BURs: add size requirements for implications.

Implications now have the following rules:

* The child tag must have at least 10 posts.
* The child tag must be at least 0.01% the size of the parent tag.
* The child tag can't make up more than 90% of the parent tag.
* These rules only apply to general tags.

app/models/tag_implication.rb

@@ -1,4 +1,8 @@
 class TagImplication < TagRelationship
+  MINIMUM_TAG_COUNT = 10
+  MINIMUM_TAG_PERCENTAGE = 0.0001
+  MAXIMUM_TAG_PERCENTAGE = 0.9
+
   has_many :child_implications, class_name: "TagImplication", primary_key: :consequent_name, foreign_key: :antecedent_name
   has_many :parent_implications, class_name: "TagImplication", primary_key: :antecedent_name, foreign_key: :consequent_name
 
@@ -8,6 +12,7 @@ class TagImplication < TagRelationship
   validate :antecedent_is_not_aliased
   validate :consequent_is_not_aliased
   validate :tag_categories_are_compatible
+  validate :meets_tag_size_requirements, on: :request
   validate :has_wiki_page, on: :request
 
   concerning :HierarchyMethods do
@@ -100,6 +105,26 @@ class TagImplication < TagRelationship
       end
     end
 
+    # Require tags to have at least 10 posts or be at least 0.01% the size of
+    # the parent tag, and not make up more than 90% of the parent tag. Only
+    # applies to general tags. Doesn't apply when the parent tag is empty to
+    # allow creating new umbrella tags.
+    def meets_tag_size_requirements
+      return unless antecedent_tag.general?
+      return if consequent_tag.empty?
+
+      if antecedent_tag.post_count < MINIMUM_TAG_COUNT
+        errors[:base] << "'#{antecedent_name}' must have at least #{MINIMUM_TAG_COUNT} posts"
+      elsif antecedent_tag.post_count < (MINIMUM_TAG_PERCENTAGE * consequent_tag.post_count)
+        errors[:base] << "'#{antecedent_name}' must have at least #{(MINIMUM_TAG_PERCENTAGE * consequent_tag.post_count).to_i} posts"
+      end
+
+      max_count = MAXIMUM_TAG_PERCENTAGE * PostQueryBuilder.new("~#{antecedent_name} ~#{consequent_name}").fast_count.to_i
+      if antecedent_tag.post_count > max_count && max_count > 0
+        errors[:base] << "'#{antecedent_name}' can't make up than #{(MAXIMUM_TAG_PERCENTAGE * 100).to_i}% of '#{consequent_name}'"
+      end
+    end
+
     def has_wiki_page
       if !antecedent_tag.empty? && antecedent_wiki.blank?
         errors[:base] << "'#{antecedent_name}' must have a wiki page"

test/unit/bulk_update_request_test.rb

@@ -152,6 +152,21 @@ class BulkUpdateRequestTest < ActiveSupport::TestCase
           assert_equal(false, @bur.valid?)
           assert_equal(["Can't create implication hatsune_miku -> vocaloid (Can't imply a character tag to a copyright tag)"], @bur.errors.full_messages)
         end
+
+        should "fail for a child tag that is too small" do
+          @t1 = create(:tag, name: "white_shirt", post_count: 9)
+          @t2 = create(:tag, name: "shirt", post_count: 1000000)
+          create(:wiki_page, title: "white_shirt")
+          create(:wiki_page, title: "shirt")
+          @bur = build(:bulk_update_request, script: "imply white_shirt -> shirt")
+
+          assert_equal(false, @bur.valid?)
+          assert_equal(["Can't create implication white_shirt -> shirt ('white_shirt' must have at least 10 posts)"], @bur.errors.full_messages)
+
+          @t1.update!(post_count: 99)
+          assert_equal(false, @bur.valid?)
+          assert_equal(["Can't create implication white_shirt -> shirt ('white_shirt' must have at least 100 posts)"], @bur.errors.full_messages)
+        end
       end
 
       context "the remove alias command" do
@@ -342,8 +357,8 @@ class BulkUpdateRequestTest < ActiveSupport::TestCase
 
       context "requesting an implication for a populated tag without a wiki" do
         should "fail" do
-          create(:tag, name: "a", post_count: 1)
-          create(:tag, name: "b", post_count: 1)
+          create(:tag, name: "a", post_count: 10)
+          create(:tag, name: "b", post_count: 100)
           @bur = build(:bulk_update_request, script: "imply a -> b")
 
           assert_equal(false, @bur.valid?)