aboutsummaryrefslogtreecommitdiff
path: root/ext/js/dom/dom-text-scanner.js
blob: 7bed94a92e8aac8419af5b163be42392b81b1c62 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
/*
 * Copyright (C) 2020-2022  Yomichan Authors
 *
 * 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/>.
 */

/**
 * A class used to scan text in a document.
 */
class DOMTextScanner {
    /**
     * Creates a new instance of a DOMTextScanner.
     * @param {Node} node The DOM Node to start at.
     * @param {number} offset The character offset in to start at when node is a text node.
     *   Use 0 for non-text nodes.
     * @param {boolean} forcePreserveWhitespace Whether or not whitespace should be forced to be preserved,
     *   regardless of CSS styling.
     * @param {boolean} generateLayoutContent Whether or not newlines should be added based on CSS styling.
     */
    constructor(node, offset, forcePreserveWhitespace=false, generateLayoutContent=true) {
        const ruby = DOMTextScanner.getParentRubyElement(node);
        const resetOffset = (ruby !== null);
        if (resetOffset) { node = ruby; }

        this._node = node;
        this._offset = offset;
        this._content = '';
        this._remainder = 0;
        this._resetOffset = resetOffset;
        this._newlines = 0;
        this._lineHasWhitespace = false;
        this._lineHasContent = false;
        this._forcePreserveWhitespace = forcePreserveWhitespace;
        this._generateLayoutContent = generateLayoutContent;
    }

    /**
     * Gets the current node being scanned.
     * @type {Node}
     */
    get node() {
        return this._node;
    }

    /**
     * Gets the current offset corresponding to the node being scanned.
     * This value is only applicable for text nodes.
     * @type {number}
     */
    get offset() {
        return this._offset;
    }

    /**
     * Gets the remaining number of characters that weren't scanned in the last seek() call.
     * This value is usually 0 unless the end of the document was reached.
     * @type {number}
     */
    get remainder() {
        return this._remainder;
    }

    /**
     * Gets the accumulated content string resulting from calls to seek().
     * @type {string}
     */
    get content() {
        return this._content;
    }

    /**
     * Seeks a given length in the document and accumulates the text content.
     * @param {number} length A positive or negative integer corresponding to how many characters
     *   should be added to content. Content is only added to the accumulation string,
     *   never removed, so mixing seek calls with differently signed length values
     *   may give unexpected results.
     * @returns {DOMTextScanner} this
     */
    seek(length) {
        const forward = (length >= 0);
        this._remainder = (forward ? length : -length);
        if (length === 0) { return this; }

        const TEXT_NODE = Node.TEXT_NODE;
        const ELEMENT_NODE = Node.ELEMENT_NODE;

        const generateLayoutContent = this._generateLayoutContent;
        let node = this._node;
        let lastNode = node;
        let resetOffset = this._resetOffset;
        let newlines = 0;
        while (node !== null) {
            let enterable = false;
            const nodeType = node.nodeType;

            if (nodeType === TEXT_NODE) {
                lastNode = node;
                if (!(
                    forward ?
                    this._seekTextNodeForward(node, resetOffset) :
                    this._seekTextNodeBackward(node, resetOffset)
                )) {
                    // Length reached
                    break;
                }
            } else if (nodeType === ELEMENT_NODE) {
                lastNode = node;
                this._offset = 0;
                ({enterable, newlines} = DOMTextScanner.getElementSeekInfo(node));
                if (newlines > this._newlines && generateLayoutContent) {
                    this._newlines = newlines;
                }
            }

            const exitedNodes = [];
            node = DOMTextScanner.getNextNode(node, forward, enterable, exitedNodes);

            for (const exitedNode of exitedNodes) {
                if (exitedNode.nodeType !== ELEMENT_NODE) { continue; }
                ({newlines} = DOMTextScanner.getElementSeekInfo(exitedNode));
                if (newlines > this._newlines && generateLayoutContent) {
                    this._newlines = newlines;
                }
            }

            resetOffset = true;
        }

        this._node = lastNode;
        this._resetOffset = resetOffset;

        return this;
    }

    // Private

    /**
     * Reads a code point in a string in the forward direction.
     * @param {string} text The text to read the code point from.
     * @param {number} position The index of the first character to read.
     * @returns {string} The code point from the string.
     */
    _readCodePointForward(text, position) {
        let char = text[position];
        const charCode = char.charCodeAt(0);
        if (charCode >= 0xd800 && charCode < 0xdc00 && ++position < text.length) {
            const char2 = text[position];
            const charCode2 = char2.charCodeAt(0);
            if (charCode2 >= 0xdc00 && charCode2 < 0xe000) {
                char += char2;
            }
        }
        return char;
    }

    /**
     * Reads a code point in a string in the backward direction.
     * @param {string} text The text to read the code point from.
     * @param {number} position The index of the first character to read.
     * @returns {string} The code point from the string.
     */
    _readCodePointBackward(text, position) {
        let char = text[position];
        const charCode = char.charCodeAt(0);
        if (charCode >= 0xdc00 && charCode < 0xe000 && position > 0) {
            const char2 = text[position - 1];
            const charCode2 = char2.charCodeAt(0);
            if (charCode2 >= 0xd800 && charCode2 < 0xdc00) {
                char = char2 + char;
            }
        }
        return char;
    }

    /**
     * Seeks forward in a text node.
     * @param {Text} textNode The text node to use.
     * @param {boolean} resetOffset Whether or not the text offset should be reset.
     * @returns {boolean} `true` if scanning should continue, or `false` if the scan length has been reached.
     */
    _seekTextNodeForward(textNode, resetOffset) {
        const nodeValue = textNode.nodeValue;
        const nodeValueLength = nodeValue.length;
        const {preserveNewlines, preserveWhitespace} = this._getWhitespaceSettings(textNode);

        let lineHasWhitespace = this._lineHasWhitespace;
        let lineHasContent = this._lineHasContent;
        let content = this._content;
        let offset = resetOffset ? 0 : this._offset;
        let remainder = this._remainder;
        let newlines = this._newlines;

        while (offset < nodeValueLength) {
            const char = this._readCodePointForward(nodeValue, offset);
            offset += char.length;
            const charAttributes = DOMTextScanner.getCharacterAttributes(char, preserveNewlines, preserveWhitespace);

            if (charAttributes === 0) {
                // Character should be ignored
                continue;
            } else if (charAttributes === 1) {
                // Character is collapsible whitespace
                lineHasWhitespace = true;
            } else {
                // Character should be added to the content
                if (newlines > 0) {
                    if (content.length > 0) {
                        const useNewlineCount = Math.min(remainder, newlines);
                        content += '\n'.repeat(useNewlineCount);
                        remainder -= useNewlineCount;
                        newlines -= useNewlineCount;
                    } else {
                        newlines = 0;
                    }
                    lineHasContent = false;
                    lineHasWhitespace = false;
                    if (remainder <= 0) {
                        offset -= char.length; // Revert character offset
                        break;
                    }
                }

                lineHasContent = (charAttributes === 2); // 3 = character is a newline

                if (lineHasWhitespace) {
                    if (lineHasContent) {
                        content += ' ';
                        lineHasWhitespace = false;
                        if (--remainder <= 0) {
                            offset -= char.length; // Revert character offset
                            break;
                        }
                    } else {
                        lineHasWhitespace = false;
                    }
                }

                content += char;

                if (--remainder <= 0) { break; }
            }
        }

        this._lineHasWhitespace = lineHasWhitespace;
        this._lineHasContent = lineHasContent;
        this._content = content;
        this._offset = offset;
        this._remainder = remainder;
        this._newlines = newlines;

        return (remainder > 0);
    }

    /**
     * Seeks backward in a text node.
     * This function is nearly the same as _seekTextNodeForward, with the following differences:
     * - Iteration condition is reversed to check if offset is greater than 0.
     * - offset is reset to nodeValueLength instead of 0.
     * - offset is decremented instead of incremented.
     * - offset is decremented before getting the character.
     * - offset is reverted by incrementing instead of decrementing.
     * - content string is prepended instead of appended.
     * @param {Text} textNode The text node to use.
     * @param {boolean} resetOffset Whether or not the text offset should be reset.
     * @returns {boolean} `true` if scanning should continue, or `false` if the scan length has been reached.
     */
    _seekTextNodeBackward(textNode, resetOffset) {
        const nodeValue = textNode.nodeValue;
        const nodeValueLength = nodeValue.length;
        const {preserveNewlines, preserveWhitespace} = this._getWhitespaceSettings(textNode);

        let lineHasWhitespace = this._lineHasWhitespace;
        let lineHasContent = this._lineHasContent;
        let content = this._content;
        let offset = resetOffset ? nodeValueLength : this._offset;
        let remainder = this._remainder;
        let newlines = this._newlines;

        while (offset > 0) {
            const char = this._readCodePointBackward(nodeValue, offset - 1);
            offset -= char.length;
            const charAttributes = DOMTextScanner.getCharacterAttributes(char, preserveNewlines, preserveWhitespace);

            if (charAttributes === 0) {
                // Character should be ignored
                continue;
            } else if (charAttributes === 1) {
                // Character is collapsible whitespace
                lineHasWhitespace = true;
            } else {
                // Character should be added to the content
                if (newlines > 0) {
                    if (content.length > 0) {
                        const useNewlineCount = Math.min(remainder, newlines);
                        content = '\n'.repeat(useNewlineCount) + content;
                        remainder -= useNewlineCount;
                        newlines -= useNewlineCount;
                    } else {
                        newlines = 0;
                    }
                    lineHasContent = false;
                    lineHasWhitespace = false;
                    if (remainder <= 0) {
                        offset += char.length; // Revert character offset
                        break;
                    }
                }

                lineHasContent = (charAttributes === 2); // 3 = character is a newline

                if (lineHasWhitespace) {
                    if (lineHasContent) {
                        content = ' ' + content;
                        lineHasWhitespace = false;
                        if (--remainder <= 0) {
                            offset += char.length; // Revert character offset
                            break;
                        }
                    } else {
                        lineHasWhitespace = false;
                    }
                }

                content = char + content;

                if (--remainder <= 0) { break; }
            }
        }

        this._lineHasWhitespace = lineHasWhitespace;
        this._lineHasContent = lineHasContent;
        this._content = content;
        this._offset = offset;
        this._remainder = remainder;
        this._newlines = newlines;

        return (remainder > 0);
    }

    /**
     * Gets information about how whitespace characters are treated.
     * @param {Text} textNode The text node to check.
     * @returns {{preserveNewlines: boolean, preserveWhitespace: boolean}} Information about the whitespace.
     *   The value of `preserveNewlines` indicates whether or not newline characters are treated as line breaks.
     *   The value of `preserveWhitespace` indicates whether or not sequences of whitespace characters are collapsed.
     */
    _getWhitespaceSettings(textNode) {
        if (this._forcePreserveWhitespace) {
            return {preserveNewlines: true, preserveWhitespace: true};
        }
        const element = DOMTextScanner.getParentElement(textNode);
        if (element !== null) {
            const style = window.getComputedStyle(element);
            switch (style.whiteSpace) {
                case 'pre':
                case 'pre-wrap':
                case 'break-spaces':
                    return {preserveNewlines: true, preserveWhitespace: true};
                case 'pre-line':
                    return {preserveNewlines: true, preserveWhitespace: false};
            }
        }
        return {preserveNewlines: false, preserveWhitespace: false};
    }

    // Static helpers

    /**
     * Gets the next node in the document for a specified scanning direction.
     * @param {Node} node The current DOM Node.
     * @param {boolean} forward Whether to scan forward in the document or backward.
     * @param {boolean} visitChildren Whether the children of the current node should be visited.
     * @param {Node[]} exitedNodes An array which stores nodes which were exited.
     * @returns {?Node} The next node in the document, or `null` if there is no next node.
     */
    static getNextNode(node, forward, visitChildren, exitedNodes) {
        let next = visitChildren ? (forward ? node.firstChild : node.lastChild) : null;
        if (next === null) {
            while (true) {
                exitedNodes.push(node);

                next = (forward ? node.nextSibling : node.previousSibling);
                if (next !== null) { break; }

                next = node.parentNode;
                if (next === null) { break; }

                node = next;
            }
        }
        return next;
    }

    /**
     * Gets the parent element of a given Node.
     * @param {Node} node The node to check.
     * @returns {?Node} The parent element if one exists, otherwise `null`.
     */
    static getParentElement(node) {
        while (node !== null && node.nodeType !== Node.ELEMENT_NODE) {
            node = node.parentNode;
        }
        return node;
    }

    /**
     * Gets the parent <ruby> element of a given node, if one exists. For efficiency purposes,
     * this only checks the immediate parent elements and does not check all ancestors, so
     * there are cases where the node may be in a ruby element but it is not returned.
     * @param {Node} node The node to check.
     * @returns {?HTMLElement} A <ruby> node if the input node is contained in one, otherwise `null`.
     */
    static getParentRubyElement(node) {
        node = DOMTextScanner.getParentElement(node);
        if (node !== null && node.nodeName.toUpperCase() === 'RT') {
            node = node.parentNode;
            if (node !== null && node.nodeName.toUpperCase() === 'RUBY') {
                return node;
            }
        }
        return null;
    }

    /**
     * Gets seek information about an element.
     * @param {Element} element The element to check.
     * @returns {{enterable: boolean, newlines: number}} The seek information.
     *   The `enterable` value indicates whether the content of this node should be entered.
     *   The `newlines` value corresponds to the number of newline characters that should be added.
     *     1 newline corresponds to a simple new line in the layout.
     *     2 newlines corresponds to a significant visual distinction since the previous content.
     */
    static getElementSeekInfo(element) {
        let enterable = true;
        switch (element.nodeName.toUpperCase()) {
            case 'HEAD':
            case 'RT':
            case 'SCRIPT':
            case 'STYLE':
                return {enterable: false, newlines: 0};
            case 'BR':
                return {enterable: false, newlines: 1};
            case 'TEXTAREA':
            case 'INPUT':
            case 'BUTTON':
                enterable = false;
                break;
        }

        const style = window.getComputedStyle(element);
        const display = style.display;

        const visible = (display !== 'none' && DOMTextScanner.isStyleVisible(style));
        let newlines = 0;

        if (!visible) {
            enterable = false;
        } else {
            switch (style.position) {
                case 'absolute':
                case 'fixed':
                case 'sticky':
                    newlines = 2;
                    break;
            }
            if (newlines === 0 && DOMTextScanner.doesCSSDisplayChangeLayout(display)) {
                newlines = 1;
            }
        }

        return {enterable, newlines};
    }

    /**
     * Gets attributes for the specified character.
     * @param {string} character A string containing a single character.
     * @param {boolean} preserveNewlines Whether or not newlines should be preserved.
     * @param {boolean} preserveWhitespace Whether or not whitespace should be preserved.
     * @returns {number} An integer representing the attributes of the character.
     *   0: Character should be ignored.
     *   1: Character is collapsible whitespace.
     *   2: Character should be added to the content.
     *   3: Character should be added to the content and is a newline.
     */
    static getCharacterAttributes(character, preserveNewlines, preserveWhitespace) {
        switch (character.charCodeAt(0)) {
            case 0x09: // Tab ('\t')
            case 0x0c: // Form feed ('\f')
            case 0x0d: // Carriage return ('\r')
            case 0x20: // Space (' ')
                return preserveWhitespace ? 2 : 1;
            case 0x0a: // Line feed ('\n')
                return preserveNewlines ? 3 : 1;
            case 0x200b: // Zero-width space
            case 0x200c: // Zero-width non-joiner
                return 0;
            default: // Other
                return 2;
        }
    }

    /**
     * Checks whether a given style is visible or not.
     * This function does not check `style.display === 'none'`.
     * @param {CSSStyleDeclaration} style An object implementing the CSSStyleDeclaration interface.
     * @returns {boolean} `true` if the style should result in an element being visible, otherwise `false`.
     */
    static isStyleVisible(style) {
        return !(
            style.visibility === 'hidden' ||
            parseFloat(style.opacity) <= 0 ||
            parseFloat(style.fontSize) <= 0 ||
            (
                !DOMTextScanner.isStyleSelectable(style) &&
                (
                    DOMTextScanner.isCSSColorTransparent(style.color) ||
                    DOMTextScanner.isCSSColorTransparent(style.webkitTextFillColor)
                )
            )
        );
    }

    /**
     * Checks whether a given style is selectable or not.
     * @param {CSSStyleDeclaration} style An object implementing the CSSStyleDeclaration interface.
     * @returns {boolean} `true` if the style is selectable, otherwise `false`.
     */
    static isStyleSelectable(style) {
        return !(
            style.userSelect === 'none' ||
            style.webkitUserSelect === 'none' ||
            style.MozUserSelect === 'none' ||
            style.msUserSelect === 'none'
        );
    }

    /**
     * Checks whether a CSS color is transparent or not.
     * @param {string} cssColor A CSS color string, expected to be encoded in rgb(a) form.
     * @returns {false} `true` if the color is transparent, otherwise `false`.
     */
    static isCSSColorTransparent(cssColor) {
        return (
            typeof cssColor === 'string' &&
            cssColor.startsWith('rgba(') &&
            /,\s*0.?0*\)$/.test(cssColor)
        );
    }

    /**
     * Checks whether a CSS display value will cause a layout change for text.
     * @param {string} cssDisplay A CSS string corresponding to the value of the display property.
     * @returns {boolean} `true` if the layout is changed by this value, otherwise `false`.
     */
    static doesCSSDisplayChangeLayout(cssDisplay) {
        let pos = cssDisplay.indexOf(' ');
        if (pos >= 0) {
            // Truncate to <display-outside> part
            cssDisplay = cssDisplay.substring(0, pos);
        }

        pos = cssDisplay.indexOf('-');
        if (pos >= 0) {
            // Truncate to first part of kebab-case value
            cssDisplay = cssDisplay.substring(0, pos);
        }

        switch (cssDisplay) {
            case 'block':
            case 'flex':
            case 'grid':
            case 'list': // list-item
            case 'table': // table, table-*
                return true;
            case 'ruby': // ruby-*
                return (pos >= 0);
            default:
                return false;
        }
    }
}