## Permalink structure

> Replacement patterns for dynamically constructing permalinks, as well as the corresponding directory structures.

Permalinks are **appended to the dest directory**. So given this config:

```js
assemble: {
  blog: {
    options: {
      permalinks: {
        structure: ':year/:month/:day/:basename:ext'
      }
    },
    files: {
      'blog/archives/': ['archives/*.hbs']
    }
  }
}
// the generated directory structure and resulting path would look something like:
//=> 'blog/archives/2011/01/01/an-inspiring-post.html'
```

## How replacement patterns work

This plugin comes with a number of built-in replacement patterns that will automatically parse and convert the built-in variables into the appropriate string. Since Assemble provides a number of generic variables for accessing page data, such as `basename`, `ext`, `filename` etc., this plugin simply dynamically builds the replacement patterns from those generic variables.

Barring a few exceptions (`_page`, `data`, `filePair`, `page`, `pageName`), you should be able to use any _valid_ variable that is on the page context in your replacement patterns.

For example, assuming we have a file, `./templates/overview.hbs`:

* `:ext`: would result in the `dest` extension: `.html`
* `:extname`: alias for `:ext`.
* `:basename`: would result in `overview`
* `:filename`: would result in the dest file name, `overview.html`
* `:pagename`: alias for `:filename`.
* `:category`: Slugified version of _the very first category_ for a page.


## Special patterns

> A few special replacement patterns were created for this lib.

### `:num`
Automatically adds sequential, "padded" numbers based on the length of the pages array in the current target.

For example, given the structure `:num-:basename`:

* 1-9 pages would result in `1-foo.html`, `2-bar.html`, `3-baz.html` and so on.
* 1,000 pages would result in `0001-foo.html`, `0002-bar.html`, `0003-baz.html`, ... `1000-quux.html`.

### `:000`
Adds sequential digits. Similar to `:num`, but the number of digits is determined by the number of zeros defined.

Example:

* `:00` will result in two-digit numbers
* `:000` will result in three-digit numbers
* `:00000000` will result in eight-digit numbers, and so on...

### `:random(Pattern, Number)`
Adds randomized characters based on the pattern provided in the parentheses. The first parameter defines the pattern you wish to use, and an optional second parameter defines the number of characters to generate.

For example, `:random(A, 4)` (whitespace insenstive) would result in randomized 4-digit uppercase letters, like, `ZAKH`, `UJSL`... and so on.

**no second parameter**

If a second parameter is not provided, then the  `length()` of the characters used in the first parameter will be used to determine the number of digits to output. For example:

* `:random(AAAA)` is equivelant to `:random(A, 4)`
* `:random(AAA0)` and `:random(AA00)` and `:random(A0A0)` are equivelant to `:random(A0, 4)`

**valid characters (and examples)**

* `:random(aa)`: results in double-digit, randomized, lower-case letters (`abcdefghijklmnopqrstuvwxyz`)
* `:random(AAA)`: results in triple-digit, randomized, upper-case letters (`ABCDEFGHIJKLMNOPQRSTUVWXYZ`)
* `:random(0, 6)`: results in six-digit, randomized nubmers (`0123456789`)
* `:random(!, 5)`: results in single-digit randomized, _valid_ non-letter characters (`~!@#$%^&()_+-={}[];\',.`)
* `:random(A!a0, 9)`: results in nine-digit, randomized characters (any of the above)

_The order in which the characters are provided has no impact on the outcome._


### Custom replacement patterns

If you have some patterns you'd like to implement, if you think they're common enough that they should be built into this plugin, please submit a pull request.

Adding patterns is easy, just add a `patterns: []` property to the `permalinks` option, then add any number of patterns to the array. For example, let's say we want to add the `:project` variable to our permalinks:

```js
options: {
  permalinks: {
    structure: ':year/:month/:day/:project/:slug:ext',
    patterns: []
  }
}
...
```

Since `:project` is not a built-in variable, we need to add a replacement pattern so that any permalinks that include this variable will actually work:

```js
options: {
  permalinks: {
    structure: ':year/:month/:day/:project/:slug:ext',
    patterns: [
      {
        pattern: ':project',
        replacement: '<%= pkg.name %>'
      }
    ]
  }
}
...
```
### with custom properties

Any string pattern is acceptable, as long as a `:` precedes the variable, but don't forget that there must also be a matching property in the context or Assemble will might an error (or worse, not). In other words, when you add a replacement pattern for `:foo`, it's good practice to make sure this property exists:

```yaml
---
foo: bar
slug:
---
```

## [Moment.js](http://momentjs.com/) date patterns

> This plugin uses the incredibly feature rich and flexible [moment.js](http://momentjs.com/) for parsing dates. If you have a feature request, please don't hesitate to create an issue or make a pull request.

For the date variables to work, a `date` property must exist on the page object.

```yaml
---
date: 2014-01-29 3:45 PM
---
```

Or

```js
pages: [
  {
    data: {
      title: 'All about permalinks, the novel.',
      description: 'This rivoting sequel to War & Peace will have you sleeping in no time.'
      date: '2014-01-29 3:45 PM'
    },
    content: ""
  }
]
```

### Common date patterns

* `:year`: The year of the date, four digits, for example `2014`
* `:month`: Month of the year, for example `01`
* `:day`: Day of the month, for example `13`
* `:hour`: Hour of the day, for example `24`
* `:minute`: Minute of the hour, for example `01`
* `:second`: Second of the minute, for example `59`

For the following examples, let's assume we have a date in the YAML front matter of a page formatted like this:

```yaml
---
date: 2014-01-29 3:45 PM
---
```
(_note that this property doesn't have to be in YAML front matter, it just needs to be in the `page.data` object, so this works fine with `options.pages` collections as well._)

### Full date
* `:date`:       Eqivelant to the full date: `YYYY-MM-DD`. Example: `2014-01-29`

### Year
* `:YYYY`:      The full year of the date. Example: `2014`
* `:YY`:        The two-digit year of the date. Example: `14`
* `:year`:      alias for `YYYY`

### Month name
* `:MMMM`:      The full name of the month. Example `January`.
* `:MMM`:       The name of the month. Example: `Jan`
* `:monthname`: alias for `MMMM`

### Month number
* `:MM`:        The double-digit number of the month. Example: `01`
* `:M`:         The single-digit number of the month. Example: `1`
* `:month`:     alias for `MM`
* `:mo`:        alias for `M`

### Day of the month
* `:day`:       alias for `DD`
* `:DD`:        The double-digit day of the month. Example: `29`
* `:D`:         The double-digit day of the month. Example: `29`

### Day of the week
* `:dddd`:      Day of the week. Example: `monday`
* `:ddd`:       Day of the week. Example: `mon`
* `:dd`:        Day of the week. Example: `Mo`
* `:d`:         Day of the week. Example: `2`

### Hour
* `:HH`:        The double-digit time of day on a 24 hour clock. Example `15`
* `:H`:         The single-digit time of day on a 24 hour clock. Example `3`
* `:hh`:        The double-digit time of day on a 12 hour clock. Example `03`
* `:h`:         The single-digit time of day on a 12 hour clock. Example `3`
* `:hour`:      alias for `HH`

### Minute
* `:mm`:        Minutes. Example: `45`.
* `:m`:         Minutes. Example: `45`.
* `:min`:       Alias for `mm`|`m`.
* `:minute`:    Alias for `mm`|`m`.

### Second
* `:ss`:        Seconds. Example: `09`.
* `:s`:         Seconds. Example: `9`.
* `:sec`:       Alias for `ss`|`s`.
* `:second`:    Alias for `ss`|`s`.