From 25ed0fdf6e48872432d580679990433448b987db Mon Sep 17 00:00:00 2001
From: Mike Bostock <mbostock@gmail.com>
Date: Tue, 10 Jan 2023 21:23:10 -0800
Subject: [PATCH] adopt nice

---
 src/contours.js       |  8 +++++---
 test/contours-test.js | 10 ++++++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/contours.js b/src/contours.js
index ea3a0a4..90faf82 100644
--- a/src/contours.js
+++ b/src/contours.js
@@ -1,4 +1,4 @@
-import {extent, thresholdSturges, ticks, tickStep} from "d3-array";
+import {extent, nice, thresholdSturges, ticks} from "d3-array";
 import {slice} from "./array.js";
 import ascending from "./ascending.js";
 import area from "./area.js";
@@ -36,8 +36,10 @@ export default function() {
 
     // Convert number of thresholds into uniform thresholds.
     if (!Array.isArray(tz)) {
-      const e = extent(values, finite), ts = tickStep(e[0], e[1], tz);
-      tz = ticks(Math.floor(e[0] / ts) * ts, Math.floor(e[1] / ts - 1) * ts, tz);
+      const e = extent(values, finite);
+      tz = ticks(...nice(e[0], e[1], tz), tz);
+      while (tz[tz.length - 1] >= e[1]) tz.pop();
+      while (tz[1] < e[0]) tz.shift();
     } else {
       tz = tz.slice().sort(ascending);
     }
diff --git a/test/contours-test.js b/test/contours-test.js
index 94baa33..6cfaa31 100644
--- a/test/contours-test.js
+++ b/test/contours-test.js
@@ -288,3 +288,13 @@ it("contour(values, invalid value) throws an error", () => {
     assert.throws(() => contours().size([3, 3]).contour([1, 2, 3, 4, 5, 6, 7, 8, 9], value),  /invalid value/);
   }
 });
+
+it("contours(values) uses the expected nice thresholds", () => {
+  assert.deepStrictEqual(contours().size([2, 1]).thresholds(14)([-149.76192742819748, 321.19300631539585]).map((c) => c.value), [-150, -100, -50, 0, 50, 100, 150, 200, 250, 300]);
+  assert.deepStrictEqual(contours().size([2, 1]).thresholds(5)([-149.76192742819748, 321.19300631539585]).map((c) => c.value), [-200, -100, 0, 100, 200, 300]);
+  assert.deepStrictEqual(contours().size([2, 1]).thresholds(14)([149.76192742819748, -321.19300631539585]).map((c) => c.value), [-350, -300, -250, -200, -150, -100, -50, 0, 50, 100]);
+  assert.deepStrictEqual(contours().size([2, 1]).thresholds(5)([149.76192742819748, -321.19300631539585]).map((c) => c.value), [-400, -300, -200, -100, 0, 100]);
+  assert.deepStrictEqual(contours().size([2, 1]).thresholds(12)([-29, 50]).map((c) => c.value), [-30, -25, -20, -15, -10, -5, 0, 5, 10, 15, 20, 25, 30, 35, 40, 45]);
+  assert.deepStrictEqual(contours().size([2, 1]).thresholds(10)([-41, 245]).map((c) => c.value), [-50, 0, 50, 100, 150, 200]);
+  assert.deepStrictEqual(contours().size([2, 1]).thresholds(9)([-22, 242]).map((c) => c.value), [-50, 0, 50, 100, 150, 200]);
+});