package config

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"chub/internal/domain"
)

const currentVersion = 1

var ErrDefaultConfigUnavailable = errors.New("default config is unavailable")

type Settings struct {
	ChromePath           string `json:"chromePath"`
	EdgePath             string `json:"edgePath"`
	DefaultDir           string `json:"defaultUserDataDir"`
	LogDir               string `json:"logDir"`
	RemoteDebugStartPort int    `json:"remoteDebugStartPort"`
	CloseOnExit          bool   `json:"closeOnExit"`
}

type Instance struct {
	ID                       string            `json:"id"`
	Name                     string            `json:"name"`
	ProxyID                  string            `json:"proxyId,omitempty"`
	PreferredRemoteDebugPort int               `json:"preferredRemoteDebugPort,omitempty"`
	Launch                   domain.LaunchSpec `json:"launch"`
	UpdatedAt                time.Time         `json:"updatedAt"`
}

// ProxyProfile is deliberately limited to a display name and a validated,
// non-authenticated endpoint. Credentials must never enter local config.
type ProxyProfile struct {
	ID        string    `json:"id"`
	Name      string    `json:"name"`
	Server    string    `json:"server"`
	UpdatedAt time.Time `json:"updatedAt"`
}

type File struct {
	Version   int            `json:"version"`
	Settings  Settings       `json:"settings"`
	Instances []Instance     `json:"instances"`
	Proxies   []ProxyProfile `json:"proxies"`
}

type Store struct{ path string }

func New(path string) (*Store, error) {
	if path == "" {
		return nil, errors.New("config path is required")
	}
	return &Store{path: filepath.Clean(path)}, nil
}

func DefaultPath() (string, error) {
	executable, err := os.Executable()
	if err != nil {
		return "", fmt.Errorf("%w: resolve executable", ErrDefaultConfigUnavailable)
	}
	return defaultPathForExecutable(executable)
}

// LegacyPath is the pre-portable configuration location. It is read only when
// the executable-side config does not exist yet.
func LegacyPath() (string, error) {
	dir, err := os.UserConfigDir()
	if err != nil {
		return "", fmt.Errorf("%w: resolve legacy config directory", ErrDefaultConfigUnavailable)
	}
	return filepath.Join(dir, "chub", "config.json"), nil
}

// OpenDefault returns the config store beside the currently executing binary.
// A valid legacy user config is copied there once only when the target does not
// already exist. The legacy file is deliberately retained for recovery.
func OpenDefault() (*Store, error) {
	target, err := DefaultPath()
	if err != nil {
		return nil, err
	}
	store, targetExists, err := defaultStore(target)
	if err != nil || targetExists {
		return store, err
	}
	legacy, err := LegacyPath()
	if err != nil {
		return nil, err
	}
	return migrateLegacyConfig(store, legacy)
}

func (s *Store) Path() string { return s.path }

func defaultPathForExecutable(executable string) (string, error) {
	path := strings.TrimSpace(executable)
	if path == "" || !filepath.IsAbs(path) {
		return "", fmt.Errorf("%w: executable path must be absolute", ErrDefaultConfigUnavailable)
	}
	return filepath.Join(filepath.Dir(filepath.Clean(path)), "config.json"), nil
}

func openDefaultAt(target, legacy string) (*Store, error) {
	store, targetExists, err := defaultStore(target)
	if err != nil || targetExists {
		return store, err
	}
	return migrateLegacyConfig(store, legacy)
}

func defaultStore(target string) (*Store, bool, error) {
	store, err := New(target)
	if err != nil {
		return nil, false, fmt.Errorf("%w: initialize target store", ErrDefaultConfigUnavailable)
	}
	info, err := os.Stat(store.Path())
	if errors.Is(err, os.ErrNotExist) {
		return store, false, nil
	}
	if err != nil {
		return nil, false, fmt.Errorf("%w: inspect target config", ErrDefaultConfigUnavailable)
	}
	if info.IsDir() {
		return nil, false, fmt.Errorf("%w: target config is a directory", ErrDefaultConfigUnavailable)
	}
	return store, true, nil
}

func migrateLegacyConfig(target *Store, legacyPath string) (*Store, error) {
	if target == nil {
		return nil, fmt.Errorf("%w: target store is unavailable", ErrDefaultConfigUnavailable)
	}
	legacy, err := New(legacyPath)
	if err != nil {
		return nil, fmt.Errorf("%w: initialize legacy store", ErrDefaultConfigUnavailable)
	}
	if filepath.Clean(target.Path()) == filepath.Clean(legacy.Path()) {
		return target, nil
	}
	info, err := os.Stat(legacy.Path())
	if errors.Is(err, os.ErrNotExist) {
		return target, nil
	}
	if err != nil || info.IsDir() {
		return nil, fmt.Errorf("%w: inspect legacy config", ErrDefaultConfigUnavailable)
	}
	value, err := legacy.Load()
	if err != nil {
		return nil, fmt.Errorf("%w: validate legacy config", ErrDefaultConfigUnavailable)
	}
	if err := target.Save(value); err != nil {
		return nil, fmt.Errorf("%w: migrate legacy config", ErrDefaultConfigUnavailable)
	}
	return target, nil
}

func (s *Store) Load() (File, error) {
	data, err := os.ReadFile(s.path)
	if errors.Is(err, os.ErrNotExist) {
		return File{Version: currentVersion, Settings: DefaultSettings()}, nil
	}
	if err != nil {
		return File{}, fmt.Errorf("read config: %w", err)
	}
	var result File
	if err := json.Unmarshal(data, &result); err != nil {
		return File{}, fmt.Errorf("decode config: %w", err)
	}
	if result.Version == 0 {
		result.Version = currentVersion
	}
	if result.Version != currentVersion {
		return File{}, fmt.Errorf("unsupported config version %d", result.Version)
	}
	if result.Settings.RemoteDebugStartPort == 0 {
		result.Settings.RemoteDebugStartPort = domain.DefaultRemoteDebugPort
	}
	if err := normalizeInstanceRemoteDebugPorts(&result); err != nil {
		return File{}, err
	}
	if err := normalizeProxyConfig(&result); err != nil {
		return File{}, err
	}
	return result, nil
}

func DefaultSettings() Settings {
	return Settings{
		ChromePath:           `C:\Program Files\Google\Chrome\Application\chrome.exe`,
		EdgePath:             `C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe`,
		DefaultDir:           `C:\Users\Public\chub\profiles`,
		LogDir:               `C:\Users\Public\chub\logs`,
		RemoteDebugStartPort: domain.DefaultRemoteDebugPort,
		CloseOnExit:          true,
	}
}

func (s *Store) Save(value File) error {
	value.Version = currentVersion
	if value.Settings.RemoteDebugStartPort == 0 {
		value.Settings.RemoteDebugStartPort = domain.DefaultRemoteDebugPort
	}
	if value.Instances == nil {
		value.Instances = []Instance{}
	}
	if value.Proxies == nil {
		value.Proxies = []ProxyProfile{}
	}
	if err := normalizeInstanceRemoteDebugPorts(&value); err != nil {
		return err
	}
	if err := normalizeProxyConfig(&value); err != nil {
		return err
	}
	data, err := json.MarshalIndent(value, "", "  ")
	if err != nil {
		return fmt.Errorf("encode config: %w", err)
	}
	if err := os.MkdirAll(filepath.Dir(s.path), 0o700); err != nil {
		return fmt.Errorf("create config dir: %w", err)
	}
	tmp, err := os.CreateTemp(filepath.Dir(s.path), ".config-*.tmp")
	if err != nil {
		return fmt.Errorf("create config temp: %w", err)
	}
	tmpName := tmp.Name()
	defer os.Remove(tmpName)
	if err := tmp.Chmod(0o600); err != nil {
		_ = tmp.Close()
		return fmt.Errorf("protect config temp: %w", err)
	}
	if _, err := tmp.Write(data); err != nil {
		_ = tmp.Close()
		return fmt.Errorf("write config temp: %w", err)
	}
	if err := tmp.Sync(); err != nil {
		_ = tmp.Close()
		return fmt.Errorf("sync config temp: %w", err)
	}
	if err := tmp.Close(); err != nil {
		return fmt.Errorf("close config temp: %w", err)
	}
	if err := replace(s.path, tmpName); err != nil {
		return err
	}
	return nil
}

func normalizeInstanceRemoteDebugPorts(value *File) error {
	if value == nil {
		return errors.New("config is required")
	}
	start := value.Settings.RemoteDebugStartPort
	if !domain.ValidRemoteDebugPort(start) {
		return fmt.Errorf("invalid remote debug start port %d", start)
	}
	used := make(map[int]struct{}, len(value.Instances))
	for _, instance := range value.Instances {
		port := instance.PreferredRemoteDebugPort
		if port == 0 {
			continue
		}
		if !domain.ValidRemoteDebugPort(port) {
			return fmt.Errorf("invalid preferred remote debug port %d", port)
		}
		if _, exists := used[port]; exists {
			return fmt.Errorf("duplicate preferred remote debug port %d", port)
		}
		used[port] = struct{}{}
	}
	for index := range value.Instances {
		if value.Instances[index].PreferredRemoteDebugPort != 0 {
			continue
		}
		port, err := nextPreferredRemoteDebugPort(start, used)
		if err != nil {
			return err
		}
		value.Instances[index].PreferredRemoteDebugPort = port
		used[port] = struct{}{}
	}
	return nil
}

func nextPreferredRemoteDebugPort(start int, used map[int]struct{}) (int, error) {
	for port := start; port <= domain.MaxRemoteDebugPort; port++ {
		if _, exists := used[port]; !exists {
			return port, nil
		}
	}
	return 0, errors.New("no preferred remote debug port is available")
}

func normalizeProxyConfig(value *File) error {
	if value == nil {
		return errors.New("config is required")
	}
	byID := make(map[string]ProxyProfile, len(value.Proxies))
	names := make(map[string]struct{}, len(value.Proxies))
	for i := range value.Proxies {
		profile := &value.Proxies[i]
		profile.ID = strings.TrimSpace(profile.ID)
		profile.Name = strings.TrimSpace(profile.Name)
		if profile.ID == "" || profile.Name == "" {
			return errors.New("invalid proxy configuration")
		}
		if _, exists := byID[profile.ID]; exists {
			return errors.New("duplicate proxy configuration")
		}
		nameKey := strings.ToLower(profile.Name)
		if _, exists := names[nameKey]; exists {
			return errors.New("duplicate proxy configuration")
		}
		server, err := domain.NormalizeProxyServer(profile.Server)
		if err != nil || server == "" {
			return errors.New("invalid proxy configuration")
		}
		profile.Server = server
		byID[profile.ID] = *profile
		names[nameKey] = struct{}{}
	}

	legacyByServer := make(map[string]string, len(value.Proxies))
	for _, profile := range value.Proxies {
		legacyByServer[profile.Server] = profile.ID
	}
	for i := range value.Instances {
		instance := &value.Instances[i]
		instance.ProxyID = strings.TrimSpace(instance.ProxyID)
		if instance.ProxyID != "" {
			if _, exists := byID[instance.ProxyID]; !exists {
				return errors.New("instance refers to an unavailable proxy")
			}
			instance.Launch.ProxyServer = ""
			continue
		}
		if strings.TrimSpace(instance.Launch.ProxyServer) == "" {
			continue
		}
		server, err := domain.NormalizeProxyServer(instance.Launch.ProxyServer)
		if err != nil || server == "" {
			return errors.New("invalid proxy configuration")
		}
		proxyID := legacyByServer[server]
		if proxyID == "" {
			proxyID = nextLegacyProxyID(byID)
			profile := ProxyProfile{ID: proxyID, Name: "导入代理 " + strconv.Itoa(len(value.Proxies)+1), Server: server}
			value.Proxies = append(value.Proxies, profile)
			byID[proxyID] = profile
			legacyByServer[server] = proxyID
		}
		instance.ProxyID = proxyID
		instance.Launch.ProxyServer = ""
	}
	return nil
}

func nextLegacyProxyID(existing map[string]ProxyProfile) string {
	for index := 1; ; index++ {
		candidate := "legacy-proxy-" + strconv.Itoa(index)
		if _, exists := existing[candidate]; !exists {
			return candidate
		}
	}
}

func replace(target, temp string) error {
	backup := target + ".bak"
	_, statErr := os.Stat(target)
	if statErr == nil {
		_ = os.Remove(backup)
		if err := os.Rename(target, backup); err != nil {
			return fmt.Errorf("backup config: %w", err)
		}
	}
	if err := os.Rename(temp, target); err != nil {
		if statErr == nil {
			_ = os.Rename(backup, target)
		}
		return fmt.Errorf("replace config: %w", err)
	}
	_ = os.Remove(backup)
	return nil
}