From 43dada11afe18286c4c3b2bad64127004474b127 Mon Sep 17 00:00:00 2001
From: Dan Strong <danielstrong@mac.com>
Date: Sun, 16 Aug 2026 18:17:51 -0800
Subject: [PATCH] test: cover poster page tiling calculations

---
 src/lib/paper.test.ts | 100 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 src/lib/paper.test.ts

diff --git a/src/lib/paper.test.ts b/src/lib/paper.test.ts
new file mode 100644
index 0000000..9f5d48e
--- /dev/null
+++ b/src/lib/paper.test.ts
@@ -0,0 +1,100 @@
+import { describe, expect, it } from "vitest";
+import { describeSize, gridFor, paperPt, PT_PER_MM, tileCount } from "./paper";
+
+describe("paperPt", () => {
+  it("converts A4 millimetres to points in portrait orientation", () => {
+    const size = paperPt("a4", true);
+
+    expect(size.w).toBeCloseTo(210 * PT_PER_MM);
+    expect(size.h).toBeCloseTo(297 * PT_PER_MM);
+  });
+
+  it("swaps the paper dimensions in landscape orientation", () => {
+    const portrait = paperPt("a4", true);
+    const landscape = paperPt("a4", false);
+
+    expect(landscape.w).toBeCloseTo(portrait.h);
+    expect(landscape.h).toBeCloseTo(portrait.w);
+  });
+});
+
+describe("tileCount", () => {
+  it("uses one tile for an exact fit", () => {
+    expect(tileCount(100, 100, 0)).toBe(1);
+  });
+
+  it("allows the 0.5 point fit tolerance", () => {
+    expect(tileCount(100.5, 100, 0)).toBe(1);
+  });
+
+  it("adds a tile at the first overflow beyond the tolerance", () => {
+    expect(tileCount(100.500001, 100, 0)).toBe(2);
+  });
+
+  it("counts multiple sheets along one dimension", () => {
+    expect(tileCount(300, 100, 0)).toBe(3);
+  });
+
+  it("increases the sheet count when overlap reduces the usable step", () => {
+    expect(tileCount(300, 100, 25)).toBe(4);
+  });
+});
+
+describe("gridFor", () => {
+  it("honours explicit portrait and landscape orientations", () => {
+    const portrait = gridFor(1_000, 1_000, "a4", "portrait", 0);
+    const landscape = gridFor(1_000, 1_000, "a4", "landscape", 0);
+
+    expect(portrait.tileW).toBeCloseTo(210 * PT_PER_MM);
+    expect(portrait.tileH).toBeCloseTo(297 * PT_PER_MM);
+    expect(landscape.tileW).toBeCloseTo(297 * PT_PER_MM);
+    expect(landscape.tileH).toBeCloseTo(210 * PT_PER_MM);
+  });
+
+  it("reports count as the product of columns and rows", () => {
+    const grid = gridFor(1_600, 1_600, "a4", "portrait", 0);
+
+    expect(grid.count).toBe(grid.cols * grid.rows);
+  });
+
+  it("selects portrait paper for a tall page when it uses fewer sheets", () => {
+    const grid = gridFor(500, 1_600, "a4", "auto", 0);
+
+    expect(grid.count).toBe(2);
+    expect(grid.tileW).toBeCloseTo(210 * PT_PER_MM);
+    expect(grid.tileH).toBeCloseTo(297 * PT_PER_MM);
+  });
+
+  it("selects landscape paper for a wide page when it uses fewer sheets", () => {
+    const grid = gridFor(1_600, 500, "a4", "auto", 0);
+
+    expect(grid.count).toBe(2);
+    expect(grid.tileW).toBeCloseTo(297 * PT_PER_MM);
+    expect(grid.tileH).toBeCloseTo(210 * PT_PER_MM);
+  });
+
+  it("selects portrait deterministically when orientations tie", () => {
+    const grid = gridFor(500, 500, "a4", "auto", 0);
+
+    expect(grid.count).toBe(1);
+    expect(grid.tileW).toBeCloseTo(210 * PT_PER_MM);
+    expect(grid.tileH).toBeCloseTo(297 * PT_PER_MM);
+  });
+});
+
+describe("describeSize", () => {
+  it("recognises A-series sizes in either orientation", () => {
+    expect(describeSize(210 * PT_PER_MM, 297 * PT_PER_MM)).toBe(
+      "A4 (210 × 297 mm)",
+    );
+    expect(describeSize(420 * PT_PER_MM, 297 * PT_PER_MM)).toBe(
+      "A3 (420 × 297 mm)",
+    );
+  });
+
+  it("rounds custom dimensions to whole millimetres", () => {
+    expect(describeSize(123.4 * PT_PER_MM, 456.6 * PT_PER_MM)).toBe(
+      "123 × 457 mm",
+    );
+  });
+});