Info("zone updated",
				"zone", zone,
				"records", len(subdomains),
				"added", stats.Added,
				"removed", stats.Removed,
				"changed", stats.Changed,
			)
		} else {
			slog.Info("zone unchanged", "zone", zone, "records", len(subdomains))
		}
	}

	changed, err := GitStatusChanged(cfg)
	if err != nil {
		slog.Error("git status check failed", "error", err)
		return
	}
	if !changed {
		slog.Info("reconcile complete — no changes to commit")
		return
	}

	msg := fmt.Sprintf(
		"chore(dns): reconcile dynamic records from traefik\n\nadded: %d, removed: %d, updated: %d",
		total.Added, total.Removed, total.Changed,
	)
	if err := GitCommitAndPush(cfg, msg); err != nil {
		slog.Error("failed to commit/push DNS changes", "error", err)
		return
	}

	slog.Info("reconcile complete — changes pushed",
		"added", total.Added,
		"removed", total.Removed,
		"updated", total.Changed,
	)
}