From 22b4ca835e957c1013805a0f8128138523f68d92 Mon Sep 17 00:00:00 2001
From: Max Okorokov <max@okorokov.com>
Date: Fri, 4 Oct 2019 16:18:51 +0200
Subject: [PATCH] fix(datepicker): performance issues when huge min/max dates
 (#3357)

Fixes #3338
---
 src/datepicker/datepicker-service.spec.ts | 10 ++++++----
 src/datepicker/datepicker-tools.spec.ts   |  6 +++---
 src/datepicker/datepicker-tools.ts        | 12 +++++++++---
 3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/src/datepicker/datepicker-service.spec.ts b/src/datepicker/datepicker-service.spec.ts
index 722e0d663f..1a21f310a4 100644
--- a/src/datepicker/datepicker-service.spec.ts
+++ b/src/datepicker/datepicker-service.spec.ts
@@ -552,7 +552,7 @@ describe('ngb-datepicker-service', () => {
         expect(model.selectBoxes.years).toEqual(range(2010, 2030));
       });
 
-      it(`should generate [min, +10] 'years' when max date is missing`, () => {
+      it(`should generate [min/-500, +10] 'years' when max date is missing`, () => {
         service.minDate = new NgbDate(2010, 1, 1);
         service.open(new NgbDate(2011, 1, 1));
         expect(model.selectBoxes.years).toEqual(range(2010, 2021));
@@ -560,11 +560,12 @@ describe('ngb-datepicker-service', () => {
         service.minDate = new NgbDate(2015, 1, 1);
         expect(model.selectBoxes.years).toEqual(range(2015, 2025));
 
+        // -500
         service.minDate = new NgbDate(1000, 1, 1);
-        expect(model.selectBoxes.years).toEqual(range(1000, 2025));
+        expect(model.selectBoxes.years).toEqual(range(1515, 2025));
       });
 
-      it(`should generate [min, +10] 'years' when min date is missing`, () => {
+      it(`should generate [-10, +500/max] 'years' when min date is missing`, () => {
         service.maxDate = new NgbDate(2010, 1, 1);
         service.open(new NgbDate(2009, 1, 1));
         expect(model.selectBoxes.years).toEqual(range(1999, 2010));
@@ -572,8 +573,9 @@ describe('ngb-datepicker-service', () => {
         service.maxDate = new NgbDate(2005, 1, 1);
         expect(model.selectBoxes.years).toEqual(range(1995, 2005));
 
+        // +500
         service.maxDate = new NgbDate(3000, 1, 1);
-        expect(model.selectBoxes.years).toEqual(range(1995, 3000));
+        expect(model.selectBoxes.years).toEqual(range(1995, 2505));
       });
 
       it(`should generate 'months' when min/max dates are missing`, () => {
diff --git a/src/datepicker/datepicker-tools.spec.ts b/src/datepicker/datepicker-tools.spec.ts
index 89916c51be..01d88a06e3 100644
--- a/src/datepicker/datepicker-tools.spec.ts
+++ b/src/datepicker/datepicker-tools.spec.ts
@@ -566,17 +566,17 @@ describe(`datepicker-tools`, () => {
     it(`should generate years correctly`, () => {
       // both 'min' and 'max' are set
       test(new NgbDate(2017, 1, 1), new NgbDate(2018, 1, 1), new NgbDate(2019, 1, 1), range(2017, 2019));
-      test(new NgbDate(2000, 1, 1), new NgbDate(2018, 1, 1), new NgbDate(3000, 1, 1), range(2000, 3000));
+      test(new NgbDate(1000, 1, 1), new NgbDate(2018, 1, 1), new NgbDate(3000, 1, 1), range(1518, 2518));
       test(new NgbDate(2018, 1, 1), new NgbDate(2018, 1, 1), new NgbDate(2018, 1, 1), [2018]);
 
       // 'min' is not set
       test(null, new NgbDate(2018, 1, 1), new NgbDate(2019, 1, 1), range(2008, 2019));
-      test(null, new NgbDate(2018, 1, 1), new NgbDate(3000, 1, 1), range(2008, 3000));
+      test(null, new NgbDate(2018, 1, 1), new NgbDate(3000, 1, 1), range(2008, 2518));
       test(null, new NgbDate(2018, 1, 1), new NgbDate(2018, 1, 1), range(2008, 2018));
 
       // 'max' is not set
       test(new NgbDate(2017, 1, 1), new NgbDate(2018, 1, 1), null, range(2017, 2028));
-      test(new NgbDate(2000, 1, 1), new NgbDate(2018, 1, 1), null, range(2000, 2028));
+      test(new NgbDate(1000, 1, 1), new NgbDate(2018, 1, 1), null, range(1518, 2028));
       test(new NgbDate(2018, 1, 1), new NgbDate(2018, 1, 1), null, range(2018, 2028));
 
       // both are not set
diff --git a/src/datepicker/datepicker-tools.ts b/src/datepicker/datepicker-tools.ts
index 631211722f..74fe233a80 100644
--- a/src/datepicker/datepicker-tools.ts
+++ b/src/datepicker/datepicker-tools.ts
@@ -71,10 +71,16 @@ export function generateSelectBoxYears(date: NgbDate, minDate: NgbDate, maxDate:
     return [];
   }
 
-  const start = minDate && minDate.year || date.year - 10;
-  const end = maxDate && maxDate.year || date.year + 10;
+  const start = minDate ? Math.max(minDate.year, date.year - 500) : date.year - 10;
+  const end = maxDate ? Math.min(maxDate.year, date.year + 500) : date.year + 10;
 
-  return Array.from({length: end - start + 1}, (e, i) => start + i);
+  const length = end - start + 1;
+  const numbers = Array(length);
+  for (let i = 0; i < length; i++) {
+    numbers[i] = start + i;
+  }
+
+  return numbers;
 }
 
 export function nextMonthDisabled(calendar: NgbCalendar, date: NgbDate, maxDate: NgbDate) {