// Package usage 异步记账：请求完成后写入 usage_logs，批量落库（PLANNING §3.2）。
// 每个请求在 flush 时同步完成：写明细 + 扣余额 + 写流水 + 日聚合。
package usage

import (
	"log"
	"sync"
	"time"

	"github.com/openteam/server/internal/store"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

// Recorder 异步记账器：缓冲队列 + 批量事务落库。
type Recorder struct {
	db     *gorm.DB
	ch     chan *store.UsageLog
	wg     sync.WaitGroup
	closed chan struct{}
}

const batchSize = 32

func NewRecorder(db *gorm.DB) *Recorder {
	r := &Recorder{
		db:     db,
		ch:     make(chan *store.UsageLog, 512),
		closed: make(chan struct{}),
	}
	r.wg.Add(1)
	go r.run()
	return r
}

// Record 提交一条用量（非阻塞；队列满时同步写入，保证不丢账）。
func (r *Recorder) Record(l *store.UsageLog) {
	select {
	case r.ch <- l:
	default:
		if err := r.flush([]*store.UsageLog{l}); err != nil {
			log.Printf("usage: sync write failed: %v", err)
		}
	}
}

func (r *Recorder) Close() {
	close(r.closed)
	r.wg.Wait()
	close(r.ch)
}

func (r *Recorder) run() {
	defer r.wg.Done()
	buf := make([]*store.UsageLog, 0, batchSize)
	tick := time.NewTicker(2 * time.Second)
	defer tick.Stop()
	for {
		select {
		case l, ok := <-r.ch:
			if !ok {
				return
			}
			buf = append(buf, l)
			if len(buf) >= batchSize {
				if err := r.flush(buf); err != nil {
					log.Printf("usage: batch write failed: %v", err)
				}
				buf = buf[:0]
			}
		case <-r.closed:
			if len(buf) > 0 {
				if err := r.flush(buf); err != nil {
					log.Printf("usage: final batch write failed: %v", err)
				}
			}
			return
		case <-tick.C:
			if len(buf) > 0 {
				if err := r.flush(buf); err != nil {
					log.Printf("usage: batch write failed: %v", err)
				}
				buf = buf[:0]
			}
		}
	}
}

// flush 批量插入用量明细，并同步更新余额、余额流水与日聚合。
// 记账口径：单次成本 = in×in_price + out×out_price + cache_read×cache_read_price（每百万 token）。
func (r *Recorder) flush(logs []*store.UsageLog) error {
	if len(logs) == 0 {
		return nil
	}
	return r.db.Transaction(func(tx *gorm.DB) error {
		if err := tx.Create(logs).Error; err != nil {
			return err
		}
		for _, l := range logs {
			// 计费范围：success（正常完成）与 canceled（流式中断，按已生成部分收费）
			if (l.Status != store.UsageStatusSuccess && l.Status != store.UsageStatusCanceled) || l.Cost <= 0 {
				continue
			}
			// 扣余额（余额可为负：流式请求不中断；后续请求被拒）
			var user store.User
			if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).First(&user, l.UserID).Error; err != nil {
				continue
			}
			newBalance := user.Balance - l.Cost
			if err := tx.Model(&store.User{}).Where("id = ?", l.UserID).Update("balance", newBalance).Error; err != nil {
				continue
			}
			tx.Create(&store.BalanceLog{
				UserID:       l.UserID,
				Change:       -l.Cost,
				BalanceAfter: newBalance,
				Type:         store.BalanceTypeUsage,
				RefID:        usageRefID(l.TraceID),
				Remark:       "usage: " + l.ModelName,
			})

			// 日聚合 upsert
			date := l.CreatedAt.UTC().Format("2006-01-02")
			tx.Clauses(clause.OnConflict{
				Columns: []clause.Column{{Name: "user_id"}, {Name: "model_id"}, {Name: "date"}},
				DoUpdates: clause.Assignments(map[string]any{
					"requests":          gorm.Expr("requests + 1"),
					"input_tokens":      gorm.Expr("input_tokens + ?", l.InputTokens),
					"output_tokens":     gorm.Expr("output_tokens + ?", l.OutputTokens),
					"cache_read_tokens": gorm.Expr("cache_read_tokens + ?", l.CacheReadTokens),
					"cost":              gorm.Expr("cost + ?", l.Cost),
				}),
			}).Create(&store.UsageDaily{
				UserID:          l.UserID,
				ModelID:         l.ModelID,
				Date:            date,
				Requests:        1,
				InputTokens:     l.InputTokens,
				OutputTokens:    l.OutputTokens,
				CacheReadTokens: l.CacheReadTokens,
				Cost:            l.Cost,
			})
		}
		return nil
	})
}

func usageRefID(traceID string) string {
	if traceID == "" {
		traceID = "unknown"
	}
	return "usage:" + traceID
}