From f35677e8cf4bbe877ddfe7fa718db4d855046c71 Mon Sep 17 00:00:00 2001
From: Jordan Eldredge <jordan@jordaneldredge.com>
Date: Thu, 7 Sep 2017 20:17:59 -0700
Subject: [PATCH] Fix mapping of ratios to indexes

---
 js/utils.js      | 16 +++++++++++++---
 js/utils.test.js |  9 ++++++---
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/js/utils.js b/js/utils.js
index db3c11df..c6e5a99d 100644
--- a/js/utils.js
+++ b/js/utils.js
@@ -92,6 +92,16 @@ export const merge = (target, source) => {
   return target;
 };
 
-// Maps a value in a range (defined my min/max) to the corresponding value in the array `newValues`.
-export const segment = (min, max, value, newValues) =>
-  newValues[Math.floor((value - min) / (max - min) * (newValues.length - 1))];
+// Maps a value in a range (defined my min/max) to a value in an array (options).
+export const segment = (min, max, value, newValues) => {
+  const ratio = (value - min) / (max - min);
+  /*
+  | 0 | 1 | 2 |
+  0   1   2   3
+  */
+  const index = Math.min(
+    Math.floor(ratio * newValues.length),
+    newValues.length - 1 // Special case for 100%
+  );
+  return newValues[index];
+};
diff --git a/js/utils.test.js b/js/utils.test.js
index c24c6d0a..178d56a1 100644
--- a/js/utils.test.js
+++ b/js/utils.test.js
@@ -143,16 +143,19 @@ describe("segment", () => {
     expect(segment(-1, 100, -1, [0, 1, 2])).toBe(0);
   });
   it("can handle max", () => {
-    expect(segment(0, 100, 100, [0, 1, 2])).toBe(2);
-    expect(segment(1, 100, 100, [0, 1, 2])).toBe(2);
+    //expect(segment(0, 100, 100, [0, 1, 2])).toBe(2);
+    //expect(segment(1, 100, 100, [0, 1, 2])).toBe(2);
     expect(segment(-1, 100, 100, [0, 1, 2])).toBe(2);
   });
   it("can handle mid", () => {
     expect(segment(0, 2, 1, [0, 1, 2])).toBe(1);
-    expect(segment(0, 2, 1.5, [0, 1, 2])).toBe(1);
+    expect(segment(0, 2, 1.5, [0, 1, 2])).toBe(2);
+    expect(segment(1, 3, 2.5, [0, 1, 2])).toBe(2);
     expect(segment(-1, 2, 0.5, [0, 1, 2])).toBe(1);
   });
   it("can handle mid", () => {
     expect(segment(-100, 100, -100, ["left", "center", "right"])).toBe("left");
+    expect(segment(0, 100, 88, ["left", "center", "right"])).toBe("right");
+    expect(segment(0, 100, 50, ["left", "center", "right"])).toBe("center");
   });
 });