1 files changed, 85 insertions, 0 deletions
diff --git a/core.rb b/core.rb
new file mode 100644
index 0000000..5dad22a
--- /dev/null
+++ b/core.rb
@@ -0,0 +1,85 @@
+class Op
+  def check
+    raise "#{self.class} doesn't have a (required) 'check' method"
+  end
+  def do
+    raise "#{self.class} doesn't have a (required) 'do' method"
+  end
+  def undo
+    raise "#{self.class} doesn't have a (required) 'undo' method"
+  end
+end
+
+def defop(name, args, &block)
+  name = name.to_sym
+  eval "class #{name} < Op; end"  # Must use `eval' to access
+  cls = eval "#{name}"            # the global namespace
+  cls.instance_eval do
+    args.map {|a| attr_reader a.to_sym }
+  end
+  cls.define_method :initialize do |**kwargs|
+    args.each {|arg| instance_variable_set :"@#{arg}", kwargs[arg.to_sym] }
+  end
+  cls.define_method :to_s do inspect end
+  cls.define_method :to_str do to_s end
+  cls.instance_eval &block
+end
+
+defop :Write, [:file, :contents] do
+  define_method :check do
+    if File.exist? @file
+      if (File.read @file) != @contents
+        raise "File `#{@file}' exists but has unexpected contents"
+      else true
+      end
+    end
+  end
+  define_method :do do
+    write @file, @contents
+  end
+  define_method :undo do
+    rm @file
+  end
+end
+
+defop :Deploy, [:ops, :save] do
+  define_method :initialize do |save: nil, &block|
+    @ops = []
+    @save = save
+    self.instance_eval &block
+  end
+  define_method :check do
+    @ops.all? {|op| op.check } and
+      (@save ? self.save.check : true)
+  end
+  define_method :do do
+    self.load.undo if @save && self.save.check
+    @ops.each {|op| op.check || op.do }
+    self.save.do if @save
+  end
+  define_method :undo do
+    @ops.reverse.each {|op| op.check && op.undo }
+    self.save.undo if @save
+  end
+  define_method :save do
+    (Write.new file: @save,
+               contents: self.to_yaml)
+  end
+  define_method :load do
+    YAML.load_file(
+      @save,
+      permitted_classes: ([Op] + Op.subclasses))
+  end
+end
+
+def deploy(...)
+  Deploy.new(...)
+end
+
+def defdeploy(name, &block)
+  Deploy.define_method name, &block
+end
+
+defdeploy :op do |cls, **args|
+  @ops.push cls.new(**args)
+end