1 files changed, 62 insertions, 0 deletions
diff --git a/app/graphql/resolvers/blame_resolver.rb b/app/graphql/resolvers/blame_resolver.rb
new file mode 100644
index 00000000000..f8b985e6582
--- /dev/null
+++ b/app/graphql/resolvers/blame_resolver.rb
@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+module Resolvers
+  class BlameResolver < BaseResolver
+    include Gitlab::Graphql::Authorize::AuthorizeResource
+
+    type Types::Blame::BlameType, null: true
+    calls_gitaly!
+
+    argument :from_line, GraphQL::Types::Int,
+      required: false,
+      default_value: 1,
+      description: 'Range starting from the line. Cannot be less than 1 or greater than `to_line`.'
+    argument :to_line, GraphQL::Types::Int,
+      required: false,
+      default_value: 1,
+      description: 'Range ending on the line. Cannot be less than 1 or less than `to_line`.'
+
+    alias_method :blob, :object
+
+    def ready?(**args)
+      validate_line_params!(args) if feature_enabled?
+
+      super
+    end
+
+    def resolve(from_line:, to_line:)
+      return unless feature_enabled?
+
+      authorize!
+
+      Gitlab::Blame.new(blob, blob.repository.commit(blob.commit_id),
+        range: (from_line..to_line))
+    end
+
+    private
+
+    def authorize!
+      read_code? || raise_resource_not_available_error!
+    end
+
+    def read_code?
+      Ability.allowed?(current_user, :read_code, blob.repository.project)
+    end
+
+    def feature_enabled?
+      Feature.enabled?(:graphql_git_blame, blob.repository.project)
+    end
+
+    def validate_line_params!(args)
+      if args[:from_line] <= 0 || args[:to_line] <= 0
+        raise Gitlab::Graphql::Errors::ArgumentError,
+          '`from_line` and `to_line` must be greater than or equal to 1'
+      end
+
+      return unless args[:from_line] > args[:to_line]
+
+      raise Gitlab::Graphql::Errors::ArgumentError,
+        '`to_line` must be greater than or equal to `from_line`'
+    end
+  end
+end