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https://github.com/obsidian/oak

A Crystal radix implementation
https://github.com/obsidian/oak

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A Crystal radix implementation

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# Oak

Another [radix tree](https://en.wikipedia.org/wiki/Radix_tree) implementation for crystal-lang



[![Build Status](https://img.shields.io/travis/obsidian/oak.svg)](https://travis-ci.org/obsidian/oak)

[![Latest Tag](https://img.shields.io/github/tag/obsidian/oak.svg)](https://github.com/obsidian/oak/tags)



## Installation



Add this to your application's `shard.yml`:



```yaml

dependencies:

  oak:

    github: obsidian/oak

```



## Usage



### Building Trees



You can associate one or more *payloads* with each path added to the tree:



```crystal

require "oak"



tree = Oak::Tree(Symbol).new

tree.add "/products", :products

tree.add "/products/featured", :featured



results = tree.search "/products/featured"



if result = results.first?

  puts result.payload # => :featured

end

```



The types allowed for a payload are defined on Tree definition:



```crystal

tree = Oak::Tree(Symbol).new



# Good, since Symbol is allowed as payload

tree.add "/", :root



# Compilation error, Int32 is not allowed

tree.add "/meaning-of-life", 42

```



Can combine multiple types if needed:



```crystal

tree = Oak::Tree(Int32 | String | Symbol).new



tree.add "/", :root

tree.add "/meaning-of-life", 42

tree.add "/hello", "world"

```



### Lookup and placeholders



You can also extract values from placeholders (as named or globbed segments):



```crystal

tree.add "/products/:id", :product



result = tree.find "/products/1234"



if result

  puts result.params["id"]? # => "1234"

end

```



Please see `Oak::Tree#add` documentation for more usage examples.



## Optionals



Oak has the ability to add optional paths, i.e. `foo(/bar)/:id`, which will expand

into two routes: `foo/bar/:id` and `foo/:id`. In the following example, both results

will match and return the same payload.



```crystal

tree.add "/products(/free)/:id", :product



if result = tree.find "/products/1234"

  puts result.params["id"]? # => "1234"

  puts result.payload # => :product

end



if result = tree.find "/products/free/1234"

  puts result.params["id"]? # => "1234"

  puts result.payload # => :product

end

```



## Caveats



### Multiple results



Due the the dynamic nature of this radix tree, and to allow for a more flexible

experience for the implementer, the `.search` method will return a list of results.

Alternatively, you can interact with the results by providing a block.



```crystal

matching_payload = nil

@tree.search(path) do |result|

  unless matching_payload

    context.request.path_params = result.params

    matching_payload = result.payloads.find do |payload|

      payload.matches_constraints? context.request

    end

    matching_payload.try &.call(context)

  end

end

```



### Multiple Leaves



In order to allow for a more flexible experience for the implementer, this

implementation of radix will not error if a multiple payloads are added at the

same path/key. You can either call the `.payload` method to grab the first payload,

or you can use the `.payloads` method, which will return all the payloads.



### Shared Keys



When designing and adding *paths* to a Tree, please consider that two different

named parameters cannot share the same level:



```crystal

tree.add "/", :root

tree.add "/:post", :post

tree.add "/:category/:post", :category_post # => Radix::Tree::SharedKeyError

```



This is because different named parameters at the same level will result in

incorrect `params` when lookup is performed, and sometimes the value for

`post` or `category` parameters will not be stored as expected.



To avoid this issue, usage of explicit keys that differentiate each path is

recommended.



For example, following a good SEO practice will be consider `/:post` as

absolute permalink for the post and have a list of categories which links to

a permalink of the posts under that category:



```crystal

tree.add "/", :root

tree.add "/:post", :post                    # this is post permalink

tree.add "/categories", :categories         # list of categories

tree.add "/categories/:category", :category # listing of posts under each category

```

## Roadmap



* [X] Support multiple payloads at the same level in the tree.

* [X] Return multiple matches when searching the tree.

* [X] Support optionals in the key path.

* [ ] Overcome shared key caveat.



## Implementation



This project has been inspired and adapted from:

[luislavena](https://github.com/luislavena/radix)



## Contributing



1. Fork it ( https://github.com/obsidian/oak/fork )

2. Create your feature branch (`git checkout -b my-new-feature`)

3. Commit your changes (`git commit -am 'Add some feature'`)

4. Push to the branch (`git push origin my-new-feature`)

5. Create a new Pull Request



## Contributors



- [Jason Waldrip](https://github.com/jwaldrip) - creator, maintainer