Apply contents signature of directories

src/library/title.cr

@@ -32,6 +32,7 @@ class Title
       })
     end
     @id = id
+    @contents_signature = Dir.contents_signature dir
     @title = File.basename dir
     @encoded_title = URI.encode @title
     @title_ids = [] of String
@@ -71,12 +72,13 @@ class Title
 
   def examine : Bool
     return false unless Dir.exists? @dir # no title, should be removed
-    signature = Dir.signature @dir
-    # `signature` doesn't reflect movings, renames in nested titles
-    # return true if @signature == signature # not changed, preserve
+    contents_signature = Dir.contents_signature @dir
+    # not changed, preserve
+    return true if @contents_signature == contents_signature
 
     # fix title
-    @signature = signature
+    @contents_signature = contents_signature
+    @signature = Dir.signature @dir
     storage = Storage.default
     id = storage.get_title_id dir, signature
     if id.nil?

src/util/signature.cr

@@ -48,4 +48,27 @@ class Dir
     end
     Digest::CRC32.checksum(signatures.sort.join).to_u64
   end
+
+  # Returns the contents signature of the directory at dirname for checking
+  #   to rescan.
+  # Rescan conditions:
+  #   - When a file added, moved, removed, renamed (including which in nested
+  #       directories)
+  def self.contents_signature(dirname) : String
+    signatures = [] of String
+    self.open dirname do |dir|
+      dir.entries.sort.each do |fn|
+        next if fn.starts_with? "."
+        path = File.join dirname, fn
+        if File.directory? path
+          signatures << Dir.contents_signature path
+        else
+          # Only add its signature value to `signatures` when it is a
+          #   supported file
+          signatures << fn if is_supported_file fn
+        end
+      end
+    end
+    Digest::SHA1.hexdigest(signatures.sort.join)
+  end
 end