Allow passing blocks to is_enabled? to determine default_result (#33)

- add docs relevant to feature in README
- add unit tests

.rubocop.yml

@@ -52,6 +52,9 @@ Style/HashTransformKeys:
 Style/HashTransformValues:
   Enabled: true
 
+Style/DoubleNegation:
+  Enabled: false
+
 Style/IfInsideElse:
   Exclude:
     - 'bin/unleash-client'

README.md

@@ -201,6 +201,40 @@ if UNLEASH.is_enabled? "AwesomeFeature", @unleash_context, true
 end
 ```
 
+Another possibility is to send a block, [Lambda](https://ruby-doc.org/core-3.0.1/Kernel.html#method-i-lambda) or [Proc](https://ruby-doc.org/core-3.0.1/Proc.html#method-i-yield)
+to evaluate the default value:
+
+```ruby
+net_check_proc = proc do |feature_name, context|
+  context.remote_address.starts_with?("10.0.0.")
+end
+
+if UNLEASH.is_enabled?("AwesomeFeature", @unleash_context, &net_check_proc)
+  puts "AwesomeFeature is enabled by default if you are in the 10.0.0.* network."
+end
+```
+
+or
+
+```ruby
+awesomeness = 10
+@unleash_context.properties[:coolness] = 10
+
+if UNLEASH.is_enabled?("AwesomeFeature", @unleash_context) { |feat, ctx| awesomeness >= 6 && ctx.properties[:coolness] >= 8 }
+  puts "AwesomeFeature is enabled by default if both the user has a high enought coolness and the application has a high enough awesomeness"
+end
+```
+
+Note:
+- The block/lambda/proc can use feature name and context as an arguments.
+- The client will evaluate the fallback function once per call of `is_enabled()`.
+  Please keep this in mind when creating your fallback function!
+- The returned value of the block should be a boolean.
+  However the client will coerce the result to boolean via `!!`.
+- If both a `default_value` and `fallback_function` are supplied,
+  the client will define the default value by `OR`ing the default value and the output of the fallback function.
+
+
 Alternatively by using `if_enabled` you can send a code block to be executed as a parameter:
 
 ```ruby
@@ -209,6 +243,8 @@ UNLEASH.if_enabled "AwesomeFeature", @unleash_context, true do
 end
 ```
 
+Note: `if_enabled` only supports `default_value`, but not `fallback_function`.
+
 ##### Variations
 
 If no variant is found in the server, use the fallback variant.
@@ -232,6 +268,7 @@ Method Name | Description | Return Type |
 `shutdown` | Save metrics to disk, flush metrics to server, and then kill ToggleFetcher and MetricsReporter threads. A safe shutdown. Not really useful in long running applications, like web applications. | nil |
 `shutdown!` | Kill ToggleFetcher and MetricsReporter threads immediately. | nil |
 
+For the full method signatures, please see [client.rb](lib/unleash/client.rb)
 
 ## Local test client
 

lib/unleash/client.rb

@@ -28,9 +28,15 @@ def initialize(*opts)
       start_metrics unless Unleash.configuration.disable_metrics
     end
 
-    def is_enabled?(feature, context = nil, default_value = false)
+    def is_enabled?(feature, context = nil, default_value_param = false, &fallback_blk)
       Unleash.logger.debug "Unleash::Client.is_enabled? feature: #{feature} with context #{context}"
 
+      if block_given?
+        default_value = default_value_param || !!fallback_blk.call(feature, context)
+      else
+        default_value = default_value_param
+      end
+
       if Unleash.configuration.disable_client
         Unleash.logger.warn "unleash_client is disabled! Always returning #{default_value} for feature #{feature}!"
         return default_value

spec/unleash/client_spec.rb

@@ -212,19 +212,131 @@
     expect(WebMock).not_to have_requested(:post, 'http://test-url//client/metrics')
   end
 
-  it "should return default results if running with disable_client" do
+  it "should return default results via block or param if running with disable_client" do
     Unleash.configure do |config|
       config.disable_client = true
     end
     unleash_client = Unleash::Client.new
 
+    expect(
+      unleash_client.is_enabled?('any_feature')
+    ).to be false
+
     expect(
       unleash_client.is_enabled?('any_feature', {}, true)
-    ).to eq(true)
+    ).to be true
 
     expect(
       unleash_client.is_enabled?('any_feature2', {}, false)
-    ).to eq(false)
+    ).to be false
+
+    expect(
+      unleash_client.is_enabled?('any_feature3') { true }
+    ).to be true
+
+    expect(
+      unleash_client.is_enabled?('any_feature3') { false }
+    ).to be false
+
+    expect(
+      unleash_client.is_enabled?('any_feature3', {}) { true }
+    ).to be true
+
+    expect(
+      unleash_client.is_enabled?('any_feature3', {}) { false }
+    ).to be false
+
+    expect(
+      unleash_client.is_enabled?('any_feature5', {}) { nil }
+    ).to be false
+
+    # should never really send both the default value and a default block,
+    # but if it is done, we OR the two values
+    expect(
+      unleash_client.is_enabled?('any_feature3', {}, true) { true }
+    ).to be true
+
+    expect(
+      unleash_client.is_enabled?('any_feature3', {}, false) { true }
+    ).to be true
+
+    expect(
+      unleash_client.is_enabled?('any_feature3', {}, true) { false }
+    ).to be true
+
+    expect(
+      unleash_client.is_enabled?('any_feature3', {}, false) { false }
+    ).to be false
+
+    expect(
+      unleash_client.is_enabled?('any_feature5', {}) { 'random_string' }
+    ).to be true # expect "a string".to be_truthy
+
+    expect do |b|
+      unleash_client.is_enabled?('any_feature3', &b).to yield_with_no_args
+    end
+
+    expect do |b|
+      unleash_client.is_enabled?('any_feature3', {}, &b).to yield_with_no_args
+    end
+
+    expect do |b|
+      unleash_client.is_enabled?('any_feature3', {}, true, &b).to yield_with_no_args
+    end
+
+    number_eight = 8
+    expect(
+      unleash_client.is_enabled?('any_feature5', {}) do
+        number_eight >= 5
+      end
+    ).to be true
+
+    expect(
+      unleash_client.is_enabled?('any_feature5', {}) do
+        number_eight < 5
+      end
+    ).to be false
+
+    context_params = {
+      session_id: 'verylongsesssionid',
+      remote_address: '127.0.0.2',
+      properties: {
+        env: 'dev'
+      }
+    }
+    unleash_context = Unleash::Context.new(context_params)
+    expect(
+      unleash_client.is_enabled?('any_feature6', unleash_context) do |feature, context|
+        feature == 'any_feature6' && \
+        context.remote_address == '127.0.0.2' && context.session_id.length == 18 && context.properties[:env] == 'dev'
+      end
+    ).to be true
+
+    proc = proc do |_feat, ctx|
+      ctx.remote_address.starts_with?("127.0.0.")
+    end
+    expect(
+      unleash_client.is_enabled?('any_feature6', unleash_context) { proc }
+    ).to be true
+    expect(
+      unleash_client.is_enabled?('any_feature6', unleash_context, true) { proc }
+    ).to be true
+    expect(
+      unleash_client.is_enabled?('any_feature6', unleash_context, false) { proc }
+    ).to be true
+
+    proc_feat = proc do |feat, _ctx|
+      feat != 'feature6'
+    end
+    expect(
+      unleash_client.is_enabled?('feature6', unleash_context, &proc_feat)
+    ).to be false
+    expect(
+      unleash_client.is_enabled?('feature6', unleash_context, true, &proc_feat)
+    ).to be true
+    expect(
+      unleash_client.is_enabled?('feature6', unleash_context, false, &proc_feat)
+    ).to be false
   end
 
   it "should not connect anywhere if running with disable_client" do