Functional goes objects

Co-authored-by: Szymon Fiedler <[email protected]>
Co-authored-by: Piotr Jurewicz <[email protected]>

examples/decider/lib/project_management/command_handler.rb

@@ -2,21 +2,22 @@ module ProjectManagement
   class CommandHandler
     def initialize(event_store)
       @event_store = event_store
-      @decider = Issue
     end
 
     def handle(cmd)
-      state, version =
-        @event_store
-          .read
-          .stream(stream_name(cmd.id))
-          .reduce(
-            [@decider.initial_state(cmd.id), -1]
-          ) do |(state, version), event|
-            [@decider.evolve(state, event), version + 1]
-          end
+      decider = Issue.new(cmd.id)
+      version = -1
 
-      case result = @decider.decide(cmd, state)
+      @event_store
+        .read
+        .stream(stream_name(cmd.id))
+        .each
+        .with_index do |event, idx|
+          decider.evolve(event)
+          version = idx
+        end
+
+      case result = decider.decide(cmd)
       when StandardError
         raise Error
       else

examples/decider/lib/project_management/issue.rb

@@ -1,68 +1,74 @@
 module ProjectManagement
-  module Issue
+  class Issue
     InvalidTransition = Class.new(StandardError)
     State = Data.define(:id, :status)
+    private_constant :State
 
-    def self.decide(command, state)
+    def initialize(id)
+      @state = initial_state(id)
+    end
+
+    def decide(command)
       case command
       when CreateIssue
-        if state.status
+        if @state.status
           InvalidTransition.new
         else
-          IssueOpened.new(data: { issue_id: state.id })
+          IssueOpened.new(data: { issue_id: @state.id })
         end
       when ResolveIssue
-        if %i[open in_progress reopened].include? state.status
-          IssueResolved.new(data: { issue_id: state.id })
+        if %i[open in_progress reopened].include? @state.status
+          IssueResolved.new(data: { issue_id: @state.id })
         else
           InvalidTransition.new
         end
       when CloseIssue
-        if %i[open in_progress resolved reopened].include? state.status
-          IssueClosed.new(data: { issue_id: state.id })
+        if %i[open in_progress resolved reopened].include? @state.status
+          IssueClosed.new(data: { issue_id: @state.id })
         else
           InvalidTransition.new
         end
       when ReopenIssue
-        if %i[resolved closed].include? state.status
-          IssueReopened.new(data: { issue_id: state.id })
+        if %i[resolved closed].include? @state.status
+          IssueReopened.new(data: { issue_id: @state.id })
         else
           InvalidTransition.new
         end
       when StartIssueProgress
-        if %i[open reopened].include? state.status
-          IssueProgressStarted.new(data: { issue_id: state.id })
+        if %i[open reopened].include? @state.status
+          IssueProgressStarted.new(data: { issue_id: @state.id })
         else
           InvalidTransition.new
         end
       when StopIssueProgress
-        if %i[in_progress].include? state.status
-          IssueProgressStopped.new(data: { issue_id: state.id })
+        if %i[in_progress].include? @state.status
+          IssueProgressStopped.new(data: { issue_id: @state.id })
         else
           InvalidTransition.new
         end
       end
     end
 
-    def self.evolve(state, event)
-      case event
-      when IssueOpened
-        state.with(status: :open)
-      when IssueResolved
-        state.with(status: :resolved)
-      when IssueClosed
-        state.with(status: :closed)
-      when IssueReopened
-        state.with(status: :reopened)
-      when IssueProgressStarted
-        state.with(status: :in_progress)
-      when IssueProgressStopped
-        state.with(status: :open)
-      end
+    def evolve(event)
+      @state =
+        case event
+        when IssueOpened
+          @state.with(status: :open)
+        when IssueResolved
+          @state.with(status: :resolved)
+        when IssueClosed
+          @state.with(status: :closed)
+        when IssueReopened
+          @state.with(status: :reopened)
+        when IssueProgressStarted
+          @state.with(status: :in_progress)
+        when IssueProgressStopped
+          @state.with(status: :open)
+        end
     end
 
-    def self.initial_state(id)
-      State.new(id: id, status: nil)
-    end
+    private
+
+    def initial_state(id) = State.new(id: id, status: nil)
   end
 end