From bd4e7c1699128cd3fab43be5cbcb4b19894b56f6 Mon Sep 17 00:00:00 2001
From: Kenny Daniel <platypii@gmail.com>
Date: Sun, 12 May 2024 20:41:39 -0700
Subject: [PATCH] Actually fix conversion of decimals

---
 demo.js              |  1 +
 src/convert.js       | 20 +++++++++++---------
 test/convert.test.js |  8 ++++----
 3 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/demo.js b/demo.js
index dc6f1c4..82031fd 100644
--- a/demo.js
+++ b/demo.js
@@ -127,6 +127,7 @@ async function render(asyncBuffer, metadata, name) {
 function renderSidebar(asyncBuffer, metadata, name) {
   label.innerText = name
   // render file layout
+  layout.innerHTML = ''
   layout.appendChild(fileLayout(metadata, asyncBuffer.byteLength))
   // display metadata
   metadataDiv.innerHTML = ''
diff --git a/src/convert.js b/src/convert.js
index c58b676..353020e 100644
--- a/src/convert.js
+++ b/src/convert.js
@@ -9,7 +9,6 @@ const dayMillis = 86400000 // 1 day in milliseconds
  * @returns {DecodedArray} series of rich types
  */
 export function convert(data, schemaElement) {
-  if (!Array.isArray(data)) return data
   const ctype = schemaElement.converted_type
   if (ctype === 'UTF8') {
     const decoder = new TextDecoder()
@@ -17,24 +16,27 @@ export function convert(data, schemaElement) {
   }
   if (ctype === 'DECIMAL') {
     const scale = schemaElement.scale || 0
-    const precision = schemaElement.precision || 0
-    const factor = Math.pow(10, scale - precision)
+    const factor = Math.pow(10, -scale)
     if (typeof data[0] === 'number') {
-      return factor === 1 ? data : data.map(v => v * factor)
+      if (factor === 1) return data
+      return Array.from(data).map(v => v * factor)
     } else if (typeof data[0] === 'bigint') {
-      return factor === 1 ? data : data.map(v => v * BigInt(factor))
+      if (factor === 1) return data
+      // @ts-expect-error data is either BigInt64Array or bigint[]
+      if (factor > 1) return data.map(v => v * BigInt(factor))
+      return Array.from(data).map(v => Number(v) * factor)
     } else {
-      return data.map(v => parseDecimal(v) * factor)
+      return Array.from(data).map(v => parseDecimal(v) * factor)
     }
   }
   if (ctype === 'DATE') {
-    return data.map(v => new Date(v * dayMillis))
+    return Array.from(data).map(v => new Date(v * dayMillis))
   }
   if (ctype === undefined && schemaElement.type === 'INT96') {
-    return data.map(parseInt96Date)
+    return Array.from(data).map(parseInt96Date)
   }
   if (ctype === 'TIME_MILLIS') {
-    return data.map(v => new Date(v))
+    return Array.from(data).map(v => new Date(v))
   }
   if (ctype === 'JSON') {
     return data.map(v => JSON.parse(v))
diff --git a/test/convert.test.js b/test/convert.test.js
index 2588395..5987478 100644
--- a/test/convert.test.js
+++ b/test/convert.test.js
@@ -31,7 +31,7 @@ describe('convert function', () => {
     const data = [100, 200]
     /** @type {SchemaElement} */
     const schemaElement = { name, converted_type: 'DECIMAL', scale: 2 }
-    expect(convert(data, schemaElement)).toEqual([10000, 20000])
+    expect(convert(data, schemaElement)).toEqual([1, 2])
   })
 
   it('converts bigint to DECIMAL', () => {
@@ -42,10 +42,10 @@ describe('convert function', () => {
   })
 
   it('converts bigint to DECIMAL with scale', () => {
-    const data = [BigInt(1000), BigInt(2000)]
+    const data = [BigInt(10), BigInt(20)]
     /** @type {SchemaElement} */
-    const schemaElement = { name, converted_type: 'DECIMAL', scale: 3 }
-    expect(convert(data, schemaElement)).toEqual([1000000n, 2000000n])
+    const schemaElement = { name, converted_type: 'DECIMAL', scale: 2 }
+    expect(convert(data, schemaElement)).toEqual([0.1, 0.2])
   })
 
   it('converts byte arrays to DECIMAL', () => {