Add configuration class

lib/mosaik.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "forwardable"
+require "yaml"
 
 require "active_support/all"
 require "zeitwerk"
@@ -16,6 +17,10 @@ def options
       @options ||= Options.new
     end
 
+    def configuration
+      @configuration ||= Configuration.from(File.join(options.directory, "mosaik.yml"))
+    end
+
     def logger
       @logger ||= Logger.new
     end

lib/mosaik/configuration.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module MOSAIK
+  class Configuration
+    attr_reader :include, :exclude
+
+    def initialize(include = [], exclude = [])
+      @include = include
+      @exclude = exclude
+    end
+
+    def self.from(file)
+      raise ConfigurationError, "Configuration file not found: #{file}" unless File.exist?(file)
+
+      configuration = YAML.load_file(file)
+
+      new(
+        configuration["include"],
+        configuration["exclude"],
+      )
+    end
+  end
+end

lib/mosaik/error.rb

@@ -12,4 +12,7 @@ class UsageError < Error; end
 
   # Raised when options are invalid
   class OptionError < Error; end
+
+  # Raise when configuration is invalid
+  class ConfigurationError < Error; end
 end

spec/fixtures/mosaik.yml

@@ -0,0 +1,10 @@
+---
+# List of patterns for folder paths to include
+include:
+  - foo
+  - bar
+
+# List of patterns for folder paths to exclude
+exclude:
+  - baz
+  - qux

spec/mosaik/configuration_spec.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+RSpec.describe MOSAIK::Configuration do
+  subject(:configuration) { described_class.new }
+
+  describe ".from" do
+    context "when the configuration file exists" do
+      let(:file) { "spec/fixtures/mosaik.yml" }
+
+      it "creates a new configuration instance" do
+        expect(described_class.from(file)).to be_a(described_class)
+      end
+
+      it "sets the include attribute" do
+        expect(described_class.from(file).include).to eq(["foo", "bar"])
+      end
+
+      it "sets the exclude attribute" do
+        expect(described_class.from(file).exclude).to eq(["baz", "qux"])
+      end
+    end
+
+    context "when the configuration file does not exist" do
+      let(:file) { "spec/fixtures/missing.yml" }
+
+      it "raises an error" do
+        expect { described_class.from(file) }.to raise_error(MOSAIK::ConfigurationError, "Configuration file not found: #{file}")
+      end
+    end
+  end
+end