package httpapi

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strconv"
	"strings"
	"time"

	"data-terminal-cloud/internal/identity"
	"data-terminal-cloud/internal/webevents"
)

func StreamWebEventsHandler(service *webevents.Service) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		principal, ok := identity.PrincipalFromContext(r.Context())
		if !ok {
			WriteError(w, r, http.StatusUnauthorized, "AUTHENTICATION_REQUIRED", "请先登录后再访问")
			return
		}
		lastIDText := strings.TrimSpace(r.Header.Get("Last-Event-ID"))
		var cursor int64
		var err error
		if lastIDText == "" {
			cursor, err = service.StartingCursor(r.Context(), principal)
		} else {
			cursor, err = strconv.ParseInt(lastIDText, 10, 64)
			if err == nil && cursor < 1 {
				err = errors.New("cursor must be positive")
			}
			if err == nil {
				err = service.ValidateCursor(r.Context(), principal, cursor)
			}
		}
		if err != nil {
			status := http.StatusBadRequest
			code := "EVENT_CURSOR_INVALID"
			message := "状态事件编号无效"
			if errors.Is(err, webevents.ErrCursorUnavailable) {
				status = http.StatusGone
				code = "EVENT_CURSOR_EXPIRED"
				message = "状态事件续传窗口已过期，请重新载入页面"
			}
			WriteError(w, r, status, code, message)
			return
		}

		w.Header().Set("Content-Type", "text/event-stream; charset=utf-8")
		w.Header().Set("Cache-Control", "no-store")
		w.Header().Set("Connection", "keep-alive")
		w.Header().Set("X-Accel-Buffering", "no")
		controller := http.NewResponseController(w)
		_ = controller.SetWriteDeadline(time.Time{})
		if _, err := fmt.Fprintf(w, "retry: 2000\nid: %d\n\n", cursor); err != nil {
			return
		}
		if err := controller.Flush(); err != nil {
			return
		}

		poll := time.NewTicker(500 * time.Millisecond)
		heartbeat := time.NewTicker(10 * time.Second)
		end := time.NewTimer(25 * time.Second)
		defer poll.Stop()
		defer heartbeat.Stop()
		defer end.Stop()
		for {
			select {
			case <-r.Context().Done():
				return
			case <-end.C:
				return
			case <-heartbeat.C:
				if _, err := fmt.Fprint(w, ": heartbeat\n\n"); err != nil {
					return
				}
				if err := controller.Flush(); err != nil {
					return
				}
			case <-poll.C:
				items, err := service.ListAfter(r.Context(), principal, cursor, 100)
				if err != nil {
					return
				}
				for _, item := range items {
					payload, err := json.Marshal(item)
					if err != nil {
						return
					}
					if _, err := fmt.Fprintf(w, "id: %d\nevent: %s\ndata: %s\n\n", item.ID, item.Type, payload); err != nil {
						return
					}
					cursor = item.ID
				}
				if len(items) > 0 {
					if err := controller.Flush(); err != nil {
						return
					}
				}
			}
		}
	})
}