From fb96b9230da7be5c24210e76df01c8c468124dff Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Pacana?= <pawel.pacana@gmail.com>
Date: Wed, 22 Nov 2023 14:15:11 +0100
Subject: [PATCH] Communicate with exceptions

Co-authored-by: Szymon Fiedler <szymon.fiedler@gmail.com>
Co-authored-by: Piotr Jurewicz <pjurewicz93@gmail.com>
---
 .../lib/project_management/command_handler.rb | 17 +++----
 .../decider/lib/project_management/issue.rb   | 49 +++++++------------
 2 files changed, 24 insertions(+), 42 deletions(-)

diff --git a/examples/decider/lib/project_management/command_handler.rb b/examples/decider/lib/project_management/command_handler.rb
index d539213..936a229 100644
--- a/examples/decider/lib/project_management/command_handler.rb
+++ b/examples/decider/lib/project_management/command_handler.rb
@@ -17,16 +17,13 @@ def handle(cmd)
           version = idx
         end
 
-      case result = decider.decide(cmd)
-      when StandardError
-        raise Error
-      else
-        @event_store.publish(
-          result,
-          stream_name: stream_name(cmd.id),
-          expected_version: version
-        )
-      end
+      @event_store.publish(
+        decider.decide(cmd),
+        stream_name: stream_name(cmd.id),
+        expected_version: version
+      )
+    rescue Issue::InvalidTransition
+      raise Error
     end
 
     private
diff --git a/examples/decider/lib/project_management/issue.rb b/examples/decider/lib/project_management/issue.rb
index 93154ed..39734ba 100644
--- a/examples/decider/lib/project_management/issue.rb
+++ b/examples/decider/lib/project_management/issue.rb
@@ -1,6 +1,7 @@
 module ProjectManagement
   class Issue
     InvalidTransition = Class.new(StandardError)
+
     State = Data.define(:id, :status)
     private_constant :State
 
@@ -46,53 +47,37 @@ def evolve(event)
     private
 
     def open
-      if @state.status
-        InvalidTransition.new
-      else
-        IssueOpened.new(data: { issue_id: @state.id })
-      end
+      fail if @state.status
+      IssueOpened.new(data: { issue_id: @state.id })
     end
 
     def resolve
-      if %i[open in_progress reopened].include? @state.status
-        IssueResolved.new(data: { issue_id: @state.id })
-      else
-        InvalidTransition.new
-      end
+      fail unless %i[open in_progress reopened].include? @state.status
+      IssueResolved.new(data: { issue_id: @state.id })
     end
 
     def close
-      if %i[open in_progress resolved reopened].include? @state.status
-        IssueClosed.new(data: { issue_id: @state.id })
-      else
-        InvalidTransition.new
-      end
+      fail unless %i[open in_progress resolved reopened].include? @state.status
+      IssueClosed.new(data: { issue_id: @state.id })
     end
 
     def reopen
-      if %i[resolved closed].include? @state.status
-        IssueReopened.new(data: { issue_id: @state.id })
-      else
-        InvalidTransition.new
-      end
+      fail unless %i[resolved closed].include? @state.status
+      IssueReopened.new(data: { issue_id: @state.id })
     end
 
-    def stop
-      if %i[in_progress].include? @state.status
-        IssueProgressStopped.new(data: { issue_id: @state.id })
-      else
-        InvalidTransition.new
-      end
+    def start
+      fail unless %i[open reopened].include? @state.status
+      IssueProgressStarted.new(data: { issue_id: @state.id })
     end
 
-    def start
-      if %i[open reopened].include? @state.status
-        IssueProgressStarted.new(data: { issue_id: @state.id })
-      else
-        InvalidTransition.new
-      end
+    def stop
+      fail unless %i[in_progress].include? @state.status
+      IssueProgressStopped.new(data: { issue_id: @state.id })
     end
 
+    def fail = raise InvalidTransition
+
     def initial_state(id) = State.new(id: id, status: nil)
   end
 end