Fix inconsistent number formatting between mobile and web (#6384)

* Manual truncation & identify factor points for each lang

* Reduce indirection

* Add test

Co-authored-by: khuddite <biliie811028@hotmail.com>

* Handle big numbers, clarify special case

* Clarify the reason

---------

Co-authored-by: Dan Abramov <dan.abramov@gmail.com>

1 files changed, 41 insertions, 6 deletions

diff --git a/src/view/com/util/numeric/format.ts b/src/view/com/util/numeric/format.ts
index cca9fc7e7..0c3d24957 100644
--- a/src/view/com/util/numeric/format.ts
+++ b/src/view/com/util/numeric/format.ts
@@ -1,12 +1,47 @@
-import type {I18n} from '@lingui/core'
+import {I18n} from '@lingui/core'
+
+const truncateRounding = (num: number, factors: Array<number>): number => {
+  for (let i = factors.length - 1; i >= 0; i--) {
+    let factor = factors[i]
+    if (num >= 10 ** factor) {
+      if (factor === 10) {
+        // CA and ES abruptly jump from "9999,9 M" to "10 mil M"
+        factor--
+      }
+      const precision = 1
+      const divisor = 10 ** (factor - precision)
+      return Math.floor(num / divisor) * divisor
+    }
+  }
+  return num
+}
+
+const koFactors = [3, 4, 8, 12]
+const hiFactors = [3, 5, 7, 9, 11, 13]
+const esCaFactors = [3, 6, 10, 12]
+const itDeFactors = [6, 9, 12]
+const jaZhFactors = [4, 8, 12]
+const restFactors = [3, 6, 9, 12]
 
 export const formatCount = (i18n: I18n, num: number) => {
-  return i18n.number(num, {
+  const locale = i18n.locale
+  let truncatedNum: number
+  if (locale === 'hi') {
+    truncatedNum = truncateRounding(num, hiFactors)
+  } else if (locale === 'ko') {
+    truncatedNum = truncateRounding(num, koFactors)
+  } else if (locale === 'es' || locale === 'ca') {
+    truncatedNum = truncateRounding(num, esCaFactors)
+  } else if (locale === 'ja' || locale === 'zh-CN' || locale === 'zh-TW') {
+    truncatedNum = truncateRounding(num, jaZhFactors)
+  } else if (locale === 'it' || locale === 'de') {
+    truncatedNum = truncateRounding(num, itDeFactors)
+  } else {
+    truncatedNum = truncateRounding(num, restFactors)
+  }
+  return i18n.number(truncatedNum, {
     notation: 'compact',
     maximumFractionDigits: 1,
-    // `1,953` shouldn't be rounded up to 2k, it should be truncated.
-    // @ts-expect-error: `roundingMode` doesn't seem to be in the typings yet
-    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat/NumberFormat#roundingmode
-    roundingMode: 'trunc',
+    // Ideally we'd use roundingMode: 'trunc' but it isn't supported on RN.
   })
 }