package codes

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

	"github.com/redis/go-redis/v9"
	libcodes "github.com/wangjia/codes"
	"github.com/wangjia/codes/redisx"
	"github.com/wangjia/pangolin/server/internal/apierr"
)

// RedeemRequest carries the inputs to a single redemption attempt.
type RedeemRequest struct {
	UserID int64  // authenticated user
	Code   string // raw code string from the client (will be canonicalized)
}

// RedeemResult carries the outcome of a successful redemption.
type RedeemResult struct {
	// Idempotent indicates this user already redeemed this code; the result is
	// from the original redemption.
	Idempotent   bool
	PlanCode     PlanCode
	DurationDays int
	// ExpiresAt is the updated/new subscription expiry (UTC).
	ExpiresAt time.Time
	// SubscriptionID is the subscription that was extended or newly created.
	SubscriptionID int64
}

// Service handles activation-code redemption on top of the shared codes lib.
type Service struct {
	store   *Store
	limiter libcodes.RateLimiter // nil → GuardedRedeem 内部 Noop(cmd/codegen 传 rdb=nil 的场景)
}

// NewService creates a Service. failMax/lockDur mirror the old per-user
// redeem lockout (5 次失败锁 1 小时), now backed by codes/redisx.
func NewService(store *Store, rdb *redis.Client, failMax int, lockDur time.Duration) *Service {
	var limiter libcodes.RateLimiter
	if rdb != nil {
		limiter = redisx.NewRateLimiter(rdb, "redeem:fail:", failMax, lockDur)
	}
	return &Service{store: store, limiter: limiter}
}

// grantOutcome is the host-side grant result threaded through Redeem[T].
type grantOutcome struct {
	subID     int64
	expiresAt time.Time
}

// Redeem processes a redemption request through the shared codes library's
// GuardedRedeem (rate-limit + code state-machine + idempotency), with a host
// grant callback that extends/creates the pangolin subscription and writes
// the legacy audit_log row inside the SAME transaction as the code flip.
func (svc *Service) Redeem(ctx context.Context, req RedeemRequest) (*RedeemResult, *apierr.Error) {
	ref := "user:" + strconv.FormatInt(req.UserID, 10)

	// 1. 锁检查先于格式检查(行为等价:旧 service.go:118-124 顺序)。
	if svc.limiter != nil {
		allowed, err := svc.limiter.Allowed(ctx, ref)
		if err != nil {
			return nil, apierr.ErrInternal
		}
		if !allowed {
			return nil, apierr.ErrLocked
		}
	}

	// 2. Canonicalize;格式错也计一次失败(旧 service.go:127-131)。
	canonical, cerr := Canonicalize(req.Code)
	if cerr != nil {
		if svc.limiter != nil {
			_ = svc.limiter.RecordFailure(ctx, ref)
		}
		return nil, apierr.ErrInvalidCode
	}

	// 3. 宿主事务:码状态翻转 + 订阅授予 + 双审计,一个 tx 原子提交。
	tx, err := svc.store.BeginTx(ctx)
	if err != nil {
		return nil, apierr.ErrInternal
	}
	committed := false
	defer func() {
		if !committed {
			_ = tx.Rollback()
		}
	}()

	res, err := libcodes.GuardedRedeem(ctx, svc.store.Lib(), svc.limiter, tx,
		Hash(canonical), ref, svc.grantSubscription(req.UserID))
	if err != nil {
		switch {
		case errors.Is(err, libcodes.ErrLocked):
			return nil, apierr.ErrLocked
		case errors.Is(err, libcodes.ErrCodeNotFound):
			return nil, apierr.ErrCodeNotFound
		case errors.Is(err, libcodes.ErrCodeRedeemed):
			return nil, apierr.ErrCodeRedeemed
		case errors.Is(err, libcodes.ErrCodeVoid):
			return nil, apierr.ErrCodeVoid
		default:
			return nil, apierr.ErrInternal
		}
	}

	dur, derr := res.Code.Entitlement.DecodeDuration()
	if derr != nil {
		return nil, apierr.ErrInternal
	}

	if res.Idempotent {
		// 只读路径:回滚(旧 service.go:162-171 同款),ExpiresAt 留空由 /v1/me 兜底。
		_ = tx.Rollback()
		committed = true
		return &RedeemResult{
			Idempotent:   true,
			PlanCode:     PlanCode(dur.Plan),
			DurationDays: dur.Days,
		}, nil
	}

	if err := tx.Commit(); err != nil {
		return nil, apierr.ErrInternal
	}
	committed = true

	return &RedeemResult{
		Idempotent:     false,
		PlanCode:       PlanCode(dur.Plan),
		DurationDays:   dur.Days,
		ExpiresAt:      res.Grant.expiresAt,
		SubscriptionID: res.Grant.subID,
	}, nil
}

// grantSubscription returns the GrantFunc executed by the lib INSIDE the same
// tx as the code flip. It reproduces the old applySubscription semantics
// byte-for-byte (service.go:235-287 pre-migration) and writes the legacy
// audit_log row the admin audit page reads (non-fatal, old behavior).
func (svc *Service) grantSubscription(userID int64) libcodes.GrantFunc[grantOutcome] {
	return func(ctx context.Context, tx *sql.Tx, code libcodes.Code) (grantOutcome, error) {
		dur, err := code.Entitlement.DecodeDuration()
		if err != nil {
			return grantOutcome{}, err
		}
		planID, err := svc.store.GetPlanIDTx(ctx, tx, PlanCode(dur.Plan))
		if err != nil {
			return grantOutcome{}, err
		}
		subID, expiresAt, err := svc.applySubscription(ctx, tx, userID, planID, dur.Days, "code")
		if err != nil {
			return grantOutcome{}, err
		}

		// 旧式审计(数据源:admin/store.go:188,197 读 audit_log);失败不中断。
		meta, _ := json.Marshal(map[string]any{
			"plan":          dur.Plan,
			"duration_days": dur.Days,
			"batch_id":      code.BatchID,
			"sub_id":        subID,
		})
		_ = svc.store.WriteAuditLog(ctx, tx,
			fmt.Sprintf("user:%d", userID), "redeem",
			"code_hash:"+code.CodeHash[:16]+"...", string(meta))

		return grantOutcome{subID: subID, expiresAt: expiresAt}, nil
	}
}

// applySubscription:同 plan 有活跃订阅 → 取最晚到期那条 max(expires,now)+days
// 原地延长;否则新建一行 max(now, latestSamePlan)+days,source 记录新建行的
// 创建者("code"=兑换码,"pay"=支付)。算法体与迁移前完全一致,仅签名从
// (*CodeRow, *apierr.Error) 改为 (planID, days, source, error)。
// ExtendSubscription 路径不看 source:延长的是既有行,行上的 source 仍是
// 该行最初创建者,不因后续延长(不论来源)而改写——台账/审计保留完整出处。
func (svc *Service) applySubscription(
	ctx context.Context, tx *sql.Tx, userID, planID int64, durationDays int, source string,
) (int64, time.Time, error) {
	subs, err := svc.store.GetActiveSubscriptions(ctx, tx, userID)
	if err != nil {
		return 0, time.Time{}, err
	}
	var samePlanSub *SubscriptionRow
	var latestSamePlan time.Time
	for i := range subs {
		if subs[i].PlanID == planID {
			if samePlanSub == nil || subs[i].ExpiresAt.After(samePlanSub.ExpiresAt) {
				samePlanSub = &subs[i]
			}
			if subs[i].ExpiresAt.After(latestSamePlan) {
				latestSamePlan = subs[i].ExpiresAt
			}
		}
	}
	now := time.Now().UTC()
	if samePlanSub != nil {
		if err := svc.store.ExtendSubscription(ctx, tx, samePlanSub.ID, durationDays); err != nil {
			return 0, time.Time{}, err
		}
		base := samePlanSub.ExpiresAt
		if now.After(base) {
			base = now
		}
		return samePlanSub.ID, base.AddDate(0, 0, durationDays), nil
	}
	newSubID, err := svc.store.CreateSubscription(ctx, tx, userID, planID, durationDays, latestSamePlan, source)
	if err != nil {
		return 0, time.Time{}, err
	}
	base := now
	if latestSamePlan.After(now) {
		base = latestSamePlan
	}
	return newSubID, base.AddDate(0, 0, durationDays), nil
}

// --------------------------------------------------------------------------
// Batch generation service
// --------------------------------------------------------------------------

// BatchRequest holds the parameters for a bulk code-generation job.
type BatchRequest struct {
	PlanCode     PlanCode
	DurationDays int
	Count        int
	Channel      BatchChannel
	Note         string
	CreatedBy    string // e.g. "admin:1" or "cli"
}

// BatchResult contains the generated plaintext codes (only occurrence ever)
// and the batch metadata.
type BatchResult struct {
	BatchID      int64
	Codes        []string // plaintext canonical codes – NOT stored in DB
	PlanCode     PlanCode
	DurationDays int
	Channel      BatchChannel
}

// CreateBatch generates Count activation codes via the shared library's Mint
// (all-or-nothing: batch + code hashes commit in one tx) and returns the
// plaintext codes — the only time they ever appear.
func (svc *Service) CreateBatch(ctx context.Context, req BatchRequest) (*BatchResult, error) {
	// 未知 plan 先拒(行为等价:旧实现先查 GetPlanID)。
	if _, err := svc.store.GetPlanID(ctx, req.PlanCode); err != nil {
		return nil, fmt.Errorf("CreateBatch: unknown plan %s: %w", req.PlanCode, err)
	}
	ent, err := libcodes.NewDurationEntitlement(string(req.PlanCode), req.DurationDays)
	if err != nil {
		return nil, fmt.Errorf("CreateBatch: %w", err)
	}
	res, err := libcodes.Mint(ctx, svc.store.Lib(), libcodes.MintRequest{
		Channel:     string(req.Channel),
		Entitlement: ent,
		Count:       req.Count,
		CreatedBy:   req.CreatedBy,
		Note:        req.Note,
	})
	if err != nil {
		return nil, fmt.Errorf("CreateBatch: %w", err)
	}
	return &BatchResult{
		BatchID:      res.BatchID,
		Codes:        res.Codes,
		PlanCode:     req.PlanCode,
		DurationDays: req.DurationDays,
		Channel:      req.Channel,
	}, nil
}