Katakana to hiragana conversion options (#1965)

* Refactor convertKatakanaToHiragana

* Add keepProlongedSoundMarks option

* Test keepProlongedSoundMarks option

* Refactor

* Add keepProlongedSoundMarks option to hiragana handlebars helper

* Update documentation

4 files changed, 37 insertions, 18 deletions

diff --git a/docs/templates.md b/docs/templates.md
index 638c79a6..778b8e2d 100644
--- a/docs/templates.md
+++ b/docs/templates.md
@@ -786,11 +786,14 @@ Converts katakana text to hiragana.
 <details>
   <summary>Syntax:</summary>
 
-  <code>{{#hiragana <i>value</i>}}{{/hiragana}}</code><br>
-  <code>{{#hiragana}}<i>value</i>{{/hiragana}}</code><br>
+  <code>{{#hiragana <i>value</i> <i>[keepProlongedSoundMarks=true|false]</i>}}{{/hiragana}}</code><br>
+  <code>{{#hiragana <i>[keepProlongedSoundMarks=true|false]</i>}}<i>value</i>{{/hiragana}}</code><br>
 
   * _`value`_ <br>
     The text to convert.
+  * _`keepProlongedSoundMarks`_ _(optional)_ <br>
+    Whether or not the `ー` character should be kept or converted to a vowel character.
+    Defaults to `false` if not specified.
 </details>
 <details>
   <summary>Example:</summary>
@@ -798,12 +801,16 @@ Converts katakana text to hiragana.
   ```handlebars
   {{#hiragana "よみちゃん ヨミちゃん ヨミチャン"}}{{/hiragana}}
   {{#hiragana}}よみちゃん ヨミちゃん ヨミチャン{{/hiragana}}
+  {{#hiragana}}ローマ字{{/hiragana}}
+  {{#hiragana keepProlongedSoundMarks=true}}ローマ字{{/hiragana}}
   ```
 
   Output:
   ```html
   よみちゃん よみちゃん よみちゃん
   よみちゃん よみちゃん よみちゃん
+  ろうま字
+  ろーま字
   ```
 </details>
 
diff --git a/ext/js/language/sandbox/japanese-util.js b/ext/js/language/sandbox/japanese-util.js
index 9b58d255..a7542e79 100644
--- a/ext/js/language/sandbox/japanese-util.js
+++ b/ext/js/language/sandbox/japanese-util.js
@@ -297,20 +297,27 @@ const JapaneseUtil = (() => {
             return this._wanakana !== null;
         }
 
-        convertKatakanaToHiragana(text) {
+        convertKatakanaToHiragana(text, keepProlongedSoundMarks=false) {
             let result = '';
             const offset = (HIRAGANA_CONVERSION_RANGE[0] - KATAKANA_CONVERSION_RANGE[0]);
             for (let char of text) {
                 const codePoint = char.codePointAt(0);
-                if (codePoint === KATAKANA_SMALL_KA_CODE_POINT || codePoint === KATAKANA_SMALL_KE_CODE_POINT) {
-                    // No change
-                } else if (codePoint === KANA_PROLONGED_SOUND_MARK_CODE_POINT) {
-                    if (result.length > 0) {
-                        const char2 = getProlongedHiragana(result[result.length - 1]);
-                        if (char2 !== null) { char = char2; }
-                    }
-                } else if (isCodePointInRange(codePoint, KATAKANA_CONVERSION_RANGE)) {
-                    char = String.fromCodePoint(codePoint + offset);
+                switch (codePoint) {
+                    case KATAKANA_SMALL_KA_CODE_POINT:
+                    case KATAKANA_SMALL_KE_CODE_POINT:
+                        // No change
+                        break;
+                    case KANA_PROLONGED_SOUND_MARK_CODE_POINT:
+                        if (!keepProlongedSoundMarks && result.length > 0) {
+                            const char2 = getProlongedHiragana(result[result.length - 1]);
+                            if (char2 !== null) { char = char2; }
+                        }
+                        break;
+                    default:
+                        if (isCodePointInRange(codePoint, KATAKANA_CONVERSION_RANGE)) {
+                            char = String.fromCodePoint(codePoint + offset);
+                        }
+                        break;
                 }
                 result += char;
             }
diff --git a/ext/js/templates/sandbox/anki-template-renderer.js b/ext/js/templates/sandbox/anki-template-renderer.js
index b721fadc..ae89aade 100644
--- a/ext/js/templates/sandbox/anki-template-renderer.js
+++ b/ext/js/templates/sandbox/anki-template-renderer.js
@@ -607,13 +607,16 @@ class AnkiTemplateRenderer {
 
     _hiragana(context, ...args) {
         const ii = args.length - 1;
-        const value = (ii > 0 ? args[0] : args[ii].fn(context));
-        return this._japaneseUtil.convertKatakanaToHiragana(value);
+        const options = args[ii];
+        const {keepProlongedSoundMarks} = options.hash;
+        const value = (ii > 0 ? args[0] : options.fn(context));
+        return this._japaneseUtil.convertKatakanaToHiragana(value, keepProlongedSoundMarks === true);
     }
 
     _katakana(context, ...args) {
         const ii = args.length - 1;
-        const value = (ii > 0 ? args[0] : args[ii].fn(context));
+        const options = args[ii];
+        const value = (ii > 0 ? args[0] : options.fn(context));
         return this._japaneseUtil.convertHiraganaToKatakana(value);
     }
 }
diff --git a/test/test-japanese-util.js b/test/test-japanese-util.js
index f3b53844..cf1ee87e 100644
--- a/test/test-japanese-util.js
+++ b/test/test-japanese-util.js
@@ -130,11 +130,13 @@ function testConvertKatakanaToHiragana() {
         ['ヒラガナひらがな', 'ひらがなひらがな'],
         ['chikaraちからチカラ力', 'chikaraちからちから力'],
         ['katakana', 'katakana'],
-        ['hiragana', 'hiragana']
+        ['hiragana', 'hiragana'],
+        ['カーナー', 'かあなあ'],
+        ['カーナー', 'かーなー', true]
     ];
 
-    for (const [string, expected] of data) {
-        assert.strictEqual(jp.convertKatakanaToHiragana(string), expected);
+    for (const [string, expected, keepProlongedSoundMarks=false] of data) {
+        assert.strictEqual(jp.convertKatakanaToHiragana(string, keepProlongedSoundMarks), expected);
     }
 }