package chat

import (
	"encoding/json"
	"fmt"
	"net/http"
	"strconv"

	"github.com/go-chi/chi/v5"

	"github.com/yan1h/agent-coding-workflow/internal/infra/errs"
)

// streamMessages implements GET /api/v1/conversations/{id}/stream.
// It upgrades the connection to a Server-Sent Events stream and forwards
// SSEEvents produced by MessageService.Stream until the channel closes or
// the client disconnects.
func (h *Handler) streamMessages(w http.ResponseWriter, r *http.Request) {
	uid, err := h.userID(r)
	if err != nil {
		writeErr(w, r, err)
		return
	}
	convID, err := parseUUID(chi.URLParam(r, "id"))
	if err != nil {
		writeErr(w, r, err)
		return
	}
	var since int64
	if s := r.URL.Query().Get("since"); s != "" {
		since, _ = strconv.ParseInt(s, 10, 64)
	}

	flusher, ok := w.(http.Flusher)
	if !ok {
		http.Error(w, "streaming unsupported", http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")
	w.Header().Set("X-Accel-Buffering", "no")
	w.WriteHeader(http.StatusOK)

	ch, err := h.msgSvc.Stream(r.Context(), uid, convID, since)
	if err != nil {
		writeSSEError(w, flusher, err)
		return
	}
	for {
		select {
		case <-r.Context().Done():
			return
		case ev, ok := <-ch:
			if !ok {
				return
			}
			writeSSE(w, flusher, ev)
		}
	}
}

// writeSSE writes a single SSE frame to w and flushes.
func writeSSE(w http.ResponseWriter, f http.Flusher, ev SSEEvent) {
	data, _ := json.Marshal(ev.Data)
	fmt.Fprintf(w, "id: %d\nevent: %s\ndata: %s\n\n", ev.ID, ev.Event, data)
	f.Flush()
}

// writeSSEError writes an error event to the SSE stream and flushes.
func writeSSEError(w http.ResponseWriter, f http.Flusher, err error) {
	code := errs.CodeInternal
	msg := err.Error()
	if ae, ok := errs.As(err); ok {
		code = ae.Code
		msg = ae.Message
	}
	payload := map[string]string{"code": string(code), "message": msg}
	data, _ := json.Marshal(payload)
	fmt.Fprintf(w, "event: error\ndata: %s\n\n", data)
	f.Flush()
}