svg-tools/tests/domain/path.test.ts

import { describe, expect, it } from "vitest";
import {
  arcEndpointToCenter,
  describePathCommand,
  movePathHandle,
  parsePathData,
  pathHandles,
  pointOnArc,
  reversePath,
  serializePathData,
  splitSegment,
  transformPath,
} from "../../src/domain/path";

describe("application-owned SVG path model", () => {
  it("normalizes every command family, relatives, repeats and shorthand controls", () => {
    const model = parsePathData(
      "m 10 10 5 5 h 10 v 10 c 1 2 3 4 5 6 s 7 8 9 10 q 2 3 4 5 t 6 7 a 8 9 30 0 1 10 11 z",
    );
    expect(model.segments.map((segment) => segment.kind)).toEqual([
      "M",
      "L",
      "L",
      "L",
      "C",
      "C",
      "Q",
      "Q",
      "A",
      "Z",
    ]);
    const firstCubic = model.segments[4];
    const smoothCubic = model.segments[5];
    expect(firstCubic?.kind).toBe("C");
    expect(smoothCubic?.kind).toBe("C");
    if (firstCubic?.kind === "C" && smoothCubic?.kind === "C") {
      expect(smoothCubic.control1).toEqual({
        x: 2 * smoothCubic.from.x - firstCubic.control2.x,
        y: 2 * smoothCubic.from.y - firstCubic.control2.y,
      });
      expect(smoothCubic).toMatchObject({
        derivedControl1: true,
        sourceForm: { command: "s", relative: true },
      });
      const derived = pathHandles(model).find(
        (handle) => handle.segmentIndex === 5 && handle.role === "control-1",
      )!;
      expect(derived.derived).toBe(true);
      const explicit = movePathHandle(model, derived, {
        x: derived.point.x + 1,
        y: derived.point.y,
      });
      expect(explicit.segments[5]).toMatchObject({ derivedControl1: false });
    }
    expect(model.segments[7]).toMatchObject({
      derivedControl: true,
      sourceForm: { command: "t" },
    });
    expect(
      model.segments.every(
        ({ sourceForm }) =>
          sourceForm !== undefined &&
          sourceForm.sourceRange.to > sourceForm.sourceRange.from,
      ),
    ).toBe(true);
  });

  it("supports compact numbers, exponent notation and packed arc flags", () => {
    const model = parsePathData("M.5.6L10-5e-1A5 6 0 0110 20");
    expect(model.segments).toHaveLength(3);
    expect(model.segments[0]).toMatchObject({ to: { x: 0.5, y: 0.6 } });
    expect(model.segments[1]).toMatchObject({ to: { x: 10, y: -0.5 } });
    expect(model.segments[2]).toMatchObject({
      kind: "A",
      largeArc: false,
      sweep: true,
      to: { x: 10, y: 20 },
    });
  });

  it("round-trips normalized geometry and rejects malformed data", () => {
    const model = parsePathData(
      "M0 0 C1 2 3 4 5 6 Q7 8 9 10 A4 3 20 1 0 12 13 Z",
    );
    expect(serializePathData(parsePathData(serializePathData(model)))).toBe(
      serializePathData(model),
    );
    expect(() => parsePathData("L 1 2")).toThrow(/begin with a moveto/u);
    expect(() => parsePathData("M 0 0 A 5 5 0 2 0 10 10")).toThrow(
      /flag must be 0 or 1/u,
    );
    expect(() => parsePathData("M 0,")).toThrow(/comma/iu);
    expect(() => parsePathData("M0 0 1 1 2 2", 2)).toThrow(/segment limit/u);
  });

  it("splits cubic geometry with de Casteljau and reverses arc sweep", () => {
    const cubic = parsePathData("M0 0 C10 0 10 10 20 10");
    const split = splitSegment(cubic, 1, 0.5);
    expect(split.segments).toHaveLength(3);
    expect(split.segments[1]).toMatchObject({ kind: "C", to: { x: 10, y: 5 } });
    expect(split.segments[2]).toMatchObject({
      kind: "C",
      from: { x: 10, y: 5 },
    });
    const arc = parsePathData("M0 0 A10 5 20 0 1 20 0");
    const reversed = reversePath(arc);
    expect(reversed.segments[1]).toMatchObject({ kind: "A", sweep: false });
    expect(serializePathData(reversePath(reversed))).toBe(
      serializePathData(arc),
    );
  });

  it("derives arc center/radius controls and moves path handles", () => {
    const model = parsePathData("M0 0 A4 3 30 0 1 12 0");
    const segment = model.segments[1];
    expect(segment?.kind).toBe("A");
    if (segment?.kind !== "A") return;
    const center = arcEndpointToCenter(segment)!;
    expect(pointOnArc(center, center.startAngle).x).toBeCloseTo(segment.from.x);
    const anchor = pathHandles(model).find(
      (handle) => handle.role === "anchor" && handle.segmentIndex === 1,
    )!;
    expect(
      movePathHandle(model, anchor, { x: 14, y: 2 }).segments[1],
    ).toMatchObject({ to: { x: 14, y: 2 } });
  });

  it("bakes nonsingular affine matrices and flips arc sweep under reflection", () => {
    const model = parsePathData("M0 0 A10 5 20 0 1 20 0");
    const transformed = transformPath(model, {
      a: -2,
      b: 0.5,
      c: 0.25,
      d: 3,
      e: 4,
      f: 8,
    });
    expect(transformed.segments[1]).toMatchObject({ kind: "A", sweep: false });
    expect(() =>
      transformPath(model, { a: 1, b: 0, c: 0, d: 0, e: 0, f: 0 }),
    ).toThrow(/singular/u);
  });
  it("describes source form, endpoints, controls, derived shorthand and arc flags", () => {
    const source = "m 1 2 3 4 s 5 6 7 8 t 9 10 a 11 12 30 1 0 13 14";
    const segments = parsePathData(source).segments;

    expect(describePathCommand(segments[1]!, source)).toMatchObject({
      sourceCommand: "m",
      normalizedCommand: "L",
      sourceFragment: "3 4",
      form: "relative · implicit repeat",
      endpoint: "4, 6",
    });
    expect(describePathCommand(segments[2]!, source).details).toEqual([
      { label: "C1", value: "4, 6", derived: true },
      { label: "C2", value: "9, 12", derived: false },
    ]);
    expect(describePathCommand(segments[3]!, source).details[0]).toMatchObject({
      label: "C",
      derived: true,
    });
    expect(describePathCommand(segments[4]!, source).details).toEqual([
      { label: "Radii", value: "11 × 12", derived: false },
      { label: "Rotation", value: "30°", derived: false },
      { label: "Flags", value: "large 1 · sweep 0", derived: false },
    ]);
  });
});