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Simpler, safer and more composable operations

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<h1 align="center">FService</h1>

<p align="center">
    <i>Simpler, safer and more composable operations</i>
    <br>
    <br>
    <img src="https://img.shields.io/gem/v/f_service">
    <img src="https://github.com/Fretadao/f_service/workflows/Ruby/badge.svg">
    <a href="https://github.com/Fretadao/f_service/blob/master/LICENSE">
      <img src="https://img.shields.io/github/license/Fretadao/f_service.svg" alt="License">
    </a>
  </p>
</p>

FService is a small gem that provides a base class for your services (aka operations).
The goal is to make services simpler, safer, and more composable.
It uses the Result monad for handling operations.

## Installation

Add this line to your application's Gemfile:

```ruby
gem 'f_service'
```

And then execute:

$ bundle

Or install it yourself as:

$ gem install f_service

## Usage

### Creating your service

To start using it, you have to create your service class inheriting from FService::Base.

```ruby
class User::Create < FService::Base
end
```

Now, define your initializer to setup data.

```ruby
class User::Create < FService::Base
  def initialize(name:)
    @name = name
  end
end
```

The next step is writing the `#run` method, which is where the work should be done.
Use the methods `#Success` and `#Failure` to handle your return values.
You can optionally specify a list of types which represents that result and a value for your result.

```ruby
class User::Create < FService::Base
  # ...
  def run
    return Failure(:no_name, :invalid_attribute) if @name.nil?

user = UserRepository.create(name: @name)
    if user.save
      Success(:success, :created, data: user)
    else
      Failure(:creation_failed, data: user.errors)
    end
  end
end
```

> Remember, you **have** to return an `FService::Result` at the end of your services.

### Using your service

To run your service, use the method `#call` provided by `FService::Base`. We like to use the [implicit call](https://stackoverflow.com/a/19108981/8650655), but you can use it in the form you like most.

```ruby
User::Create.(name: name)
# or
User::Create.call(name: name)
```

> We do **not** recommend manually initializing and running your service because it **will not**
> type check your result (and you could lose nice features like [pattern
> matching](#pattern-matching) and [service chaining](#chaining-services))!

### Using the result

Use the methods `#successful?` and `#failed?` to check the status of your result. If it is successful, you can access the value with `#value`, and if your service fails, you can access the error with `#error`.

A hypothetical controller action using the example service could look like this:

```ruby
class UsersController < BaseController
  def create
    result = User::Create.(user_params)

if result.successful?
      json_success(result.value)
    else
      json_error(result.error)
    end
  end
end
```

> Note that you're not limited to using services inside controllers. They're just PORO's (Play Old Ruby Objects), so you can use in controllers, models, etc. (even other services!).

### Pattern matching

The code above could be rewritten using the `#on_success` and `#on_failure` hooks. They work similar to pattern matching:

```ruby
class UsersController < BaseController
  def create
    User::Create.(user_params)
                .on_success { |value| return json_success(value) }
                .on_failure { |error| return json_error(error) }
  end
end
```

Or else it is possible to specify an unhandled option to ensure that the callback will process that message anyway the
error.

```ruby
class UsersController < BaseController
  def create
    User::Create.(user_params)
                .on_success(unhandled: true) { |value| return json_success(value) }
                .on_failure(unhandled: true) { |error| return json_error(error) }
  end
end
```

> You can ignore any of the callbacks, if you want to.

Going further, you can match the Result type, in case you want to handle them differently:

```ruby
class UsersController < BaseController
  def create
    User::Create.(user_params)
                .on_success(:user_created) { |value| return json_success(value) }
                .on_success(:user_already_exists) { |value| return json_success(value) }
                .on_failure(:invalid_data) { |error| return json_error(error) }
                .on_failure(:critical_error) do |error|
                  MyLogger.report_failure(error)

return json_error(error)
                end
  end
end
```

It's possible to provide multiple types to the hooks too. If the result type matches any of the given types,
the hook will run.

```ruby
class UsersController < BaseController
  def create
    User::Create.(user_params)
                .on_success(:user_created, :user_already_exists) { |value| return json_success(value) }
                .on_failure(:invalid_data) { |error| return json_error(error) }
                .on_failure(:critical_error) do |error|
                  MyLogger.report_failure(error)

return json_error(error)
                end
  end
end
```

### Type precedence

FService matches the service's types from left to right, from more specific to more generic.
For example, the following result `Failure(:unprocessable_entity, :client_error, :http_response)` will match in the following order:
1. `:unprocessable_entity`;
2. `:client_error`;
3. `:http_response`;
4. unmatched block;

### Chaining services

Since all services return Results, you can chain service calls making a data pipeline.
If some step fails, it will short circuit the call chain.

```ruby
class UsersController < BaseController
  def create
    result = User::Create.(user_params)
                         .and_then { |user| User::Login.(user) }
                         .and_then { |user| User::SendWelcomeEmail.(user) }

if result.successful?
      json_success(result.value)
    else
      json_error(result.error)
    end
  end
end
```

You can use the `.to_proc` method on FService::Base to avoid explicit inputs when chaining services:

```ruby
class UsersController < BaseController
  def create
    result = User::Create.(user_params)
                         .and_then(&User::Login)
                         .and_then(&User::SendWelcomeEmail)
    # ...
  end
end
```

### `Check` and `Try`

You can use `Check` to converts a boolean to a Result, truthy values map to `Success`, and falsey values map to `Failures`:

```ruby
Check(:math_works) { 1 < 2 }
# => #<Success @value=true, @types=[:math_works]>

Check(:math_works) { 1 > 2 }
# => #<Failure @error=false, @types=[:math_works]>
```

`Try` transforms an exception into a `Failure` if some exception is raised for the given block. You can specify which exception class to watch for
using the parameter `catch`.

```ruby
class IHateEvenNumbers < FService::Base
  def run
    Try(:rand_int) do
      n = rand(1..10)
      raise "Yuck! It's a #{n}" if n.even?

n
    end
  end
end

IHateEvenNumbers.call
# => #<Success @value=9, @types=[:rand_int]>

IHateEvenNumbers.call
# => #<Failure @error=#<RuntimeError: Yuck! It's a 4>, @types=[:rand_int]>
```

## Testing

We provide some helpers and matchers to make ease to test code envolving Fservice services.

To make available in the system, in the file 'spec/spec_helper.rb' or 'spec/rails_helper.rb'

add the folowing require:

```rb
require 'f_service/rspec'
```

### Mocking a result

```rb
mock_service(Uer::Create)
# => Mocks a successful result with all values nil

mock_service(Uer::Create, result: :success)
# => Mocks a successful result with all values nil

mock_service(Uer::Create, result: :success, types: [:created, :success])
# => Mocks a successful result with type created

mock_service(Uer::Create, result: :success, types: :created, value: instance_spy(User))
# => Mocks a successful result with type created and a value

mock_service(Uer::Create, result: :failure)
# => Mocs a failure with all nil values

mock_service(User::Create, result: :failure, types: [:unprocessable_entity, :client_error])
# => Mocs a failure with a failure type

mock_service(User::Create, result: :failure, types: [:unprocessable_entity, :client_error], value: { name: ["can't be blank"] })
# => Mocs a failure with a failure type and an error value
```

### Matching a result

```rb
expect(User::Create.(name: 'Joe')).to have_succeed_with(:created)

expect(User::Create.(name: 'Joe')).to have_succeed_with(:created).and_value(an_instance_of(User))

expect(User::Create.(name: nil)).to have_failed_with(:invalid_attributes)

expect(User::Create.(name: nil)).to have_failed_with(:invalid_attributes).and_error({ name: ["can't be blank"] })

expect(User::Create.(name: nil)).to have_failed_with(:invalid_attributes).and_error(a_hash_including(name: ["can't be blank"]))
```

## API Docs

You can access the API docs [here](https://www.rubydoc.info/gems/f_service/).

## Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that allows you to experiment.

To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/Fretadao/f_service.

## License

The gem is available as open-source under the terms of the [MIT License](https://opensource.org/licenses/MIT).

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