LHS
===

LHS uses [LHC](//github.com/local-ch/LHC) for http requests.

## Very Short Introduction

Access data that is provided by an http json service with ease using a LHS::Record.

```ruby
class Record < LHS::Record

  endpoint ':service/v2/records'
  endpoint ':service/v2/association/:association_id/records'

end

record = Record.find_by(email: 'somebody@mail.com') #<Record>
record.review # "Lunch was great"
```

## Where to store LHS::Records

Please store all defined LHS::Records in `app/models` as they are not autoloaded by rails otherwise.

## Endpoints

You setup a LHS::Record by configuring one or multiple endpoints. You can also add request options for an endpoint (see following example).

```ruby
class Record < LHS::Record

  endpoint ':service/v2/association/:association_id/records'
  endpoint ':service/v2/association/:association_id/records/:id'
  endpoint ':service/v2/records', cache: true, cache_expires_in: 1.day
  endpoint ':service/v2/records/:id', cache: true, cache_expires_in: 1.day

end
```

Please use placeholders when configuring endpoints also for hosts. Otherwise LHS will match them strictly, which can result in problems when mixing URLs containing `http`, `https` or no protocol at all.
[https://github.com/local-ch/lhc/blob/master/docs/configuration.md#placeholders](LHC Placeholder Configuration)

If you try to setup a LHS::Record with clashing endpoints it will immediately raise an exception.

```ruby
class Record < LHS::Record

  endpoint ':service/v2/records'
  endpoint ':service/v2/something_else'

end
# raises: Clashing endpoints.
```

## Find multiple records

You can query a service for records by using `where`.

```ruby
  Record.where(color: 'blue')
```

This uses the `:service/v2/records` endpoint, cause `:association_id` was not provided. In addition it would add `?color=blue` to the get parameters.

```ruby
  Record.where(association_id: 'fq-a81ngsl1d')
```

Uses the `:service/v2/association/:association_id/records` endpoint.

## Chaining where statements

LHS supports chaining where statements. 
That allows you to chain multiple where-queries:

```ruby
class Record < LHS::Record
  endpoint 'records/'
  endpoint 'records/:id'
end

records = Record.where(color: 'blue')
...
records.where(available: true).each do |record|
  ...
end
```

The example would fetch records with the following parameters: `{color: blue, available: true}`.

## Where values hash

Returns a hash of where conditions.
Common to use in tests, as where queries are not performing any HTTP-requests when no data is accessed.

```ruby
records = Record.where(color: 'blue').where(available: true).where(color: 'red')

expect(
  records
).to have_requested(:get, %r{records/})
  .with(query: hash_including(color: 'blue', available: true))
# will fail as no http request is made (no data requested)

expect(
  records.where_values_hash
).to eq {color: 'red', available: true}
```

## Scopes: Reuse where statements

In order to make common where statements reusable you can organise them in scopes:

```ruby
class Record < LHS::Record
  endpoint 'records/'
  endpoint 'records/:id'
  scope :blue, -> { where(color: 'blue') }
  scope :available, ->(state) { where(available: state) }
end

records = Record.blue.available(true)
The example would fetch records with the following parameters: `{color: blue, visible: true}`.
```

## Error handling with chains

One benefit of chains is lazy evaluation. This means they get resolved when data is accessed. This makes it hard to catch errors with normal `rescue` blocks.

To simplify error handling with chains, you can also chain error handlers to be resolved, as part of the chain.

In case no matchin error handler is found the error gets re-raised.

```ruby
record = Record.where(color: 'blue')
  .handle(LHC::BadRequest, ->(error){ show_error })
  .handle(LHC::Unauthorized, ->(error){ authorize })
```

[List of possible error classes](https://github.com/local-ch/lhc/tree/master/lib/lhc/errors)

## Find single records

`find` finds a unique record by uniqe identifier (usualy id).

If no record is found an error is raised.

`find` can also be used to find a single uniqe record with parameters:

```ruby
  Record.find(association_id: 123, id: 456)
```

`find_by` finds the first record matching the specified conditions.

If no record is found, `nil` is returned.

`find_by!` raises LHC::NotFound if nothing was found.

```ruby
  Record.find_by(id: 'z12f-3asm3ngals')
  Record.find_by(id: 'doesntexist') # nil
```

`first` is an alias for finding the first record without parameters.

```ruby
  Record.first
```

If no record is found, `nil` is returned.

`first!` raises LHC::NotFound if nothing was found.

# Find multiple single records in parallel

In case you want to fetch multiple records by id in parallel, you can also do this with `find`:

```ruby
Record.find(1, 2, 3)
```

If you want to inject values for the failing records, that might not have been found, you can inject values for them with error handlers:

```ruby
data = Record
  .handle(LHC::Unauthorized, ->(response) { Record.new(name: 'unknown') })
  .find(1, 2, 3)
data[1].name # 'unknown'
```

## Navigate data

After fetching [single](#find-single-records) or [multiple](#find-multiple-records) records you can navigate the received data with ease.

```ruby
  records = Record.where(color: 'blue')
  records.collection? # true
  record = records.first
  record.item? # true
  record.parent == records # true
```

## Request based options

You can apply options to the request chain. Those options will be forwarded to the request perfomed by the chain/query.

```ruby
  # Authenticate with OAuth
  options = { auth: { bearer: '123456' } }
  
  AuthenticatedRecord = Record.options(options)
  
  blue_records = AuthenticatedRecord.where(color: 'blue')
  active_records = AuthenticatedRecord.where(active: true)

  AuthenticatedRecord.create(color: 'red')
  
  record = AuthenticatedRecord.find(123)
  # Find resolves the current query and applies all options from the chain
  # All further requests are made from scratch and not based on the previous options
  record.name = 'Walter'

  authenticated_record = record.options(options)
  authenticated_record.valid?
  authenticated_record.save
  authenticated_record.destroy
  authenticated_record.update(name: 'Steve')
```

## Batch processing

**Be careful using methods for batch processing. They could result in a lot of HTTP requests!**

`all` fetches all records from the service by doing multiple requests if necessary.

```ruby
data = Record.all
data.count # 998
data.length # 998
```

[Count vs. Length](#count-vs-length)

`find_each` is a more fine grained way to process single records that are fetched in batches.

```ruby
Record.find_each(start: 50, batch_size: 20, params: { has_reviews: true }) do |record|
  # Iterates over each record. Starts with record nr. 50 and fetches 20 records each batch.
  record
  break if record.some_attribute == some_value
end
```

`find_in_batches` is used by `find_each` and processes batches.
```ruby
Record.find_in_batches(start: 50, batch_size: 20, params: { has_reviews: true }) do |records|
  # Iterates over multiple records (batch size is 20). Starts with record nr. 50 and fetches 20 records each batch.
  records
  break if records.first.name == some_value
end
```

## Create records

```ruby
  record = Record.create(
    recommended: true,
    source_id: 'aaa',
    content_ad_id: '1z-5r1fkaj'
  )
```

When creation fails, the object contains errors. It provides them through the `errors` attribute:

```ruby
  record.errors #<LHS::Errors>
  record.errors.include?(:ratings) # true
  record.errors[:ratings] # ['REQUIRED_PROPERTY_VALUE']
  record.errors.messages # {:ratings=>["REQUIRED_PROPERTY_VALUE"], :recommended=>["REQUIRED_PROPERTY_VALUE"]}
  record.errors.message # ratings must be set when review or name or review_title is set | The property value is required; it cannot be null, empty, or blank."
```

## Create records through associations (nested resources)

```ruby
  class Review < LHS::Record
    endpoint ':service/reviews'
  end 

  class Comment < LHS::Record
    endpoint ':service/reviews/:review_id/comments'
  end
```

### Item
```ruby
  review = Review.find(1)
  # Review#1
  # :href => ':service/reviews/1
  # :text => 'Simply awesome'
  # :comment => { :href => ':service/reviews/1/comments }

  review.comment.create(text: 'Thank you!')
  # Comment#1
  # :href => ':service/reviews/1/comments
  # :text => 'Thank you!'

  review
  # Review#1
  # :href => ':service/reviews/1
  # :text => 'Simply awesome'
  # :comment => { :href => ':service/reviews/1/comments, :text => 'Thank you!' }
```

If the item already exists `ArgumentError` is raised.

### Expanded collection
```ruby
  review = Review.includes(:comments).find(1)
  # Review#1
  # :href => ':service/reviews/1'
  # :text => 'Simply awesome'
  # :comments => { :href => ':service/reviews/1/comments, :items => [] }

  review.comments.create(text: 'Thank you!')
  # Comment#1
  # :href => ':service/reviews/1/comments/1'
  # :text => 'Thank you!'

  review
  # Review#1
  # :href => ':service/reviews/1'
  # :text => 'Simply awesome'
  # :comments => { :href => ':service/reviews/1/comments, :items => [{ :href => ':service/reviews/1/comments/1', :text => 'Thank you!' }] }
```

### Not expanded collection
```ruby
  review = Review.find(1)
  # Review#1
  # :href => ':service/reviews/1'
  # :text => 'Simply awesome'
  # :comments => { :href => ':service/reviews/1/comments' }

  review.comments.create(text: 'Thank you!')
  # Comment#1
  # :href => ':service/reviews/1/comments/1'
  # :text => 'Thank you!'

  review
  # Review#1
  # :href => ':service/reviews/1
  # :text => 'Simply awesome'
  # :comments => { :href => ':service/reviews/1/comments', :items => [{ :href => ':service/reviews/1/comments/1', :text => 'Thank you!' }] }
```

## Build new records

Build and persist new items from scratch are done either with `new` or it's alias `build`.

```ruby
  record = Record.new(recommended: true)
  record.save
```

## Custom setters and getters

Sometimes it is the case that you want to have your custom getters and setters and convert the data to a processable format behind the scenes. 
The initializer will now use custom setter if one is defined:

```ruby

module RatingsConversions
  def ratings=(values)
    super(
      values.map { |k, v| { name: k, value: v } }
    )
  end
end

class Record < LHS::Record
  prepend RatingsConversions
end

record = Record.new(ratings: { quality: 3 })
record.ratings # [{ :name=>:quality, :value=>3 }]

```

If you have an accompanying getter the whole data manipulation would be internal only.

```ruby
module RatingsConversions
  def ratings=(values)
    super(
      values.map { |k, v| { name: k, value: v } }
    )
  end

  def ratings
    super.map { |r| [r[:name], r[:value]] }]
  end
end

class Record < LHS::Record
  prepend RatingsConversions
end

record = Record.new(ratings: { quality: 3 }) # [{ :name=>:quality, :value=>3 }]
record.ratings # {:quality=>3}

```

## Include linked resources

When fetching records, you can specify in advance all the linked resources that you want to include in the results. With `includes`, LHS ensures that all matching and explicitly linked resources are loaded and merged, if they're included in the server response.

The implementation is heavily influenced by [http://guides.rubyonrails.org/active_record_class_querying](http://guides.rubyonrails.org/active_record_class_querying.html#eager-loading-associations) and you should read it to understand this feature in all its glory.

### One-Level `includes`

```ruby
  # a claim has a localch_account
  claims = Claims.includes(:localch_account).where(place_id: 'huU90mB_6vAfUdVz_uDoyA')
  claims.first.localch_account.email # 'test@email.com'
```

Before include:
```json
{
  "href" : "http://datastore/v2/places/huU90mB_6vAfUdVz_uDoyA/claims",
  "items" : [
    {
      "href" : "http://datastore/v2/localch-accounts/6bSss0y93lK0MrVsgdNNdg/claims/huU90mB_6vAfUdVz_uDoyA",
      "localch_account" : {
        "href" : "http://datastore/v2/localch-accounts/6bSss0y93lK0MrVsgdNNdg"
      }
    }
  ]
}
```

After include:
```json
{
  "href" : "http://datastore/v2/places/huU90mB_6vAfUdVz_uDoyA/claims",
  "items" : [
    {
      "href" : "http://datastore/v2/localch-accounts/6bSss0y93lK0MrVsgdNNdg/claims/huU90mB_6vAfUdVz_uDoyA",
      "localch_account" : {
        "href" : "http://datastore/v2/localch-accounts/6bSss0y93lK0MrVsgdNNdg",
        "id" : "6bSss0y93lK0MrVsgdNNdg",
        "name" : "Myriam",
        "phone" : "12345678",
        "email" : "email@gmail.com"
      }
    }
  ]
}
```

### Two-Level `includes`

```ruby
  # a record has a association, which has an entry
  records = Record.includes(association: :entry).where(has_reviews: true)
  records.first.association.entry.name # 'Casa Ferlin'
```

### Multiple `includes`

```ruby
  # list of includes
  claims = Claims.includes(:localch_account, :entry).where(place_id: 'huU90mB_6vAfUdVz_uDoyA')

  # array of includes
  claims = Claims.includes([:localch_account, :entry]).where(place_id: 'huU90mB_6vAfUdVz_uDoyA')

  # Two-level with array of includes
  records = Record.includes(campaign: [:entry, :user]).where(has_reviews: true)
```

### Known LHS::Records are used to request linked resources

When including linked resources with `includes`, known/defined services and endpoints are used to make those requests.
That also means that options for endpoints of linked resources are applied when requesting those in addition.
This allows you to include protected resources (e.g. Basic auth) as endpoint options for oauth authentication get applied.

The [Auth Inteceptor](https://github.com/local-ch/lhc-core-interceptors#auth-interceptor) from [lhc-core-interceptors](https://github.com/local-ch/lhc-core-interceptors) is used to configure the following endpoints.

```ruby
class Favorite < LHS::Record

  endpoint ':service/:user_id/favorites', auth: { basic: { username: 'steve', password: 'can' } }
  endpoint ':service/:user_id/favorites/:id', auth: { basic: { username: 'steve', password: 'can' } }

end

class Place < LHS::Record

  endpoint ':service/v2/places', auth: { basic: { username: 'steve', password: 'can' } }
  endpoint ':service/v2/places/:id', auth: { basic: { username: 'steve', password: 'can' } }

end

Favorite.includes(:place).where(user_id: current_user.id)
# Will include places and applies endpoint options to authenticate the request.
```

### Forward options used for request made to include referenced resources

Provide options to the requests made to include referenced resources:

```

  Favorite.includes(:place).references(place: { auth: { bearer: '123' }})

```

## Map data

To influence how data is accessed/provied, you can use mappings to either map deep nested data or to manipulate data when its accessed. Simply create methods inside the LHS::Record. They can access underlying data:

```ruby
class LocalEntry < LHS::Record
  endpoint ':service/v2/local-entries'

  def name
    addresses.first.business.identities.first.name
  end

end
```

### Nested records

Nested records (in nested data) are automaticaly casted when the href matches any defined endpoint of any LHS::Record.

```ruby
class Place < LHS::Record
  endpoint ':service/v2/places'

  def name
    addresses.first.business.identities.first.name
  end
end

class Favorite < LHS::Record
  endpoint ':service/v2/favorites'
end

favorite = Favorite.includes(:place).find(1)
favorite.place.name # local.ch AG
```

If automatic-detection of nested records does not work, make sure your LHS::Records are stored in `app/models`!

## Setters

You can change attributes of LHS::Records:

```ruby
  record = Record.find(id: 'z12f-3asm3ngals')
  rcord.recommended = false
```

## Save

You can persist changes with `save`. `save` will return `false` if persisting fails. `save!` instead will raise an exception.

```ruby
  record = Record.find('1z-5r1fkaj')
  record.recommended = false
  record.save
```

## Update

`update` will return false if persisting fails. `update!` instead will an raise exception.

`update` always updates the data of the local object first, before it tries to sync with an endpoint. So even if persisting fails, the local object is updated.

```ruby
record = Record.find('1z-5r1fkaj')
record.update(recommended: false)
```

## Destroy

You can delete records remotely by calling `destroy` on an LHS::Record.

```ruby
  record = Record.find('1z-5r1fkaj')
  record.destroy
```

You can also destroy records directly without fetching them first:

```ruby
  destroyed_record = Record.destroy('1z-5r1fkaj')
```

or with parameters:

```ruby
  destroyed_records = Record.destroy(name: 'Steve')
```

## Validation

In order to validate LHS::Records before persisting them, you can use the `valid?` (`validate` alias) method.

The specific endpoint has to support validations without peristance. An endpoint has to be enabled (opt-in) for validations in the service configuration.

```ruby
class User < LHS::Record
  endpoint ':service/v2/users', validates: { params: { persist: false } }
end

user = User.build(email: 'im not an email address')
unless user.valid?
  fail(user.errors[:email])
end
```

The parameters passed to the `validates` endpoint option are used to perform the validation:

```ruby
  endpoint ':service/v2/users', validates: { params: { persist: false } }  # will add ?persist=false to the request
  endpoint ':service/v2/users', validates: { params: { publish: false } }  # will add ?publish=false to the request
  endpoint ':service/v2/users', validates: { params: { validates: true } } # will add ?validates=true to the request
  endpoint ':service/v2/users', validates: { path: 'validate' }            # will perform a validation via :service/v2/users/validate
```

## Custom validation errors

In case you want to add custom validation errors to an instance of LHS::Record:

```ruby
user.errors.add(:name, 'The name you provided is not valid.')
```

### Know issue with `ActiveModel::Validations`
If you are using `ActiveModel::Validations` and add errors to the LHS::Record instance - as described above - then those errors will be overwritten by the errors from `ActiveModel::Validations` when using `save`  or `valid?`. [Open issue](https://github.com/local-ch/lhs/issues/159)

## Pagination

LHS supports paginated APIs and it also supports various pagination strategies and by providing configuration possibilities.

LHS diffentiates between the *pagination strategy* (how items/pages are navigated) itself and *pagination keys* (how stuff is named).

*Example 1 "offset"-strategy (default configuration)*
```ruby
# API response
{
  items: [{...}, ...]
  total: 300,
  limit: 100,
  offset: 0
}
# Next 'pages' are navigated with offset: 100, offset: 200, ...

# Nothing has to be configured in LHS because this is default pagination naming and strategy
class Results < LHS::Record
  endpoint 'results'
end
```

*Example 2 "page"-strategy and some naming configuration*
```ruby
# API response
{
  docs: [{...}, ...]
  totalPages: 3,
  limit: 100,
  page: 1
}
# Next 'pages' are navigated with page: 1, offset: 2, ...

# How LHS has to be configured
class Results < LHS::Record
  configuration items_key: 'docs', total_key: 'totalPages', pagination_key: 'page', pagination_strategy: 'page'
  endpoint 'results'
end
```

*Example 3 "start"-strategy and naming configuration*
```ruby
# API response
{
  results: [{...}, ...]
  total: 300,
  badgeSize: 100,
  startAt: 1
}
# Next 'pages' are navigated with startWith: 101, startWith: 201, ...

# How LHS has to be configured
class Results < LHS::Record
  configuration items_key: 'results', limit_key: 'badgeSize', pagination_key: 'startAt', pagination_strategy: 'start'
  endpoint 'results'
end
```

`items_key` key used to determine items of the current page (e.g. `docs`, `items`, etc.).

`limit_key` key used to work with page limits (e.g. `size`, `limit`, etc.)

`pagination_key` key used to paginate multiple pages (e.g. `offset`, `page`, `startAt` etc.).

`pagination_strategy` used to configure the strategy used for navigating (e.g. `offset`, `page`, `start`, etc.).

`total_key` key used to determine the total amount of items (e.g. `total`, `totalResults`, etc.).

In case of paginated resources it's important to know the difference between [count vs. length](#count-vs-length)

### Pagination Chains

You can use chainable pagination in combination with query chains:

```ruby
  class Record < LHS::Record
    endpoint ':service/records'
  end
  Record.page(3).per(20).where(color: 'blue')
  # /records?offset=40&limit=20&color=blue
```

The applied pagination strategy depends on the actual configured pagination, so the interface is the same for all strategies:

```ruby
  class Record < LHS::Record
    endpoint ':service/records'
    configuration pagination_strategy: 'page'
  end
  Record.page(3).per(20).where(color: 'blue')
  # /records?page=3&limit=20&color=blue
```

```ruby
  class Record < LHS::Record
    endpoint ':service/records'
    configuration pagination_strategy: 'start'
  end
  Record.page(3).per(20).where(color: 'blue')
  # /records?start=41&limit=20&color=blue
```

`limit(argument)` is an alias for `per(argument)`. Take notice that `limit` without argument instead, makes the query resolve and provides the current limit from the responds.

### Partial Kaminari support

LHS implements an interface that makes it partially working with Kaminari.

The kaminari’s page parameter is in params[:page]. For example, you can use kaminari to render paginations based on LHS Records. Typically, your code will look like this:

```ruby
# controller
@items = Record.page(params[:page]).per(100)
```

```ruby
# view
= paginate @items
```

## form_for Helper
Rails `form_for` view-helper can be used in combination with instances of LHS::Record to autogenerate forms:
```ruby
<%= form_for(@instance, url: '/create') do |f| %>
  <%= f.text_field :name %>
  <%= f.text_area :text %>
  <%= f.submit "Create" %>
<% end %>
```

## Count vs. Length

The behaviour of `count` and `length` is based on ActiveRecord's behaviour.

`count` Determine the number of elements by taking the number of total elements that is provided by the endpoint/api.

`length` This returns the number of elements loaded from an endpoint/api. In case of paginated resources this can be different to count, as it depends on how many pages have been loaded.

## Inheritance

You can inherit from previously defined records and also inherit endpoints that way:

```
class Base < LHS::Record
  endpoint 'records/:id'
end

class Example < Base
end

Example.find(1) # GET records/1
```

## License

[GNU Affero General Public License Version 3.](https://www.gnu.org/licenses/agpl-3.0.en.html)