Add reverse_each method to db

README.md

@@ -21,7 +21,7 @@ sudo apt-get install libleveldb-dev libleveldb1v5 libsnappy1v5
 dependencies:
   leveldb:
     github: "crystal-community/leveldb"
-    version: "~> 0.2.0"
+    version: "~> 0.3.0"
 ```
 
 ## Usage

shard.yml

@@ -1,5 +1,5 @@
 name: leveldb
-version: 0.2.0
+version: 0.3.0
 
 authors:
   - Sergey Potapov <[email protected]>

spec/leveldb/db_spec.cr

@@ -139,6 +139,27 @@ describe LevelDB do
       end
     end
 
+    describe "#reverse_each" do
+      it "iterates through all the keys in reverse" do
+        FileUtils.rm_r(TEST_DB) if Dir.exists?(TEST_DB)
+        db = LevelDB::DB.new(TEST_DB)
+
+        out = ""
+
+        db.put("k1", "v1")
+        db.put("k2", "v2")
+        db.put("k3", "v3")
+
+        db.reverse_each do |key, val|
+          out += "#{key}=#{val};"
+        end
+
+        out.should eq "k3=v3;k2=v2;k1=v1;"
+
+        db.close
+      end
+    end
+
     describe "#clear" do
       it "removes all the keys" do
         FileUtils.rm_r(TEST_DB) if Dir.exists?(TEST_DB)

spec/leveldb/iterator_spec.cr

@@ -27,6 +27,12 @@ describe LevelDB::Iterator do
     iterator.seek_to_last
     iterator.key.should eq "k2"
 
+    iterator.prev
+    iterator.key.should eq "k1"
+
+    iterator.prev
+    iterator.valid?.should eq false
+
     iterator.destroy
     db.close
   end

src/leveldb/db.cr

@@ -106,13 +106,15 @@ module LevelDB
     end
 
     def each : Void
-      iterator = Iterator.new(self)
-      iterator.seek_to_first
-      while iterator.valid?
-        yield(iterator.key, iterator.value)
-        iterator.next
+      iterate do |key, value|
+        yield(key, value)
+      end
+    end
+
+    def reverse_each : Void
+      iterate(true) do |key, value|
+        yield(key, value)
       end
-      iterator.destroy
     end
 
     def clear
@@ -141,5 +143,24 @@ module LevelDB
         raise(Error.new(message))
       end
     end
+
+    private def iterate(reversed : Bool = false) : Void
+      iterator = Iterator.new(self)
+      if reversed
+        iterator.seek_to_last
+      else
+        iterator.seek_to_first
+      end
+
+      while iterator.valid?
+        yield(iterator.key, iterator.value)
+        if reversed
+          iterator.prev
+        else
+          iterator.next
+        end
+      end
+      iterator.destroy
+    end
   end
 end

src/leveldb/iterator.cr

@@ -36,6 +36,10 @@ module LevelDB
       LibLevelDB.leveldb_iter_next(@iter_ptr)
     end
 
+    def prev
+      LibLevelDB.leveldb_iter_prev(@iter_ptr)
+    end
+
     def destroy
       LibLevelDB.leveldb_iter_destroy(@iter_ptr)
     end

src/leveldb/lib_leveldb.cr

@@ -37,6 +37,7 @@ lib LibLevelDB
   fun leveldb_create_iterator(db : Void*, roptions : Void*) : Void*
   fun leveldb_iter_destroy(iterator : Void*)
   fun leveldb_iter_next(iterator : Void*)
+  fun leveldb_iter_prev(iterator : Void*)
   fun leveldb_iter_key(iterator : Void*, klen : SizeT*) : UInt8*
   fun leveldb_iter_value(iterator : Void*, vlen : SizeT*) : UInt8*
   fun leveldb_iter_get_error(iterator : Void*, errptr : Void*)