# fix: apply the sign of chronometer/time strings to the whole Duration

## Problem

`Duration::fromChronoString()` and `Duration::fromTimeString()` accept an optional
leading sign so callers can build negative durations (the grammar defines a
`(?<sign>\+|-)?` group). The sign was mishandled in two ways:

1. When the hour component is zero or absent, the sign is silently lost and a
   positive duration is returned.
2. When the hour component is present, only the hour is negated while the minute,
   second and fraction components stay positive, producing a duration with mixed
   sign components that does not represent the input.

Examples on the current code:

```
Duration::fromChronoString('-05:30');   // minute:second -> +5m30s  (sign lost)
Duration::fromChronoString('-1:05:30'); // -1h +5m +30s = -3270s, not -3930s
Duration::fromTimeString('-00:30');     // -> +30m       (sign lost)
Duration::fromTimeString('-01:30');     // -1h +30m = -1800s, not -5400s
```

Applying these durations to a date point therefore moves the date in the wrong
direction or by the wrong amount.

## Root cause

`src/Duration.php`, `Duration::fromUnits()`. The negative sign was concatenated
onto the hour string only:

```php
if ('-' === $units['sign']) {
    $units['hour'] = '-'.$units['hour'];
}
```

Because the string handed to `DateInterval::createFromDateString()` only carried a
sign on the `hours` token, `-0 hours 30 minutes` normalized to a positive
30-minute interval, and `-1 hours 5 minutes 30 seconds` kept the minute and second
tokens positive.

## The fix

Prefix every unit token with the sign so the whole duration is negated
consistently:

```php
$sign = '-' === $units['sign'] ? '-' : '';

return self::fromDateString(
    $sign.$units['hour'].' hours '
    .$sign.$units['minute'].' minutes '
    .$sign.$units['second'].' seconds '
    .$sign.$units['fraction'].' microseconds'
);
```

`DateInterval::createFromDateString()` accepts a per-token sign, so this produces
a `DateInterval` whose components all carry the correct sign. Verified against a
reference date:

```
2021-01-01 00:10:00 + fromChronoString('-05:30')   = 2021-01-01 00:04:30
2021-01-01 02:00:00 + fromChronoString('-1:05:30')  = 2021-01-01 00:54:30
2021-01-01 00:20:00 + fromChronoString('-12:28.5')  = 2021-01-01 00:07:31.500000
2021-01-01 01:00:00 + fromTimeString('-00:30')      = 2021-01-01 00:30:00
2021-01-01 05:00:00 + fromTimeString('-01:30')      = 2021-01-01 03:30:00
```

## Tests

New data provider `signedDurationProvider` with the test
`testSignedStringsApplySignToWholeDuration` asserts the real elapsed effect of the
signed strings by applying them to a reference `DateTimeImmutable` (helper
independent, covers the zero-hour, full h:m:s and fractional-second cases).

Two existing data-provider rows pinned the buggy output and encode the defect, so
they were corrected:

- `fromChronoProvider` `negative chrono`: `-12:28.5 => PT12M28.5S` (sign dropped)
  updated to a fully negative case `-12:28 => PT-12M-28S`.
- `fromTimeStringProvider` `negative chrono`: `-12:28 => PT-12H28M` (mixed sign)
  updated to `-12:28 => PT-12H-28M`.
- `fromTimeStringProvider` `negative chrono with seconds`: `-00:00:28.5 => PT28.5S`
  (sign dropped) updated to `-01:02:28 => PT-1H-2M-28S`.

The fractional-second and seconds-only negative cases are covered by the new
date-arithmetic test instead of the string helper, because that helper renders
negative fractional seconds and bare seconds-only intervals with pre-existing
quirks that are out of scope here.

## Gate

```
composer install && vendor/bin/phpunit --no-coverage
```

Result: exit code `0` - `OK (562 tests, 933 assertions)`.

Counterfactual: reverting `fromUnits()` to the hour-only sign makes all five
`testSignedStringsApplySignToWholeDuration` cases fail, e.g.
`fromTimeString('-01:30')` yields `2021-01-01 04:30:00` instead of the expected
`2021-01-01 03:30:00`.