✨ Add BLMPOP (#1199)

* ✨ Add BLMPOP

* 🚨 Fix rubocop error

lib/redis/commands/lists.rb

@@ -183,6 +183,34 @@ def brpoplpush(source, destination, timeout: 0)
         send_blocking_command(command, timeout)
       end
 
+      # Pops one or more elements from the first non-empty list key from the list
+      # of provided key names. If lists are empty, blocks until timeout has passed.
+      #
+      # @example Popping a element
+      #   redis.blmpop(1.0, 'list')
+      #   #=> ['list', ['a']]
+      # @example With count option
+      #   redis.blmpop(1.0, 'list', count: 2)
+      #   #=> ['list', ['a', 'b']]
+      #
+      # @params timeout [Float] a float value specifying the maximum number of seconds to block) elapses.
+      #   A timeout of zero can be used to block indefinitely.
+      # @params key [String, Array<String>] one or more keys with lists
+      # @params modifier [String]
+      #  - when `"LEFT"` - the elements popped are those from the left of the list
+      #  - when `"RIGHT"` - the elements popped are those from the right of the list
+      # @params count [Integer] a number of elements to pop
+      #
+      # @return [Array<String, Array<String, Float>>] list of popped elements or nil
+      def blmpop(timeout, *keys, modifier: "LEFT", count: nil)
+        raise ArgumentError, "Pick either LEFT or RIGHT" unless modifier == "LEFT" || modifier == "RIGHT"
+
+        args = [:lmpop, keys.size, *keys, modifier]
+        args << "COUNT" << Integer(count) if count
+
+        send_blocking_command(args, timeout)
+      end
+
       # Pops one or more elements from the first non-empty list key from the list
       # of provided key names.
       #

lib/redis/distributed.rb

@@ -542,7 +542,14 @@ def ltrim(key, start, stop)
       node_for(key).ltrim(key, start, stop)
     end
 
-    # Iterate over keys, removing elements from the first non list set found.
+    # Iterate over keys, blocking and removing elements from the first non empty liist found.
+    def blmpop(timeout, *keys, modifier: "LEFT", count: nil)
+      ensure_same_node(:blmpop, keys) do |node|
+        node.blmpop(timeout, *keys, modifier: modifier, count: count)
+      end
+    end
+
+    # Iterate over keys, removing elements from the first non list found.
     def lmpop(*keys, modifier: "LEFT", count: nil)
       ensure_same_node(:lmpop, keys) do |node|
         node.lmpop(*keys, modifier: modifier, count: count)

test/lint/lists.rb

@@ -203,6 +203,19 @@ def test_variadic_rpoplpush_expand
       assert_equal 'c', redis.rpoplpush('{1}foo', '{1}bar')
     end
 
+    def test_blmpop
+      target_version('7.0') do
+        assert_nil r.blmpop(1.0, '{1}foo')
+
+        r.lpush('{1}foo', %w[a b c d e f g])
+        assert_equal ['{1}foo', ['g']], r.blmpop(1.0, '{1}foo')
+        assert_equal ['{1}foo', ['f', 'e']], r.blmpop(1.0, '{1}foo', count: 2)
+
+        r.lpush('{1}foo2', %w[a b])
+        assert_equal ['{1}foo', ['a']], r.blmpop(1.0, '{1}foo', '{1}foo2', modifier: "RIGHT")
+      end
+    end
+
     def test_lmpop
       target_version('7.0') do
         assert_nil r.lmpop('{1}foo')