Skrift-Konfigurator-Neu/Docker Backend/src/lib/svg-font-engine.js

const fs = require('fs');
const path = require('path');
const config = require('../config');

// Cache je Fontdatei
const FONT_CACHE = {};

// Attribut aus einem Tag lesen (mit Wortgrenze, um z.B. 'd' vs 'id' zu unterscheiden)
function getAttr(tag, name) {
  const re = new RegExp(`\\b${name}="([^"]*)"`);
  const m = tag.match(re);
  return m ? m[1] : null;
}

// SVG-Font parsen und Metriken plus Glyphen extrahieren
function parseSvgFont(fontFileName) {
  if (FONT_CACHE[fontFileName]) return FONT_CACHE[fontFileName];

  const fontPath = path.join(config.paths.fonts, fontFileName);
  const svg = fs.readFileSync(fontPath, 'utf8');

  const fontFaceMatch = svg.match(/<font-face[\s\S]*?>/);
  if (!fontFaceMatch) {
    throw new Error(`Kein <font-face> in ${fontFileName} gefunden`);
  }

  const fontFaceTag = fontFaceMatch[0];
  const unitsPerEm = parseFloat(getAttr(fontFaceTag, 'units-per-em') || '1000');
  const ascent = parseFloat(getAttr(fontFaceTag, 'ascent') || '0');
  const descent = parseFloat(getAttr(fontFaceTag, 'descent') || '0');

  const glyphRegex = /<glyph[\s\S]*?\/>/g;
  const glyphs = {};
  let m;

  while ((m = glyphRegex.exec(svg)) !== null) {
    const tag = m[0];
    const unicode = getAttr(tag, 'unicode');
    const d = getAttr(tag, 'd');
    const adv = parseFloat(getAttr(tag, 'horiz-adv-x') || '0');

    if (!unicode || !d) continue;

    glyphs[unicode] = {
      d,
      adv,
    };
  }

  const fontData = {
    unitsPerEm,
    ascent,
    descent,
    glyphs,
  };

  FONT_CACHE[fontFileName] = fontData;
  return fontData;
}

/**
 * Breite einer Textzeile in Pixeln messen.
 */
function measureTextWidthPx({ text, fontFileName, fontSizePx }) {
  const { unitsPerEm, glyphs } = parseSvgFont(fontFileName);
  const scale = fontSizePx / unitsPerEm;

  let x = 0;

  for (const ch of String(text || '')) {
    const glyph = glyphs[ch];

    if (!glyph) {
      // Fallback für Leerzeichen / unbekannte Zeichen
      const spacePx = fontSizePx * 0.4;
      x += spacePx;
      continue;
    }

    const advPx = (glyph.adv || unitsPerEm * 0.5) * scale;
    x += advPx;
  }

  return x;
}

/**
 * Text nach verfügbarer Breite umbrechen.
 * Garantiert: keine Zeile wird breiter als maxWidthPx.
 */
function wrapTextToLinesByWidth({
  text,
  maxWidthPx,
  fontFileName,
  fontSizePx,
}) {
  const paragraphs = String(text || '').split(/\r?\n/);
  const allLines = [];

  const measure = (t) =>
    measureTextWidthPx({ text: t, fontFileName, fontSizePx });

  for (const para of paragraphs) {
    const words = para.split(/\s+/).filter(Boolean);
    if (words.length === 0) {
      allLines.push('');
      continue;
    }

    let currentLine = '';

    for (const word of words) {
      // Wort alleine zu breit → Zeichenweise brechen
      if (measure(word) > maxWidthPx) {
        if (currentLine) {
          allLines.push(currentLine);
          currentLine = '';
        }

        let buf = '';
        for (const ch of word) {
          const candidate = buf + ch;
          if (measure(candidate) > maxWidthPx && buf) {
            allLines.push(buf);
            buf = ch;
          } else {
            buf = candidate;
          }
        }
        if (buf) currentLine = buf;
        continue;
      }

      if (!currentLine) {
        currentLine = word;
        continue;
      }

      const candidate = `${currentLine} ${word}`;
      if (measure(candidate) <= maxWidthPx) {
        currentLine = candidate;
      } else {
        allLines.push(currentLine);
        currentLine = word;
      }
    }

    if (currentLine) {
      allLines.push(currentLine);
    }
  }

  return allLines;
}

/**
 * Textzeilen in Pfade mit Transform-Matrix umwandeln.
 */
function layoutTextToPaths({
  lines,
  fontFileName,
  fontSizePx,
  startX,
  startY,
  lineHeightPx,
}) {
  const { unitsPerEm, glyphs } = parseSvgFont(fontFileName);

  const scale = fontSizePx / unitsPerEm;

  const resultPaths = [];
  let baselineY = startY;

  for (const line of lines) {
    let x = startX;

    for (let i = 0; i < line.length; i++) {
      const ch = line[i];
      const glyph = glyphs[ch];

      if (!glyph) {
        // Leerzeichen mit festem Abstand
        const spacePx = fontSizePx * 0.4;
        x += spacePx;
        continue;
      }

      const d = glyph.d;
      const advPx = (glyph.adv || unitsPerEm * 0.5) * scale;

      // Einfache Transform-Matrix ohne Rotation
      const transform = `matrix(${scale},0,0,${-scale},${x},${baselineY})`;

      resultPaths.push({
        d,
        transform,
      });

      x += advPx;
    }

    baselineY += lineHeightPx;
  }

  return resultPaths;
}

module.exports = {
  measureTextWidthPx,
  wrapTextToLinesByWidth,
  layoutTextToPaths
};