ant-design/components/splitter/SplitBar.tsx

import React, { useState } from 'react';
import DownOutlined from '@ant-design/icons/DownOutlined';
import LeftOutlined from '@ant-design/icons/LeftOutlined';
import RightOutlined from '@ant-design/icons/RightOutlined';
import UpOutlined from '@ant-design/icons/UpOutlined';
import classNames from 'classnames';
import useEvent from 'rc-util/lib/hooks/useEvent';
import useLayoutEffect from 'rc-util/lib/hooks/useLayoutEffect';

export type ShowCollapsibleIconMode = boolean | 'auto';

export interface SplitBarProps {
  index: number;
  active: boolean;
  prefixCls: string;
  resizable: boolean;
  startCollapsible: boolean;
  endCollapsible: boolean;
  showStartCollapsibleIcon: ShowCollapsibleIconMode;
  showEndCollapsibleIcon: ShowCollapsibleIconMode;
  onOffsetStart: (index: number) => void;
  onOffsetUpdate: (index: number, offsetX: number, offsetY: number, lazyEnd?: boolean) => void;
  onOffsetEnd: (lazyEnd?: boolean) => void;
  onCollapse: (index: number, type: 'start' | 'end') => void;
  vertical: boolean;
  ariaNow: number;
  ariaMin: number;
  ariaMax: number;
  lazy?: boolean;
  containerSize: number;
}

function getValidNumber(num: number | undefined): number {
  return typeof num === 'number' && !Number.isNaN(num) ? Math.round(num) : 0;
}

const SplitBar: React.FC<SplitBarProps> = (props) => {
  const {
    prefixCls,
    vertical,
    index,
    active,
    ariaNow,
    ariaMin,
    ariaMax,
    resizable,
    startCollapsible,
    endCollapsible,
    onOffsetStart,
    onOffsetUpdate,
    onOffsetEnd,
    onCollapse,
    lazy,
    containerSize,
    showStartCollapsibleIcon,
    showEndCollapsibleIcon,
  } = props;

  const splitBarPrefixCls = `${prefixCls}-bar`;

  // ======================== Resize ========================
  const [startPos, setStartPos] = useState<[x: number, y: number] | null>(null);
  const [constrainedOffset, setConstrainedOffset] = useState<number>(0);

  const constrainedOffsetX = vertical ? 0 : constrainedOffset;
  const constrainedOffsetY = vertical ? constrainedOffset : 0;

  const onMouseDown: React.MouseEventHandler<HTMLDivElement> = (e) => {
    if (resizable && e.currentTarget) {
      setStartPos([e.pageX, e.pageY]);
      onOffsetStart(index);
    }
  };

  const onTouchStart: React.TouchEventHandler<HTMLDivElement> = (e) => {
    if (resizable && e.touches.length === 1) {
      const touch = e.touches[0];
      setStartPos([touch.pageX, touch.pageY]);
      onOffsetStart(index);
    }
  };

  // Updated constraint calculation
  const getConstrainedOffset = (rawOffset: number) => {
    const currentPos = (containerSize * ariaNow) / 100;
    const newPos = currentPos + rawOffset;

    // Calculate available space
    const minAllowed = Math.max(0, (containerSize * ariaMin) / 100);
    const maxAllowed = Math.min(containerSize, (containerSize * ariaMax) / 100);

    // Constrain new position within bounds
    const clampedPos = Math.max(minAllowed, Math.min(maxAllowed, newPos));
    return clampedPos - currentPos;
  };

  const handleLazyMove = useEvent((offsetX: number, offsetY: number) => {
    const constrainedOffsetValue = getConstrainedOffset(vertical ? offsetY : offsetX);
    setConstrainedOffset(constrainedOffsetValue);
  });

  const handleLazyEnd = useEvent(() => {
    onOffsetUpdate(index, constrainedOffsetX, constrainedOffsetY, true);
    setConstrainedOffset(0);
    onOffsetEnd(true);
  });

  const getVisibilityClass = (mode: ShowCollapsibleIconMode): string => {
    switch (mode) {
      case true:
        return `${splitBarPrefixCls}-collapse-bar-always-visible`;
      case false:
        return `${splitBarPrefixCls}-collapse-bar-always-hidden`;
      case 'auto':
        return `${splitBarPrefixCls}-collapse-bar-hover-only`;
    }
  };

  useLayoutEffect(() => {
    if (!startPos) {
      return;
    }

    const onMouseMove = (e: MouseEvent) => {
      const { pageX, pageY } = e;
      const offsetX = pageX - startPos[0];
      const offsetY = pageY - startPos[1];
      if (lazy) {
        handleLazyMove(offsetX, offsetY);
      } else {
        onOffsetUpdate(index, offsetX, offsetY);
      }
    };

    const onMouseUp = () => {
      if (lazy) {
        handleLazyEnd();
      } else {
        onOffsetEnd();
      }
      setStartPos(null);
    };

    const handleTouchMove = (e: TouchEvent) => {
      if (e.touches.length === 1) {
        const touch = e.touches[0];
        const offsetX = touch.pageX - startPos[0];
        const offsetY = touch.pageY - startPos[1];
        if (lazy) {
          handleLazyMove(offsetX, offsetY);
        } else {
          onOffsetUpdate(index, offsetX, offsetY);
        }
      }
    };

    const handleTouchEnd = () => {
      if (lazy) {
        handleLazyEnd();
      } else {
        onOffsetEnd();
      }
      setStartPos(null);
    };

    const eventHandlerMap: Partial<Record<keyof WindowEventMap, EventListener>> = {
      mousemove: onMouseMove as EventListener,
      mouseup: onMouseUp,
      touchmove: handleTouchMove as EventListener,
      touchend: handleTouchEnd,
    };

    for (const [event, handler] of Object.entries(eventHandlerMap)) {
      // eslint-disable-next-line react-web-api/no-leaked-event-listener
      window.addEventListener(event, handler);
    }

    return () => {
      for (const [event, handler] of Object.entries(eventHandlerMap)) {
        window.removeEventListener(event, handler);
      }
    };
  }, [startPos, index, lazy]);

  const transformStyle: React.CSSProperties = {
    [`--${splitBarPrefixCls}-preview-offset`]: `${constrainedOffset}px`,
  };

  // ======================== Render ========================
  const StartIcon = vertical ? UpOutlined : LeftOutlined;
  const EndIcon = vertical ? DownOutlined : RightOutlined;

  return (
    <div
      className={splitBarPrefixCls}
      role="separator"
      aria-valuenow={getValidNumber(ariaNow)}
      aria-valuemin={getValidNumber(ariaMin)}
      aria-valuemax={getValidNumber(ariaMax)}
    >
      {lazy && (
        <div
          className={classNames(`${splitBarPrefixCls}-preview`, {
            [`${splitBarPrefixCls}-preview-active`]: !!constrainedOffset,
          })}
          style={transformStyle}
        />
      )}

      <div
        className={classNames(`${splitBarPrefixCls}-dragger`, {
          [`${splitBarPrefixCls}-dragger-disabled`]: !resizable,
          [`${splitBarPrefixCls}-dragger-active`]: active,
        })}
        onMouseDown={onMouseDown}
        onTouchStart={onTouchStart}
      />

      {/* Start Collapsible */}
      {startCollapsible && (
        <div
          className={classNames(
            `${splitBarPrefixCls}-collapse-bar`,
            `${splitBarPrefixCls}-collapse-bar-start`,
            getVisibilityClass(showStartCollapsibleIcon),
          )}
          onClick={() => onCollapse(index, 'start')}
        >
          <StartIcon
            className={classNames(
              `${splitBarPrefixCls}-collapse-icon`,
              `${splitBarPrefixCls}-collapse-start`,
            )}
          />
        </div>
      )}

      {/* End Collapsible */}
      {endCollapsible && (
        <div
          className={classNames(
            `${splitBarPrefixCls}-collapse-bar`,
            `${splitBarPrefixCls}-collapse-bar-end`,
            getVisibilityClass(showEndCollapsibleIcon),
          )}
          onClick={() => onCollapse(index, 'end')}
        >
          <EndIcon
            className={classNames(
              `${splitBarPrefixCls}-collapse-icon`,
              `${splitBarPrefixCls}-collapse-end`,
            )}
          />
        </div>
      )}
    </div>
  );
};

export default SplitBar;