// Package store owns RVBox server persistence and migrations.
package store

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"net/url"
	"os"
	"path/filepath"
	"strconv"
	"sync"
	"time"

	_ "modernc.org/sqlite"
)

var (
	ErrUnsafeDataDirectory = errors.New("unsafe server data directory")
	ErrAlreadyOpen         = errors.New("server data directory is already locked")
)

type Options struct {
	DataDir           string
	BusyTimeout       time.Duration
	SegmentTargetSize uint64
	QuotaLimits       QuotaLimits
	FreeSpaceProbe    FreeSpaceProbe
	FaultInjector     FaultInjector
}

type Store struct {
	db             *sql.DB
	unlock         func() error
	dataDir        string
	segmentTarget  uint64
	quotaLimits    QuotaLimits
	freeSpaceProbe FreeSpaceProbe
	faultInjector  FaultInjector
	activeSegments map[[16]byte]*activeSegment
	mu             sync.Mutex
	writeMu        sync.Mutex
}

func Open(ctx context.Context, options Options) (*Store, error) {
	if !filepath.IsAbs(options.DataDir) || filepath.Clean(options.DataDir) == string(filepath.Separator) {
		return nil, ErrUnsafeDataDirectory
	}
	if options.BusyTimeout <= 0 {
		return nil, fmt.Errorf("busy timeout must be positive")
	}
	if options.SegmentTargetSize == 0 {
		options.SegmentTargetSize = 256 << 10
	}
	if options.SegmentTargetSize > DefaultSegmentLimit {
		return nil, fmt.Errorf("segment target exceeds hard record limit")
	}
	if options.QuotaLimits == (QuotaLimits{}) {
		options.QuotaLimits = DefaultQuotaLimits()
	}
	if err := options.QuotaLimits.Validate(); err != nil {
		return nil, err
	}
	if options.FreeSpaceProbe == nil {
		options.FreeSpaceProbe = FreeSpaceProbeFunc(filesystemFreeBytes)
	}
	if err := ensurePrivateDirectory(options.DataDir); err != nil {
		return nil, err
	}
	for _, child := range []string{"segments", "audit", "deleting"} {
		if err := ensurePrivateDirectory(filepath.Join(options.DataDir, child)); err != nil {
			return nil, err
		}
	}
	unlock, err := acquireInstanceLock(filepath.Join(options.DataDir, "server.lock"))
	if err != nil {
		return nil, err
	}

	databasePath := filepath.Join(options.DataDir, "rvbox.db")
	if err := ensurePrivateFile(databasePath); err != nil {
		_ = unlock()
		return nil, err
	}
	query := url.Values{}
	query.Add("_defensive", "1")
	query.Add("_pragma", "journal_mode(WAL)")
	query.Add("_pragma", "foreign_keys(ON)")
	query.Add("_pragma", "synchronous(FULL)")
	query.Add("_pragma", "busy_timeout("+strconv.FormatInt(options.BusyTimeout.Milliseconds(), 10)+")")
	databaseURL := &url.URL{Scheme: "file", Path: filepath.ToSlash(databasePath)}
	databaseURL.RawQuery = query.Encode()
	dsn := databaseURL.String()
	db, err := sql.Open("sqlite", dsn)
	if err != nil {
		_ = unlock()
		return nil, err
	}
	db.SetMaxOpenConns(1)
	db.SetMaxIdleConns(1)
	store := &Store{
		db: db, unlock: unlock, dataDir: options.DataDir, segmentTarget: options.SegmentTargetSize,
		quotaLimits: options.QuotaLimits, freeSpaceProbe: options.FreeSpaceProbe,
		faultInjector: options.FaultInjector, activeSegments: make(map[[16]byte]*activeSegment),
	}
	if err := db.PingContext(ctx); err != nil {
		_ = store.Close()
		return nil, fmt.Errorf("open SQLite: %w", err)
	}
	if err := applyMigrations(ctx, db); err != nil {
		_ = store.Close()
		return nil, err
	}
	return store, nil
}

func (store *Store) DB() *sql.DB {
	store.mu.Lock()
	defer store.mu.Unlock()
	return store.db
}

func (store *Store) Close() error {
	if store == nil {
		return nil
	}
	store.writeMu.Lock()
	defer store.writeMu.Unlock()
	store.mu.Lock()
	defer store.mu.Unlock()
	var result error
	for owner, active := range store.activeSegments {
		if err := active.segment.Close(); result == nil && err != nil {
			result = err
		}
		delete(store.activeSegments, owner)
	}
	if store.db != nil {
		result = store.db.Close()
		store.db = nil
	}
	if store.unlock != nil {
		if err := store.unlock(); result == nil {
			result = err
		}
		store.unlock = nil
	}
	return result
}

func ensurePrivateFile(path string) error {
	file, err := os.OpenFile(path, os.O_CREATE|os.O_EXCL|os.O_RDWR, 0o600)
	if err == nil {
		return file.Close()
	}
	if !errors.Is(err, os.ErrExist) {
		return err
	}
	info, err := os.Lstat(path)
	if err != nil {
		return err
	}
	if !info.Mode().IsRegular() || info.Mode()&os.ModeSymlink != 0 {
		return fmt.Errorf("%w: %s is not a regular file", ErrUnsafeDataDirectory, path)
	}
	if info.Mode().Perm()&0o077 != 0 {
		return fmt.Errorf("%w: %s permissions %04o expose private state", ErrUnsafeDataDirectory, path, info.Mode().Perm())
	}
	return nil
}

func ensurePrivateDirectory(path string) error {
	info, err := os.Lstat(path)
	if os.IsNotExist(err) {
		if err := os.MkdirAll(path, 0o700); err != nil {
			return err
		}
		info, err = os.Lstat(path)
	}
	if err != nil {
		return err
	}
	if info.Mode()&os.ModeSymlink != 0 || !info.IsDir() {
		return fmt.Errorf("%w: %s is not a real directory", ErrUnsafeDataDirectory, path)
	}
	if info.Mode().Perm()&0o077 != 0 {
		return fmt.Errorf("%w: %s permissions %04o expose private state", ErrUnsafeDataDirectory, path, info.Mode().Perm())
	}
	return nil
}