1import absFloor from '../utils/abs-floor';
2import { cloneWithOffset } from '../units/offset';
3import { normalizeUnits } from '../units/aliases';
4
5export function diff(input, units, asFloat) {
6    var that, zoneDelta, output;
7
8    if (!this.isValid()) {
9        return NaN;
10    }
11
12    that = cloneWithOffset(input, this);
13
14    if (!that.isValid()) {
15        return NaN;
16    }
17
18    zoneDelta = (that.utcOffset() - this.utcOffset()) * 6e4;
19
20    units = normalizeUnits(units);
21
22    switch (units) {
23        case 'year':
24            output = monthDiff(this, that) / 12;
25            break;
26        case 'month':
27            output = monthDiff(this, that);
28            break;
29        case 'quarter':
30            output = monthDiff(this, that) / 3;
31            break;
32        case 'second':
33            output = (this - that) / 1e3;
34            break; // 1000
35        case 'minute':
36            output = (this - that) / 6e4;
37            break; // 1000 * 60
38        case 'hour':
39            output = (this - that) / 36e5;
40            break; // 1000 * 60 * 60
41        case 'day':
42            output = (this - that - zoneDelta) / 864e5;
43            break; // 1000 * 60 * 60 * 24, negate dst
44        case 'week':
45            output = (this - that - zoneDelta) / 6048e5;
46            break; // 1000 * 60 * 60 * 24 * 7, negate dst
47        default:
48            output = this - that;
49    }
50
51    return asFloat ? output : absFloor(output);
52}
53
54function monthDiff(a, b) {
55    if (a.date() < b.date()) {
56        // end-of-month calculations work correct when the start month has more
57        // days than the end month.
58        return -monthDiff(b, a);
59    }
60    // difference in months
61    var wholeMonthDiff = (b.year() - a.year()) * 12 + (b.month() - a.month()),
62        // b is in (anchor - 1 month, anchor + 1 month)
63        anchor = a.clone().add(wholeMonthDiff, 'months'),
64        anchor2,
65        adjust;
66
67    if (b - anchor < 0) {
68        anchor2 = a.clone().add(wholeMonthDiff - 1, 'months');
69        // linear across the month
70        adjust = (b - anchor) / (anchor - anchor2);
71    } else {
72        anchor2 = a.clone().add(wholeMonthDiff + 1, 'months');
73        // linear across the month
74        adjust = (b - anchor) / (anchor2 - anchor);
75    }
76
77    //check for negative zero, return zero if negative zero
78    return -(wholeMonthDiff + adjust) || 0;
79}