From bbab90bfcce86b100b2576a73db9faec0a53b79b Mon Sep 17 00:00:00 2001
From: Alexey <a.raiondesu@gmail.com>
Date: Sun, 28 Oct 2018 18:52:34 +0300
Subject: [PATCH] :zap: improvement(pluralization): Extendable pluralization by
 @Raiondesu

---
 gitbook/en/api.md           | 14 +++++++
 gitbook/en/pluralization.md | 83 +++++++++++++++++++++++++++++++++++++
 src/index.js                | 32 +++++++++++++-
 src/util.js                 | 26 ------------
 test/unit/issues.test.js    | 51 +++++++++++++++++++++++
 types/index.d.ts            |  7 ++++
 6 files changed, 185 insertions(+), 28 deletions(-)

diff --git a/gitbook/en/api.md b/gitbook/en/api.md
index 6e6d7aa44..262a2d3c5 100644
--- a/gitbook/en/api.md
+++ b/gitbook/en/api.md
@@ -38,6 +38,20 @@
 
   Localize the locale message of `key` with pluralization. Localize in preferentially component locale messages than global locale messages. If not specified component locale messages, localize with global locale messages. If you specified `locale`, localize the locale messages of `locale`. If you will specify string value to `values`, localize the locale messages of value. If you will specify Array or Object value to `values`, you must specify with `values` of [$t](#t).
 
+#### getChoiceIndex
+
+- **Arguments:**
+  - `{number} choice`
+  - `{number} choicesLength`
+
+- **Return:** `finalChoice {number}`
+
+  Get pluralization index for current pluralizing number and a given amount of choices. Can be overriden through prototype mutation:
+  ```js
+    VueI18n.prototype.getChoiceIndex = /* custom implementation */
+  ```
+
+
 #### $te
 
 - **Arguments:**
diff --git a/gitbook/en/pluralization.md b/gitbook/en/pluralization.md
index 4020bc308..a37ae60e6 100644
--- a/gitbook/en/pluralization.md
+++ b/gitbook/en/pluralization.md
@@ -36,3 +36,86 @@ This will output the following HTML:
 <p>one apple</p>
 <p>10 apples</p>
 ```
+
+---
+
+## Custom pluralization
+
+Such pluralization, however, does not apply to all languages (Slavic languages, for example, have different pluralization rules).
+
+In order to implement these rules you can override the `VueI18n.prototype.getChoiceIndex` function.
+
+Very simplified example using rules for Slavic langauges (Russian, Ukrainian, etc.):
+```js
+/**
+ * @param choice {number} a choice index given by the input to $tc: `$tc('path.to.rule', choiceIndex)`
+ * @param choiceLength {number} an overall amount of available choices
+ * @returns a final choice index to select plural word by
+**/
+VueI18n.prototype.getChoiceIndex = function (choice, choicesLength) {
+  // this === VueI18n instance, so the locale property also exists here
+  if (this.locale !== 'ru') {
+    // proceed to the default implementation
+  }
+
+  if (choice === 0) {
+    return 0;
+  }
+
+  const teen = choice > 10 && choice < 20;
+  const endsWithOne = choice % 10 === 1;
+
+  if (!teen && endsWithOne) {
+    return 1;
+  }
+
+  if (!teen && choice % 10 >= 2 && choice % 10 <= 4) {
+    return 2;
+  }
+
+  return (choicesLength < 4) ? 2 : 3;
+}
+```
+
+This would effectively give this:
+
+
+```javascript
+const messages = {
+  ru: {
+    car: '0 машин | 1 машина | {n} машины | {n} машин',
+    banana: 'нет бананов | 1 банан | {n} банана | {n} бананов'
+  }
+}
+```
+Where the format is `0 things | 1 thing | few things | multiple things`.
+
+Your template still needs to use `$tc()`, not `$t()`:
+
+```html
+<p>{{ $tc('car', 1) }}</p>
+<p>{{ $tc('car', 2) }}</p>
+<p>{{ $tc('car', 4) }}</p>
+<p>{{ $tc('car', 12) }}</p>
+<p>{{ $tc('car', 21) }}</p>
+
+<p>{{ $tc('car', 0) }}</p>
+<p>{{ $tc('car', 4) }}</p>
+<p>{{ $tc('car', 11) }}</p>
+<p>{{ $tc('car', 31) }}</p>
+```
+
+Which results in:
+
+```html
+<p>1 машина</p>
+<p>2 машины</p>
+<p>4 машины</p>
+<p>12 машин</p>
+<p>21 машина</p>
+
+<p>нет бананов</p>
+<p>4 банана</p>
+<p>11 бананов</p>
+<p>31 банан</p>
+```
diff --git a/src/index.js b/src/index.js
index 1e99ef5a5..607b3f011 100644
--- a/src/index.js
+++ b/src/index.js
@@ -5,7 +5,6 @@ import {
   warn,
   isNull,
   parseArgs,
-  fetchChoice,
   isPlainObject,
   isObject,
   looseClone,
@@ -407,7 +406,36 @@ export default class VueI18n {
     const parsedArgs = parseArgs(...values)
     parsedArgs.params = Object.assign(predefined, parsedArgs.params)
     values = parsedArgs.locale === null ? [parsedArgs.params] : [parsedArgs.locale, parsedArgs.params]
-    return fetchChoice(this._t(key, _locale, messages, host, ...values), choice)
+    return this.fetchChoice(this._t(key, _locale, messages, host, ...values), choice)
+  }
+
+  fetchChoice (message: string, choice: number): ?string {
+    /* istanbul ignore if */
+    if (!message && typeof message !== 'string') { return null }
+    const choices: Array<string> = message.split('|')
+
+    choice = this.getChoiceIndex(choice, choices.length)
+    if (!choices[choice]) { return message }
+    return choices[choice].trim()
+  }
+
+  /**
+   * @param choice {number} a choice index given by the input to $tc: `$tc('path.to.rule', choiceIndex)`
+   * @param choiceLength {number} an overall amount of available choices
+   * @returns a final choice index
+  */
+  getChoiceIndex (choice: number, choicesLength: number): number {
+    choice = Math.abs(choice)
+
+    if (choicesLength === 2) {
+      return choice
+        ? choice > 1
+          ? 1
+          : 0
+        : 1
+    }
+
+    return choice ? Math.min(choice, 2) : 0
   }
 
   tc (key: Path, choice?: number, ...values: any): TranslateResult {
diff --git a/src/util.js b/src/util.js
index b661472a6..ae1c17e2d 100644
--- a/src/util.js
+++ b/src/util.js
@@ -50,32 +50,6 @@ export function parseArgs (...args: Array<mixed>): Object {
   return { locale, params }
 }
 
-function getOldChoiceIndexFixed (choice: number): number {
-  return choice
-    ? choice > 1
-      ? 1
-      : 0
-    : 1
-}
-
-function getChoiceIndex (choice: number, choicesLength: number): number {
-  choice = Math.abs(choice)
-
-  if (choicesLength === 2) { return getOldChoiceIndexFixed(choice) }
-
-  return choice ? Math.min(choice, 2) : 0
-}
-
-export function fetchChoice (message: string, choice: number): ?string {
-  /* istanbul ignore if */
-  if (!message && typeof message !== 'string') { return null }
-  const choices: Array<string> = message.split('|')
-
-  choice = getChoiceIndex(choice, choices.length)
-  if (!choices[choice]) { return message }
-  return choices[choice].trim()
-}
-
 export function looseClone (obj: Object): Object {
   return JSON.parse(JSON.stringify(obj))
 }
diff --git a/test/unit/issues.test.js b/test/unit/issues.test.js
index a3f3b3b9a..04ef020e4 100644
--- a/test/unit/issues.test.js
+++ b/test/unit/issues.test.js
@@ -1,5 +1,6 @@
 import messages from './fixture/index'
 import { parse } from '../../src/format'
+import VueI18n from '../../src'
 const compiler = require('vue-template-compiler')
 
 describe('issues', () => {
@@ -382,4 +383,54 @@ describe('issues', () => {
       )
     })
   })
+
+  describe('#78', () => {
+    it('should allow custom pluralization', () => {
+      const defaultImpl = VueI18n.prototype.getChoiceIndex
+      VueI18n.prototype.getChoiceIndex = function (choice, choicesLength) {
+        if (this.locale !== 'ru') {
+          return defaultImpl.apply(this, arguments)
+        }
+
+        if (choice === 0) {
+          return 0
+        }
+
+        const teen = choice > 10 && choice < 20
+        const endsWithOne = choice % 10 === 1
+
+        if (choicesLength < 4) {
+          return (!teen && endsWithOne) ? 1 : 2
+        }
+
+        if (!teen && endsWithOne) {
+          return 1
+        }
+
+        if (!teen && choice % 10 >= 2 && choice % 10 <= 4) {
+          return 2
+        }
+
+        return (choicesLength < 4) ? 2 : 3
+      }
+
+
+      i18n = new VueI18n({
+        locale: 'en',
+        messages: {
+          ru: {
+            car: '0 машин | 1 машина | {n} машины | {n} машин'
+          }
+        }
+      })
+      vm = new Vue({ i18n })
+
+      assert(vm.$tc('car', 0), '0 машин')
+      assert(vm.$tc('car', 1), '1 машина')
+      assert(vm.$tc('car', 2), '2 машины')
+      assert(vm.$tc('car', 4), '4 машины')
+      assert(vm.$tc('car', 12), '12 машин')
+      assert(vm.$tc('car', 21), '21 машина')
+    })
+  })
 })
diff --git a/types/index.d.ts b/types/index.d.ts
index 21f8b20c5..2a0219c3d 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -140,6 +140,13 @@ declare class VueI18n {
   setNumberFormat(locale: VueI18n.Locale, format: VueI18n.NumberFormat): void;
   mergeNumberFormat(locale: VueI18n.Locale, format: VueI18n.NumberFormat): void;
 
+  /**
+   * @param choice {number} a choice index given by the input to $tc: `$tc('path.to.rule', choiceIndex)`
+   * @param choiceLength {number} an overall amount of available choices
+   * @returns a final choice index
+  */
+  getChoiceIndex: (choice: number, choicesLength: number) => number;
+
   static install: PluginFunction<never>;
   static version: string;
   static availabilities: VueI18n.IntlAvailability;