Keep the highest _id given out in Fbe.fb so a deleted one is never reused

lib/fbe/fb.rb

@@ -47,10 +47,11 @@ def Fbe.fb(fb: $fb, global: $global, options: $options, loog: $loog) # rubocop:d
           "(and \n#{rules.join("\n")}\n)",
           uid: '_id'
         )
+        top = 0
         fbe =
           Factbase::Pre.new(fbe) do |f, fbt|
-            max = fbt.query('(max _id)').one
-            f._id = (max.nil? ? 0 : max) + 1
+            top = [top, fbt.query('(max _id)').one || 0].max + 1
+            f._id = top
             f._time = Time.now
             f._version = [Factbase::VERSION, Judges::VERSION, options.action_version].compact.join('/')
             f._job = Integer(options.job_id.to_s, 10) if options.job_id

test/fbe/test_fb.rb

@@ -114,4 +114,52 @@ def test_adds_meta_properties
     refute_nil(f._version)
     refute_nil(f._job)
   end
+
+  def test_dont_reuse_id_of_deleted_fact
+    seed = Random.new_seed
+    count = Random.new(seed).rand(2..16)
+    fbx = Fbe.fb(fb: Factbase.new, global: {}, options: Judges::Options.new, loog: Loog::NULL)
+    count.times { |i| fbx.insert.foo = i }
+    fbx.query("(eq _id #{count})").delete!
+    f = fbx.insert
+    f.foo = 'ünïque'
+    assert_equal(count + 1, f._id, "id of a deleted fact is given out again, seed #{seed}")
+  end
+
+  def test_dont_reuse_ids_when_every_fact_is_deleted
+    seed = Random.new_seed
+    count = Random.new(seed).rand(1..16)
+    fbx = Fbe.fb(fb: Factbase.new, global: {}, options: Judges::Options.new, loog: Loog::NULL)
+    count.times { |i| fbx.insert.foo = i }
+    fbx.query('(always)').delete!
+    f = fbx.insert
+    f.foo = 'ünïque'
+    assert_equal(count + 1, f._id, "numbering starts over after deleting every fact, seed #{seed}")
+  end
+
+  def test_numbers_after_highest_id_of_origin
+    seed = Random.new_seed
+    id = Random.new(seed).rand(1..1_000_000)
+    fb = Factbase.new
+    fb.insert._id = id
+    fbx = Fbe.fb(fb:, global: {}, options: Judges::Options.new, loog: Loog::NULL)
+    f = fbx.insert
+    f.foo = 'ünïque'
+    assert_equal(id + 1, f._id, "new fact does not follow the highest id of the origin, seed #{seed}")
+  end
+
+  def test_dont_reuse_id_of_fact_deleted_in_the_same_transaction
+    seed = Random.new_seed
+    count = Random.new(seed).rand(1..16)
+    fbx = Fbe.fb(fb: Factbase.new, global: {}, options: Judges::Options.new, loog: Loog::NULL)
+    count.times { |i| fbx.insert.foo = i }
+    fbx.txn do |fbt|
+      fbt.query("(eq _id #{count})").delete!
+      fbt.insert.foo = 'ünïque'
+    end
+    assert_equal(
+      [count + 1], fbx.query("(eq foo 'ünïque')").each.first['_id'],
+      "id is given out twice in a transaction, seed #{seed}"
+    )
+  end
 end