From c6de8530bad965d04c04bf8380b28cba8a28802e Mon Sep 17 00:00:00 2001
From: Jan Dudulski <jan@dudulski.pl>
Date: Wed, 2 Jul 2025 22:10:18 +0200
Subject: [PATCH] decide.rb example

---
 README.md                                     | 15 ++++
 examples/decide.rb/.mutant.yml                | 14 ++++
 examples/decide.rb/Gemfile                    |  9 +++
 examples/decide.rb/Gemfile.lock               | 43 +++++++++++
 examples/decide.rb/Makefile                   | 10 +++
 examples/decide.rb/lib/project_management.rb  |  6 ++
 .../lib/project_management/handler.rb         | 57 +++++++++++++++
 .../decide.rb/lib/project_management/issue.rb | 71 +++++++++++++++++++
 .../lib/project_management/repository.rb      | 31 ++++++++
 examples/decide.rb/test/issue_test.rb         | 19 +++++
 mise.toml                                     |  2 +
 11 files changed, 277 insertions(+)
 create mode 100644 examples/decide.rb/.mutant.yml
 create mode 100644 examples/decide.rb/Gemfile
 create mode 100644 examples/decide.rb/Gemfile.lock
 create mode 100644 examples/decide.rb/Makefile
 create mode 100644 examples/decide.rb/lib/project_management.rb
 create mode 100644 examples/decide.rb/lib/project_management/handler.rb
 create mode 100644 examples/decide.rb/lib/project_management/issue.rb
 create mode 100644 examples/decide.rb/lib/project_management/repository.rb
 create mode 100644 examples/decide.rb/test/issue_test.rb
 create mode 100644 mise.toml

diff --git a/README.md b/README.md
index 06df7fe..fe8b028 100644
--- a/README.md
+++ b/README.md
@@ -93,3 +93,18 @@ More: https://blog.arkency.com/make-your-ruby-code-more-modular-and-functional-w
 - aggregate not aware of events
 - aggregate object is still responsible for holding invariants
 - no id in domain class
+
+### Decider
+
+[source](examples/decider)
+
+- clear separation of state sourcing (with projection)
+- aggregate with decider pattern
+
+### Decider with decide.rb gem
+
+[source](examples/decide.rb)
+
+- clear separation of state sourcing (with projection) with expected version
+- aggregate with decider pattern and decide.rb DSL
+- mapping between infra (RES) events and domain events used inside decider
diff --git a/examples/decide.rb/.mutant.yml b/examples/decide.rb/.mutant.yml
new file mode 100644
index 0000000..d14ff20
--- /dev/null
+++ b/examples/decide.rb/.mutant.yml
@@ -0,0 +1,14 @@
+integration:
+  name: minitest
+includes:
+  - lib
+requires:
+  - project_management
+matcher:
+  subjects:
+    - ProjectManagement*
+  ignore:
+    - ProjectManagement::Test*
+coverage_criteria:
+  process_abort: true
+usage: opensource
\ No newline at end of file
diff --git a/examples/decide.rb/Gemfile b/examples/decide.rb/Gemfile
new file mode 100644
index 0000000..422a201
--- /dev/null
+++ b/examples/decide.rb/Gemfile
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+gem "ruby_event_store"
+gem "decide.rb", require: "decider"
+gem "minitest"
+gem "mutant"
+gem "mutant-minitest"
diff --git a/examples/decide.rb/Gemfile.lock b/examples/decide.rb/Gemfile.lock
new file mode 100644
index 0000000..b6aa790
--- /dev/null
+++ b/examples/decide.rb/Gemfile.lock
@@ -0,0 +1,43 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    ast (2.4.2)
+    concurrent-ruby (1.3.4)
+    decide.rb (0.6.2)
+      concurrent-ruby (~> 1.3)
+    diff-lcs (1.5.1)
+    minitest (5.25.1)
+    mutant (0.12.4)
+      diff-lcs (~> 1.3)
+      parser (~> 3.3.0)
+      regexp_parser (~> 2.9.0)
+      sorbet-runtime (~> 0.5.0)
+      unparser (~> 0.6.14)
+    mutant-minitest (0.12.4)
+      minitest (~> 5.11)
+      mutant (= 0.12.4)
+    parser (3.3.6.0)
+      ast (~> 2.4.1)
+      racc
+    racc (1.8.1)
+    regexp_parser (2.9.2)
+    ruby_event_store (2.15.0)
+      concurrent-ruby (~> 1.0, >= 1.1.6)
+    sorbet-runtime (0.5.11647)
+    unparser (0.6.15)
+      diff-lcs (~> 1.3)
+      parser (>= 3.3.0)
+
+PLATFORMS
+  arm64-darwin
+  x86_64-linux
+
+DEPENDENCIES
+  decide.rb
+  minitest
+  mutant
+  mutant-minitest
+  ruby_event_store
+
+BUNDLED WITH
+   2.5.23
diff --git a/examples/decide.rb/Makefile b/examples/decide.rb/Makefile
new file mode 100644
index 0000000..6895980
--- /dev/null
+++ b/examples/decide.rb/Makefile
@@ -0,0 +1,10 @@
+install:
+	@bundle install
+
+test:
+	@bundle exec ruby -Ilib -rproject_management test/issue_test.rb
+
+mutate:
+	@bundle exec mutant run
+
+.PHONY: install test mutate
diff --git a/examples/decide.rb/lib/project_management.rb b/examples/decide.rb/lib/project_management.rb
new file mode 100644
index 0000000..77e09d7
--- /dev/null
+++ b/examples/decide.rb/lib/project_management.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+require_relative "../../../shared/lib/project_management"
+require_relative "project_management/handler"
+require_relative "project_management/issue"
+require_relative "project_management/repository"
diff --git a/examples/decide.rb/lib/project_management/handler.rb b/examples/decide.rb/lib/project_management/handler.rb
new file mode 100644
index 0000000..ccd4ee9
--- /dev/null
+++ b/examples/decide.rb/lib/project_management/handler.rb
@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+module ProjectManagement
+  class Handler
+    def initialize(event_store)
+      @decider = Issue::Decider.dimap_on_event(
+        fl: ->(event) { infra_to_domain(event) },
+        fr: ->(event) { domain_to_infra(event) }
+      )
+      @repository = Repository.new(event_store)
+    end
+
+    def call(cmd)
+      state = @repository.load(cmd.id, @decider)
+      events = @decider.decide(cmd, state)
+      @repository.store(cmd.id, events)
+    end
+
+    private
+
+    def infra_to_domain(event)
+      case event
+      in IssueOpened
+        Issue::IssueOpened.new(issue_id: event.data[:issue_id])
+      in IssueResolved
+        Issue::IssueResolved.new(issue_id: event.data[:issue_id])
+      in IssueClosed
+        Issue::IssueClosed.new(issue_id: event.data[:issue_id])
+      in IssueReopened
+        Issue::IssueReopened.new(issue_id: event.data[:issue_id])
+      in IssueProgressStarted
+        Issue::IssueProgressStarted.new(issue_id: event.data[:issue_id])
+      in IssueProgressStopped
+        Issue::IssueProgressStopped.new(issue_id: event.data[:issue_id])
+      end
+    end
+
+    def domain_to_infra(event)
+      case event
+      in Issue::IssueOpened
+        IssueOpened.new(data: { issue_id: event.issue_id })
+      in Issue::IssueResolved
+        IssueResolved.new(data: { issue_id: event.issue_id })
+      in Issue::IssueClosed
+        IssueClosed.new(data: { issue_id: event.issue_id })
+      in Issue::IssueReopened
+        IssueReopened.new(data: { issue_id: event.issue_id })
+      in Issue::IssueProgressStarted
+        IssueProgressStarted.new(data: { issue_id: event.issue_id })
+      in Issue::IssueProgressStopped
+        IssueProgressStopped.new(data: { issue_id: event.issue_id })
+      in Issue::InvalidTransition
+        raise Error
+      end
+    end
+  end
+end
diff --git a/examples/decide.rb/lib/project_management/issue.rb b/examples/decide.rb/lib/project_management/issue.rb
new file mode 100644
index 0000000..f1b31a9
--- /dev/null
+++ b/examples/decide.rb/lib/project_management/issue.rb
@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+require "decider"
+
+module ProjectManagement
+  module Issue
+    IssueOpened = Data.define(:issue_id)
+    IssueResolved = Data.define(:issue_id)
+    IssueClosed = Data.define(:issue_id)
+    IssueReopened = Data.define(:issue_id)
+    IssueProgressStarted = Data.define(:issue_id)
+    IssueProgressStopped = Data.define(:issue_id)
+    InvalidTransition = Data.define
+
+    Decider = Decider.define do
+      initial_state :none
+
+      decide CreateIssue, :none do
+        emit IssueOpened.new(issue_id: command.id)
+      end
+
+      decide proc { [command, state] in [ResolveIssue, :open | :in_progress | :reopened] } do
+        emit IssueResolved.new(issue_id: command.id)
+      end
+
+      decide proc { [command, state] in [CloseIssue, :open | :in_progress | :resolved | :reopened] } do
+        emit IssueClosed.new(issue_id: command.id)
+      end
+
+      decide proc { [command, state] in [ReopenIssue, :resolved | :closed] } do
+        emit IssueReopened.new(issue_id: command.id)
+      end
+
+      decide proc { [command, state] in [StartIssueProgress, :open | :reopened] } do
+        emit IssueProgressStarted.new(issue_id: command.id)
+      end
+
+      decide StopIssueProgress, :in_progress do
+        emit IssueProgressStopped.new(issue_id: command.id)
+      end
+
+      decide proc { true } do
+        emit InvalidTransition.new
+      end
+
+      evolve IssueOpened do
+        :open
+      end
+
+      evolve IssueResolved do
+        :resolved
+      end
+
+      evolve IssueClosed do
+        :closed
+      end
+
+      evolve IssueReopened do
+        :reopened
+      end
+
+      evolve IssueProgressStarted do
+        :in_progress
+      end
+
+      evolve IssueProgressStopped do
+        :open
+      end
+    end
+  end
+end
diff --git a/examples/decide.rb/lib/project_management/repository.rb b/examples/decide.rb/lib/project_management/repository.rb
new file mode 100644
index 0000000..0796cf4
--- /dev/null
+++ b/examples/decide.rb/lib/project_management/repository.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module ProjectManagement
+  class Repository
+    def initialize(event_store)
+      @event_store = event_store
+    end
+
+    def load(id, decider)
+      stream = @event_store
+        .read
+        .stream(stream_name(id))
+
+      @expected_version = stream.count - 1
+
+      stream.reduce(decider.initial_state, &decider.evolve)
+    end
+
+    def store(id, events)
+      @event_store.append(
+        events,
+        stream_name: stream_name(id),
+        expected_version: @expected_version
+      )
+    end
+
+    private
+
+    def stream_name(id) = "Issue$#{id}"
+  end
+end
diff --git a/examples/decide.rb/test/issue_test.rb b/examples/decide.rb/test/issue_test.rb
new file mode 100644
index 0000000..c14358d
--- /dev/null
+++ b/examples/decide.rb/test/issue_test.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require "minitest/autorun"
+require "minitest/mock"
+require "mutant/minitest/coverage"
+require "ruby_event_store"
+
+require_relative "../lib/project_management"
+
+module ProjectManagement
+  class IssueTest < Minitest::Test
+    include Test.with(
+      handler: ->(event_store) { Handler.new(event_store) },
+      event_store: -> { RubyEventStore::Client.new }
+    )
+
+    cover "ProjectManagement::Issue*"
+  end
+end
diff --git a/mise.toml b/mise.toml
new file mode 100644
index 0000000..c8650bc
--- /dev/null
+++ b/mise.toml
@@ -0,0 +1,2 @@
+[tools]
+ruby = "3.2.2"