package bsdaily

import (
	"errors"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"sort"
	"time"
)

var errNoSnapshots = errors.New("no daily snapshots found")

// FindLatestDailySnapshot locates the newest daily ZFS snapshot that
// contains the firehose database and returns its directory and date.
func FindLatestDailySnapshot() (string, time.Time, error) {
	entries, err := os.ReadDir(SnapshotBase)
	if err != nil {
		return "", time.Time{}, fmt.Errorf(
			"reading snapshot directory %s: %w", SnapshotBase, err)
	}

	type snapshot struct {
		name string
		date time.Time
	}

	var snapshots []snapshot

	for _, e := range entries {
		if !e.IsDir() {
			continue
		}

		m := snapshotPattern.FindStringSubmatch(e.Name())
		if m == nil {
			continue
		}

		d, perr := time.Parse("2006-01-02", m[1])
		if perr != nil {
			slog.Warn("skipping snapshot with unparseable date",
				"name", e.Name(), "error", perr)

			continue
		}

		snapshots = append(snapshots, snapshot{name: e.Name(), date: d})
	}

	if len(snapshots) == 0 {
		return "", time.Time{}, fmt.Errorf("%w in %s", errNoSnapshots, SnapshotBase)
	}

	sort.Slice(snapshots, func(i, j int) bool {
		return snapshots[i].date.After(snapshots[j].date)
	})

	latest := snapshots[0]
	dir := filepath.Join(SnapshotBase, latest.name)

	dbPath := filepath.Join(dir, DBFilename)

	_, err = os.Stat(dbPath)
	if err != nil {
		return "", time.Time{}, fmt.Errorf(
			"database not found in snapshot %s: %w", dir, err)
	}

	return dir, latest.date, nil
}