mergeMap((action: actions.FetchContentFulfilled) => {
      const state: AppState = state$.value;

      const contentRef = action.payload.contentRef;

      const content = selectors.content(state, { contentRef });

      if (
        !content ||
        content.type !== "notebook" ||
        content.model.type !== "notebook"
      ) {
        // This epic only handles notebook content
        return empty();
      }

      const filepath = content.filepath;
      const notebook = content.model.notebook;

      const { cwd, kernelSpecName } = extractNewKernel(filepath, notebook);

      return of(
        actions.launchKernelByName({
          kernelSpecName,
          cwd,
          kernelRef: action.payload.kernelRef,
          selectNextKernel: true,
          contentRef: action.payload.contentRef
        })
      );
    })

    mergeMap((contentRef: ContentRef) => {
      const state = state$.value;
      const content = selectors.content(state, { contentRef });

      let isVisible = false;

      // document.hidden appears well supported
      if (document.hidden) {
        // Opera 12.10 and Firefox 18 and later support
        isVisible = !document.hidden;
      } else if ((document as any).msHidden) {
        isVisible = !(document as any).msHidden;
      } else if ((document as any).webkitHidden) {
        isVisible = !(document as any).webkitHidden;
      } else {
        // Final fallback -- this will say the window is hidden when devtools is open or if the
        // user is interacting with an iframe
        isVisible = document.hasFocus();
      }

      if (
        isVisible &&
        // Don't bother saving nothing
        content &&
        // Only files and notebooks
        (content.type === "file" || content.type === "notebook") &&
        // Only save if they have a real filepath
        content.filepath !== ""
      ) {
        return of(actions.save({ contentRef }));
      } else {
        return empty();
      }
    })

      (
        action: actions.Save | actions.DownloadContent
      ):
        | Observable<
            | actions.DownloadContentFailed
            | actions.DownloadContentFulfilled
            | actions.SaveFailed
            | actions.SaveFulfilled
          >
        | Observable<never> => {
        const state = state$.value;

        const host = selectors.currentHost(state);
        if (host.type !== "jupyter") {
          // Dismiss any usage that isn't targeting a jupyter server
          return empty();
        }
        const contentRef = action.payload.contentRef;
        const content = selectors.content(state, { contentRef });

        // NOTE: This could save by having selectors for each model type
        //       have toDisk() selectors
        //       It will need to be cased off when we have more than one type
        //       of content we actually save
        if (!content) {
          const errorPayload = {
            error: new Error("Content was not set."),
            contentRef: action.payload.contentRef
          };
          if (action.type === actions.DOWNLOAD_CONTENT) {
            return of(actions.downloadContentFailed(errorPayload));
          }
          return of(actions.saveFailed(errorPayload));
        }

        if (content.type === "directory") {
          // Don't save directories
          return empty();
        }

        let filepath = content.filepath;

        // This could be object for notebook, or string for files
        let serializedData: Notebook | string;
        let saveModel: Partial<contents.Payload> = {};
        if (content.type === "notebook") {
          const appVersion = selectors.appVersion(state);

          // contents API takes notebook as raw JSON whereas downloading takes
          // a string
          serializedData = toJS(
            content.model.notebook.setIn(
              ["metadata", "nteract", "version"],
              appVersion
            )
          );
          saveModel = {
            content: serializedData,
            type: content.type
          };
        } else if (content.type === "file") {
          serializedData = content.model.text;
          saveModel = {
            content: serializedData,
            type: content.type,
            format: "text"
          };
        } else {
          // We shouldn't save directories
          return empty();
        }

        switch (action.type) {
          case actions.DOWNLOAD_CONTENT: {
            // FIXME: Convert this to downloadString, so it works for both files & notebooks
            if (
              content.type === "notebook" &&
              typeof serializedData === "object"
            ) {
              downloadString(
                stringifyNotebook(serializedData),
                filepath || "notebook.ipynb",
                "application/json"
              );
            } else if (
              content.type === "file" &&
              typeof serializedData === "string"
            ) {
              downloadString(
                serializedData,
                filepath,
                content.mimetype || "application/octet-stream"
              );
            } else {
              // This shouldn't happen, is here for safety
              return empty();
            }
            return of(
              actions.downloadContentFulfilled({
                contentRef: action.payload.contentRef
//.........这里部分代码省略.........

    switchMap((action: actions.LaunchKernelByNameAction) => {
      const state = state$.value;
      const host = selectors.currentHost(state);
      if (host.type !== "jupyter") {
        // Dismiss any usage that isn't targeting a jupyter server
        return empty();
      }
      const serverConfig: ServerConfig = selectors.serverConfig(host);

      const {
        payload: { kernelSpecName, cwd, kernelRef, contentRef }
      } = action;

      const content = selectors.content(state, { contentRef });
      if (!content || content.type !== "notebook") {
        return empty();
      }

      // TODO: Create a START_SESSION action instead (?)
      const sessionPayload = {
        kernel: {
          id: null,
          name: kernelSpecName
        },
        name: "",
        // TODO: Figure where the leading slash comes from in the content store
        path: content.filepath.replace(/^\/+/g, ""),
        type: "notebook"
      };

      // TODO: Handle failure cases here
      return sessions.create(serverConfig, sessionPayload).pipe(
        mergeMap(data => {
          const session = data.response;

          const sessionId = castToSessionId(session.id);

          const kernel: RemoteKernelProps = Object.assign({}, session.kernel, {
            type: "websocket",
            info: null,
            sessionId,
            cwd,
            channels: kernels.connect(
              serverConfig,
              session.kernel.id,
              sessionId
            ),
            kernelSpecName
          });

          kernel.channels.next(kernelInfoRequest());

          return of(
            actions.launchKernelSuccessful({
              kernel,
              kernelRef,
              contentRef: action.payload.contentRef,
              selectNextKernel: true
            })
          );
        }),
        catchError(error => {
          return of(actions.launchKernelFailed({ error }));
        })
      );
    })