feat: add DXF (R12) and SVG exporters

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lib/export-dxf.ts

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+import { formatMm, shapeSize } from './geometry';
+import type { Shape } from './types';
+
+/** Minimal ASCII DXF R12: one closed POLYLINE per ring, units mm, Y axis up. */
+export function toDxf(shapeMm: Shape): string {
+  const { height } = shapeSize(shapeMm);
+  const out: (string | number)[] = [
+    0, 'SECTION', 2, 'HEADER',
+    9, '$ACADVER', 1, 'AC1009',
+    9, '$INSUNITS', 70, 4,
+    0, 'ENDSEC',
+    0, 'SECTION', 2, 'ENTITIES',
+  ];
+  for (const ring of [shapeMm.outer, ...shapeMm.holes]) {
+    out.push(0, 'POLYLINE', 8, '0', 66, 1, 70, 1, 10, '0.0', 20, '0.0', 30, '0.0');
+    for (const p of ring) {
+      out.push(0, 'VERTEX', 8, '0', 10, formatMm(p.x), 20, formatMm(height - p.y), 30, '0.0');
+    }
+    out.push(0, 'SEQEND', 8, '0');
+  }
+  out.push(0, 'ENDSEC', 0, 'EOF');
+  // RDWorks is a Windows tool; CRLF is the most widely accepted DXF line ending.
+  return out.join('\r\n') + '\r\n';
+}

src/lib/export-svg.ts

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+import { formatMm, shapeSize } from './geometry';
+import type { Point, Shape } from './types';
+
+export function toSvg(shapeMm: Shape): string {
+  const { width, height } = shapeSize(shapeMm);
+  const w = formatMm(width);
+  const h = formatMm(height);
+  const d = [shapeMm.outer, ...shapeMm.holes].map(ringPath).join(' ');
+  return [
+    '<?xml version="1.0" encoding="UTF-8"?>',
+    `<svg xmlns="http://www.w3.org/2000/svg" width="${w}mm" height="${h}mm" viewBox="0 0 ${w} ${h}">`,
+    `  <path d="${d}" fill="none" fill-rule="evenodd" stroke="#ff0000" stroke-width="0.1"/>`,
+    '</svg>',
+    '',
+  ].join('\n');
+}
+
+function ringPath(ring: Point[]): string {
+  return 'M' + ring.map((p) => `${formatMm(p.x)},${formatMm(p.y)}`).join(' L') + ' Z';
+}

tests/export-dxf.test.ts

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+import { describe, expect, it } from 'vitest';
+import { toDxf } from '../src/lib/export-dxf';
+
+const shape = {
+  outer: [{ x: 0, y: 0 }, { x: 100, y: 0 }, { x: 100, y: 50 }, { x: 0, y: 50 }],
+  holes: [[{ x: 10, y: 10 }, { x: 20, y: 10 }, { x: 20, y: 20 }]],
+};
+
+/** Split DXF text into [groupCode, value] pairs. */
+function pairs(dxf: string): [string, string][] {
+  const lines = dxf.split('\r\n');
+  if (lines[lines.length - 1] === '') lines.pop();
+  const out: [string, string][] = [];
+  for (let i = 0; i < lines.length; i += 2) out.push([lines[i].trim(), lines[i + 1]]);
+  return out;
+}
+
+describe('toDxf', () => {
+  it('is a well-formed R12 file in mm with CRLF line endings', () => {
+    const dxf = toDxf(shape);
+    expect(dxf).not.toMatch(/[^\r]\n/);
+    const p = pairs(dxf);
+    expect(p[0]).toEqual(['0', 'SECTION']);
+    expect(p).toContainEqual(['1', 'AC1009']);
+    const unitsIdx = p.findIndex(([c, v]) => c === '9' && v === '$INSUNITS');
+    expect(p[unitsIdx + 1]).toEqual(['70', '4']);
+    expect(p[p.length - 1]).toEqual(['0', 'EOF']);
+  });
+
+  it('writes one closed POLYLINE per ring with all vertices', () => {
+    const p = pairs(toDxf(shape));
+    const entities = p.filter(([c]) => c === '0').map(([, v]) => v);
+    expect(entities.filter((e) => e === 'POLYLINE')).toHaveLength(2);
+    expect(entities.filter((e) => e === 'VERTEX')).toHaveLength(7);
+    expect(entities.filter((e) => e === 'SEQEND')).toHaveLength(2);
+    const polyIdx = p.findIndex(([c, v]) => c === '0' && v === 'POLYLINE');
+    const flags = p.slice(polyIdx, polyIdx + 8).find(([c]) => c === '70');
+    expect(flags).toEqual(['70', '1']);
+  });
+
+  it('flips Y so the piece is not mirrored', () => {
+    const p = pairs(toDxf(shape));
+    const firstVertex = p.findIndex(([c, v]) => c === '0' && v === 'VERTEX');
+    const x = p.slice(firstVertex).find(([c]) => c === '10')![1];
+    const y = p.slice(firstVertex).find(([c]) => c === '20')![1];
+    expect([x, y]).toEqual(['0', '50']); // (0,0) top-left → (0,50) in Y-up space
+  });
+});

tests/export-svg.test.ts

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+import { describe, expect, it } from 'vitest';
+import { toSvg } from '../src/lib/export-svg';
+
+const shape = {
+  outer: [{ x: 0, y: 0 }, { x: 100, y: 0 }, { x: 100, y: 50 }, { x: 0, y: 50 }],
+  holes: [[{ x: 10, y: 10 }, { x: 20, y: 10 }, { x: 20, y: 20.5 }]],
+};
+
+describe('toSvg', () => {
+  it('declares its size in mm with a matching viewBox', () => {
+    const svg = toSvg(shape);
+    expect(svg).toContain('width="100mm"');
+    expect(svg).toContain('height="50mm"');
+    expect(svg).toContain('viewBox="0 0 100 50"');
+  });
+
+  it('writes one closed subpath per ring in a single evenodd path', () => {
+    const svg = toSvg(shape);
+    const d = svg.match(/ d="([^"]+)"/)![1];
+    expect(d.match(/M/g)).toHaveLength(2);
+    expect(d.match(/Z/g)).toHaveLength(2);
+    expect(d).toContain('M0,0 L100,0 L100,50 L0,50 Z');
+    expect(d).toContain('20,20.5');
+    expect(svg).toContain('fill-rule="evenodd"');
+    expect(svg).toContain('fill="none"');
+  });
+});