# Business

Date calculations based on business calendars.


## But other libraries already do this

Another gem, business_time, also exists for this purpose. We previously used
business_time, but encountered several issues that prompted us to create
business.

Firstly, business_time works by monkey-patching `Date`, `Time`, and `FixNum`.
While this enables syntax like `Time.now + 1.business_day`, it means that all
configuration has to be global. GoCardless handles payments across multiple
geographies, so being able to work with multiple working-day calendars is
essential for us. Business provides a simple `Calendar` class, that is
initialized with a configuration that specifies which days of the week are
considered to be working days, and which dates are holidays.

Secondly, business_time supports calculations on times as well as dates. For
our purposes, date-based calculations are sufficient. Supporting time-based
calculations as well makes the code significantly more complex. We chose to
avoid this extra complexity by sticking solely to date-based mathematics.


## Documentation

### Getting started

Get stareted with business by creating an instance of the calendar class,
passing in a hash that specifies with days of the week are considered working
days, and which days are holidays.

```ruby
calendar = Business::Calendar.new(
  working_days: %w( mon tue wed thu fri ),
  holidays: ["01/01/2014", "03/01/2014"]
)
```

A few calendar configs are bundled with the gem. Load them by calling the
`load` class method on `Calendar`. The `load_cached` variant of this method
caches the calendars by name after loading them, to avoid reading and
parsing the config file multiple times.

```ruby
calendar = Business::Calendar.load("weekdays")
calendar = Business::Calendar.load_cached("weekdays")
```

### Checking for business days

To check whether a given date is a business day (falls on one of the specified
working days, and is not a holiday), use the `business_day?` method on
`Calendar`.

```ruby
calendar.business_day?(Date.parse("Monday, 9 June 2014"))
# => true
calendar.business_day?(Date.parse("Sunday, 8 June 2014"))
# => false
```

### Business day arithmetic

The `add_business_days` and `subtract_business_days` are used to perform
business day arithemtic on dates.

```ruby
date = Date.parse("Thursday, 12 June 2014")
calendar.add_business_days(date, 4).strftime("%A, %d %B %Y")
# => "Wednesday, 18 June 2014"
calendar.subtract_business_days(date, 4).strftime("%A, %d %B %Y")
# => "Friday, 06 June 2014"
```

The `roll_forward` and `roll_backward` methods snap a date to a nearby business
day. If provided with a business day, they will return that date. Otherwise,
they will advance (forward for `roll_forward` and backward for `roll_backward`)
until a business day is found.

```ruby
date = Date.parse("Saturday, 14 June 2014")
calendar.roll_forward(date).strftime("%A, %d %B %Y")
# => "Monday, 16 June 2014"
calendar.roll_backward(date).strftime("%A, %d %B %Y")
# => "Friday, 13 June 2014"
```

To count the number of business days between two dates, pass the dates to
`business_days_between`. This method counts from start of the first date to
start of the second date. So, assuming no holidays, there would be two business
days between a Monday and a Wednesday.

```ruby
date = Date.parse("Saturday, 14 June 2014")
calendar.business_days_between(date, date + 7)
# => 5
```