# All files / src/hooks useEventSelection.ts

100% Statements 97/97
100% Branches 29/29
100% Functions 1/1
100% Lines 97/97

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     /**
     * Selection state management for the multi-select feature in EventStream.
     *
     * Manages entering/exiting selection mode, toggling individual events,
     * shift-click range selection, select all, and clipboard copy.
     *
     * @module
     */

    import { useState, useRef, useCallback, useMemo } from "react";
    import type { DisplayEvent } from "../utils/sessionEvents.js";
    import { isContentBearingEvent } from "../utils/eventContent.js";

    /** Options for the useEventSelection hook. */
    export interface UseEventSelectionOptions {
      /** All events currently in the stream. */
      events: DisplayEvent[];
      /** Formats events as text for the clipboard. */
      formatForClipboard: (events: DisplayEvent[]) => string;
    }

    /** Return value of the useEventSelection hook. */
    export interface UseEventSelectionReturn {
      /** Whether selection mode is active. */
      isSelecting: boolean;
      /** Set of selected event indices (from the events array). */
      selectedIndices: ReadonlySet<number>;
      /** Number of selected events. */
      selectedCount: number;
      /** Enter selection mode, optionally selecting an initial event. */
      enterSelectionMode: (initialIndex?: number) => void;
      /** Exit selection mode and clear all selections. */
      cancelSelection: () => void;
      /** Toggle an event at the given index. When shiftKey is true, selects the range from the last-toggled anchor. */
      toggleEvent: (index: number, shiftKey?: boolean) => void;
      /** Select all content-bearing events. */
      selectAll: () => void;
      /** Deselect all events but stay in selection mode. */
      deselectAll: () => void;
      /** Copy selected events to clipboard. Returns true on success. */
      copySelected: () => Promise<boolean>;
    }

    /**
     * Hook that manages event selection state for the EventStream multi-select feature.
     *
     * The caller is responsible for rendering checkboxes, highlights, and action bars
     * based on the returned state. The `copySelected` method uses `navigator.clipboard`
     * and will return `false` in environments where the Clipboard API is unavailable.
     */
    export function useEventSelection({
      events,
      formatForClipboard,
    }: UseEventSelectionOptions): UseEventSelectionReturn {
      const [isSelecting, setIsSelecting] = useState(false);
      const [selectedIndices, setSelectedIndices] = useState<ReadonlySet<number>>(new Set());
      /** Anchor index for shift-click range selection. */
      const anchorRef = useRef<number | undefined>(undefined);

      const selectedCount = useMemo(() => selectedIndices.size, [selectedIndices]);

      const enterSelectionMode = useCallback((initialIndex?: number) => {
        setIsSelecting(true);
        if (initialIndex !== undefined) {
          setSelectedIndices(new Set([initialIndex]));
          anchorRef.current = initialIndex;
        } else {
          setSelectedIndices(new Set());
          anchorRef.current = undefined;
        }
      }, []);

      const cancelSelection = useCallback(() => {
        setIsSelecting(false);
        setSelectedIndices(new Set());
        anchorRef.current = undefined;
      }, []);

      const toggleEvent = useCallback(
        (index: number, shiftKey?: boolean) => {
          if (shiftKey && anchorRef.current !== undefined) {
            // Range selection: select all content-bearing events between anchor and index
            const start = Math.min(anchorRef.current, index);
            const end = Math.max(anchorRef.current, index);
            setSelectedIndices((prev) => {
              const next = new Set(prev);
              for (let i = start; i <= end; i++) {
                if (i < events.length && isContentBearingEvent(events[i])) {
                  next.add(i);
                }
              }
              return next;
            });
          } else {
            // Single toggle — exit selection mode if deselecting the last item
            setSelectedIndices((prev) => {
              const next = new Set(prev);
              if (next.has(index)) {
                next.delete(index);
              } else {
                next.add(index);
              }
              if (next.size === 0) {
                setIsSelecting(false);
                anchorRef.current = undefined;
              } else {
                anchorRef.current = index;
              }
              return next;
            });
          }
        },
        [events],
      );

      const selectAll = useCallback(() => {
        const all = new Set<number>();
        for (let i = 0; i < events.length; i++) {
          if (isContentBearingEvent(events[i])) {
            all.add(i);
          }
        }
        setSelectedIndices(all);
      }, [events]);

      const deselectAll = useCallback(() => {
        setSelectedIndices(new Set());
      }, []);

      const copySelected = useCallback(async (): Promise<boolean> => {
        const sorted = [...selectedIndices].sort((a, b) => a - b);
        const selectedEvents = sorted.filter((i) => i < events.length).map((i) => events[i]);
        if (selectedEvents.length === 0) {
          return false;
        }
        const text = formatForClipboard(selectedEvents);
        try {
          await navigator.clipboard.writeText(text);
          return true;
        } catch {
          return false;
        }
      }, [selectedIndices, events, formatForClipboard]);

      return {
        isSelecting,
        selectedIndices,
        selectedCount,
        enterSelectionMode,
        cancelSelection,
        toggleEvent,
        selectAll,
        deselectAll,
        copySelected,
      };
    }