package storage

import (
	"context"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"time"
)

const (
	snapshotPrefix  = "tug-"
	snapshotSuffix  = ".sqlite3"
	snapshotPartial = ".partial"
	snapshotStamp   = "20060102T150405Z"
)

func (s *Store) Snapshot(ctx context.Context, dir string, at time.Time) (string, error) {
	const operation = "snapshot"
	if err := s.checkOpen(operation); err != nil {
		return "", err
	}
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return "", classify(operation+" directory", err)
	}
	if err := os.Chmod(dir, 0o700); err != nil {
		return "", classify(operation+" directory", err)
	}
	final := filepath.Join(dir, snapshotPrefix+at.UTC().Format(snapshotStamp)+snapshotSuffix)
	partial := final + snapshotPartial
	file, err := os.OpenFile(partial, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o600)
	if err != nil {
		return "", classify(operation+" create", err)
	}
	if err := file.Close(); err != nil {
		os.Remove(partial)
		return "", classify(operation+" create", err)
	}
	if _, err := s.sql.ExecContext(ctx, `VACUUM INTO ?`, partial); err != nil {
		os.Remove(partial)
		return "", classify(operation, err)
	}
	if err := syncPath(partial); err != nil {
		os.Remove(partial)
		return "", classify(operation+" sync", err)
	}
	if err := os.Rename(partial, final); err != nil {
		os.Remove(partial)
		return "", classify(operation+" rename", err)
	}
	return final, classify(operation+" sync directory", syncPath(dir))
}

func PruneSnapshots(dir string, keep int) ([]string, error) {
	if keep < 1 {
		return nil, fmt.Errorf("prune snapshots: keep %d is below one", keep)
	}
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, fmt.Errorf("prune snapshots: %w", err)
	}
	var kept, doomed []string
	for _, e := range entries {
		name := e.Name()
		if !e.Type().IsRegular() || !strings.HasPrefix(name, snapshotPrefix) {
			continue
		}
		stamp, partial := strings.CutSuffix(name, snapshotSuffix+snapshotPartial)
		if !partial {
			stamp, _ = strings.CutSuffix(name, snapshotSuffix)
		}
		if _, err := time.Parse(snapshotStamp, strings.TrimPrefix(stamp, snapshotPrefix)); err != nil || stamp == name {
			continue
		}
		if partial {
			doomed = append(doomed, name)
			continue
		}
		kept = append(kept, name)
	}
	slices.Sort(kept)
	if len(kept) > keep {
		doomed = append(doomed, kept[:len(kept)-keep]...)
	}
	var errs []error
	var removed []string
	for _, name := range doomed {
		if err := os.Remove(filepath.Join(dir, name)); err != nil {
			errs = append(errs, err)
			continue
		}
		removed = append(removed, name)
	}
	return removed, errors.Join(errs...)
}

func syncPath(path string) error {
	f, err := os.Open(path)
	if err != nil {
		return err
	}
	if err := f.Sync(); err != nil {
		f.Close()
		return err
	}
	return f.Close()
}

func NewestSnapshot(dir string) (time.Time, bool) {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return time.Time{}, false
	}
	var newest time.Time
	for _, e := range entries {
		stamp, ok := strings.CutSuffix(e.Name(), snapshotSuffix)
		if !ok || !e.Type().IsRegular() {
			continue
		}
		at, err := time.Parse(snapshotStamp, strings.TrimPrefix(stamp, snapshotPrefix))
		if err == nil && strings.HasPrefix(stamp, snapshotPrefix) && at.After(newest) {
			newest = at
		}
	}
	return newest, !newest.IsZero()
}