package gateway

import (
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"time"

	apperr "git.yeij.top/AskaEth/Cyrene_v2/internal/errors"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/history"
)

// This file owns the D4 read-cursor surface (Android collaboration B3): the
// POST /api/v1/sessions/{id}/read endpoint that advances a session's read cursor,
// plus the `session_read` realtime frame it broadcasts so the account's other
// browsers clear the unread badge without a re-read. The cursor itself lives in
// chat_sessions.read_at (internal/runtime/history); GET /sessions derives the
// unreadCount from it (history.go). The cursor is session-scoped and single-owner:
// one account, one cursor per session — reading on any one end marks the session
// read for every end.

// wsSessionRead is the WS event type for a read-cursor advance.
const wsSessionRead = "session_read"

// sessionReadRequest is the POST /api/v1/sessions/{id}/read body. Before is a
// pointer so an absent field (an empty body) is distinguishable from an explicit
// value: absent means "now" — the client marks everything it has seen read.
type sessionReadRequest struct {
	Before *int64 `json:"before"`
}

// handleMarkSessionRead advances a session's read cursor and answers
// {data:{sessionId, readAt}} with the resulting cursor in Unix milliseconds.
// It is owner/admin-gated like the other history writes (writeAuth).
//
// body {before?} is an optional millisecond timestamp bounding what is marked
// read — messages with created_at <= readAt become read. Absent (or an empty body)
// means now. A present non-positive or non-numeric before answers 400: the cursor
// is a real millisecond timestamp, and "unread by a negative cursor" is not a
// meaningful client request. An unknown session id answers 404; a missing
// HistoryStore answers 501.
//
// On success the new cursor is broadcast as a `session_read` frame so the account's
// other browsers clear the badge too (reading on one end = read everywhere). A
// failure path broadcasts nothing.
func (s *Server) handleMarkSessionRead(w http.ResponseWriter, r *http.Request) {
	if s.history == nil {
		writeError(w, &apperr.AppError{Code: "not_implemented", Message: "会话历史服务未配置（未注入 HistoryStore）", HTTPCode: http.StatusNotImplemented})
		return
	}
	id := r.PathValue("id")
	if id == "" {
		writeError(w, apperr.Wrap(apperr.ErrBadRequest, "bad_request", "session id is required"))
		return
	}
	var req sessionReadRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil && !errors.Is(err, io.EOF) {
		writeError(w, apperr.Wrap(apperr.ErrBadRequest, "bad_request", "invalid request body"))
		return
	}
	var before time.Time
	if req.Before != nil {
		if *req.Before <= 0 {
			writeError(w, apperr.Wrap(apperr.ErrBadRequest, "bad_request", "before must be a positive millisecond timestamp"))
			return
		}
		before = time.UnixMilli(*req.Before)
	}
	readAt, err := s.history.MarkSessionRead(r.Context(), id, before)
	if err != nil {
		if errors.Is(err, history.ErrSessionNotFound) {
			writeError(w, apperr.Wrap(apperr.ErrNotFound, "not_found", "session %q not found", id))
			return
		}
		s.log.Error("history mark session read", "err", err, "session", id)
		writeError(w, apperr.Wrap(apperr.ErrInternal, "session_failed", "failed to mark session read"))
		return
	}
	s.hub.broadcastSessionRead(id, readAt)
	writeJSON(w, http.StatusOK, map[string]any{"sessionId": id, "readAt": readAt})
}

// broadcastSessionRead fans a read-cursor advance out to every client as a
// `session_read` frame carrying the session's new cursor, so the same account's
// other ends clear the session's unread badge without a re-read. Like the other
// history frames it is an all-connections broadcast (the hub has no per-session
// subscription), and the client filters it by sessionId; the cursor's single source
// of truth stays chat_sessions.read_at, so a client that missed the frame converges
// on its next GET /sessions.
func (h *hub) broadcastSessionRead(sessionID string, readAt int64) {
	h.broadcast(wsEvent{
		Type:      wsSessionRead,
		SessionID: sessionID,
		Data:      map[string]any{"readAt": readAt},
	})
}