# Sainsbury's Date

Basic functions to convert a date object or string into Sainsbury's financial calendar components or vice-versa.

## Usage

Run `npm install sainsburys-date` to install the package into your application, then use `import` (or `require`) to bring it in.

```js
import sainsburysDate from 'sainsburys-date'
```

### `fromDate(date | dateStr)`

This converts a `Date` object or `yyyy-mm-dd` string into it's Sainsbury's calendar parts.

```js
const date = sainsburysDate.fromDate('2015-10-05')

console.log(date.year) // 2015
console.log(date.quarter) // 3
console.log(date.period) // 8
console.log(date.week) // 2
```

### `toDate({ year, quarter, period, week, day })`

This calculates the date represented by the passed Sainsbury's calendar parts. Dates are calculated starting from the year `option`, offset by the `quarter`, `period`, `week` and `day` optional parts (summated in their respective order).

```js
const a = sainsburysDate.toDate({ year: 2015, period: 8, week: 2 })
const b = sainsburysDate.toDate({ year: 2015, week: 30 })
const c = sainsburysDate.toDate({ year: 2017, day: 15 })
const d = sainsburysDate.toDate({ year: 2017, quarter: 4 })

console.log(a) // new Date('2015-10-04')
console.log(b) // new Date('2015-10-04')
console.log(c) // new Date('2017-03-26')
console.log(d) // new Date('2017-12-17')
```

## Sainsbury's Leap Week / Period?

At some point Sainsbury's will need to introduce a "leap" week or period otherwise the start of the financial year will fall into the previous year!

However, a decision on how to introduce this hasn't been made yet and this won't be a problem until `Sun Dec 31 2073` (which will otherwise be the Q1 for 2074)