package service

import (
	"context"
	"errors"
	"math"
	"strings"
	"time"

	infraerrors "github.com/Wei-Shaw/sub2api/internal/pkg/errors"
	"github.com/Wei-Shaw/sub2api/internal/pkg/logger"
)

var (
	ErrAffiliateProfileNotFound = infraerrors.NotFound("AFFILIATE_PROFILE_NOT_FOUND", "affiliate profile not found")
	ErrAffiliateCodeInvalid     = infraerrors.BadRequest("AFFILIATE_CODE_INVALID", "invalid affiliate code")
	ErrAffiliateCodeTaken       = infraerrors.Conflict("AFFILIATE_CODE_TAKEN", "affiliate code already in use")
	ErrAffiliateAlreadyBound    = infraerrors.Conflict("AFFILIATE_ALREADY_BOUND", "affiliate inviter already bound")
	ErrAffiliateQuotaEmpty      = infraerrors.BadRequest("AFFILIATE_QUOTA_EMPTY", "no affiliate quota available to transfer")
)

const (
	affiliateInviteesLimit = 100
	// AffiliateCodeMinLength / AffiliateCodeMaxLength bound both system-generated
	// 12-char codes and admin-customized codes (e.g. "VIP2026").
	AffiliateCodeMinLength = 4
	AffiliateCodeMaxLength = 32
)

// affiliateCodeValidChar accepts uppercase letters, digits, underscore and dash.
// All input passes through strings.ToUpper before validation, so lowercase from
// users is normalized — admins may supply mixed case in their UI.
var affiliateCodeValidChar = func() [256]bool {
	var tbl [256]bool
	for c := byte('A'); c <= 'Z'; c++ {
		tbl[c] = true
	}
	for c := byte('0'); c <= '9'; c++ {
		tbl[c] = true
	}
	tbl['_'] = true
	tbl['-'] = true
	return tbl
}()

// isValidAffiliateCodeFormat validates code format for both binding (user input)
// and admin updates. Caller is expected to upper-case the input first.
func isValidAffiliateCodeFormat(code string) bool {
	if len(code) < AffiliateCodeMinLength || len(code) > AffiliateCodeMaxLength {
		return false
	}
	for i := 0; i < len(code); i++ {
		if !affiliateCodeValidChar[code[i]] {
			return false
		}
	}
	return true
}

type AffiliateSummary struct {
	UserID               int64     `json:"user_id"`
	AffCode              string    `json:"aff_code"`
	AffCodeCustom        bool      `json:"aff_code_custom"`
	AffRebateRatePercent *float64  `json:"aff_rebate_rate_percent,omitempty"`
	InviterID            *int64    `json:"inviter_id,omitempty"`
	AffCount             int       `json:"aff_count"`
	AffQuota             float64   `json:"aff_quota"`
	AffHistoryQuota      float64   `json:"aff_history_quota"`
	CreatedAt            time.Time `json:"created_at"`
	UpdatedAt            time.Time `json:"updated_at"`
}

type AffiliateInvitee struct {
	UserID    int64      `json:"user_id"`
	Email     string     `json:"email"`
	Username  string     `json:"username"`
	CreatedAt *time.Time `json:"created_at,omitempty"`
}

type AffiliateDetail struct {
	UserID          int64              `json:"user_id"`
	AffCode         string             `json:"aff_code"`
	InviterID       *int64             `json:"inviter_id,omitempty"`
	AffCount        int                `json:"aff_count"`
	AffQuota        float64            `json:"aff_quota"`
	AffHistoryQuota float64            `json:"aff_history_quota"`
	// EffectiveRebateRatePercent 是当前用户作为邀请人时实际生效的返利比例：
	// 优先用户自己的专属比例（aff_rebate_rate_percent），否则回退到全局比例。
	// 用于在用户的 /affiliate 页面直观展示「分享后能拿到多少」。
	EffectiveRebateRatePercent float64            `json:"effective_rebate_rate_percent"`
	Invitees                   []AffiliateInvitee `json:"invitees"`
}

type AffiliateRepository interface {
	EnsureUserAffiliate(ctx context.Context, userID int64) (*AffiliateSummary, error)
	GetAffiliateByCode(ctx context.Context, code string) (*AffiliateSummary, error)
	BindInviter(ctx context.Context, userID, inviterID int64) (bool, error)
	AccrueQuota(ctx context.Context, inviterID, inviteeUserID int64, amount float64) (bool, error)
	TransferQuotaToBalance(ctx context.Context, userID int64) (float64, float64, error)
	ListInvitees(ctx context.Context, inviterID int64, limit int) ([]AffiliateInvitee, error)

	// 管理端：用户级专属配置
	UpdateUserAffCode(ctx context.Context, userID int64, newCode string) error
	ResetUserAffCode(ctx context.Context, userID int64) (string, error)
	SetUserRebateRate(ctx context.Context, userID int64, ratePercent *float64) error
	BatchSetUserRebateRate(ctx context.Context, userIDs []int64, ratePercent *float64) error
	ListUsersWithCustomSettings(ctx context.Context, filter AffiliateAdminFilter) ([]AffiliateAdminEntry, int64, error)
}

// AffiliateAdminFilter 列表筛选条件
type AffiliateAdminFilter struct {
	Search   string
	Page     int
	PageSize int
}

// AffiliateAdminEntry 专属用户列表条目
type AffiliateAdminEntry struct {
	UserID               int64    `json:"user_id"`
	Email                string   `json:"email"`
	Username             string   `json:"username"`
	AffCode              string   `json:"aff_code"`
	AffCodeCustom        bool     `json:"aff_code_custom"`
	AffRebateRatePercent *float64 `json:"aff_rebate_rate_percent,omitempty"`
	AffCount             int      `json:"aff_count"`
}

type AffiliateService struct {
	repo                 AffiliateRepository
	settingService       *SettingService
	authCacheInvalidator APIKeyAuthCacheInvalidator
	billingCacheService  *BillingCacheService
}

func NewAffiliateService(repo AffiliateRepository, settingService *SettingService, authCacheInvalidator APIKeyAuthCacheInvalidator, billingCacheService *BillingCacheService) *AffiliateService {
	return &AffiliateService{
		repo:                 repo,
		settingService:       settingService,
		authCacheInvalidator: authCacheInvalidator,
		billingCacheService:  billingCacheService,
	}
}

// IsEnabled reports whether the affiliate (邀请返利) feature is turned on.
func (s *AffiliateService) IsEnabled(ctx context.Context) bool {
	if s == nil || s.settingService == nil {
		return AffiliateEnabledDefault
	}
	return s.settingService.IsAffiliateEnabled(ctx)
}

func (s *AffiliateService) EnsureUserAffiliate(ctx context.Context, userID int64) (*AffiliateSummary, error) {
	if userID <= 0 {
		return nil, infraerrors.BadRequest("INVALID_USER", "invalid user")
	}
	if s == nil || s.repo == nil {
		return nil, infraerrors.ServiceUnavailable("SERVICE_UNAVAILABLE", "affiliate service unavailable")
	}
	return s.repo.EnsureUserAffiliate(ctx, userID)
}

func (s *AffiliateService) GetAffiliateDetail(ctx context.Context, userID int64) (*AffiliateDetail, error) {
	summary, err := s.EnsureUserAffiliate(ctx, userID)
	if err != nil {
		return nil, err
	}
	invitees, err := s.listInvitees(ctx, userID)
	if err != nil {
		return nil, err
	}
	return &AffiliateDetail{
		UserID:                     summary.UserID,
		AffCode:                    summary.AffCode,
		InviterID:                  summary.InviterID,
		AffCount:                   summary.AffCount,
		AffQuota:                   summary.AffQuota,
		AffHistoryQuota:            summary.AffHistoryQuota,
		EffectiveRebateRatePercent: s.resolveRebateRatePercent(ctx, summary),
		Invitees:                   invitees,
	}, nil
}

func (s *AffiliateService) BindInviterByCode(ctx context.Context, userID int64, rawCode string) error {
	code := strings.ToUpper(strings.TrimSpace(rawCode))
	if code == "" {
		return nil
	}
	if s == nil || s.repo == nil {
		return infraerrors.ServiceUnavailable("SERVICE_UNAVAILABLE", "affiliate service unavailable")
	}
	// 总开关关闭时，注册阶段静默忽略 aff 参数（不报错，避免阻断注册流程）
	if !s.IsEnabled(ctx) {
		return nil
	}
	if !isValidAffiliateCodeFormat(code) {
		return ErrAffiliateCodeInvalid
	}

	selfSummary, err := s.repo.EnsureUserAffiliate(ctx, userID)
	if err != nil {
		return err
	}
	if selfSummary.InviterID != nil {
		return nil
	}

	inviterSummary, err := s.repo.GetAffiliateByCode(ctx, code)
	if err != nil {
		if errors.Is(err, ErrAffiliateProfileNotFound) {
			return ErrAffiliateCodeInvalid
		}
		return err
	}
	if inviterSummary == nil || inviterSummary.UserID <= 0 || inviterSummary.UserID == userID {
		return ErrAffiliateCodeInvalid
	}

	bound, err := s.repo.BindInviter(ctx, userID, inviterSummary.UserID)
	if err != nil {
		return err
	}
	if !bound {
		return ErrAffiliateAlreadyBound
	}
	return nil
}

func (s *AffiliateService) AccrueInviteRebate(ctx context.Context, inviteeUserID int64, baseRechargeAmount float64) (float64, error) {
	if s == nil || s.repo == nil {
		return 0, nil
	}
	if inviteeUserID <= 0 || baseRechargeAmount <= 0 || math.IsNaN(baseRechargeAmount) || math.IsInf(baseRechargeAmount, 0) {
		return 0, nil
	}
	// 总开关关闭时，新充值不再产生返利
	if !s.IsEnabled(ctx) {
		return 0, nil
	}

	inviteeSummary, err := s.repo.EnsureUserAffiliate(ctx, inviteeUserID)
	if err != nil {
		return 0, err
	}
	if inviteeSummary.InviterID == nil || *inviteeSummary.InviterID <= 0 {
		return 0, nil
	}

	// 加载邀请人 profile，优先使用专属比例（覆盖全局）
	inviterSummary, err := s.repo.EnsureUserAffiliate(ctx, *inviteeSummary.InviterID)
	if err != nil {
		return 0, err
	}
	rebateRatePercent := s.resolveRebateRatePercent(ctx, inviterSummary)
	rebate := roundTo(baseRechargeAmount*(rebateRatePercent/100), 8)
	if rebate <= 0 {
		return 0, nil
	}

	applied, err := s.repo.AccrueQuota(ctx, *inviteeSummary.InviterID, inviteeUserID, rebate)
	if err != nil {
		return 0, err
	}
	if !applied {
		return 0, nil
	}
	return rebate, nil
}

// resolveRebateRatePercent returns the inviter's exclusive rate when set,
// otherwise the global setting value (clamped to [Min, Max]).
func (s *AffiliateService) resolveRebateRatePercent(ctx context.Context, inviter *AffiliateSummary) float64 {
	if inviter != nil && inviter.AffRebateRatePercent != nil {
		v := *inviter.AffRebateRatePercent
		if math.IsNaN(v) || math.IsInf(v, 0) {
			return s.globalRebateRatePercent(ctx)
		}
		return clampAffiliateRebateRate(v)
	}
	return s.globalRebateRatePercent(ctx)
}

// globalRebateRatePercent reads the system-wide rebate rate via SettingService,
// returning the documented default when SettingService is unavailable.
func (s *AffiliateService) globalRebateRatePercent(ctx context.Context) float64 {
	if s == nil || s.settingService == nil {
		return AffiliateRebateRateDefault
	}
	return s.settingService.GetAffiliateRebateRatePercent(ctx)
}

func (s *AffiliateService) TransferAffiliateQuota(ctx context.Context, userID int64) (float64, float64, error) {
	if s == nil || s.repo == nil {
		return 0, 0, infraerrors.ServiceUnavailable("SERVICE_UNAVAILABLE", "affiliate service unavailable")
	}

	transferred, balance, err := s.repo.TransferQuotaToBalance(ctx, userID)
	if err != nil {
		return 0, 0, err
	}
	if transferred > 0 {
		s.invalidateAffiliateCaches(ctx, userID)
	}
	return transferred, balance, nil
}

func (s *AffiliateService) listInvitees(ctx context.Context, inviterID int64) ([]AffiliateInvitee, error) {
	if s == nil || s.repo == nil {
		return nil, infraerrors.ServiceUnavailable("SERVICE_UNAVAILABLE", "affiliate service unavailable")
	}
	invitees, err := s.repo.ListInvitees(ctx, inviterID, affiliateInviteesLimit)
	if err != nil {
		return nil, err
	}
	for i := range invitees {
		invitees[i].Email = maskEmail(invitees[i].Email)
	}
	return invitees, nil
}

func roundTo(v float64, scale int) float64 {
	factor := math.Pow10(scale)
	return math.Round(v*factor) / factor
}

func maskEmail(email string) string {
	email = strings.TrimSpace(email)
	if email == "" {
		return ""
	}
	at := strings.Index(email, "@")
	if at <= 0 || at >= len(email)-1 {
		return "***"
	}

	local := email[:at]
	domain := email[at+1:]
	dot := strings.LastIndex(domain, ".")

	maskedLocal := maskSegment(local)
	if dot <= 0 || dot >= len(domain)-1 {
		return maskedLocal + "@" + maskSegment(domain)
	}

	domainName := domain[:dot]
	tld := domain[dot:]
	return maskedLocal + "@" + maskSegment(domainName) + tld
}

func maskSegment(s string) string {
	r := []rune(s)
	if len(r) == 0 {
		return "***"
	}
	if len(r) == 1 {
		return string(r[0]) + "***"
	}
	return string(r[0]) + "***"
}

func (s *AffiliateService) invalidateAffiliateCaches(ctx context.Context, userID int64) {
	if s.authCacheInvalidator != nil {
		s.authCacheInvalidator.InvalidateAuthCacheByUserID(ctx, userID)
	}
	if s.billingCacheService != nil {
		if err := s.billingCacheService.InvalidateUserBalance(ctx, userID); err != nil {
			logger.LegacyPrintf("service.affiliate", "[Affiliate] Failed to invalidate billing cache for user %d: %v", userID, err)
		}
	}
}

// =========================
// Admin: 专属配置管理
// =========================

// validateExclusiveRate ensures a per-user override is finite and within
// [Min, Max]. nil is always valid (means "clear / fall back to global").
func validateExclusiveRate(ratePercent *float64) error {
	if ratePercent == nil {
		return nil
	}
	v := *ratePercent
	if math.IsNaN(v) || math.IsInf(v, 0) {
		return infraerrors.BadRequest("INVALID_RATE", "invalid rebate rate")
	}
	if v < AffiliateRebateRateMin || v > AffiliateRebateRateMax {
		return infraerrors.BadRequest("INVALID_RATE", "rebate rate out of range")
	}
	return nil
}

// AdminUpdateUserAffCode 管理员改写用户的邀请码（专属邀请码）。
func (s *AffiliateService) AdminUpdateUserAffCode(ctx context.Context, userID int64, rawCode string) error {
	if s == nil || s.repo == nil {
		return infraerrors.ServiceUnavailable("SERVICE_UNAVAILABLE", "affiliate service unavailable")
	}
	code := strings.ToUpper(strings.TrimSpace(rawCode))
	if !isValidAffiliateCodeFormat(code) {
		return ErrAffiliateCodeInvalid
	}
	return s.repo.UpdateUserAffCode(ctx, userID, code)
}

// AdminResetUserAffCode 重置用户邀请码为系统随机码。
func (s *AffiliateService) AdminResetUserAffCode(ctx context.Context, userID int64) (string, error) {
	if s == nil || s.repo == nil {
		return "", infraerrors.ServiceUnavailable("SERVICE_UNAVAILABLE", "affiliate service unavailable")
	}
	return s.repo.ResetUserAffCode(ctx, userID)
}

// AdminSetUserRebateRate 设置/清除用户专属返利比例。ratePercent==nil 表示清除。
func (s *AffiliateService) AdminSetUserRebateRate(ctx context.Context, userID int64, ratePercent *float64) error {
	if s == nil || s.repo == nil {
		return infraerrors.ServiceUnavailable("SERVICE_UNAVAILABLE", "affiliate service unavailable")
	}
	if err := validateExclusiveRate(ratePercent); err != nil {
		return err
	}
	return s.repo.SetUserRebateRate(ctx, userID, ratePercent)
}

// AdminBatchSetUserRebateRate 批量设置/清除用户专属返利比例。
func (s *AffiliateService) AdminBatchSetUserRebateRate(ctx context.Context, userIDs []int64, ratePercent *float64) error {
	if s == nil || s.repo == nil {
		return infraerrors.ServiceUnavailable("SERVICE_UNAVAILABLE", "affiliate service unavailable")
	}
	if err := validateExclusiveRate(ratePercent); err != nil {
		return err
	}
	cleaned := make([]int64, 0, len(userIDs))
	for _, uid := range userIDs {
		if uid > 0 {
			cleaned = append(cleaned, uid)
		}
	}
	if len(cleaned) == 0 {
		return nil
	}
	return s.repo.BatchSetUserRebateRate(ctx, cleaned, ratePercent)
}

// AdminListCustomUsers 列出有专属配置的用户。
func (s *AffiliateService) AdminListCustomUsers(ctx context.Context, filter AffiliateAdminFilter) ([]AffiliateAdminEntry, int64, error) {
	if s == nil || s.repo == nil {
		return nil, 0, infraerrors.ServiceUnavailable("SERVICE_UNAVAILABLE", "affiliate service unavailable")
	}
	return s.repo.ListUsersWithCustomSettings(ctx, filter)
}