From bd3a0adfed8f7caf1b5f662d9ac3bb519cd6d285 Mon Sep 17 00:00:00 2001
From: Miguel Camba <miguel.camba@gmail.com>
Date: Fri, 25 Oct 2024 18:19:13 +0200
Subject: [PATCH] Improve flow detection when elements have one element is
 shorter than its siblings and vertically centered.

---
 assets/svelte/utils/drag-helpers.ts | 63 ++++++++++++++++-------------
 1 file changed, 34 insertions(+), 29 deletions(-)

diff --git a/assets/svelte/utils/drag-helpers.ts b/assets/svelte/utils/drag-helpers.ts
index f65df57f..829335f8 100644
--- a/assets/svelte/utils/drag-helpers.ts
+++ b/assets/svelte/utils/drag-helpers.ts
@@ -24,44 +24,49 @@ export function mouseDiff(mouseMovement: CoordsDiff): Coords {
   }
 }
 
-function centerInAxis(rect: DOMRect, axis: "x" | "y"): number {
-  return axis === "x" ? rect.x + rect.width / 2 : rect.y + rect.height / 2
-}
 // Detects if elements flow generally in an horizontal direction, a vertical one or
 // both (e.g. they form a grid or overflow to the the next line)
 function detectFlow(rects: DOMRect[]) {
-  let horizontal = false
-  let vertical = false
+  // Sort elements by their left position (to analyze horizontal arrangement)
+  const sortedByLeft = [...rects].sort((a, b) => a.left - b.left);
+  // Sort elements by their top position (to analyze vertical arrangement)
+  const sortedByTop = [...rects].sort((a, b) => a.top - b.top);
+
+  // Calculate the average horizontal and vertical spacing between elements
+  const avgHorizontalDiff = getAverageDifference(sortedByLeft, 'left');
+  const avgVerticalDiff = getAverageDifference(sortedByTop, 'top');
+
+  // Determine the dominant flow
+  if (avgHorizontalDiff > avgVerticalDiff) {
+      // Check if all elements are roughly centered vertically
+      const isCenteredHorizontally = checkVerticalCenterAlignment(sortedByLeft);
+      return isCenteredHorizontally ? 'horizontal' : 'both';
+  } else if (avgVerticalDiff > avgHorizontalDiff) {
+      return 'vertical';
+  }
+  return 'both';
+}
 
-  const threshold = 5
+// Helper to calculate average difference for a given property (top or left)
+function getAverageDifference(rects, property) {
+  let totalDiff = 0;
   for (let i = 1; i < rects.length; i++) {
-    let prevRect = rects[i - 1]
-    let currentRect = rects[i]
-
-    // Use the centers in each axis to determine flow, not the top/left corners because
-    // when elements have different heights/widths but are vertically/horizontally aligned
-    // their corners might not be aligned but the general direction is still clear
-    let xChange = Math.abs(centerInAxis(currentRect, "x") - centerInAxis(prevRect, "x"))
-    let yChange = Math.abs(centerInAxis(currentRect, "y") - centerInAxis(prevRect, "y"))
-
-    // Check for horizontal flow: significant x change with minimal y change
-    if (xChange > threshold && yChange < threshold) {
-      horizontal = true
-    }
-    if (yChange > threshold) {
-      vertical = true
-    }
+      totalDiff += Math.abs(rects[i][property] - rects[i - 1][property]);
   }
+  return totalDiff / (rects.length - 1);
+}
 
-  if (horizontal && vertical) {
-    return "both"
-  } else if (horizontal) {
-    return "horizontal"
-  } else {
-    return "vertical"
-  }
+// Helper to check if elements are centered vertically relative to each other
+function checkVerticalCenterAlignment(rects) {
+  const centers = rects.map(rect => (rect.top + rect.bottom) / 2);
+  const minCenter = Math.min(...centers);
+  const maxCenter = Math.max(...centers);
+  return (maxCenter - minCenter) < 17; // tolerance for alignment, adjust as needed
 }
 
+
+
+
 // Determines if the drag of the current element should vertical or horizontal based on the
 // flow of its siblings
 // If prefers a practical approach, checking if the last element is further down (or right)