Add LTRIM (#48)

spec/redis_spec.cr

@@ -119,6 +119,34 @@ describe Redis::Client do
       redis.lrange(key, 0, 0).should eq %w[one]
       redis.lrange(key, "-3", "2").should eq %w[one two three]
     end
+
+    test "can trim lists" do
+      redis.rpush key, %w[0 1 2 3 4 5 6 7 8 9]
+
+      # String indices
+      redis.ltrim key, "0", "8"
+      redis.lrange(key, 0, -1).should eq %w[0 1 2 3 4 5 6 7 8]
+
+      # Int indices
+      redis.ltrim key, 0, 7
+      redis.lrange(key, 0, -1).should eq %w[0 1 2 3 4 5 6 7]
+
+      # String range with inclusive end
+      redis.ltrim key, "0".."6"
+      redis.lrange(key, 0, -1).should eq %w[0 1 2 3 4 5 6]
+
+      # String range with exclusive end
+      redis.ltrim key, "0"..."5"
+      redis.lrange(key, 0, -1).should eq %w[0 1 2 3 4 5]
+
+      # Range with inclusive end
+      redis.ltrim key, 0..4
+      redis.lrange(key, 0, -1).should eq %w[0 1 2 3 4]
+
+      # Range with exclusive end
+      redis.ltrim key, 0...3
+      redis.lrange(key, 0, -1).should eq %w[0 1 2]
+    end
   end
 
   describe "sets" do

src/commands/list.cr

@@ -99,6 +99,14 @@ module Redis::Commands::List
     run({"rpush", key} + values)
   end
 
+  def rpush(key : String, values : Enumerable(String))
+    command = Array(String).new(initial_capacity: 2 + values.size)
+    command << "rpush" << key
+    values.each { |value| command << value }
+
+    run command
+  end
+
   # Remove and return an element from the end of the given list. If the list
   # is empty or the key does not exist, this method waits the specified amount
   # of time for an element to be added to it by another connection. If the
@@ -262,6 +270,49 @@ module Redis::Commands::List
     run({"lrem", key, count.to_s, value})
   end
 
+  # Trim the list contained in `key` so that it contains only the values at the
+  # indices in the given range.
+  #
+  # ```
+  # redis.rpush "ids", %w[0 1 2 3 4 5 6 7 8 9]
+  # start, stop = "1,2".split(',')
+  # redis.ltrim "ids", start..stop
+  # ```
+  def ltrim(key : String, range : Range(String, String))
+    if range.excludes_end?
+      ltrim key, range.begin.to_i, range.end.to_i
+    else
+      ltrim key, range.begin, range.end
+    end
+  end
+
+  # Trim the list contained in `key` so that it contains only the values at the
+  # indices in the given range.
+  #
+  # ```
+  # redis.rpush "ids", %w[0 1 2 3 4 5 6 7 8 9]
+  # redis.ltrim "ids", 1..2
+  # ```
+  def ltrim(key : String, range : Range(Int32, Int32))
+    range_end = range.end
+    if range.excludes_end?
+      range_end -= 1
+    end
+
+    ltrim key, range.begin, range_end
+  end
+
+  # Trim the list contained in `key` so that it contains only the values at the
+  # indices in the given range.
+  #
+  # ```
+  # redis.rpush "ids", %w[0 1 2 3 4 5 6 7 8 9]
+  # redis.ltrim "ids", 1, 2
+  # ```
+  def ltrim(key : String, start : String | Int, stop : String | Int)
+    run({"ltrim", key, start.to_s, stop.to_s})
+  end
+
   def brpop(keys : Enumerable(String), timeout : Int)
     command = Array(String).new(initial_capacity: 2 + keys.size)
     command << "brpop"