package httpapi

import (
	"context"
	"database/sql"
	"net/http"

	"git.yeij.top/AskaEth/Scoreboard/server/internal/realtime"
)

// Realtime 是实时层的最小接口；未接入时写操作只落库，不推送。
type Realtime interface {
	Broadcast(changes []realtime.Change)
	LoadChanges(ctx context.Context, sinceVersion int64, limit int) ([]realtime.Change, error)
	Instances() []realtime.Instance
}

// broadcastChanges 在写请求成功返回后，把本次请求写入 change_log 的变更推给实时层。
// 版本号取请求开始时的最大 id，因此只推送本次写入，不会重复补发历史变更。
func (s *server) broadcastChanges(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if s.realtime == nil || s.ev == nil || !isWriteMethod(r.Method) {
			next.ServeHTTP(w, r)
			return
		}
		before, ok := s.changeVersion(r.Context())
		if !ok {
			next.ServeHTTP(w, r)
			return
		}

		rec := &statusRecorder{ResponseWriter: w, status: http.StatusOK}
		next.ServeHTTP(rec, r)
		if rec.status >= http.StatusBadRequest {
			return
		}

		// 请求结束后 r.Context() 可能已被取消，推送不应因此中断。
		ctx := context.WithoutCancel(r.Context())
		changes, err := s.realtime.LoadChanges(ctx, before, 0)
		if err != nil {
			s.logger.Error("读取实时变更失败", "err", err)
			return
		}
		if len(changes) > 0 {
			s.realtime.Broadcast(changes)
		}
	})
}

// changeVersion 读取 change_log 当前最大 id；失败时调用方跳过本次推送。
func (s *server) changeVersion(ctx context.Context) (int64, bool) {
	var v sql.NullInt64
	if err := s.ev.QueryRowContext(ctx, `SELECT MAX(id) FROM change_log`).Scan(&v); err != nil {
		s.logger.Error("读取变更版本失败", "err", err)
		return 0, false
	}
	return v.Int64, true
}

func isWriteMethod(method string) bool {
	switch method {
	case http.MethodGet, http.MethodHead, http.MethodOptions:
		return false
	default:
		return true
	}
}

// statusRecorder 记录响应状态码，用于判断写请求是否成功。
type statusRecorder struct {
	http.ResponseWriter
	status  int
	written bool
}

func (w *statusRecorder) WriteHeader(code int) {
	if !w.written {
		w.status = code
		w.written = true
	}
	w.ResponseWriter.WriteHeader(code)
}

func (w *statusRecorder) Write(b []byte) (int, error) {
	if !w.written {
		w.written = true
	}
	return w.ResponseWriter.Write(b)
}

// displayInstancesHandler 返回在线大屏实例列表（在线看板）。
func (s *server) displayInstancesHandler(w http.ResponseWriter, r *http.Request) (any, error) {
	if s.realtime == nil {
		return []realtime.Instance{}, nil
	}
	list := s.realtime.Instances()
	if list == nil {
		list = []realtime.Instance{}
	}
	return list, nil
}