From 5e76c5ea2f2c73983a6c6e04fb98f4f19a3372dd Mon Sep 17 00:00:00 2001
From: James Hadfield <hadfield.james@gmail.com>
Date: Mon, 1 Mar 2021 16:23:08 +1300
Subject: [PATCH] Correctly format BCE dates

BCE dates were correctly interpreted but incorrectly rendered
due to a bug in the final string-prettying step. This would
result in a tree with the correct layout and positioning, but
incorrect labels ("-undefined"). This commit remedies this and
adds a test.
---
 src/util/dateHelpers.js | 8 +++++++-
 test/dates.test.js      | 1 +
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/util/dateHelpers.js b/src/util/dateHelpers.js
index 1d7fe5998..77b5a9727 100644
--- a/src/util/dateHelpers.js
+++ b/src/util/dateHelpers.js
@@ -153,7 +153,13 @@ export const prettifyDate = (unit, date) => {
   const stringDate = typeof date ==="number" ? numericToCalendar(date) :
     date instanceof Date ? dateToString(date) :
       date;
-  const [year, month, day] = stringDate.split("-");
+  let year, month, day;
+  if (!stringDate.startsWith("-")) {
+    [year, month, day] = stringDate.split("-");
+  } else {
+    [year, month, day] = stringDate.slice(1).split("-");
+    year = `-${year}`;
+  }
   switch (unit) {
     case "CENTURY": // falls through
     case "DECADE": // falls through
diff --git a/test/dates.test.js b/test/dates.test.js
index 8ae5e9154..463a57f56 100644
--- a/test/dates.test.js
+++ b/test/dates.test.js
@@ -91,4 +91,5 @@ test("dates are prettified as expected", () => {
   expect(prettifyDate("YEAR", "2020-01-01")).toStrictEqual("2020");
   expect(prettifyDate("MONTH", "2020-01-05")).toStrictEqual("2020-Jan-05");
   expect(prettifyDate("MONTH", "2020-01-01")).toStrictEqual("2020-Jan");
+  expect(prettifyDate("CENTURY", "-3000-01-01")).toStrictEqual("-3000"); // BCE
 });