Fix week 0 for early January dates

.verb.md

@@ -5,4 +5,9 @@ var week = require('week');
 
 week();
 //=> '50' (December)
+
+week(new Date(2017, 0, 3));
+//=> '1'
 ```
+
+Week numbers are **1-indexed**. Week 1 is the week that contains January 1, and weeks start on Sunday. This is a simple helper (similar to 1-based `M`/`MM` month numbers), not ISO 8601 week numbering.

README.md

@@ -17,8 +17,13 @@ var week = require('week');
 
 week();
 //=> '50' (December)
+
+week(new Date(2017, 0, 3));
+//=> '1'
 ```
 
+Week numbers are **1-indexed**. Week 1 is the week that contains January 1, and weeks start on Sunday. This is a simple helper (similar to 1-based `M`/`MM` month numbers), not ISO 8601 week numbering.
+
 ## About
 
 ### Related projects

index.js

@@ -12,5 +12,5 @@ module.exports = function week(date) {
   var first = new Date(date.getFullYear(), 0, 1);
   var diff = ((date - first) / 86400000);
   var days = (diff + first.getDay());
-  return Math.floor(days / 7).toString();
+  return (Math.floor(days / 7) + 1).toString();
 };

test.js

@@ -7,11 +7,40 @@
 
 require('mocha');
 var assert = require('assert');
-var moment = require('moment');
 var week = require('./');
 
 describe('week()', function () {
-  it('should return an object with the number and name of the current week', function () {
-    assert.equal(week(), moment(new Date()).format('WW'));
+  it('should return the current week as a 1-indexed numeric string', function () {
+    var current = week();
+    assert.equal(typeof current, 'string');
+    assert.ok(/^[1-9]\d*$/.test(current), 'expected a 1-indexed week string, got ' + current);
+    var n = +current;
+    assert.ok(n >= 1 && n <= 53);
+  });
+
+  it('should not return week 0 for 3 January 2017 (#3)', function () {
+    // Reporter: week() emitted "0" on 3 January 2017 (Tue; Jan 1 was Sunday).
+    assert.equal(week(new Date(2017, 0, 3)), '1');
+  });
+
+  it('should treat January 1 through the first Saturday as week 1', function () {
+    assert.equal(week(new Date(2017, 0, 1)), '1');
+    assert.equal(week(new Date(2017, 0, 2)), '1');
+    assert.equal(week(new Date(2017, 0, 7)), '1');
+    assert.equal(week(new Date(2017, 0, 8)), '2');
+  });
+
+  it('should stay 1-indexed when January 1 is not Sunday', function () {
+    // 1 January 2016 was a Friday — previously emitted "0".
+    assert.equal(week(new Date(2016, 0, 1)), '1');
+    assert.equal(week(new Date(2016, 0, 2)), '1');
+    // First Sunday of 2016 starts week 2.
+    assert.equal(week(new Date(2016, 0, 3)), '2');
+  });
+
+  it('should preserve Sunday-start numbering later in the year', function () {
+    // 13 March 2017 was reported as week 10 (off-by-one); week 1 started Jan 1.
+    assert.equal(week(new Date(2017, 2, 13)), '11');
+    assert.equal(week(new Date(2017, 11, 31)), '53');
   });
 });