package chathub

import (
	"context"
	"fmt"
	"time"

	"hfb_sys/backend/internal/middleware"
	"hfb_sys/backend/pkg/response"

	"github.com/gin-gonic/gin"
	"go.uber.org/zap"
)

const heartbeatInterval = 30 * time.Second

type Handler struct {
	hub    *Hub
	logger *zap.Logger
}

func NewHandler(hub *Hub, logger *zap.Logger) *Handler {
	if logger == nil {
		logger = zap.NewNop()
	}
	return &Handler{hub: hub, logger: logger}
}

// UserEvents 处理用户端 SSE 连接: GET /api/chats/events
func (h *Handler) UserEvents(c *gin.Context) {
	value, ok := c.Get(middleware.ContextUserID)
	if !ok {
		response.Unauthorized(c, "缺少用户上下文")
		return
	}
	userID, ok := value.(uint64)
	if !ok {
		response.Unauthorized(c, "用户上下文无效")
		return
	}
	h.serveSSE(c, "user", userID)
}

// AdminEvents 处理管理端 SSE 连接: GET /api/admin/chats/events
func (h *Handler) AdminEvents(c *gin.Context) {
	value, ok := c.Get(middleware.ContextAdminID)
	if !ok {
		response.Unauthorized(c, "缺少管理员上下文")
		return
	}
	adminID, ok := value.(uint64)
	if !ok {
		response.Unauthorized(c, "管理员上下文无效")
		return
	}
	h.serveSSE(c, "admin", adminID)
}

func (h *Handler) serveSSE(c *gin.Context, pType string, pID uint64) {
	startedAt := time.Now()
	disconnectReason := "handler_completed"
	var disconnectErr error
	ch := h.hub.Subscribe(pType, pID)
	h.logger.Info("SSE 连接建立", h.connectionLogFields(c, pType, pID)...)
	defer func() {
		h.hub.Unsubscribe(pType, pID, ch)
		fields := h.connectionLogFields(c, pType, pID)
		fields = append(fields,
			zap.String("disconnect_reason", disconnectReason),
			zap.Float64("lifetime_ms", float64(time.Since(startedAt).Microseconds())/1000),
		)
		if disconnectErr != nil {
			fields = append(fields, zap.Error(disconnectErr))
		}
		h.logger.Info("SSE 连接断开", fields...)
	}()

	c.Header("Content-Type", "text/event-stream")
	c.Header("Cache-Control", "no-cache")
	c.Header("Connection", "keep-alive")
	c.Header("X-Accel-Buffering", "no")

	// 发送初始连接确认
	if _, err := fmt.Fprintf(c.Writer, "event: connected\ndata: {\"ok\":true}\n\n"); err != nil {
		disconnectReason = "initial_write_error"
		disconnectErr = err
		return
	}
	c.Writer.Flush()

	heartbeat := time.NewTicker(heartbeatInterval)
	defer heartbeat.Stop()

	clientGone := c.Request.Context().Done()

	for {
		select {
		case <-clientGone:
			disconnectReason = contextDisconnectReason(c.Request.Context().Err())
			return
		case <-heartbeat.C:
			if _, err := fmt.Fprintf(c.Writer, ":heartbeat\n\n"); err != nil {
				disconnectReason = "heartbeat_write_error"
				disconnectErr = err
				return
			}
			c.Writer.Flush()
		case event, ok := <-ch:
			if !ok {
				disconnectReason = "subscription_closed"
				return
			}
			data := MarshalEvent(event)
			if _, err := fmt.Fprintf(c.Writer, "event: %s\ndata: %s\n\n", event.Type, data); err != nil {
				disconnectReason = "event_write_error"
				disconnectErr = err
				return
			}
			c.Writer.Flush()
		}
	}
}

func (h *Handler) connectionLogFields(c *gin.Context, pType string, pID uint64) []zap.Field {
	fields := []zap.Field{
		zap.String("request_id", middleware.GetRequestID(c)),
		zap.String("principal_type", pType),
		zap.Uint64("principal_id", pID),
		zap.String("client_ip", c.ClientIP()),
		zap.Int("active_sse_connections", h.hub.OnlineCount()),
		zap.Int("active_principal_type_connections", h.hub.OnlineCountByType(pType)),
	}
	if pType == "admin" {
		fields = append(fields, zap.Uint64("admin_id", pID))
	} else {
		fields = append(fields, zap.Uint64("user_id", pID))
	}
	return fields
}

func contextDisconnectReason(err error) string {
	switch err {
	case context.Canceled:
		return "context_canceled"
	case context.DeadlineExceeded:
		return "context_deadline_exceeded"
	default:
		return "context_closed"
	}
}