From 9ee13a45bbfba643dc462962e6dc8b75c793fc36 Mon Sep 17 00:00:00 2001
From: ramseshk <45832522+ramseshk@users.noreply.github.com>
Date: Fri, 7 Aug 2026 15:26:42 +0800
Subject: [PATCH] =?UTF-8?q?fix:=20LTTB=20downsampling=20crashes=20on=20str?=
 =?UTF-8?q?ing=20timestamps=20+=20abs=E2=86=92Math.abs?=
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- _lttb_downsample: equity curve timestamps are ISO strings,
  not numeric. Rewrote to use array indices for triangle area
  instead of trying to multiply string * float.
- Fixed IndexError from reusing 'a' variable incorrectly
- Also fixed earlier: abs(dd) → Math.abs(dd) in vbt.html
---
 dashboard/server.py | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/dashboard/server.py b/dashboard/server.py
index 7c22f73..8534f30 100644
--- a/dashboard/server.py
+++ b/dashboard/server.py
@@ -586,27 +586,28 @@ def _lttb_downsample(points: list[dict], target: int) -> list[dict]:
         return points
     bucket_size = (n - 2) / (target - 2)
     result = [points[0]]
-    a = 0
+    a = 0  # index of last point in result (within original points array)
     for i in range(target - 2):
-        avg_x_start = int((i + 0) * bucket_size) + 1
-        avg_x_end   = int((i + 1) * bucket_size) + 1
-        avg_range   = points[avg_x_start:avg_x_end]
-        avg_x       = sum(p.get("t", 0) if isinstance(p.get("t"), (int, float)) else 0 for p in avg_range) / max(len(avg_range), 1)
-        avg_y       = sum(p["v"] for p in avg_range) / max(len(avg_range), 1)
-        range_offs  = int((i + 1) * bucket_size) + 1
-        range_to    = int((i + 2) * bucket_size) + 1
-        max_area    = -1.0
+        avg_start = int((i + 0) * bucket_size) + 1
+        avg_end   = int((i + 1) * bucket_size) + 1
+        avg_range = points[avg_start:avg_end]
+        avg_y     = sum(p["v"] for p in avg_range) / max(len(avg_range), 1)
+        avg_x     = int((avg_start + avg_end - 1) / 2)
+        range_offs = int((i + 1) * bucket_size) + 1
+        range_to   = int((i + 2) * bucket_size) + 1
+        max_area   = -1.0
+        next_pt    = range_offs
         for j in range(range_offs, min(range_to + 1, n)):
-            pa = result[a]
+            pa = points[a]
             pc = points[j]
-            area = abs((pa.get("t", 0) if isinstance(pa.get("t"), (int, float)) else a) * (pc["v"] - avg_y) +
-                       pc.get("t", 0) * (avg_y - pa["v"]) +
-                       avg_x * (pa["v"] - pc["v"])) * 0.5
+            area = abs((a - j) * (pc["v"] - avg_y) +
+                       (j - avg_x) * (avg_y - pa["v"]) +
+                       (avg_x - a) * (pa["v"] - pc["v"])) * 0.5
             if area > max_area:
                 max_area = area
-                next_a = j
-        result.append(points[next_a])
-        a = next_a
+                next_pt = j
+        result.append(points[next_pt])
+        a = next_pt
     result.append(points[-1])
     return result