Improve kana segmentation (#1446)

* Improve edge case furigana distribution for mixed hiragana/katakana

* Update/add tests

2 files changed, 38 insertions, 6 deletions

diff --git a/ext/js/language/japanese-util.js b/ext/js/language/japanese-util.js
index c2ce9627..e47cdf55 100644
--- a/ext/js/language/japanese-util.js
+++ b/ext/js/language/japanese-util.js
@@ -521,8 +521,11 @@ const JapaneseUtil = (() => {
                         groupsStart + 1
                     );
                     if (segments !== null) {
-                        const furigana = reading.startsWith(text) ? '' : reading.substring(0, textLength);
-                        segments.unshift(this._createFuriganaSegment(text, furigana));
+                        if (reading.startsWith(text)) {
+                            segments.unshift(this._createFuriganaSegment(text, ''));
+                        } else {
+                            segments.unshift(...this._getFuriganaKanaSegments(text, reading));
+                        }
                         return segments;
                     }
                 }
@@ -554,6 +557,22 @@ const JapaneseUtil = (() => {
             }
         }
 
+        _getFuriganaKanaSegments(text, reading) {
+            const textLength = text.length;
+            const newSegments = [];
+            let start = 0;
+            let state = (reading[0] === text[0]);
+            for (let i = 1; i < textLength; ++i) {
+                const newState = (reading[i] === text[i]);
+                if (state === newState) { continue; }
+                newSegments.push(this._createFuriganaSegment(text.substring(start, i), state ? '' : reading.substring(start, i)));
+                state = newState;
+                start = i;
+            }
+            newSegments.push(this._createFuriganaSegment(text.substring(start, textLength), state ? '' : reading.substring(start, textLength)));
+            return newSegments;
+        }
+
         _getWanakana() {
             const wanakana = this._wanakana;
             if (wanakana === null) { throw new Error('Functions which use WanaKana are not supported in this context'); }
diff --git a/test/test-japanese.js b/test/test-japanese.js
index 590d3157..1a4fc494 100644
--- a/test/test-japanese.js
+++ b/test/test-japanese.js
@@ -402,7 +402,8 @@ function testDistributeFurigana() {
         [
             ['スズメの涙', 'すずめのなみだ'],
             [
-                {text: 'スズメの', furigana: 'すずめの'},
+                {text: 'スズメ', furigana: 'すずめ'},
+                {text: 'の', furigana: ''},
                 {text: '涙', furigana: 'なみだ'}
             ]
         ],
@@ -464,14 +465,16 @@ function testDistributeFurigana() {
         [
             ['くノ一', 'くのいち'],
             [
-                {text: 'くノ', furigana: 'くの'},
+                {text: 'く', furigana: ''},
+                {text: 'ノ', furigana: 'の'},
                 {text: '一', furigana: 'いち'}
             ]
         ],
         [
             ['くノ一', 'くのいち'],
             [
-                {text: 'くノ', furigana: 'くの'},
+                {text: 'く', furigana: ''},
+                {text: 'ノ', furigana: 'の'},
                 {text: '一', furigana: 'いち'}
             ]
         ],
@@ -691,9 +694,19 @@ function testDistributeFurigana() {
         [
             ['ページ違反', 'ぺーじいはん'],
             [
-                {text: 'ページ', furigana: 'ぺーじ'},
+                {text: 'ペ', furigana: 'ぺ'},
+                {text: 'ー', furigana: ''},
+                {text: 'ジ', furigana: 'じ'},
                 {text: '違反', furigana: 'いはん'}
             ]
+        ],
+        // Mismatched kana
+        [
+            ['サボる', 'サボル'],
+            [
+                {text: 'サボ', furigana: ''},
+                {text: 'る', furigana: 'ル'}
+            ]
         ]
     ];