feat(email.validator): define a strict email validator, validates Champs::EmailChamp.value only on validation context

Co-authored-by: Paul Chavard <github@paul.chavard.net>

app/models/champs/email_champ.rb

@@ -1,2 +1,3 @@
 class Champs::EmailChamp < Champs::TextChamp
+  validates :value, format: { with: StrictEmailValidator::REGEXP }, if: :validate_champ_value?
 end

app/validators/strict_email_validator.rb

@@ -0,0 +1,31 @@
+class StrictEmailValidator < ActiveModel::EachValidator
+  # default devise email is : /\A[^@\s]+@[^@\s]+\z/
+  #   saying that it's quite permissive
+  #   but we want more, we want to ensure it's a domain with extension
+  #   so we append \.[A-Za-z]{2,}
+  REGEXP = /\A[^@\s]+@[^@\s\.]+\.[^@\s]{2,}\z/
+
+  def validate_each(record, attribute, value)
+    if value.present? && !REGEXP.match?(value)
+      record.errors.add(attribute, :format)
+    end
+  end
+
+  def self.elligible_to_new_validation?(record)
+    return false if !strict_validation_enabled?
+    return false if (record.created_at || Time.now) < date_since_strict_email_validation
+    true
+  end
+
+  def self.strict_validation_enabled?
+    ENV.key?('STRICT_EMAIL_VALIDATION_STARTS_AT')
+  end
+
+  def self.date_since_strict_email_validation
+    DateTime.parse(ENV['STRICT_EMAIL_VALIDATION_STARTS_AT'])
+  rescue
+    DateTime.new(1789, 5, 5, 0, 0) # french revolution, ds was not yet launched
+  end
+
+
+end