# All files / src/components/display VirtualEventItem.tsx

57.5% Statements 69/120
54.54% Branches 6/11
40% Functions 2/5
57.5% Lines 69/120

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     import { memo, useCallback, type JSX } from "react";
    import { EventRenderer } from "./EventRenderer.js";
    import { EventHoverRow } from "./EventHoverRow.js";
    import { isContentBearingEvent, getEventCopyText } from "../../utils/eventContent.js";
    import type { DisplayEvent } from "../../utils/sessionEvents.js";
    import type { SessionEvent } from "../../hooks/types.js";
    import styles from "./EventStream.module.scss";

    /** Build a descriptive label for the selection checkbox aria-label. */
    function buildCheckboxLabel(event: SessionEvent): string {
      const time = new Date(event.timestamp).toLocaleTimeString();
      switch (event.eventType) {
        case "text":
        case "output":
          return `Select message from assistant at ${time}`;
        case "user_input":
          return `Select message from user at ${time}`;
        case "tool_result":
        case "tool_use":
          return `Select tool event at ${time}`;
        case "error":
          return `Select error at ${time}`;
        default:
          return `Select event at ${time}`;
      }
    }

    /** Props for the virtualized event item. */
    export interface VirtualEventItemProps {
      /** The display event to render. */
      event: DisplayEvent;
      /** Original index in the chronological events array (used for selection). */
      originalIndex: number;
      /** Whether multi-select mode is active. */
      isSelecting: boolean;
      /** Whether this event is currently selected. */
      isSelected: boolean;
      /** Called when the user clicks the Select hover action. */
      onSelect: (originalIndex: number) => void;
      /** Called when the user toggles selection (checkbox click or row click). */
      onToggle: (originalIndex: number, shiftKey: boolean) => void;
      /** Called after a successful single-event copy from the hover row. */
      onCopied: () => void;
      /** Sandbox proxy origin URL for rendering MCP Apps widget events. */
      sandboxProxyUrl?: string;
      /** Open a file in the live-docs pane. */
      onOpenDocument?: (uri: string) => void;
      /** Whether this event is newly appended (triggers entry animation). */
      isNew: boolean;
      /** Whether the stream is in reversed (newest-at-top) mode. */
      isReversed: boolean;
    }

    /** Custom equality check for React.memo — avoids re-rendering unchanged items. */
    /** Compare toolUseCtx by fields (pairToolEvents recreates these objects each render). */
    function toolCtxEqual(a: DisplayEvent["toolUseCtx"], b: DisplayEvent["toolUseCtx"]): boolean {
      if (a === b) {
        return true;
      }
      if (!a || !b) {
        return false;
      }
      return (
        a.tool === b.tool &&
        a.detailedResult === b.detailedResult &&
        JSON.stringify(a.args) === JSON.stringify(b.args)
      );
    }

    /** Compare events by stable fields that affect rendering. */
    function eventsEqual(a: DisplayEvent, b: DisplayEvent): boolean {
      if (a === b) {
        return true;
      }
      return (
        a.sessionId === b.sessionId &&
        a.timestamp === b.timestamp &&
        a.eventType === b.eventType &&
        a.content === b.content &&
        a.toolCallId === b.toolCallId &&
        a.toolError === b.toolError &&
        a.raw === b.raw &&
        a.settled === b.settled &&
        toolCtxEqual(a.toolUseCtx, b.toolUseCtx)
      );
    }

    function arePropsEqual(
      prev: Readonly<VirtualEventItemProps>,
      next: Readonly<VirtualEventItemProps>,
    ): boolean {
      return (
        eventsEqual(prev.event, next.event) &&
        prev.originalIndex === next.originalIndex &&
        prev.isSelecting === next.isSelecting &&
        prev.isSelected === next.isSelected &&
        prev.onSelect === next.onSelect &&
        prev.onToggle === next.onToggle &&
        prev.onCopied === next.onCopied &&
        prev.sandboxProxyUrl === next.sandboxProxyUrl &&
        prev.onOpenDocument === next.onOpenDocument &&
        prev.isNew === next.isNew &&
        prev.isReversed === next.isReversed
      );
    }

    /**
     * Memoized event row for the virtualized EventStream.
     * Wraps EventHoverRow + EventRenderer. Measurement and positioning are
     * handled by the parent VirtualList component.
     */
    export const VirtualEventItem: React.NamedExoticComponent<VirtualEventItemProps> = memo(
      function VirtualEventItem({
        event,
        originalIndex,
        isSelecting,
        isSelected,
        onSelect,
        onToggle,
        onCopied,
        sandboxProxyUrl,
        onOpenDocument,
        isNew,
        isReversed,
      }: VirtualEventItemProps): JSX.Element {
        const handleSelect = useCallback(() => {
          onSelect(originalIndex);
        }, [onSelect, originalIndex]);

        const handleToggle = useCallback(
          (shiftKey: boolean) => {
            onToggle(originalIndex, shiftKey);
          },
          [onToggle, originalIndex],
        );

        const copyText = getEventCopyText(event);
        const contentBearing = isContentBearingEvent(event);
        const checkboxLabel = buildCheckboxLabel(event);

        const animationClass = isNew
          ? isReversed
            ? styles.eventFadeInReversed
            : styles.eventFadeIn
          : undefined;

        return (
          <div className={animationClass}>
            <EventHoverRow
              copyText={copyText}
              isContentBearing={contentBearing}
              isSelecting={isSelecting}
              isSelected={isSelected}
              checkboxLabel={checkboxLabel}
              onSelect={handleSelect}
              onToggle={handleToggle}
              onCopied={onCopied}
            >
              <EventRenderer
                event={event}
                toolUseCtx={event.toolUseCtx}
                settled={event.settled}
                sandboxProxyUrl={sandboxProxyUrl}
                onOpenDocument={onOpenDocument}
              />
            </EventHoverRow>
          </div>
        );
      },
      arePropsEqual,
    );