package storage

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path"
	"path/filepath"
	"regexp"
	"strings"
	"sync"

	"softbox.local/core/domain"
)

const (
	installedAppFileName       = "installed-app.json"
	installedAppBackupFileName = "installed-app.json.backup"
	installedAppSchemaVersion  = 1
	transactionFileName        = "install-transaction.json"
	transactionBackupFileName  = "install-transaction.json.backup"
)

var (
	ErrInstalledAppInvalid = errors.New("installed app record is invalid")
	ErrStorageLayoutUnsafe = errors.New("installed app storage layout is unsafe")
	appIDPattern           = regexp.MustCompile(`^[a-z0-9-]+$`)
	sha256Pattern          = regexp.MustCompile(`^[0-9A-Fa-f]{64}$`)
)

// InstalledFile records one installed payload file.
type InstalledFile struct {
	Path   string `json:"path"`
	Size   int64  `json:"size"`
	SHA256 string `json:"sha256"`
}

// InstalledApp is the local installed-app.json v1 protocol.
type InstalledApp struct {
	SchemaVersion int             `json:"schema_version"`
	ID            string          `json:"id"`
	Version       string          `json:"version"`
	Architecture  string          `json:"architecture"`
	Channel       string          `json:"channel"`
	Files         []InstalledFile `json:"files"`
}

// InstallationSnapshot contains disk facts without deriving UI status.
type InstallationSnapshot struct {
	Record          *InstalledApp
	RecoveryPending bool
}

// InstalledAppStore atomically reads and writes records below apps/<id>/.
type InstalledAppStore struct {
	appsRoot string
	mu       sync.Mutex
}

// NewInstalledAppStore creates a store rooted at the SoftBoxData apps folder.
func NewInstalledAppStore(appsRoot string) *InstalledAppStore {
	return &InstalledAppStore{appsRoot: appsRoot}
}

// Write validates and atomically replaces one installed-app.json.
func (store *InstalledAppStore) Write(record InstalledApp) error {
	store.mu.Lock()
	defer store.mu.Unlock()

	if err := record.validate(); err != nil {
		return err
	}
	appRoot, err := store.ensureAppRoot(record.ID)
	if err != nil {
		return err
	}
	document, err := json.Marshal(record)
	if err != nil {
		return fmt.Errorf("encode installed app record: %w", err)
	}
	document = append(document, '\n')
	return replaceInstalledAppFile(
		appRoot,
		filepath.Join(appRoot, installedAppFileName),
		filepath.Join(appRoot, installedAppBackupFileName),
		document,
	)
}

// Read returns one installed record. found is false when neither current nor
// crash-recovery backup exists.
func (store *InstalledAppStore) Read(appID string) (record InstalledApp, found bool, err error) {
	store.mu.Lock()
	defer store.mu.Unlock()

	return store.readLocked(appID)
}

// Inspect reads the installed record and detects an unfinished install journal.
func (store *InstalledAppStore) Inspect(appID string) (InstallationSnapshot, error) {
	store.mu.Lock()
	defer store.mu.Unlock()

	record, found, err := store.readLocked(appID)
	if err != nil {
		return InstallationSnapshot{}, err
	}
	pending, err := store.recoveryPendingLocked(appID)
	if err != nil {
		return InstallationSnapshot{}, err
	}
	snapshot := InstallationSnapshot{RecoveryPending: pending}
	if found {
		recordCopy := record
		recordCopy.Files = append([]InstalledFile(nil), record.Files...)
		snapshot.Record = &recordCopy
	}
	return snapshot, nil
}

func (store *InstalledAppStore) readLocked(
	appID string,
) (record InstalledApp, found bool, err error) {
	appRoot, exists, err := store.inspectAppRoot(appID)
	if err != nil || !exists {
		return InstalledApp{}, false, err
	}
	target := filepath.Join(appRoot, installedAppFileName)
	backup := filepath.Join(appRoot, installedAppBackupFileName)
	document, err := readRegularFile(target)
	if os.IsNotExist(err) {
		document, err = readRegularFile(backup)
	}
	if os.IsNotExist(err) {
		return InstalledApp{}, false, nil
	}
	if err != nil {
		return InstalledApp{}, false, err
	}

	decoder := json.NewDecoder(bytes.NewReader(document))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(&record); err != nil {
		return InstalledApp{}, false, fmt.Errorf("%w: decode: %v", ErrInstalledAppInvalid, err)
	}
	if err := ensureInstalledAppEOF(decoder); err != nil {
		return InstalledApp{}, false, err
	}
	if err := record.validate(); err != nil {
		return InstalledApp{}, false, err
	}
	if record.ID != appID {
		return InstalledApp{}, false, fmt.Errorf(
			"%w: record id %q does not match path id %q",
			ErrInstalledAppInvalid,
			record.ID,
			appID,
		)
	}
	return record, true, nil
}

func (store *InstalledAppStore) recoveryPendingLocked(appID string) (bool, error) {
	appRoot, exists, err := store.inspectAppRoot(appID)
	if err != nil || !exists {
		return false, err
	}
	for _, name := range []string{transactionFileName, transactionBackupFileName} {
		info, err := os.Lstat(filepath.Join(appRoot, name))
		if os.IsNotExist(err) {
			continue
		}
		if err != nil {
			return false, fmt.Errorf("inspect install transaction: %w", err)
		}
		if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
			return false, fmt.Errorf(
				"%w: %s is not a regular file",
				ErrStorageLayoutUnsafe,
				name,
			)
		}
		return true, nil
	}
	return false, nil
}

func (store *InstalledAppStore) ensureAppRoot(appID string) (string, error) {
	if !appIDPattern.MatchString(appID) {
		return "", fmt.Errorf("%w: invalid app id %q", ErrInstalledAppInvalid, appID)
	}
	if store.appsRoot == "" {
		return "", fmt.Errorf("%w: empty apps root", ErrStorageLayoutUnsafe)
	}
	absoluteRoot, err := filepath.Abs(store.appsRoot)
	if err != nil {
		return "", fmt.Errorf("%w: %v", ErrStorageLayoutUnsafe, err)
	}
	if err := os.MkdirAll(absoluteRoot, 0o700); err != nil {
		return "", fmt.Errorf("create apps root: %w", err)
	}
	if err := requireRealDirectory(absoluteRoot); err != nil {
		return "", err
	}
	appRoot := filepath.Join(absoluteRoot, appID)
	if err := os.Mkdir(appRoot, 0o700); err != nil && !os.IsExist(err) {
		return "", fmt.Errorf("create app root: %w", err)
	}
	if err := requireRealDirectory(appRoot); err != nil {
		return "", err
	}
	return appRoot, nil
}

func (store *InstalledAppStore) inspectAppRoot(appID string) (string, bool, error) {
	if !appIDPattern.MatchString(appID) {
		return "", false, fmt.Errorf("%w: invalid app id %q", ErrInstalledAppInvalid, appID)
	}
	if store.appsRoot == "" {
		return "", false, fmt.Errorf("%w: empty apps root", ErrStorageLayoutUnsafe)
	}
	absoluteRoot, err := filepath.Abs(store.appsRoot)
	if err != nil {
		return "", false, fmt.Errorf("%w: %v", ErrStorageLayoutUnsafe, err)
	}
	info, err := os.Lstat(absoluteRoot)
	if os.IsNotExist(err) {
		return "", false, nil
	}
	if err != nil {
		return "", false, fmt.Errorf("inspect apps root: %w", err)
	}
	if info.Mode()&os.ModeSymlink != 0 || !info.IsDir() {
		return "", false, fmt.Errorf("%w: apps root is not a real directory", ErrStorageLayoutUnsafe)
	}

	appRoot := filepath.Join(absoluteRoot, appID)
	info, err = os.Lstat(appRoot)
	if os.IsNotExist(err) {
		return "", false, nil
	}
	if err != nil {
		return "", false, fmt.Errorf("inspect app root: %w", err)
	}
	if info.Mode()&os.ModeSymlink != 0 || !info.IsDir() {
		return "", false, fmt.Errorf("%w: app root is not a real directory", ErrStorageLayoutUnsafe)
	}
	return appRoot, true, nil
}

func (record InstalledApp) validate() error {
	if record.SchemaVersion != installedAppSchemaVersion {
		return fmt.Errorf(
			"%w: schema_version=%d",
			ErrInstalledAppInvalid,
			record.SchemaVersion,
		)
	}
	if !appIDPattern.MatchString(record.ID) {
		return fmt.Errorf("%w: invalid id %q", ErrInstalledAppInvalid, record.ID)
	}
	if _, err := domain.ParseSemVer(record.Version); err != nil {
		return fmt.Errorf("%w: version: %v", ErrInstalledAppInvalid, err)
	}
	if record.Architecture != "386" && record.Architecture != "amd64" {
		return fmt.Errorf(
			"%w: architecture=%q",
			ErrInstalledAppInvalid,
			record.Architecture,
		)
	}
	if record.Channel != "stable" {
		return fmt.Errorf("%w: channel=%q", ErrInstalledAppInvalid, record.Channel)
	}
	if record.Files == nil {
		return fmt.Errorf("%w: files must be an array", ErrInstalledAppInvalid)
	}

	seenPaths := make(map[string]struct{}, len(record.Files))
	for index, installedFile := range record.Files {
		if !validInstalledPath(installedFile.Path) {
			return fmt.Errorf(
				"%w: files[%d].path=%q",
				ErrInstalledAppInvalid,
				index,
				installedFile.Path,
			)
		}
		if installedFile.Size < 0 {
			return fmt.Errorf(
				"%w: files[%d].size=%d",
				ErrInstalledAppInvalid,
				index,
				installedFile.Size,
			)
		}
		if !sha256Pattern.MatchString(installedFile.SHA256) {
			return fmt.Errorf(
				"%w: files[%d].sha256",
				ErrInstalledAppInvalid,
				index,
			)
		}
		foldedPath := strings.ToLower(installedFile.Path)
		if _, exists := seenPaths[foldedPath]; exists {
			return fmt.Errorf(
				"%w: duplicate file path %q",
				ErrInstalledAppInvalid,
				installedFile.Path,
			)
		}
		seenPaths[foldedPath] = struct{}{}
	}
	return nil
}

func validInstalledPath(value string) bool {
	if value == "" || strings.Contains(value, `\`) || strings.Contains(value, ":") {
		return false
	}
	cleaned := path.Clean(value)
	return cleaned == value &&
		cleaned != "." &&
		!strings.HasPrefix(cleaned, "/") &&
		cleaned != ".." &&
		!strings.HasPrefix(cleaned, "../")
}

func requireRealDirectory(directory string) error {
	info, err := os.Lstat(directory)
	if err != nil {
		return fmt.Errorf("inspect storage directory: %w", err)
	}
	if info.Mode()&os.ModeSymlink != 0 || !info.IsDir() {
		return fmt.Errorf("%w: %s is not a real directory", ErrStorageLayoutUnsafe, directory)
	}
	return nil
}

func readRegularFile(filePath string) ([]byte, error) {
	info, err := os.Lstat(filePath)
	if err != nil {
		return nil, err
	}
	if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
		return nil, fmt.Errorf("%w: %s is not a regular file", ErrStorageLayoutUnsafe, filePath)
	}
	return os.ReadFile(filePath)
}

func ensureInstalledAppEOF(decoder *json.Decoder) error {
	var extra any
	if err := decoder.Decode(&extra); err != io.EOF {
		if err == nil {
			return fmt.Errorf("%w: trailing JSON value", ErrInstalledAppInvalid)
		}
		return fmt.Errorf("%w: trailing data: %v", ErrInstalledAppInvalid, err)
	}
	return nil
}

func replaceInstalledAppFile(directory, target, backup string, document []byte) error {
	temporary, err := os.CreateTemp(directory, ".installed-app-*.tmp")
	if err != nil {
		return fmt.Errorf("create installed app temp file: %w", err)
	}
	temporaryPath := temporary.Name()
	defer os.Remove(temporaryPath)

	if err := temporary.Chmod(0o600); err != nil {
		temporary.Close()
		return fmt.Errorf("protect installed app temp file: %w", err)
	}
	if _, err := temporary.Write(document); err != nil {
		temporary.Close()
		return fmt.Errorf("write installed app temp file: %w", err)
	}
	if err := temporary.Sync(); err != nil {
		temporary.Close()
		return fmt.Errorf("sync installed app temp file: %w", err)
	}
	if err := temporary.Close(); err != nil {
		return fmt.Errorf("close installed app temp file: %w", err)
	}

	movedTarget := false
	hadBackup := false
	if info, err := os.Lstat(target); err == nil {
		if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
			return fmt.Errorf("%w: installed app target is not regular", ErrStorageLayoutUnsafe)
		}
		if err := removeRegularBackup(backup); err != nil {
			return err
		}
		if err := os.Rename(target, backup); err != nil {
			return fmt.Errorf("backup installed app record: %w", err)
		}
		movedTarget = true
	} else if !os.IsNotExist(err) {
		return fmt.Errorf("inspect installed app record: %w", err)
	} else {
		backupInfo, backupErr := os.Lstat(backup)
		switch {
		case backupErr == nil:
			if backupInfo.Mode()&os.ModeSymlink != 0 || !backupInfo.Mode().IsRegular() {
				return fmt.Errorf(
					"%w: installed app backup is not regular",
					ErrStorageLayoutUnsafe,
				)
			}
			hadBackup = true
		case !os.IsNotExist(backupErr):
			return fmt.Errorf("inspect installed app backup: %w", backupErr)
		}
	}

	if err := os.Rename(temporaryPath, target); err != nil {
		if movedTarget {
			_ = os.Rename(backup, target)
		}
		return fmt.Errorf("activate installed app record: %w", err)
	}
	if movedTarget || hadBackup {
		if err := os.Remove(backup); err != nil && !os.IsNotExist(err) {
			return fmt.Errorf("remove installed app backup: %w", err)
		}
	}
	return nil
}

func removeRegularBackup(backup string) error {
	info, err := os.Lstat(backup)
	if os.IsNotExist(err) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("inspect installed app backup: %w", err)
	}
	if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
		return fmt.Errorf("%w: installed app backup is not regular", ErrStorageLayoutUnsafe)
	}
	if err := os.Remove(backup); err != nil {
		return fmt.Errorf("remove installed app backup: %w", err)
	}
	return nil
}