Adding new validation to validate URL formatted attributes

spec/avram/validations_spec.cr

@@ -464,4 +464,30 @@ describe Avram::Validations do
       nil_attribute.valid?.should be_true
     end
   end
+
+  describe "validate_url_format" do
+    it "validates" do
+      valid_url_attribute = attribute("https://luckyframework.org")
+      result = Avram::Validations.validate_url_format(valid_url_attribute)
+      result.should eq(true)
+      valid_url_attribute.valid?.should be_true
+
+      invalid_url_attribute = attribute("http://luckyframework.org")
+      result = Avram::Validations.validate_url_format(invalid_url_attribute)
+      result.should eq(false)
+      invalid_url_attribute.valid?.should be_false
+      invalid_url_attribute.errors.should eq ["must be a valid URL beginning with https"]
+
+      valid_other_attribute = attribute("ftp://user:pass@host:1234/files")
+      result = Avram::Validations.validate_url_format(valid_other_attribute, scheme: "ftp")
+      result.should eq(true)
+      valid_other_attribute.valid?.should be_true
+
+      bad_attribute = attribute("  not a URL  ")
+      result = Avram::Validations.validate_url_format(bad_attribute)
+      result.should eq(false)
+      bad_attribute.valid?.should be_false
+      bad_attribute.errors.should eq ["must be a valid URL beginning with https"]
+    end
+  end
 end

src/avram/i18n_backend.cr

@@ -19,6 +19,7 @@ struct Avram::I18n < Avram::I18nBackend
       validate_numeric_nil:        "must not be nil",
       validate_required:           "is required",
       validate_uniqueness_of:      "is already taken",
+      validate_url_format:         "must be a valid URL beginning with %s",
     }[key]
   end
 end

src/avram/validations.cr

@@ -330,4 +330,20 @@ module Avram::Validations
 
     true
   end
+
+  def validate_url_format(
+    attribute : Avram::Attribute(String),
+    scheme : String = "https",
+    message : Avram::Attribute::ErrorMessage = Avram.settings.i18n_backend.get(:validate_url_format)
+  ) : Bool
+    if url = attribute.value.presence
+      uri = URI.parse(url)
+      if uri.scheme != scheme || uri.host.presence.nil?
+        attribute.add_error(message % scheme)
+        return false
+      end
+    end
+
+    true
+  end
 end