// Package draw implements POST /api/v1/lottery/draw: the transactional lottery
// draw flow. The service composes the ChanceService, RuleEvaluator,
// WeightedPicker, PrizeHandler.Registry and LedgerService primitives from the
// model layer into one atomic sequence.
//
// Ordering matters — the flow is:
//  1. feature-flag gate (config.Lottery.Enable)
//  2. Redis rate limit (per-user 1/sec)
//  3. Load activity + validate window/status
//  4. Build RuleContext (pre-tx reads)
//  5. Evaluate eligibility (pure compute)
//  6. Load prize pool snapshot (pre-tx read)
//  7. Open tx →
//     7a. Nonce dedupe: SELECT lottery_draw WHERE (user_id, client_nonce)
//     — hit returns the recorded draw
//     7b. ChanceService.Consume (SELECT FOR UPDATE + decrement)
//     7c. WeightedPicker.Pick
//     7d. Limited-stock optimistic decrement; fallback on RowsAffected=0
//     7e. INSERT lottery_draw + PrizeSnapshot + EligibilitySnapshot
//     7f. Auto-handler Dispatch (in tx)
//     7g. Update draw.dispatch_state
//     → commit
//
// Everything past step 5 uses the caller's transaction; post-commit cache
// invalidation is the handler layer's job (a future enhancement — the
// underlying UserModel already invalidates its own cache on UpdateSubscribe).
package draw

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"strconv"
	"time"

	"github.com/perfect-panel/server/internal/logic/lottery/handler"
	"github.com/perfect-panel/server/internal/model/lottery"
	"github.com/perfect-panel/server/pkg/limit"
	"github.com/perfect-panel/server/pkg/xerr"
	"gorm.io/gorm"
)

// Request is the input to Draw.
type Request struct {
	UserId      int64
	ActivityId  int64
	ClientNonce string
}

// Result is what Draw returns to the caller (user handler).
type Result struct {
	DrawId           int64
	IsWin            bool
	Prize            *PrizeSummary
	ChancesRemaining int64
	Claim            ClaimSummary
	Message          string
}

// PrizeSummary is the awarded-prize view rendered for the user.
type PrizeSummary struct {
	Slot   int
	Id     int64
	Type   string
	Name   string
	Config json.RawMessage
}

// ClaimSummary describes whether the user needs to take a further action.
type ClaimSummary struct {
	Required    bool
	AutoClaimed bool
	Message     string
	// ExpiresAt 是人工奖领奖窗口截止时间（Unix 秒；0 表示不适用）。
	ExpiresAt int64
	// ClaimFormSchema 是人工奖前端渲染领奖表单用的 JSON Schema
	// （nil 表示不适用；auto handler 与"谢谢参与"都返回 nil）。
	ClaimFormSchema json.RawMessage
}

// Service orchestrates the transactional draw flow. Deps are struct-injected
// so tests can substitute fakes and production wiring lives in ServiceContext.
type Service struct {
	deps Deps
}

// Deps groups the collaborators. Nil-safe checks live in Draw itself, not here.
type Deps struct {
	DB             *gorm.DB
	Enabled        bool
	RateLimiter    RateLimiter
	Chance         lottery.ChanceService
	Evaluator      lottery.RuleEvaluator
	Picker         lottery.WeightedPicker
	Registry       lottery.Registry
	ContextBuilder RuleContextBuilder
}

// RateLimiter admits at most 1 draw per second per user. Extracted to an
// interface so tests can supply an always-admit fake without pulling Redis.
type RateLimiter interface {
	Allow(ctx context.Context, userId int64) error
}

// RuleContextBuilder loads the per-user snapshot needed by the rule
// evaluator. Extracted so tests can inject deterministic contexts.
type RuleContextBuilder interface {
	Build(ctx context.Context, userId int64) (lottery.RuleContext, error)
}

// NewService returns a Draw service ready to serve requests.
func NewService(d Deps) *Service { return &Service{deps: d} }

// Draw runs the full lottery draw flow. Errors are xerr codes suitable for
// direct return by the HTTP handler; internal errors are wrapped as
// LotteryInternalError.
func (s *Service) Draw(ctx context.Context, req Request) (*Result, error) {
	if err := s.validateRequest(req); err != nil {
		return nil, err
	}
	if !s.deps.Enabled {
		return nil, xerr.NewErrCode(xerr.LotteryActivityEnded)
	}
	if err := s.applyRateLimit(ctx, req.UserId); err != nil {
		return nil, err
	}

	activity, err := s.loadRunningActivity(ctx, req.ActivityId)
	if err != nil {
		return nil, err
	}

	// Pre-tx reads: user context + prize pool snapshot. Cheap and out of the
	// hot-lock window; the tx step re-checks stock atomically.
	rc, err := s.buildRuleContext(ctx, req.UserId)
	if err != nil {
		return nil, wrapInternal(err)
	}

	tree, err := parseEligibilityTree(activity.Eligibility)
	if err != nil {
		return nil, wrapInternal(err)
	}
	passed, unmet, err := s.deps.Evaluator.Evaluate(ctx, tree, rc)
	if err != nil {
		return nil, wrapInternal(err)
	}
	if !passed {
		// The rejection itself is not an error to the caller — but we still
		// record an eligibility snapshot for support/audit before returning
		// the 4001. Snapshot write intentionally uses its own tx: the draw
		// itself never got issued, so there is no draw_id to correlate; we
		// omit the snapshot in that case.
		_ = unmet // unmet is available to the handler via error metadata if needed
		return nil, xerr.NewErrCode(xerr.LotteryNotEligible)
	}

	prizes, err := s.loadPrizes(ctx, req.ActivityId)
	if err != nil {
		return nil, wrapInternal(err)
	}
	if len(prizes) == 0 {
		return nil, xerr.NewErrCode(xerr.LotteryActivityEnded)
	}

	var result *Result
	txErr := s.deps.DB.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
		// (a) Nonce dedupe — race-safe idempotency check.
		if existing, existsErr := s.findExistingDraw(ctx, tx, req); existsErr != nil {
			return existsErr
		} else if existing != nil {
			result, existsErr = s.buildResultFromExistingDraw(ctx, tx, existing)
			return existsErr
		}

		// (b) Consume chance atomically. ErrNoChances → 4002.
		remaining, consumeErr := s.deps.Chance.Consume(ctx, tx, req.UserId, req.ActivityId)
		if errors.Is(consumeErr, lottery.ErrNoChances) {
			return xerr.NewErrCode(xerr.LotteryNoChances)
		}
		if consumeErr != nil {
			return wrapInternal(consumeErr)
		}

		// (c) Pick a prize.
		idx, pickErr := s.deps.Picker.Pick(prizes)
		if pickErr != nil {
			return xerr.NewErrCode(xerr.LotteryActivityEnded)
		}
		picked := prizes[idx]

		// (d) Limited-stock decrement.
		final, stockErr := s.decrementStockOrFallback(ctx, tx, picked, prizes)
		if stockErr != nil {
			return wrapInternal(stockErr)
		}

		// (e) Insert draw + snapshots.
		draw, insertErr := s.insertDraw(ctx, tx, req, final)
		if insertErr != nil {
			return wrapInternal(insertErr)
		}
		if snapErr := s.insertSnapshots(ctx, tx, draw, final, passed); snapErr != nil {
			return wrapInternal(snapErr)
		}

		// (f) Dispatch prize (auto handler) or create pending claim (manual handler).
		dispatch, claimInfo, dispatchErr := s.dispatchOrEnqueueClaim(ctx, tx, req, draw, final)
		if dispatchErr != nil {
			return dispatchErr
		}

		// (g) Update draw.dispatch_state to reflect handler outcome.
		if updateErr := s.finalizeDrawState(ctx, tx, draw, dispatch); updateErr != nil {
			return wrapInternal(updateErr)
		}

		result = buildResult(draw, final, dispatch, claimInfo, remaining)
		return nil
	})
	if txErr != nil {
		if _, ok := txErr.(*xerr.CodeError); ok {
			return nil, txErr
		}
		return nil, wrapInternal(txErr)
	}
	return result, nil
}

// ---- individual steps ------------------------------------------------------

func (s *Service) validateRequest(req Request) error {
	if req.UserId <= 0 || req.ActivityId <= 0 || req.ClientNonce == "" {
		return xerr.NewErrCode(xerr.InvalidParams)
	}
	if len(req.ClientNonce) > 64 {
		return xerr.NewErrCode(xerr.InvalidParams)
	}
	return nil
}

func (s *Service) applyRateLimit(ctx context.Context, userId int64) error {
	if s.deps.RateLimiter == nil {
		return nil
	}
	if err := s.deps.RateLimiter.Allow(ctx, userId); err != nil {
		if errors.Is(err, ErrRateLimited) {
			return xerr.NewErrCode(xerr.LotteryRateLimited)
		}
		return wrapInternal(err)
	}
	return nil
}

func (s *Service) loadRunningActivity(ctx context.Context, activityId int64) (*lottery.Activity, error) {
	var activity lottery.Activity
	now := time.Now()
	err := s.deps.DB.WithContext(ctx).
		Where("id = ?", activityId).
		First(&activity).Error
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, xerr.NewErrCode(xerr.LotteryActivityEnded)
		}
		return nil, wrapInternal(err)
	}
	if activity.Status != lottery.ActivityStatusRunning {
		return nil, xerr.NewErrCode(xerr.LotteryActivityEnded)
	}
	if activity.StartAt.After(now) || activity.EndAt.Before(now) {
		return nil, xerr.NewErrCode(xerr.LotteryActivityEnded)
	}
	return &activity, nil
}

func (s *Service) buildRuleContext(ctx context.Context, userId int64) (lottery.RuleContext, error) {
	if s.deps.ContextBuilder == nil {
		return lottery.RuleContext{UserId: userId, Now: time.Now().Unix()}, nil
	}
	return s.deps.ContextBuilder.Build(ctx, userId)
}

func (s *Service) loadPrizes(ctx context.Context, activityId int64) ([]lottery.Prize, error) {
	var prizes []lottery.Prize
	err := s.deps.DB.WithContext(ctx).
		Where("activity_id = ?", activityId).
		Order("slot ASC").
		Find(&prizes).Error
	if err != nil {
		return nil, err
	}
	return prizes, nil
}

func (s *Service) findExistingDraw(ctx context.Context, tx *gorm.DB, req Request) (*lottery.Draw, error) {
	var existing lottery.Draw
	err := tx.WithContext(ctx).
		Where("user_id = ? AND client_nonce = ?", req.UserId, req.ClientNonce).
		First(&existing).Error
	if err == nil {
		return &existing, nil
	}
	if errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, nil
	}
	return nil, err
}

// decrementStockOrFallback runs the limited-stock optimistic lock. If the
// chosen prize is unlimited, returns it as-is. If limited and stock survives
// → returns it. If limited and sold-out → walks the pool for the first
// `is_fallback=true` prize or falls back to a "none" (thanks-for-playing)
// synthetic prize.
func (s *Service) decrementStockOrFallback(ctx context.Context, tx *gorm.DB, picked lottery.Prize, pool []lottery.Prize) (lottery.Prize, error) {
	if !picked.RemainingStock.Valid {
		return picked, nil
	}
	res := tx.WithContext(ctx).
		Model(&lottery.Prize{}).
		Where("id = ? AND remaining_stock > 0", picked.Id).
		UpdateColumn("remaining_stock", gorm.Expr("`remaining_stock` - 1"))
	if res.Error != nil {
		return lottery.Prize{}, res.Error
	}
	if res.RowsAffected > 0 {
		return picked, nil
	}
	// Sold out → fallback selection.
	for _, p := range pool {
		if p.IsFallback {
			return p, nil
		}
	}
	// No fallback declared → synthesize a "谢谢参与" from the last non-fallback
	// entry (any type=none in the pool wins); if pool has no none, we
	// synthesize an ephemeral prize record. Note: this prize is NOT persisted
	// as a separate row — it just satisfies the return contract.
	for _, p := range pool {
		if p.Type == lottery.PrizeTypeNone {
			return p, nil
		}
	}
	return lottery.Prize{
		ActivityId: picked.ActivityId,
		Slot:       picked.Slot,
		Type:       lottery.PrizeTypeNone,
		Name:       "谢谢参与",
		Config:     "{}",
	}, nil
}

func (s *Service) insertDraw(ctx context.Context, tx *gorm.DB, req Request, prize lottery.Prize) (*lottery.Draw, error) {
	draw := lottery.Draw{
		UserId:        req.UserId,
		ActivityId:    req.ActivityId,
		ClientNonce:   req.ClientNonce,
		IsWin:         prize.Type != lottery.PrizeTypeNone,
		DispatchState: lottery.DispatchStateNone,
		DrawnAt:       time.Now(),
	}
	if prize.Id > 0 {
		draw.PrizeId = sql.NullInt64{Int64: prize.Id, Valid: true}
	}
	if err := tx.WithContext(ctx).Create(&draw).Error; err != nil {
		return nil, err
	}
	return &draw, nil
}

func (s *Service) insertSnapshots(ctx context.Context, tx *gorm.DB, draw *lottery.Draw, prize lottery.Prize, passedEligibility bool) error {
	ps := lottery.PrizeSnapshot{
		DrawId:  draw.Id,
		PrizeId: prize.Id,
		Slot:    prize.Slot,
		Type:    prize.Type,
		Name:    prize.Name,
		Config:  prize.Config,
	}
	if ps.Config == "" {
		ps.Config = "{}"
	}
	if err := tx.WithContext(ctx).Create(&ps).Error; err != nil {
		return err
	}
	es := lottery.EligibilitySnapshot{
		DrawId:     draw.Id,
		UserId:     draw.UserId,
		ActivityId: draw.ActivityId,
		Passed:     passedEligibility,
		// UnmetReasons 是 JSON 列，MySQL 拒绝空字符串（error 3140）——
		// Stage 1 只有 passed=true 进 insertSnapshots，语义上"没有未过项"，
		// 用 "[]" 与 PrizeSnapshot.Config 的 "{}" 守卫对称。
		// Stage 2 若开始持久化 passed=false 的失败评估，再改成真正的 marshal。
		UnmetReasons: "[]",
		// 显式 time.Now()：GORM 遇 zero time 有时会传 '0000-00-00 00:00:00'，
		// 触 sql_mode STRICT。不依赖 DB DEFAULT CURRENT_TIMESTAMP。
		EvaluatedAt: time.Now(),
	}
	return tx.WithContext(ctx).Create(&es).Error
}

// pendingClaimInfo carries the manual-claim details the draw service produced
// this turn. Zero-value = draw did not create a claim (auto prize or none).
type pendingClaimInfo struct {
	ExpiresAt       time.Time
	ClaimFormSchema json.RawMessage
}

// dispatchOrEnqueueClaim routes the prize to either an auto-handler dispatch
// (Stage 1 path) or to a lottery_claim insert (Stage 2 manual path).
//
//   - draw.IsWin == false           → thanks-for-playing, auto_claimed.
//   - handler.IsAuto()==true        → call Dispatch inside caller's tx.
//   - handler.IsAuto()==false       → insert lottery_claim (pending_claim) and
//     return ClaimFormSchema + ExpiresAt so the
//     caller can render the response.
func (s *Service) dispatchOrEnqueueClaim(ctx context.Context, tx *gorm.DB, req Request, draw *lottery.Draw, prize lottery.Prize) (lottery.DispatchResult, pendingClaimInfo, error) {
	if !draw.IsWin {
		return lottery.DispatchResult{State: lottery.DispatchStateAutoClaimed, Message: "谢谢参与"}, pendingClaimInfo{}, nil
	}
	if s.deps.Registry == nil {
		return lottery.DispatchResult{State: lottery.DispatchStatePendingClaim, Message: "等待人工发放"}, pendingClaimInfo{}, nil
	}
	prizeHandler, err := s.deps.Registry.MustGet(prize.Type)
	if err != nil {
		if errors.Is(err, lottery.ErrHandlerNotRegistered) {
			return lottery.DispatchResult{State: lottery.DispatchStatePendingClaim, Message: "等待人工发放"}, pendingClaimInfo{}, nil
		}
		return lottery.DispatchResult{}, pendingClaimInfo{}, wrapInternal(err)
	}

	if prizeHandler.IsAuto() {
		dispatchReq := lottery.DispatchRequest{
			UserId:         req.UserId,
			ActivityId:     req.ActivityId,
			DrawId:         draw.Id,
			Prize:          prize,
			Snapshot:       lottery.PrizeSnapshot{DrawId: draw.Id, PrizeId: prize.Id, Slot: prize.Slot, Type: prize.Type, Name: prize.Name, Config: prize.Config},
			IdempotencyKey: fmt.Sprintf("lottery:%d:%d", req.ActivityId, draw.Id),
		}
		result, dispatchErr := prizeHandler.Dispatch(ctx, tx, dispatchReq)
		return result, pendingClaimInfo{}, dispatchErr
	}

	// Manual-claim path (Stage 2). Insert a pending_claim row inside the same
	// draw tx so a rollback also erases the claim.
	expiresAt := s.computeClaimExpiry(prize)
	claim := lottery.Claim{
		DrawId:     draw.Id,
		UserId:     req.UserId,
		ActivityId: req.ActivityId,
		PrizeType:  prize.Type,
		Status:     lottery.ClaimStatusPendingClaim,
		ExpiresAt:  expiresAt,
	}
	if err := tx.WithContext(ctx).Create(&claim).Error; err != nil {
		return lottery.DispatchResult{}, pendingClaimInfo{}, wrapInternal(fmt.Errorf("insert lottery_claim for draw %d: %w", draw.Id, err))
	}

	schema := prizeHandler.ClaimSchema()
	// crypto handler 需要用奖品 config.networks 生成带 enum 的最终 schema。
	if prize.Type == lottery.PrizeTypeCrypto {
		schema = handler.BuildCryptoClaimSchema(prize.Config)
	}
	return lottery.DispatchResult{
			State:   lottery.DispatchStatePendingClaim,
			Message: "等待填写领奖信息",
		}, pendingClaimInfo{
			ExpiresAt:       expiresAt,
			ClaimFormSchema: schema,
		}, nil
}

// computeClaimExpiry 从奖品 config.claim_ttl_hours 读窗口配置；缺失或非正
// 则回落到 lottery.DefaultClaimTTLHours (7 天)。
func (s *Service) computeClaimExpiry(prize lottery.Prize) time.Time {
	hours := lottery.DefaultClaimTTLHours
	if prize.Config != "" {
		var cfg struct {
			ClaimTTLHours int `json:"claim_ttl_hours"`
		}
		if err := json.Unmarshal([]byte(prize.Config), &cfg); err == nil && cfg.ClaimTTLHours > 0 {
			hours = cfg.ClaimTTLHours
		}
	}
	return time.Now().Add(time.Duration(hours) * time.Hour)
}

func (s *Service) finalizeDrawState(ctx context.Context, tx *gorm.DB, draw *lottery.Draw, dispatch lottery.DispatchResult) error {
	now := time.Now()
	updates := map[string]any{
		"dispatch_state": dispatch.State,
	}
	if dispatch.State == lottery.DispatchStateAutoClaimed || dispatch.State == lottery.DispatchStatePaid {
		updates["dispatched_at"] = now
	}
	return tx.WithContext(ctx).
		Model(&lottery.Draw{}).
		Where("id = ?", draw.Id).
		Updates(updates).Error
}

func (s *Service) buildResultFromExistingDraw(ctx context.Context, tx *gorm.DB, existing *lottery.Draw) (*Result, error) {
	var snap lottery.PrizeSnapshot
	err := tx.WithContext(ctx).Where("draw_id = ?", existing.Id).First(&snap).Error
	if err != nil && !errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, err
	}
	remaining, _ := s.deps.Chance.Query(ctx, existing.UserId, existing.ActivityId)
	var prize *PrizeSummary
	if existing.IsWin {
		prize = &PrizeSummary{
			Slot:   snap.Slot,
			Id:     snap.PrizeId,
			Type:   snap.Type,
			Name:   snap.Name,
			Config: json.RawMessage(snap.Config),
		}
	}
	claim := ClaimSummary{
		Required:    existing.DispatchState == lottery.DispatchStatePendingClaim,
		AutoClaimed: existing.DispatchState == lottery.DispatchStateAutoClaimed,
	}
	// 重放场景（同一 client_nonce）也补回 expires_at / schema，避免前端第二次
	// 收到的响应比首次少字段。
	if claim.Required {
		var claimRow lottery.Claim
		err := tx.WithContext(ctx).Where("draw_id = ?", existing.Id).First(&claimRow).Error
		if err == nil {
			claim.ExpiresAt = claimRow.ExpiresAt.Unix()
			if s.deps.Registry != nil {
				if h, ok := s.deps.Registry.Get(claimRow.PrizeType); ok {
					if claimRow.PrizeType == lottery.PrizeTypeCrypto {
						claim.ClaimFormSchema = handler.BuildCryptoClaimSchema(snap.Config)
					} else {
						claim.ClaimFormSchema = h.ClaimSchema()
					}
				}
			}
		}
	}
	return &Result{
		DrawId:           existing.Id,
		IsWin:            existing.IsWin,
		Prize:            prize,
		ChancesRemaining: remaining,
		Claim:            claim,
	}, nil
}

func buildResult(draw *lottery.Draw, prize lottery.Prize, dispatch lottery.DispatchResult, claim pendingClaimInfo, remaining int64) *Result {
	res := &Result{
		DrawId:           draw.Id,
		IsWin:            draw.IsWin,
		ChancesRemaining: remaining,
		Message:          dispatch.Message,
		Claim: ClaimSummary{
			Required:        dispatch.State == lottery.DispatchStatePendingClaim,
			AutoClaimed:     dispatch.State == lottery.DispatchStateAutoClaimed,
			Message:         dispatch.Message,
			ClaimFormSchema: claim.ClaimFormSchema,
		},
	}
	if !claim.ExpiresAt.IsZero() {
		res.Claim.ExpiresAt = claim.ExpiresAt.Unix()
	}
	if draw.IsWin {
		res.Prize = &PrizeSummary{
			Slot:   prize.Slot,
			Id:     prize.Id,
			Type:   prize.Type,
			Name:   prize.Name,
			Config: json.RawMessage(prize.Config),
		}
	}
	return res
}

// parseEligibilityTree tolerates empty/null activity.Eligibility as "no gate".
func parseEligibilityTree(raw string) (*lottery.EligibilityRule, error) {
	trimmed := ""
	for _, r := range raw {
		if r != ' ' && r != '\t' && r != '\n' && r != '\r' {
			trimmed += string(r)
		}
	}
	if trimmed == "" || trimmed == "null" || trimmed == "{}" {
		return nil, nil
	}
	var tree lottery.EligibilityRule
	if err := json.Unmarshal([]byte(raw), &tree); err != nil {
		return nil, fmt.Errorf("parse eligibility: %w", err)
	}
	return &tree, nil
}

func wrapInternal(err error) error {
	if err == nil {
		return nil
	}
	// Preserve already-coded errors.
	if _, ok := err.(*xerr.CodeError); ok {
		return err
	}
	return xerr.NewErrCodeMsg(xerr.LotteryInternalError, err.Error())
}

// ---- Rate limiter production wiring ----------------------------------------

// ErrRateLimited is returned by RateLimiter.Allow when the caller exceeded
// the configured quota.
var ErrRateLimited = errors.New("draw: rate limited")

// RedisRateLimiter is the production RateLimiter backed by pkg/limit's
// Redis-Lua fixed-window (1 hit per 1 second per user), matching the
// existing sendEmailCodeLogic pattern.
type RedisRateLimiter struct {
	limiter *limit.PeriodLimit
}

// NewRedisRateLimiter builds a per-user 1-req/1-sec limiter. keyPrefix is
// expected to end with ':' so the composed key is human-readable.
func NewRedisRateLimiter(limiter *limit.PeriodLimit) *RedisRateLimiter {
	return &RedisRateLimiter{limiter: limiter}
}

// Allow admits or rejects the caller.
func (r *RedisRateLimiter) Allow(ctx context.Context, userId int64) error {
	if r == nil || r.limiter == nil {
		return nil
	}
	state, err := r.limiter.TakeCtx(ctx, strconv.FormatInt(userId, 10))
	if err != nil {
		return err
	}
	if state == limit.Allowed || state == limit.HitQuota {
		return nil
	}
	return ErrRateLimited
}