Add metadata.update key: value

lib/perron/resource.rb

@@ -19,6 +19,7 @@
 require "perron/resource/sweeper"
 require "perron/resource/adjacency"
 require "perron/resource/table_of_content"
+require "perron/resource/updatable"
 
 module Perron
   class Resource

lib/perron/resource/updatable.rb

@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+module Perron
+  class Resource
+    module Updatable
+      extend ActiveSupport::Concern
+
+      included do
+        def metadata
+          @metadata ||= Proxy.new(super, self)
+        end
+      end
+
+      class Proxy
+        def initialize(metadata, resource)
+          @metadata = metadata
+          @resource = resource
+        end
+
+        def update(attributes)
+          attributes = attributes.deep_symbolize_keys
+
+          separator = Perron::Resource::Separator.new(@resource.raw_content)
+          frontmatter = separator.frontmatter.to_h.merge(attributes)
+          yaml = frontmatter.transform_keys(&:to_s).to_yaml.sub(/\A---\n/, "")
+          body = separator.content
+
+          File.write(@resource.file_path, "---\n#{yaml}---\n\n#{body}\n")
+
+          @resource.instance_variable_set(:@frontmatter, nil)
+          attributes.each { |key, value| @metadata[key] = value }
+
+          self
+        end
+
+        def respond_to_missing?(name, include_private = false)
+          @metadata.respond_to?(name, include_private) || super
+        end
+
+        def method_missing(name, *arguments, &block)
+          @metadata.public_send(name, *arguments, &block)
+        end
+      end
+    end
+  end
+end

test/dummy/app/models/content/post.rb

@@ -1,8 +1,10 @@
 class Content::Post < Perron::Resource
+  include Perron::Resource::Updatable
+
   CATEGORIES = {
-    ruby: { title: "Ruby", description: "Ruby articles" },
-    rails: { title: "Rails", description: "Rails articles" },
-    css: { title: "CSS", description: "CSS articles" }
+    ruby: {title: "Ruby", description: "Ruby articles"},
+    rails: {title: "Rails", description: "Rails articles"},
+    css: {title: "CSS", description: "CSS articles"}
   }
 
   configure do |config|

test/perron/resource/updatable_test.rb

@@ -0,0 +1,85 @@
+require "test_helper"
+
+class Perron::Resource::UpdatableTest < ActiveSupport::TestCase
+  FIXTURE = "test/dummy/app/content/posts/2023-05-15-sample-post.md"
+
+  def setup
+    @tmp = Rails.root.join("tmp/updatable_metadata_#{SecureRandom.hex(4)}.md").to_s
+    FileUtils.cp(FIXTURE, @tmp)
+    @post = Content::Post.new(@tmp)
+  end
+
+  def teardown
+    FileUtils.rm_f(@tmp)
+  end
+
+  def original_frontmatter
+    Perron::Resource::Separator.new(File.read(FIXTURE)).frontmatter.to_h
+  end
+
+  def current_frontmatter
+    Perron::Resource::Separator.new(File.read(@tmp)).frontmatter.to_h
+  end
+
+  def original_body
+    Perron::Resource::Separator.new(File.read(FIXTURE)).content
+  end
+
+  def current_body
+    Perron::Resource::Separator.new(File.read(@tmp)).content
+  end
+
+  test "updating an existing key changes only that key" do
+    @post.metadata.update(title: "Changed Title")
+
+    updated = current_frontmatter
+    original = original_frontmatter
+
+    assert_equal "Changed Title", updated[:title]
+    assert_equal original.except(:title), updated.except(:title)
+    assert_equal original_body, current_body
+  end
+
+  test "only the changed key line differs in the file" do
+    @post.metadata.update(title: "Changed Title")
+
+    original_lines = File.readlines(FIXTURE)
+    updated_lines = File.readlines(@tmp)
+
+    diff = original_lines.zip(updated_lines).reject { |a, b| a == b }
+    assert_equal 1, diff.size
+    assert_match(/^title: Changed Title$/, diff.first.last)
+  end
+
+  test "updating a new key inserts it without disturbing others" do
+    @post.metadata.update(published_at: Date.new(2024, 1, 1))
+
+    updated = current_frontmatter
+    original = original_frontmatter
+
+    assert_equal Date.new(2024, 1, 1), updated[:published_at]
+    assert_equal original, updated.except(:published_at)
+    assert_equal original_body, current_body
+  end
+
+  test "multiline values round-trip without altering other keys" do
+    @post.metadata.update(description: "line one\nline two")
+
+    updated = current_frontmatter
+    original = original_frontmatter
+
+    assert_equal "line one\nline two", updated[:description]
+    assert_equal original.except(:description), updated.except(:description)
+    assert_equal original_body, current_body
+  end
+
+  test "in-memory metadata reflects the update immediately" do
+    @post.metadata.update(title: "In Memory")
+
+    assert_equal "In Memory", @post.metadata.title
+  end
+
+  test "update returns self for chaining" do
+    assert_equal @post.metadata, @post.metadata.update(title: "X")
+  end
+end