package user

import (
	"context"
	"errors"
	"time"
)

type Service struct {
	repo     *Repo
	reserved []string
}

func NewService(repo *Repo, reserved []string) *Service {
	return &Service{repo: repo, reserved: reserved}
}

func (s *Service) Repo() *Repo { return s.repo }

func (s *Service) Reserved() []string { return s.reserved }

// IsAvailable returns true if no active/in-grace user has the username.
func (s *Service) IsAvailable(ctx context.Context, username string) (bool, error) {
	if err := ValidateUsername(username, s.reserved); err != nil {
		return false, err
	}
	u, err := s.repo.GetByUsername(ctx, NormalizeUsername(username))
	if errors.Is(err, ErrUserNotFound) {
		return true, nil
	}
	if err != nil {
		return false, err
	}
	_ = u
	return false, nil
}

// CreateOrActivate inserts a new active user. Caller is responsible for transactional
// concerns (e.g. payments worker uses this within a tx).
func (s *Service) CreateOrActivate(ctx context.Context, pubkey, username string, sub SubscriptionType, years int, manual bool) (*User, error) {
	username = NormalizeUsername(username)
	if err := ValidateUsername(username, s.reserved); err != nil {
		return nil, err
	}
	now := time.Now().UTC()
	expiresAt := computeExpiry(sub, years, time.Time{}, now)

	u := &User{
		Pubkey:           pubkey,
		Username:         username,
		SubscriptionType: sub,
		ExpiresAt:        expiresAt,
		IsActive:         true,
		ManualUsername:   manual,
	}
	if err := s.repo.Insert(ctx, u); err != nil {
		return nil, err
	}
	return u, nil
}

// Renew extends an existing user. Used by payments worker and admin extend.
func (s *Service) Renew(ctx context.Context, u *User, sub SubscriptionType, years int) error {
	now := time.Now().UTC()
	var current time.Time
	if u.ExpiresAt != nil {
		current = *u.ExpiresAt
	}
	u.SubscriptionType = sub
	u.ExpiresAt = computeExpiry(sub, years, current, now)
	u.IsActive = true
	u.DeactivatedAt = nil
	u.ExpiringReminderSentAt = nil
	return s.repo.Update(ctx, u)
}

func (s *Service) SetUsername(ctx context.Context, pubkey, username string) (*User, error) {
	username = NormalizeUsername(username)
	if err := ValidateUsername(username, s.reserved); err != nil {
		return nil, err
	}
	u, err := s.repo.GetByPubkey(ctx, pubkey)
	if err != nil {
		return nil, err
	}
	if existing, err := s.repo.GetByUsername(ctx, username); err == nil && existing.Pubkey != pubkey {
		return nil, ErrUsernameTaken
	}
	u.Username = username
	u.ManualUsername = true
	if err := s.repo.Update(ctx, u); err != nil {
		return nil, err
	}
	return u, nil
}

func (s *Service) Delete(ctx context.Context, pubkey string) error {
	return s.repo.Delete(ctx, pubkey)
}

// computeExpiry returns *time.Time (nil for lifetime).
func computeExpiry(sub SubscriptionType, years int, current time.Time, now time.Time) *time.Time {
	if sub == SubLifetime {
		return nil
	}
	var cur time.Time
	if !current.IsZero() {
		cur = current
	}
	return YearlyTargetExpiry(&cur, years, now)
}

// YearlyTargetExpiry computes the new expiry for a yearly subscription using
// effective_start = max(now, current_expiry); new_expiry = effective_start + years.
// currentExpiry may be nil or zero for first-time purchases.
func YearlyTargetExpiry(currentExpiry *time.Time, years int, now time.Time) *time.Time {
	if years <= 0 {
		years = 1
	}
	base := now
	if currentExpiry != nil && currentExpiry.After(base) {
		base = *currentExpiry
	}
	t := base.AddDate(years, 0, 0)
	return &t
}