Merge pull request #413 from toasted-nutbread/japanese-utility

Convert Japanese utilities to a module-like style

12 files changed, 480 insertions, 430 deletions

diff --git a/ext/bg/background.html b/ext/bg/background.html
index 44abe8fd..f7cf6e55 100644
--- a/ext/bg/background.html
+++ b/ext/bg/background.html
@@ -20,6 +20,7 @@
 
         <script src="/mixed/js/core.js"></script>
         <script src="/mixed/js/dom.js"></script>
+        <script src="/mixed/js/japanese.js"></script>
 
         <script src="/bg/js/anki.js"></script>
         <script src="/bg/js/anki-note-builder.js"></script>
diff --git a/ext/bg/js/audio-uri-builder.js b/ext/bg/js/audio-uri-builder.js
index 499c3441..158006bb 100644
--- a/ext/bg/js/audio-uri-builder.js
+++ b/ext/bg/js/audio-uri-builder.js
@@ -17,7 +17,7 @@
  */
 
 /* global
- * jpIsStringEntirelyKana
+ * jp
  */
 
 class AudioUriBuilder {
@@ -66,7 +66,7 @@ class AudioUriBuilder {
         let kana = definition.reading;
         let kanji = definition.expression;
 
-        if (!kana && jpIsStringEntirelyKana(kanji)) {
+        if (!kana && jp.isStringEntirelyKana(kanji)) {
             kana = kanji;
             kanji = null;
         }
diff --git a/ext/bg/js/backend.js b/ext/bg/js/backend.js
index 978c5a4a..b217e64d 100644
--- a/ext/bg/js/backend.js
+++ b/ext/bg/js/backend.js
@@ -32,9 +32,7 @@
  * dictEnabledSet
  * dictTermsSort
  * handlebarsRenderDynamic
- * jpConvertReading
- * jpDistributeFuriganaInflected
- * jpKatakanaToHiragana
+ * jp
  * optionsLoad
  * optionsSave
  * profileConditionsDescriptor
@@ -402,13 +400,13 @@ class Backend {
                 dictTermsSort(definitions);
                 const {expression, reading} = definitions[0];
                 const source = text.substring(0, sourceLength);
-                for (const {text: text2, furigana} of jpDistributeFuriganaInflected(expression, reading, source)) {
-                    const reading2 = jpConvertReading(text2, furigana, options.parsing.readingMode);
+                for (const {text: text2, furigana} of jp.distributeFuriganaInflected(expression, reading, source)) {
+                    const reading2 = jp.convertReading(text2, furigana, options.parsing.readingMode);
                     term.push({text: text2, reading: reading2});
                 }
                 text = text.substring(source.length);
             } else {
-                const reading = jpConvertReading(text[0], null, options.parsing.readingMode);
+                const reading = jp.convertReading(text[0], null, options.parsing.readingMode);
                 term.push({text: text[0], reading});
                 text = text.substring(1);
             }
@@ -427,16 +425,16 @@ class Backend {
                 for (const {expression, reading, source} of parsedLine) {
                     const term = [];
                     if (expression !== null && reading !== null) {
-                        for (const {text: text2, furigana} of jpDistributeFuriganaInflected(
+                        for (const {text: text2, furigana} of jp.distributeFuriganaInflected(
                             expression,
-                            jpKatakanaToHiragana(reading),
+                            jp.convertKatakanaToHiragana(reading),
                             source
                         )) {
-                            const reading2 = jpConvertReading(text2, furigana, options.parsing.readingMode);
+                            const reading2 = jp.convertReading(text2, furigana, options.parsing.readingMode);
                             term.push({text: text2, reading: reading2});
                         }
                     } else {
-                        const reading2 = jpConvertReading(source, null, options.parsing.readingMode);
+                        const reading2 = jp.convertReading(source, null, options.parsing.readingMode);
                         term.push({text: source, reading: reading2});
                     }
                     result.push(term);
diff --git a/ext/bg/js/clipboard-monitor.js b/ext/bg/js/clipboard-monitor.js
index 9a881f57..c67525fc 100644
--- a/ext/bg/js/clipboard-monitor.js
+++ b/ext/bg/js/clipboard-monitor.js
@@ -17,7 +17,7 @@
  */
 
 /* global
- * jpIsStringPartiallyJapanese
+ * jp
  */
 
 class ClipboardMonitor extends EventDispatcher {
@@ -54,7 +54,7 @@ class ClipboardMonitor extends EventDispatcher {
                 text !== this._previousText
             ) {
                 this._previousText = text;
-                if (jpIsStringPartiallyJapanese(text)) {
+                if (jp.isStringPartiallyJapanese(text)) {
                     this.trigger('change', {text});
                 }
             }
diff --git a/ext/bg/js/handlebars.js b/ext/bg/js/handlebars.js
index e3ce6bd0..5fda5baa 100644
--- a/ext/bg/js/handlebars.js
+++ b/ext/bg/js/handlebars.js
@@ -18,8 +18,7 @@
 
 /* global
  * Handlebars
- * jpDistributeFurigana
- * jpIsCodePointKanji
+ * jp
  */
 
 function handlebarsEscape(text) {
@@ -33,7 +32,7 @@ function handlebarsDumpObject(options) {
 
 function handlebarsFurigana(options) {
     const definition = options.fn(this);
-    const segs = jpDistributeFurigana(definition.expression, definition.reading);
+    const segs = jp.distributeFurigana(definition.expression, definition.reading);
 
     let result = '';
     for (const seg of segs) {
@@ -49,7 +48,7 @@ function handlebarsFurigana(options) {
 
 function handlebarsFuriganaPlain(options) {
     const definition = options.fn(this);
-    const segs = jpDistributeFurigana(definition.expression, definition.reading);
+    const segs = jp.distributeFurigana(definition.expression, definition.reading);
 
     let result = '';
     for (const seg of segs) {
@@ -66,7 +65,7 @@ function handlebarsFuriganaPlain(options) {
 function handlebarsKanjiLinks(options) {
     let result = '';
     for (const c of options.fn(this)) {
-        if (jpIsCodePointKanji(c.codePointAt(0))) {
+        if (jp.isCodePointKanji(c.codePointAt(0))) {
             result += `<a href="#" class="kanji-link">${c}</a>`;
         } else {
             result += c;
diff --git a/ext/bg/js/japanese.js b/ext/bg/js/japanese.js
index 3b37754d..c5873cf1 100644
--- a/ext/bg/js/japanese.js
+++ b/ext/bg/js/japanese.js
@@ -17,442 +17,380 @@
  */
 
 /* global
+ * jp
  * wanakana
  */
 
-const JP_HALFWIDTH_KATAKANA_MAPPING = new Map([
-    ['ｦ', 'ヲヺ-'],
-    ['ｧ', 'ァ--'],
-    ['ｨ', 'ィ--'],
-    ['ｩ', 'ゥ--'],
-    ['ｪ', 'ェ--'],
-    ['ｫ', 'ォ--'],
-    ['ｬ', 'ャ--'],
-    ['ｭ', 'ュ--'],
-    ['ｮ', 'ョ--'],
-    ['ｯ', 'ッ--'],
-    ['ｰ', 'ー--'],
-    ['ｱ', 'ア--'],
-    ['ｲ', 'イ--'],
-    ['ｳ', 'ウヴ-'],
-    ['ｴ', 'エ--'],
-    ['ｵ', 'オ--'],
-    ['ｶ', 'カガ-'],
-    ['ｷ', 'キギ-'],
-    ['ｸ', 'クグ-'],
-    ['ｹ', 'ケゲ-'],
-    ['ｺ', 'コゴ-'],
-    ['ｻ', 'サザ-'],
-    ['ｼ', 'シジ-'],
-    ['ｽ', 'スズ-'],
-    ['ｾ', 'セゼ-'],
-    ['ｿ', 'ソゾ-'],
-    ['ﾀ', 'タダ-'],
-    ['ﾁ', 'チヂ-'],
-    ['ﾂ', 'ツヅ-'],
-    ['ﾃ', 'テデ-'],
-    ['ﾄ', 'トド-'],
-    ['ﾅ', 'ナ--'],
-    ['ﾆ', 'ニ--'],
-    ['ﾇ', 'ヌ--'],
-    ['ﾈ', 'ネ--'],
-    ['ﾉ', 'ノ--'],
-    ['ﾊ', 'ハバパ'],
-    ['ﾋ', 'ヒビピ'],
-    ['ﾌ', 'フブプ'],
-    ['ﾍ', 'ヘベペ'],
-    ['ﾎ', 'ホボポ'],
-    ['ﾏ', 'マ--'],
-    ['ﾐ', 'ミ--'],
-    ['ﾑ', 'ム--'],
-    ['ﾒ', 'メ--'],
-    ['ﾓ', 'モ--'],
-    ['ﾔ', 'ヤ--'],
-    ['ﾕ', 'ユ--'],
-    ['ﾖ', 'ヨ--'],
-    ['ﾗ', 'ラ--'],
-    ['ﾘ', 'リ--'],
-    ['ﾙ', 'ル--'],
-    ['ﾚ', 'レ--'],
-    ['ﾛ', 'ロ--'],
-    ['ﾜ', 'ワ--'],
-    ['ﾝ', 'ン--']
-]);
-
-const JP_HIRAGANA_RANGE = [0x3040, 0x309f];
-const JP_KATAKANA_RANGE = [0x30a0, 0x30ff];
-const JP_KANA_RANGES = [JP_HIRAGANA_RANGE, JP_KATAKANA_RANGE];
-
-const JP_CJK_COMMON_RANGE = [0x4e00, 0x9fff];
-const JP_CJK_RARE_RANGE = [0x3400, 0x4dbf];
-const JP_CJK_RANGES = [JP_CJK_COMMON_RANGE, JP_CJK_RARE_RANGE];
-
-const JP_ITERATION_MARK_CHAR_CODE = 0x3005;
-
-// Japanese character ranges, roughly ordered in order of expected frequency
-const JP_JAPANESE_RANGES = [
-    JP_HIRAGANA_RANGE,
-    JP_KATAKANA_RANGE,
-
-    JP_CJK_COMMON_RANGE,
-    JP_CJK_RARE_RANGE,
-
-    [0xff66, 0xff9f], // Halfwidth katakana
-
-    [0x30fb, 0x30fc], // Katakana punctuation
-    [0xff61, 0xff65], // Kana punctuation
-    [0x3000, 0x303f], // CJK punctuation
-
-    [0xff10, 0xff19], // Fullwidth numbers
-    [0xff21, 0xff3a], // Fullwidth upper case Latin letters
-    [0xff41, 0xff5a], // Fullwidth lower case Latin letters
-
-    [0xff01, 0xff0f], // Fullwidth punctuation 1
-    [0xff1a, 0xff1f], // Fullwidth punctuation 2
-    [0xff3b, 0xff3f], // Fullwidth punctuation 3
-    [0xff5b, 0xff60], // Fullwidth punctuation 4
-    [0xffe0, 0xffee]  // Currency markers
-];
-
-
-// Helper functions
-
-function _jpIsCodePointInRanges(codePoint, ranges) {
-    for (const [min, max] of ranges) {
-        if (codePoint >= min && codePoint <= max) {
-            return true;
+(() => {
+    const HALFWIDTH_KATAKANA_MAPPING = new Map([
+        ['ｦ', 'ヲヺ-'],
+        ['ｧ', 'ァ--'],
+        ['ｨ', 'ィ--'],
+        ['ｩ', 'ゥ--'],
+        ['ｪ', 'ェ--'],
+        ['ｫ', 'ォ--'],
+        ['ｬ', 'ャ--'],
+        ['ｭ', 'ュ--'],
+        ['ｮ', 'ョ--'],
+        ['ｯ', 'ッ--'],
+        ['ｰ', 'ー--'],
+        ['ｱ', 'ア--'],
+        ['ｲ', 'イ--'],
+        ['ｳ', 'ウヴ-'],
+        ['ｴ', 'エ--'],
+        ['ｵ', 'オ--'],
+        ['ｶ', 'カガ-'],
+        ['ｷ', 'キギ-'],
+        ['ｸ', 'クグ-'],
+        ['ｹ', 'ケゲ-'],
+        ['ｺ', 'コゴ-'],
+        ['ｻ', 'サザ-'],
+        ['ｼ', 'シジ-'],
+        ['ｽ', 'スズ-'],
+        ['ｾ', 'セゼ-'],
+        ['ｿ', 'ソゾ-'],
+        ['ﾀ', 'タダ-'],
+        ['ﾁ', 'チヂ-'],
+        ['ﾂ', 'ツヅ-'],
+        ['ﾃ', 'テデ-'],
+        ['ﾄ', 'トド-'],
+        ['ﾅ', 'ナ--'],
+        ['ﾆ', 'ニ--'],
+        ['ﾇ', 'ヌ--'],
+        ['ﾈ', 'ネ--'],
+        ['ﾉ', 'ノ--'],
+        ['ﾊ', 'ハバパ'],
+        ['ﾋ', 'ヒビピ'],
+        ['ﾌ', 'フブプ'],
+        ['ﾍ', 'ヘベペ'],
+        ['ﾎ', 'ホボポ'],
+        ['ﾏ', 'マ--'],
+        ['ﾐ', 'ミ--'],
+        ['ﾑ', 'ム--'],
+        ['ﾒ', 'メ--'],
+        ['ﾓ', 'モ--'],
+        ['ﾔ', 'ヤ--'],
+        ['ﾕ', 'ユ--'],
+        ['ﾖ', 'ヨ--'],
+        ['ﾗ', 'ラ--'],
+        ['ﾘ', 'リ--'],
+        ['ﾙ', 'ル--'],
+        ['ﾚ', 'レ--'],
+        ['ﾛ', 'ロ--'],
+        ['ﾜ', 'ワ--'],
+        ['ﾝ', 'ン--']
+    ]);
+
+    const ITERATION_MARK_CODE_POINT = 0x3005;
+
+
+    // Existing functions
+
+    const isCodePointKanji = jp.isCodePointKanji;
+    const isStringEntirelyKana = jp.isStringEntirelyKana;
+
+
+    // Conversion functions
+
+    function convertKatakanaToHiragana(text) {
+        let result = '';
+        for (const c of text) {
+            if (wanakana.isKatakana(c)) {
+                result += wanakana.toHiragana(c);
+            } else {
+                result += c;
+            }
         }
-    }
-    return false;
-}
-
-
-// Character code testing functions
 
-function jpIsCodePointKanji(codePoint) {
-    return _jpIsCodePointInRanges(codePoint, JP_CJK_RANGES);
-}
-
-function jpIsCodePointKana(codePoint) {
-    return _jpIsCodePointInRanges(codePoint, JP_KANA_RANGES);
-}
+        return result;
+    }
 
-function jpIsCodePointJapanese(codePoint) {
-    return _jpIsCodePointInRanges(codePoint, JP_JAPANESE_RANGES);
-}
+    function convertHiraganaToKatakana(text) {
+        let result = '';
+        for (const c of text) {
+            if (wanakana.isHiragana(c)) {
+                result += wanakana.toKatakana(c);
+            } else {
+                result += c;
+            }
+        }
 
+        return result;
+    }
 
-// String testing functions
+    function convertToRomaji(text) {
+        return wanakana.toRomaji(text);
+    }
 
-function jpIsStringEntirelyKana(str) {
-    if (str.length === 0) { return false; }
-    for (const c of str) {
-        if (!jpIsCodePointKana(c.codePointAt(0))) {
-            return false;
+    function convertReading(expressionFragment, readingFragment, readingMode) {
+        switch (readingMode) {
+            case 'hiragana':
+                return convertKatakanaToHiragana(readingFragment || '');
+            case 'katakana':
+                return convertHiraganaToKatakana(readingFragment || '');
+            case 'romaji':
+                if (readingFragment) {
+                    return convertToRomaji(readingFragment);
+                } else {
+                    if (isStringEntirelyKana(expressionFragment)) {
+                        return convertToRomaji(expressionFragment);
+                    }
+                }
+                return readingFragment;
+            case 'none':
+                return null;
+            default:
+                return readingFragment;
         }
     }
-    return true;
-}
-
-function jpIsStringPartiallyJapanese(str) {
-    if (str.length === 0) { return false; }
-    for (const c of str) {
-        if (jpIsCodePointJapanese(c.codePointAt(0))) {
-            return true;
+
+    function convertNumericToFullWidth(text) {
+        let result = '';
+        for (const char of text) {
+            let c = char.codePointAt(0);
+            if (c >= 0x30 && c <= 0x39) { // ['0', '9']
+                c += 0xff10 - 0x30; // 0xff10 = '0' full width
+                result += String.fromCodePoint(c);
+            } else {
+                result += char;
+            }
         }
+        return result;
     }
-    return false;
-}
 
+    function convertHalfWidthKanaToFullWidth(text, sourceMapping) {
+        let result = '';
+        const hasSourceMapping = Array.isArray(sourceMapping);
+
+        // This function is safe to use charCodeAt instead of codePointAt, since all
+        // the relevant characters are represented with a single UTF-16 character code.
+        for (let i = 0, ii = text.length; i < ii; ++i) {
+            const c = text[i];
+            const mapping = HALFWIDTH_KATAKANA_MAPPING.get(c);
+            if (typeof mapping !== 'string') {
+                result += c;
+                continue;
+            }
 
-// Conversion functions
-
-function jpKatakanaToHiragana(text) {
-    let result = '';
-    for (const c of text) {
-        if (wanakana.isKatakana(c)) {
-            result += wanakana.toHiragana(c);
-        } else {
-            result += c;
-        }
-    }
+            let index = 0;
+            switch (text.charCodeAt(i + 1)) {
+                case 0xff9e: // dakuten
+                    index = 1;
+                    break;
+                case 0xff9f: // handakuten
+                    index = 2;
+                    break;
+            }
 
-    return result;
-}
+            let c2 = mapping[index];
+            if (index > 0) {
+                if (c2 === '-') { // invalid
+                    index = 0;
+                    c2 = mapping[0];
+                } else {
+                    ++i;
+                }
+            }
 
-function jpHiraganaToKatakana(text) {
-    let result = '';
-    for (const c of text) {
-        if (wanakana.isHiragana(c)) {
-            result += wanakana.toKatakana(c);
-        } else {
-            result += c;
+            if (hasSourceMapping && index > 0) {
+                index = result.length;
+                const v = sourceMapping.splice(index + 1, 1)[0];
+                sourceMapping[index] += v;
+            }
+            result += c2;
         }
+
+        return result;
     }
 
-    return result;
-}
-
-function jpToRomaji(text) {
-    return wanakana.toRomaji(text);
-}
-
-function jpConvertReading(expressionFragment, readingFragment, readingMode) {
-    switch (readingMode) {
-        case 'hiragana':
-            return jpKatakanaToHiragana(readingFragment || '');
-        case 'katakana':
-            return jpHiraganaToKatakana(readingFragment || '');
-        case 'romaji':
-            if (readingFragment) {
-                return jpToRomaji(readingFragment);
+    function convertAlphabeticToKana(text, sourceMapping) {
+        let part = '';
+        let result = '';
+
+        for (const char of text) {
+            // Note: 0x61 is the character code for 'a'
+            let c = char.codePointAt(0);
+            if (c >= 0x41 && c <= 0x5a) { // ['A', 'Z']
+                c += (0x61 - 0x41);
+            } else if (c >= 0x61 && c <= 0x7a) { // ['a', 'z']
+                // NOP; c += (0x61 - 0x61);
+            } else if (c >= 0xff21 && c <= 0xff3a) { // ['A', 'Z'] fullwidth
+                c += (0x61 - 0xff21);
+            } else if (c >= 0xff41 && c <= 0xff5a) { // ['a', 'z'] fullwidth
+                c += (0x61 - 0xff41);
+            } else if (c === 0x2d || c === 0xff0d) { // '-' or fullwidth dash
+                c = 0x2d; // '-'
             } else {
-                if (jpIsStringEntirelyKana(expressionFragment)) {
-                    return jpToRomaji(expressionFragment);
+                if (part.length > 0) {
+                    result += convertAlphabeticPartToKana(part, sourceMapping, result.length);
+                    part = '';
                 }
+                result += char;
+                continue;
             }
-            return readingFragment;
-        case 'none':
-            return null;
-        default:
-            return readingFragment;
-    }
-}
-
-function jpDistributeFurigana(expression, reading) {
-    const fallback = [{furigana: reading, text: expression}];
-    if (!reading) {
-        return fallback;
-    }
+            part += String.fromCodePoint(c);
+        }
 
-    let isAmbiguous = false;
-    const segmentize = (reading2, groups) => {
-        if (groups.length === 0 || isAmbiguous) {
-            return [];
+        if (part.length > 0) {
+            result += convertAlphabeticPartToKana(part, sourceMapping, result.length);
         }
+        return result;
+    }
 
-        const group = groups[0];
-        if (group.mode === 'kana') {
-            if (jpKatakanaToHiragana(reading2).startsWith(jpKatakanaToHiragana(group.text))) {
-                const readingLeft = reading2.substring(group.text.length);
-                const segs = segmentize(readingLeft, groups.splice(1));
-                if (segs) {
-                    return [{text: group.text}].concat(segs);
-                }
-            }
-        } else {
-            let foundSegments = null;
-            for (let i = reading2.length; i >= group.text.length; --i) {
-                const readingUsed = reading2.substring(0, i);
-                const readingLeft = reading2.substring(i);
-                const segs = segmentize(readingLeft, groups.slice(1));
-                if (segs) {
-                    if (foundSegments !== null) {
-                        // more than one way to segmentize the tail, mark as ambiguous
-                        isAmbiguous = true;
-                        return null;
+    function convertAlphabeticPartToKana(text, sourceMapping, sourceMappingStart) {
+        const result = wanakana.toHiragana(text);
+
+        // Generate source mapping
+        if (Array.isArray(sourceMapping)) {
+            if (typeof sourceMappingStart !== 'number') { sourceMappingStart = 0; }
+            let i = 0;
+            let resultPos = 0;
+            const ii = text.length;
+            while (i < ii) {
+                // Find smallest matching substring
+                let iNext = i + 1;
+                let resultPosNext = result.length;
+                while (iNext < ii) {
+                    const t = wanakana.toHiragana(text.substring(0, iNext));
+                    if (t === result.substring(0, t.length)) {
+                        resultPosNext = t.length;
+                        break;
                     }
-                    foundSegments = [{text: group.text, furigana: readingUsed}].concat(segs);
+                    ++iNext;
                 }
-                // there is only one way to segmentize the last non-kana group
-                if (groups.length === 1) {
-                    break;
+
+                // Merge characters
+                const removals = iNext - i - 1;
+                if (removals > 0) {
+                    let sum = 0;
+                    const vs = sourceMapping.splice(sourceMappingStart + 1, removals);
+                    for (const v of vs) { sum += v; }
+                    sourceMapping[sourceMappingStart] += sum;
                 }
+                ++sourceMappingStart;
+
+                // Empty elements
+                const additions = resultPosNext - resultPos - 1;
+                for (let j = 0; j < additions; ++j) {
+                    sourceMapping.splice(sourceMappingStart, 0, 0);
+                    ++sourceMappingStart;
+                }
+
+                i = iNext;
+                resultPos = resultPosNext;
             }
-            return foundSegments;
-        }
-    };
-
-    const groups = [];
-    let modePrev = null;
-    for (const c of expression) {
-        const codePoint = c.codePointAt(0);
-        const modeCurr = jpIsCodePointKanji(codePoint) || codePoint === JP_ITERATION_MARK_CHAR_CODE ? 'kanji' : 'kana';
-        if (modeCurr === modePrev) {
-            groups[groups.length - 1].text += c;
-        } else {
-            groups.push({mode: modeCurr, text: c});
-            modePrev = modeCurr;
         }
-    }
 
-    const segments = segmentize(reading, groups);
-    if (segments && !isAmbiguous) {
-        return segments;
-    }
-    return fallback;
-}
-
-function jpDistributeFuriganaInflected(expression, reading, source) {
-    const output = [];
-
-    let stemLength = 0;
-    const shortest = Math.min(source.length, expression.length);
-    const sourceHiragana = jpKatakanaToHiragana(source);
-    const expressionHiragana = jpKatakanaToHiragana(expression);
-    while (stemLength < shortest && sourceHiragana[stemLength] === expressionHiragana[stemLength]) {
-        ++stemLength;
-    }
-    const offset = source.length - stemLength;
-
-    const stemExpression = source.substring(0, source.length - offset);
-    const stemReading = reading.substring(
-        0,
-        offset === 0 ? reading.length : reading.length - expression.length + stemLength
-    );
-    for (const segment of jpDistributeFurigana(stemExpression, stemReading)) {
-        output.push(segment);
+        return result;
     }
 
-    if (stemLength !== source.length) {
-        output.push({text: source.substring(stemLength)});
-    }
 
-    return output;
-}
-
-function jpConvertHalfWidthKanaToFullWidth(text, sourceMapping) {
-    let result = '';
-    const hasSourceMapping = Array.isArray(sourceMapping);
-
-    // This function is safe to use charCodeAt instead of codePointAt, since all
-    // the relevant characters are represented with a single UTF-16 character code.
-    for (let i = 0, ii = text.length; i < ii; ++i) {
-        const c = text[i];
-        const mapping = JP_HALFWIDTH_KATAKANA_MAPPING.get(c);
-        if (typeof mapping !== 'string') {
-            result += c;
-            continue;
-        }
+    // Furigana distribution
 
-        let index = 0;
-        switch (text.charCodeAt(i + 1)) {
-            case 0xff9e: // dakuten
-                index = 1;
-                break;
-            case 0xff9f: // handakuten
-                index = 2;
-                break;
+    function distributeFurigana(expression, reading) {
+        const fallback = [{furigana: reading, text: expression}];
+        if (!reading) {
+            return fallback;
         }
 
-        let c2 = mapping[index];
-        if (index > 0) {
-            if (c2 === '-') { // invalid
-                index = 0;
-                c2 = mapping[0];
-            } else {
-                ++i;
+        let isAmbiguous = false;
+        const segmentize = (reading2, groups) => {
+            if (groups.length === 0 || isAmbiguous) {
+                return [];
             }
-        }
 
-        if (hasSourceMapping && index > 0) {
-            index = result.length;
-            const v = sourceMapping.splice(index + 1, 1)[0];
-            sourceMapping[index] += v;
+            const group = groups[0];
+            if (group.mode === 'kana') {
+                if (convertKatakanaToHiragana(reading2).startsWith(convertKatakanaToHiragana(group.text))) {
+                    const readingLeft = reading2.substring(group.text.length);
+                    const segs = segmentize(readingLeft, groups.splice(1));
+                    if (segs) {
+                        return [{text: group.text}].concat(segs);
+                    }
+                }
+            } else {
+                let foundSegments = null;
+                for (let i = reading2.length; i >= group.text.length; --i) {
+                    const readingUsed = reading2.substring(0, i);
+                    const readingLeft = reading2.substring(i);
+                    const segs = segmentize(readingLeft, groups.slice(1));
+                    if (segs) {
+                        if (foundSegments !== null) {
+                            // more than one way to segmentize the tail, mark as ambiguous
+                            isAmbiguous = true;
+                            return null;
+                        }
+                        foundSegments = [{text: group.text, furigana: readingUsed}].concat(segs);
+                    }
+                    // there is only one way to segmentize the last non-kana group
+                    if (groups.length === 1) {
+                        break;
+                    }
+                }
+                return foundSegments;
+            }
+        };
+
+        const groups = [];
+        let modePrev = null;
+        for (const c of expression) {
+            const codePoint = c.codePointAt(0);
+            const modeCurr = isCodePointKanji(codePoint) || codePoint === ITERATION_MARK_CODE_POINT ? 'kanji' : 'kana';
+            if (modeCurr === modePrev) {
+                groups[groups.length - 1].text += c;
+            } else {
+                groups.push({mode: modeCurr, text: c});
+                modePrev = modeCurr;
+            }
         }
-        result += c2;
-    }
 
-    return result;
-}
-
-function jpConvertNumericTofullWidth(text) {
-    let result = '';
-    for (const char of text) {
-        let c = char.codePointAt(0);
-        if (c >= 0x30 && c <= 0x39) { // ['0', '9']
-            c += 0xff10 - 0x30; // 0xff10 = '0' full width
-            result += String.fromCodePoint(c);
-        } else {
-            result += char;
+        const segments = segmentize(reading, groups);
+        if (segments && !isAmbiguous) {
+            return segments;
         }
+        return fallback;
     }
-    return result;
-}
 
-function jpConvertAlphabeticToKana(text, sourceMapping) {
-    let part = '';
-    let result = '';
-    const ii = text.length;
+    function distributeFuriganaInflected(expression, reading, source) {
+        const output = [];
 
-    if (sourceMapping.length === ii) {
-        sourceMapping.length = ii;
-        sourceMapping.fill(1);
-    }
+        let stemLength = 0;
+        const shortest = Math.min(source.length, expression.length);
+        const sourceHiragana = convertKatakanaToHiragana(source);
+        const expressionHiragana = convertKatakanaToHiragana(expression);
+        while (stemLength < shortest && sourceHiragana[stemLength] === expressionHiragana[stemLength]) {
+            ++stemLength;
+        }
+        const offset = source.length - stemLength;
+
+        const stemExpression = source.substring(0, source.length - offset);
+        const stemReading = reading.substring(
+            0,
+            offset === 0 ? reading.length : reading.length - expression.length + stemLength
+        );
+        for (const segment of distributeFurigana(stemExpression, stemReading)) {
+            output.push(segment);
+        }
 
-    for (const char of text) {
-        // Note: 0x61 is the character code for 'a'
-        let c = char.codePointAt(0);
-        if (c >= 0x41 && c <= 0x5a) { // ['A', 'Z']
-            c += (0x61 - 0x41);
-        } else if (c >= 0x61 && c <= 0x7a) { // ['a', 'z']
-            // NOP; c += (0x61 - 0x61);
-        } else if (c >= 0xff21 && c <= 0xff3a) { // ['A', 'Z'] fullwidth
-            c += (0x61 - 0xff21);
-        } else if (c >= 0xff41 && c <= 0xff5a) { // ['a', 'z'] fullwidth
-            c += (0x61 - 0xff41);
-        } else if (c === 0x2d || c === 0xff0d) { // '-' or fullwidth dash
-            c = 0x2d; // '-'
-        } else {
-            if (part.length > 0) {
-                result += jpToHiragana(part, sourceMapping, result.length);
-                part = '';
-            }
-            result += char;
-            continue;
+        if (stemLength !== source.length) {
+            output.push({text: source.substring(stemLength)});
         }
-        part += String.fromCodePoint(c);
-    }
 
-    if (part.length > 0) {
-        result += jpToHiragana(part, sourceMapping, result.length);
+        return output;
     }
-    return result;
-}
-
-function jpToHiragana(text, sourceMapping, sourceMappingStart) {
-    const result = wanakana.toHiragana(text);
-
-    // Generate source mapping
-    if (Array.isArray(sourceMapping)) {
-        if (typeof sourceMappingStart !== 'number') { sourceMappingStart = 0; }
-        let i = 0;
-        let resultPos = 0;
-        const ii = text.length;
-        while (i < ii) {
-            // Find smallest matching substring
-            let iNext = i + 1;
-            let resultPosNext = result.length;
-            while (iNext < ii) {
-                const t = wanakana.toHiragana(text.substring(0, iNext));
-                if (t === result.substring(0, t.length)) {
-                    resultPosNext = t.length;
-                    break;
-                }
-                ++iNext;
-            }
 
-            // Merge characters
-            const removals = iNext - i - 1;
-            if (removals > 0) {
-                let sum = 0;
-                const vs = sourceMapping.splice(sourceMappingStart + 1, removals);
-                for (const v of vs) { sum += v; }
-                sourceMapping[sourceMappingStart] += sum;
-            }
-            ++sourceMappingStart;
-
-            // Empty elements
-            const additions = resultPosNext - resultPos - 1;
-            for (let j = 0; j < additions; ++j) {
-                sourceMapping.splice(sourceMappingStart, 0, 0);
-                ++sourceMappingStart;
-            }
-
-            i = iNext;
-            resultPos = resultPosNext;
-        }
-    }
 
-    return result;
-}
+    // Exports
+
+    Object.assign(jp, {
+        convertKatakanaToHiragana,
+        convertHiraganaToKatakana,
+        convertToRomaji,
+        convertReading,
+        convertNumericToFullWidth,
+        convertHalfWidthKanaToFullWidth,
+        convertAlphabeticToKana,
+        distributeFurigana,
+        distributeFuriganaInflected
+    });
+})();
diff --git a/ext/bg/js/translator.js b/ext/bg/js/translator.js
index 25da9bf0..6f43f7b0 100644
--- a/ext/bg/js/translator.js
+++ b/ext/bg/js/translator.js
@@ -29,13 +29,7 @@
  * dictTermsMergeBySequence
  * dictTermsSort
  * dictTermsUndupe
- * jpConvertAlphabeticToKana
- * jpConvertHalfWidthKanaToFullWidth
- * jpConvertNumericTofullWidth
- * jpDistributeFurigana
- * jpHiraganaToKatakana
- * jpIsCodePointJapanese
- * jpKatakanaToHiragana
+ * jp
  * requestJson
  */
 
@@ -275,7 +269,7 @@ class Translator {
                 const termTags = await this.expandTags(definition.termTags, definition.dictionary);
 
                 const {expression, reading} = definition;
-                const furiganaSegments = jpDistributeFurigana(expression, reading);
+                const furiganaSegments = jp.distributeFurigana(expression, reading);
 
                 definitions.push({
                     source: deinflection.source,
@@ -376,20 +370,20 @@ class Translator {
             let sourceMapping = null;
             if (halfWidth) {
                 if (sourceMapping === null) { sourceMapping = Translator.createTextSourceMapping(text2); }
-                text2 = jpConvertHalfWidthKanaToFullWidth(text2, sourceMapping);
+                text2 = jp.convertHalfWidthKanaToFullWidth(text2, sourceMapping);
             }
             if (numeric) {
-                text2 = jpConvertNumericTofullWidth(text2);
+                text2 = jp.convertNumericToFullWidth(text2);
             }
             if (alphabetic) {
                 if (sourceMapping === null) { sourceMapping = Translator.createTextSourceMapping(text2); }
-                text2 = jpConvertAlphabeticToKana(text2, sourceMapping);
+                text2 = jp.convertAlphabeticToKana(text2, sourceMapping);
             }
             if (katakana) {
-                text2 = jpHiraganaToKatakana(text2);
+                text2 = jp.convertHiraganaToKatakana(text2);
             }
             if (hiragana) {
-                text2 = jpKatakanaToHiragana(text2);
+                text2 = jp.convertKatakanaToHiragana(text2);
             }
 
             for (let i = text2.length; i > 0; --i) {
@@ -590,7 +584,7 @@ class Translator {
     }
 
     static createExpression(expression, reading, termTags=null, termFrequency=null) {
-        const furiganaSegments = jpDistributeFurigana(expression, reading);
+        const furiganaSegments = jp.distributeFurigana(expression, reading);
         return {
             expression,
             reading,
@@ -639,7 +633,7 @@ class Translator {
         if (!options.scanning.alphanumeric) {
             let newText = '';
             for (const c of text) {
-                if (!jpIsCodePointJapanese(c.codePointAt(0))) {
+                if (!jp.isCodePointJapanese(c.codePointAt(0))) {
                     break;
                 }
                 newText += c;
diff --git a/ext/bg/search.html b/ext/bg/search.html
index f4c1a737..eacc1893 100644
--- a/ext/bg/search.html
+++ b/ext/bg/search.html
@@ -74,6 +74,7 @@
         <script src="/mixed/js/core.js"></script>
         <script src="/mixed/js/dom.js"></script>
         <script src="/mixed/js/api.js"></script>
+        <script src="/mixed/js/japanese.js"></script>
 
         <script src="/bg/js/dictionary.js"></script>
         <script src="/bg/js/handlebars.js"></script>
diff --git a/ext/bg/settings.html b/ext/bg/settings.html
index 0db76d71..cfe20be4 100644
--- a/ext/bg/settings.html
+++ b/ext/bg/settings.html
@@ -1088,6 +1088,7 @@
         <script src="/mixed/js/core.js"></script>
         <script src="/mixed/js/dom.js"></script>
         <script src="/mixed/js/api.js"></script>
+        <script src="/mixed/js/japanese.js"></script>
 
         <script src="/bg/js/anki.js"></script>
         <script src="/bg/js/anki-note-builder.js"></script>
diff --git a/ext/fg/float.html b/ext/fg/float.html
index 7bbed565..3ccf68eb 100644
--- a/ext/fg/float.html
+++ b/ext/fg/float.html
@@ -43,6 +43,7 @@
         <script src="/mixed/js/core.js"></script>
         <script src="/mixed/js/dom.js"></script>
         <script src="/mixed/js/api.js"></script>
+        <script src="/mixed/js/japanese.js"></script>
 
         <script src="/fg/js/document.js"></script>
         <script src="/fg/js/source.js"></script>
diff --git a/ext/mixed/js/display-generator.js b/ext/mixed/js/display-generator.js
index 49afc44b..41f7315a 100644
--- a/ext/mixed/js/display-generator.js
+++ b/ext/mixed/js/display-generator.js
@@ -19,6 +19,7 @@
 /* global
  * TemplateHandler
  * apiGetDisplayTemplatesHtml
+ * jp
  */
 
 class DisplayGenerator {
@@ -283,7 +284,7 @@ class DisplayGenerator {
     _appendKanjiLinks(container, text) {
         let part = '';
         for (const c of text) {
-            if (DisplayGenerator._isCharacterKanji(c)) {
+            if (jp.isCodePointKanji(c.codePointAt(0))) {
                 if (part.length > 0) {
                     container.appendChild(document.createTextNode(part));
                     part = '';
@@ -300,14 +301,6 @@ class DisplayGenerator {
         }
     }
 
-    static _isCharacterKanji(c) {
-        const code = c.codePointAt(0);
-        return (
-            code >= 0x4e00 && code < 0x9fb0 ||
-            code >= 0x3400 && code < 0x4dc0
-        );
-    }
-
     static _appendMultiple(container, createItem, detailsArray, fallback=[]) {
         if (container === null) { return 0; }
 
diff --git a/ext/mixed/js/japanese.js b/ext/mixed/js/japanese.js
new file mode 100644
index 00000000..61a247b2
--- /dev/null
+++ b/ext/mixed/js/japanese.js
@@ -0,0 +1,124 @@
+/*
+ * Copyright (C) 2020  Alex Yatskov <alex@foosoft.net>
+ * Author: Alex Yatskov <alex@foosoft.net>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+const jp = (() => {
+    const HIRAGANA_RANGE = [0x3040, 0x309f];
+    const KATAKANA_RANGE = [0x30a0, 0x30ff];
+    const KANA_RANGES = [HIRAGANA_RANGE, KATAKANA_RANGE];
+
+    const CJK_UNIFIED_IDEOGRAPHS_RANGE = [0x4e00, 0x9fff];
+    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_A_RANGE = [0x3400, 0x4dbf];
+    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_B_RANGE = [0x20000, 0x2a6df];
+    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_C_RANGE = [0x2a700, 0x2b73f];
+    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_D_RANGE = [0x2b740, 0x2b81f];
+    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_E_RANGE = [0x2b820, 0x2ceaf];
+    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_F_RANGE = [0x2ceb0, 0x2ebef];
+    const CJK_COMPATIBILITY_IDEOGRAPHS_SUPPLEMENT_RANGE = [0x2f800, 0x2fa1f];
+    const CJK_UNIFIED_IDEOGRAPHS_RANGES = [
+        CJK_UNIFIED_IDEOGRAPHS_RANGE,
+        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_A_RANGE,
+        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_B_RANGE,
+        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_C_RANGE,
+        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_D_RANGE,
+        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_E_RANGE,
+        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_F_RANGE,
+        CJK_COMPATIBILITY_IDEOGRAPHS_SUPPLEMENT_RANGE
+    ];
+
+    // Japanese character ranges, roughly ordered in order of expected frequency
+    const JAPANESE_RANGES = [
+        HIRAGANA_RANGE,
+        KATAKANA_RANGE,
+
+        ...CJK_UNIFIED_IDEOGRAPHS_RANGES,
+
+        [0xff66, 0xff9f], // Halfwidth katakana
+
+        [0x30fb, 0x30fc], // Katakana punctuation
+        [0xff61, 0xff65], // Kana punctuation
+        [0x3000, 0x303f], // CJK punctuation
+
+        [0xff10, 0xff19], // Fullwidth numbers
+        [0xff21, 0xff3a], // Fullwidth upper case Latin letters
+        [0xff41, 0xff5a], // Fullwidth lower case Latin letters
+
+        [0xff01, 0xff0f], // Fullwidth punctuation 1
+        [0xff1a, 0xff1f], // Fullwidth punctuation 2
+        [0xff3b, 0xff3f], // Fullwidth punctuation 3
+        [0xff5b, 0xff60], // Fullwidth punctuation 4
+        [0xffe0, 0xffee]  // Currency markers
+    ];
+
+
+    // Character code testing functions
+
+    function isCodePointKanji(codePoint) {
+        return isCodePointInRanges(codePoint, CJK_UNIFIED_IDEOGRAPHS_RANGES);
+    }
+
+    function isCodePointKana(codePoint) {
+        return isCodePointInRanges(codePoint, KANA_RANGES);
+    }
+
+    function isCodePointJapanese(codePoint) {
+        return isCodePointInRanges(codePoint, JAPANESE_RANGES);
+    }
+
+    function isCodePointInRanges(codePoint, ranges) {
+        for (const [min, max] of ranges) {
+            if (codePoint >= min && codePoint <= max) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+
+    // String testing functions
+
+    function isStringEntirelyKana(str) {
+        if (str.length === 0) { return false; }
+        for (const c of str) {
+            if (!isCodePointKana(c.codePointAt(0))) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    function isStringPartiallyJapanese(str) {
+        if (str.length === 0) { return false; }
+        for (const c of str) {
+            if (isCodePointJapanese(c.codePointAt(0))) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+
+    // Exports
+
+    return {
+        isCodePointKanji,
+        isCodePointKana,
+        isCodePointJapanese,
+        isStringEntirelyKana,
+        isStringPartiallyJapanese
+    };
+})();