#3845 mouse placement bug

src/frontend/src/pages/GanttPage/GanttChart/GanttChartComponents/GanttTaskBar/GanttTaskBarEditView.tsx

@@ -1,6 +1,6 @@
 import { Box, Chip, Typography } from '@mui/material';
 import { useTheme } from '@mui/system';
-import { CSSProperties, DragEvent, MouseEvent, useEffect, useState } from 'react';
+import { CSSProperties, DragEvent, MouseEvent, useCallback, useEffect, useRef, useState } from 'react';
 import useMeasure from 'react-use-measure';
 import { addDaysToDate } from 'shared';
 import { GanttChange, GanttTask, GANTT_CHART_CELL_SIZE } from '../../../../../utils/gantt.utils';
@@ -15,6 +15,10 @@ import {
 import { ArcherElement } from 'react-archer';
 import { v4 as uuidv4 } from 'uuid';
 
+const CELL_SIZE_PX = 38 + 2; // 38px cell + 2px for borders (1px each side)
+const GAP_SIZE_PX = 10; // empirically determined, see note above
+const WIDTH_PER_DAY = 7.2; //width per day to use for resizing calculations, kind of arbitrary,
+
 interface GanttTaskBarEditProps<T> {
   days: Date[];
   task: GanttTask<T>;
@@ -33,18 +37,19 @@ export const GanttTaskBarEditView = <T,>({
   onAddTaskPressed
 }: GanttTaskBarEditProps<T>) => {
   const theme = useTheme();
-  const [startX, setStartX] = useState<number | null>(null);
   const [showDropPoints, setShowDropPoints] = useState(false);
   const [isResizing, setIsResizing] = useState(false);
-  const [width, setWidth] = useState(0); // current width of component, will change on resize
+  const [width, setWidth] = useState(0);
+  const [correctWidth, setCorrectWidth] = useState(0);
   const [measureRef, bounds] = useMeasure();
-  const widthPerDay = 7.2; //width per day to use for resizing calculations, kind of arbitrary,
+  const hasMeasuredRef = useRef(false);
+  const boxRef = useRef<HTMLDivElement | null>(null);
 
   const taskBarDisplayStyles: CSSProperties = {
     gridColumnStart: getStartCol(task.start),
     gridColumnEnd: getEndCol(task.end),
     height: '2rem',
-    width: task.root ? 'unset' : width === 0 ? `unset` : `${width}px`,
+    width: task.root ? 'unset' : correctWidth > 0 ? `${correctWidth}px` : 'auto',
     border: `1px solid ${isResizing ? theme.palette.text.primary : theme.palette.divider}`,
     borderRadius: '0.25rem',
     backgroundColor: task.styles ? task.styles.backgroundColor : theme.palette.background.paper,
@@ -67,48 +72,61 @@ export const GanttTaskBarEditView = <T,>({
     right: '-10'
   };
 
+  const getCorrectWidth = useCallback((rawWidth: number) => {
+    const newEventLengthInDays = floorToMultipleOf7(rawWidth / WIDTH_PER_DAY);
+    const displayWeeks = newEventLengthInDays / 7 + 1;
+    return displayWeeks * CELL_SIZE_PX + (displayWeeks - 1) * GAP_SIZE_PX;
+  }, []);
+
   useEffect(() => {
-    if (bounds.width !== 0 && width === 0) {
+    if (!hasMeasuredRef.current && bounds.width > 0) {
       setWidth(bounds.width);
+      setCorrectWidth(getCorrectWidth(bounds.width));
+      hasMeasuredRef.current = true;
     }
-  }, [bounds, width]);
+  }, [bounds.width, getCorrectWidth]);
 
   // used to make sure that any changes to the start and end dates are made in multiples of 7
-  const roundToMultipleOf7 = (num: number) => {
-    return Math.round(num / 7) * 7;
+  const floorToMultipleOf7 = (num: number) => {
+    return Math.floor(num / 7) * 7;
+  };
+
+  const getDistanceFromLeft = (clientX: number) => {
+    if (!boxRef.current) return 0;
+    const rect = boxRef.current.getBoundingClientRect();
+    return clientX - rect.left;
   };
 
   const handleMouseDown = (e: MouseEvent<HTMLElement>) => {
+    const bar = (e.currentTarget as HTMLElement).closest('[data-gantt-bar]');
+    if (!bar) return;
+
+    boxRef.current = (e.currentTarget as HTMLElement).closest('[data-gantt-bar]') as HTMLDivElement;
     setIsResizing(true);
-    setStartX(e.clientX);
   };
 
   const handleMouseMove = (e: MouseEvent<HTMLElement>) => {
-    if (isResizing) {
-      const currentX = e.clientX;
-      const deltaX = currentX - startX!;
-      setWidth(Math.max(100, width + deltaX));
-      setStartX(currentX);
-    }
+    if (!isResizing) return;
+
+    const newWidth = Math.max(100, getDistanceFromLeft(e.clientX));
+
+    setWidth(newWidth); // sync render
+    setCorrectWidth(getCorrectWidth(newWidth));
   };
 
   const handleMouseUp = () => {
     if (isResizing) {
       setIsResizing(false);
-      // Use change in width to calculate new length
-      const newEventLengthInDays = roundToMultipleOf7(width / widthPerDay);
-      // The gantt chart tasks are inclusive (their width includes the full width of their start and end date)
+      const newEventLengthInDays = floorToMultipleOf7(width / WIDTH_PER_DAY);
       const displayWeeks = newEventLengthInDays / 7 + 1;
-      // We need these magic pixel numbers to dynamically calculate the correct width of the task to keep it in sync with the stored end date
-      const correctWidth = displayWeeks * 38 + (displayWeeks - 1) * 10;
-      const newEndDate = addDaysToDate(task.start, newEventLengthInDays);
+      const correctWidth = displayWeeks * 40 + (displayWeeks - 1) * 10;
       setWidth(correctWidth);
       createChange({
         id: uuidv4(),
         element: task.element,
         type: 'change-end-date',
         originalEnd: task.end,
-        newEnd: newEndDate
+        newEnd: addDaysToDate(task.start, newEventLengthInDays)
       });
     }
   };
@@ -124,7 +142,7 @@ export const GanttTaskBarEditView = <T,>({
     e.preventDefault();
   };
   const onDrop = (day: Date) => {
-    const days = roundToMultipleOf7(differenceInDays(day, task.start));
+    const days = floorToMultipleOf7(differenceInDays(day, task.start));
     createChange({ id: uuidv4(), element: task.element, type: 'shift-by-days', days });
   };
 
@@ -156,7 +174,7 @@ export const GanttTaskBarEditView = <T,>({
             };
           })}
         >
-          <div ref={measureRef} style={taskBarDisplayStyles}>
+          <div data-gantt-bar ref={measureRef} style={taskBarDisplayStyles}>
             <Box sx={webKitBoxContainerStyles()}>
               <Box draggable={!task.root} onDrag={onDragStart} onDragEnd={onDragEnd} sx={webKitBoxStyles()}>
                 <Box sx={{ display: 'flex', flexDirection: 'row' }}>