1 files changed, 87 insertions, 0 deletions
diff --git a/app/models/diff_viewer/base.rb b/app/models/diff_viewer/base.rb
new file mode 100644
index 00000000000..0cbe714288d
--- /dev/null
+++ b/app/models/diff_viewer/base.rb
@@ -0,0 +1,87 @@
+module DiffViewer
+  class Base
+    PARTIAL_PATH_PREFIX = 'projects/diffs/viewers'.freeze
+
+    class_attribute :partial_name, :type, :extensions, :file_types, :binary, :switcher_icon, :switcher_title
+
+    # These limits relate to the sum of the old and new blob sizes.
+    # Limits related to the actual size of the diff are enforced in Gitlab::Diff::File.
+    class_attribute :collapse_limit, :size_limit
+
+    delegate :partial_path, :loading_partial_path, :rich?, :simple?, :text?, :binary?, to: :class
+
+    attr_reader :diff_file
+
+    delegate :project, to: :diff_file
+
+    def initialize(diff_file)
+      @diff_file = diff_file
+      @initially_binary = diff_file.binary?
+    end
+
+    def self.partial_path
+      File.join(PARTIAL_PATH_PREFIX, partial_name)
+    end
+
+    def self.rich?
+      type == :rich
+    end
+
+    def self.simple?
+      type == :simple
+    end
+
+    def self.binary?
+      binary
+    end
+
+    def self.text?
+      !binary?
+    end
+
+    def self.can_render?(diff_file, verify_binary: true)
+      can_render_blob?(diff_file.old_blob, verify_binary: verify_binary) &&
+        can_render_blob?(diff_file.new_blob, verify_binary: verify_binary)
+    end
+
+    def self.can_render_blob?(blob, verify_binary: true)
+      return true if blob.nil?
+      return false if verify_binary && binary? != blob.binary?
+      return true if extensions&.include?(blob.extension)
+      return true if file_types&.include?(blob.file_type)
+
+      false
+    end
+
+    def collapsed?
+      return @collapsed if defined?(@collapsed)
+      return @collapsed = true if diff_file.collapsed?
+
+      @collapsed = !diff_file.expanded? && collapse_limit && diff_file.raw_size > collapse_limit
+    end
+
+    def too_large?
+      return @too_large if defined?(@too_large)
+      return @too_large = true if diff_file.too_large?
+
+      @too_large = size_limit && diff_file.raw_size > size_limit
+    end
+
+    def binary_detected_after_load?
+      !@initially_binary && diff_file.binary?
+    end
+
+    # This method is used on the server side to check whether we can attempt to
+    # render the diff_file at all. Human-readable error messages are found in the
+    # `BlobHelper#diff_render_error_reason` helper.
+    def render_error
+      if too_large?
+        :too_large
+      end
+    end
+
+    def prepare!
+      # To be overridden by subclasses
+    end
+  end
+end