package domain

import (
	"regexp"
	"time"
)

// UserID is a strongly-typed identifier for users.
type UserID string

func (id UserID) String() string { return string(id) }
func (id UserID) IsZero() bool   { return id == "" }

// Allowed theme values.
var allowedThemes = map[string]bool{
	"light":  true,
	"dark":   true,
	"system": true,
}

// Allowed digest values.
var allowedDigests = map[string]bool{
	"daily":  true,
	"weekly": true,
	"never":  true,
}

var languageRegex = regexp.MustCompile(`^[a-z]{2}$`)

// NotificationSettings holds notification preferences.
type NotificationSettings struct {
	Email  bool
	Push   bool
	Digest string
}

// Preferences holds all user preferences.
type Preferences struct {
	UserID        UserID
	Theme         string
	Language      string
	Notifications NotificationSettings
	UpdatedAt     time.Time
}

// NewDefaultPreferences returns preferences with all defaults applied.
func NewDefaultPreferences(userID UserID) *Preferences {
	return &Preferences{
		UserID:   userID,
		Theme:    "system",
		Language: "en",
		Notifications: NotificationSettings{
			Email:  true,
			Push:   true,
			Digest: "weekly",
		},
		UpdatedAt: time.Now().UTC(),
	}
}

// Validate checks that all field values are within allowed sets.
func (p *Preferences) Validate() error {
	if !allowedThemes[p.Theme] {
		return ErrInvalidTheme
	}
	if !languageRegex.MatchString(p.Language) {
		return ErrInvalidLanguage
	}
	if !allowedDigests[p.Notifications.Digest] {
		return ErrInvalidDigest
	}
	return nil
}

// NotificationSettingsUpdate uses pointer fields to distinguish provided vs absent.
type NotificationSettingsUpdate struct {
	Email  *bool
	Push   *bool
	Digest *string
}

// PreferencesUpdate uses pointer fields to distinguish provided vs absent.
type PreferencesUpdate struct {
	Theme         *string
	Language      *string
	Notifications *NotificationSettingsUpdate
}

// MergeFrom applies a shallow merge: only overwrites fields where the update pointer is non-nil.
// For Notifications, individual sub-fields are merged when provided.
func (p *Preferences) MergeFrom(incoming *PreferencesUpdate) {
	if incoming == nil {
		return
	}
	if incoming.Theme != nil {
		p.Theme = *incoming.Theme
	}
	if incoming.Language != nil {
		p.Language = *incoming.Language
	}
	if incoming.Notifications != nil {
		if incoming.Notifications.Email != nil {
			p.Notifications.Email = *incoming.Notifications.Email
		}
		if incoming.Notifications.Push != nil {
			p.Notifications.Push = *incoming.Notifications.Push
		}
		if incoming.Notifications.Digest != nil {
			p.Notifications.Digest = *incoming.Notifications.Digest
		}
	}
}