From b44e9e5702bde89be3b3316def00eaebed40cc66 Mon Sep 17 00:00:00 2001
From: Codex Agent <agent@example.com>
Date: Mon, 9 Mar 2026 19:50:26 +0000
Subject: [PATCH] Normalize conversion factor formatting

---
 .../components/QuickConversionExample.svelte  | 34 +++++++------------
 hdyc-svelte/src/lib/utils/conversionRate.ts   |  7 +++-
 .../src/lib/utils/formatConversionValue.ts    | 17 ++++++++++
 tests/test_conversion_rate_tooltip.py         | 27 +++++++++++++++
 tests/test_quick_conversion_formatting.py     | 26 ++++++++++++++
 5 files changed, 88 insertions(+), 23 deletions(-)
 create mode 100644 hdyc-svelte/src/lib/utils/formatConversionValue.ts
 create mode 100644 tests/test_conversion_rate_tooltip.py
 create mode 100644 tests/test_quick_conversion_formatting.py

diff --git a/hdyc-svelte/src/lib/components/QuickConversionExample.svelte b/hdyc-svelte/src/lib/components/QuickConversionExample.svelte
index e75ef49..2831c77 100644
--- a/hdyc-svelte/src/lib/components/QuickConversionExample.svelte
+++ b/hdyc-svelte/src/lib/components/QuickConversionExample.svelte
@@ -1,6 +1,7 @@
 <script lang="ts">
   import { solve } from '$lib/engine';
   import type { CalculatorDef } from '$lib/data/calculators';
+  import { formatConversionValue } from '$lib/utils/formatConversionValue';
 
   export let config: CalculatorDef;
 
@@ -17,40 +18,29 @@
     ? solve(config, 1, exampleInput.toString(), '', '')
     : null;
   $: offset = config.offset ?? 0;
-  $: formulaExpression = supportsExample
-    ? `${exampleInput} × ${config.factor}${offset ? ` + ${offset}` : ''}`
+  $: hasOffset = Boolean(offset);
+  $: formattedFactorValue = supportsExample
+    ? formatConversionValue(config.factor)
+    : '';
+  $: formattedOffsetValue = hasOffset
+    ? formatConversionValue(offset)
+    : '';
+  $: formulaExpression = supportsExample
+    ? `${exampleInput} × ${formattedFactorValue}${hasOffset ? ` + ${formattedOffsetValue}` : ''}`
     : '';
-
-  const formatExampleValue = (value: number | null): string => {
-    if (value === null || Number.isNaN(value)) {
-      return '—';
-    }
-    if (!Number.isFinite(value)) {
-      return value.toString();
-    }
-    if (value === 0) {
-      return '0';
-    }
-    const rounded = parseFloat(value.toFixed(6));
-    if (rounded !== 0) {
-      return rounded.toString();
-    }
-    const precise = value.toFixed(12).replace(/\.?0+$/, '');
-    return precise || '0';
-  };
 
   $: reverseExampleValue =
     supportsExample && config.factor !== 0
       ? (1 - offset) / config.factor
       : null;
-  $: formattedReverseValue = formatExampleValue(reverseExampleValue);
+  $: formattedReverseValue = formatConversionValue(reverseExampleValue);
 </script>
 
 {#if supportsExample && result}
   <section class="example-card">
     <h3>How to convert {config.labels.in1} to {config.labels.in2}</h3>
     <p class="example-note">
-      1 {config.labels.in1} = {config.factor}{config.offset ? ` + ${config.offset}` : ''} {config.labels.in2}
+      1 {config.labels.in1} = {formattedFactorValue}{hasOffset ? ` + ${formattedOffsetValue}` : ''} {config.labels.in2}
     </p>
     <p class="example-note">
       1 {config.labels.in2} = {formattedReverseValue} {config.labels.in1}
diff --git a/hdyc-svelte/src/lib/utils/conversionRate.ts b/hdyc-svelte/src/lib/utils/conversionRate.ts
index f464085..6f54a44 100644
--- a/hdyc-svelte/src/lib/utils/conversionRate.ts
+++ b/hdyc-svelte/src/lib/utils/conversionRate.ts
@@ -1,4 +1,5 @@
 import type { CalculatorDef } from '$lib/data/calculators';
+import { formatConversionValue } from '$lib/utils/formatConversionValue';
 
 type RateConfig = Pick<CalculatorDef, 'type' | 'factor' | 'offset' | 'labels'>;
 
@@ -12,5 +13,9 @@ export const getConversionRateText = (config: RateConfig): string | null => {
     return null;
   }
 
-  return `1 ${in1} = ${config.factor}${config.offset ? ` + ${config.offset}` : ''} ${in2}`;
+  const formattedFactor = formatConversionValue(config.factor);
+  const hasOffset = Boolean(config.offset);
+  const formattedOffset = formatConversionValue(config.offset ?? 0);
+
+  return `1 ${in1} = ${formattedFactor}${hasOffset ? ` + ${formattedOffset}` : ''} ${in2}`;
 };
diff --git a/hdyc-svelte/src/lib/utils/formatConversionValue.ts b/hdyc-svelte/src/lib/utils/formatConversionValue.ts
new file mode 100644
index 0000000..fb4adbd
--- /dev/null
+++ b/hdyc-svelte/src/lib/utils/formatConversionValue.ts
@@ -0,0 +1,17 @@
+export function formatConversionValue(value: number | null | undefined): string {
+  if (value === null || value === undefined || Number.isNaN(value)) {
+    return '—';
+  }
+  if (!Number.isFinite(value)) {
+    return value.toString();
+  }
+  if (value === 0) {
+    return '0';
+  }
+  const rounded = parseFloat(value.toFixed(6));
+  if (rounded !== 0) {
+    return rounded.toString();
+  }
+  const precise = value.toFixed(12).replace(/\.?0+$/, '');
+  return precise || '0';
+}
diff --git a/tests/test_conversion_rate_tooltip.py b/tests/test_conversion_rate_tooltip.py
new file mode 100644
index 0000000..43a0dd3
--- /dev/null
+++ b/tests/test_conversion_rate_tooltip.py
@@ -0,0 +1,27 @@
+import unittest
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+CONVERSION_RATE = (
+    ROOT / "hdyc-svelte" / "src" / "lib" / "utils" / "conversionRate.ts"
+)
+
+
+class ConversionRateTooltipFormattingTests(unittest.TestCase):
+    def test_conversion_rate_text_uses_formatter(self) -> None:
+        text = CONVERSION_RATE.read_text(encoding="utf-8")
+        normalized = " ".join(text.split())
+        self.assertIn(
+            "formatConversionValue(config.factor)",
+            normalized,
+            "Conversion rate helper must format the factor before inserting it into the tooltip text",
+        )
+        self.assertIn(
+            "formatConversionValue(config.offset ?? 0)",
+            normalized,
+            "Conversion rate tooltip must format any offset before rendering",
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/test_quick_conversion_formatting.py b/tests/test_quick_conversion_formatting.py
new file mode 100644
index 0000000..5b53a1d
--- /dev/null
+++ b/tests/test_quick_conversion_formatting.py
@@ -0,0 +1,26 @@
+import unittest
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+QUICK_CONVERSION_EXAMPLE = (
+    ROOT / "hdyc-svelte" / "src" / "lib" / "components" / "QuickConversionExample.svelte"
+)
+
+
+class QuickConversionExampleFormattingTests(unittest.TestCase):
+    def test_formula_uses_formatted_factor_and_offset(self) -> None:
+        text = QUICK_CONVERSION_EXAMPLE.read_text(encoding="utf-8")
+        normalized = " ".join(text.split())
+        snippet = (
+            "1 {config.labels.in1} = {formattedFactorValue}{hasOffset ? ` + ${formattedOffsetValue}` : ''} "
+            "{config.labels.in2}"
+        )
+        self.assertIn(
+            snippet,
+            normalized,
+            "The formula snippet should render formatted factor/offset values instead of raw floats",
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()