The `Athena::Negotiation` component allows an application to support [content negotiation](https://tools.ietf.org/html/rfc7231#section-5.3).
The component has no dependencies and is framework agnostic; supporting various negotiators.

## Installation

First, install the component by adding the following to your `shard.yml`, then running `shards install`:

```yaml
dependencies:
  athena-negotiation:
    github: athena-framework/negotiation
    version: ~> 0.1.0
```

## Usage

The main type of [Athena::Negotiation][] is [ANG::AbstractNegotiator][] which is used to implement negotiators for each `Accept*` header.
`Athena::Negotiation` exposes class level getters for each negotiator; that return a lazily initialized singleton instance.
Each negotiator exposes two methods: [ANG::AbstractNegotiator#best][] and [ANG::AbstractNegotiator#ordered_elements][].

### Media Type

```crystal
negotiator = ANG.negotiator

accept_header = "text/html, application/xhtml+xml, application/xml;q=0.9"
priorities = ["text/html; charset=utf-8", "application/json", "application/xml;q=0.5"]

accept = negotiator.best(accept_header, priorities).not_nil!

accept.media_range # => "text/html"
accept.parameters  # => {"charset" => "utf-8"}
```

The [ANG::Negotiator][] type returns an [ANG::Accept][], or `nil` if negotiating the best media type has failed.

### Character Set

```crystal
negotiator = ANG.charset_negotiator

accept_header = "ISO-8859-1, utf-8; q=0.9"
priorities = ["iso-8859-1;q=0.3", "utf-8;q=0.9", "utf-16;q=1.0"]

accept = negotiator.best(accept_header, priorities).not_nil!

accept.charset # => "utf-8"
accept.quality # => 0.9
```

The [ANG::CharsetNegotiator][] type returns an [ANG::AcceptCharset][], or `nil` if negotiating the best character set has failed.

### Encoding

```crystal
negotiator = ANG.encoding_negotiator

accept_header = "gzip;q=1.0, identity; q=0.5, *;q=0"
priorities = ["gzip", "foo"]

accept = negotiator.best(accept_header, priorities).not_nil!

accept.coding # => "gzip"
```

The [ANG::EncodingNegotiator][] type returns an [ANG::AcceptEncoding][], or `nil` if negotiating the best encoding has failed.

### Language

```crystal
negotiator = ANG.language_negotiator

accept_header = "en; q=0.1, fr; q=0.4, zh-Hans-CN; q=0.9, de; q=0.2"
priorities = ["de", "zh-Hans-CN", "en"]

accept = negotiator.best(accept_header, priorities).not_nil!

accept.language # => "zh"
accept.region   # => "cn"
accept.script   # => "hans"
```

The [ANG::LanguageNegotiator][] type returns an [ANG::AcceptLanguage][], or `nil` if negotiating the best language has failed.