Move iterators into separate package

Also reduce API exposure and use standard library more - and fix bugs I
previously introduces in mongo.

graph/iterator/and_iterator_optimize_test.go

@@ -0,0 +1,110 @@
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package iterator
+
+// Tests relating to methods in and-iterator-optimize. Many are pretty simplistic, but
+// nonetheless cover a lot of basic cases.
+
+import (
+	"reflect"
+	"sort"
+	"testing"
+)
+
+func TestIteratorPromotion(t *testing.T) {
+	all := NewInt64(1, 3)
+	fixed := newFixed()
+	fixed.AddValue(3)
+	a := NewAnd()
+	a.AddSubIterator(all)
+	a.AddSubIterator(fixed)
+	all.AddTag("a")
+	fixed.AddTag("b")
+	a.AddTag("c")
+	newIt, changed := a.Optimize()
+	if !changed {
+		t.Error("Iterator didn't optimize")
+	}
+	if newIt.Type() != "fixed" {
+		t.Error("Expected fixed iterator")
+	}
+	tagsExpected := []string{"a", "b", "c"}
+	tags := newIt.Tags()
+	sort.Strings(tags)
+	if !reflect.DeepEqual(tags, tagsExpected) {
+		t.Fatal("Tags don't match")
+	}
+}
+
+func TestNullIteratorAnd(t *testing.T) {
+	all := NewInt64(1, 3)
+	null := NewNull()
+	a := NewAnd()
+	a.AddSubIterator(all)
+	a.AddSubIterator(null)
+	newIt, changed := a.Optimize()
+	if !changed {
+		t.Error("Didn't change")
+	}
+	if newIt.Type() != "null" {
+		t.Error("Expected null iterator, got ", newIt.Type())
+	}
+}
+
+func TestReorderWithTag(t *testing.T) {
+	all := NewInt64(100, 300)
+	all.AddTag("good")
+	all2 := NewInt64(1, 30000)
+	all2.AddTag("slow")
+	a := NewAnd()
+	// Make all2 the default iterator
+	a.AddSubIterator(all2)
+	a.AddSubIterator(all)
+
+	newIt, changed := a.Optimize()
+	if !changed {
+		t.Error("Expected new iterator")
+	}
+	expectedTags := []string{"good", "slow"}
+	tagsOut := make([]string, 0)
+	for _, sub := range newIt.GetSubIterators() {
+		for _, x := range sub.Tags() {
+			tagsOut = append(tagsOut, x)
+		}
+	}
+	if !reflect.DeepEqual(expectedTags, tagsOut) {
+		t.Fatal("Tags don't match")
+	}
+}
+
+func TestAndStatistics(t *testing.T) {
+	all := NewInt64(100, 300)
+	all.AddTag("good")
+	all2 := NewInt64(1, 30000)
+	all2.AddTag("slow")
+	a := NewAnd()
+	// Make all2 the default iterator
+	a.AddSubIterator(all2)
+	a.AddSubIterator(all)
+	stats1 := a.GetStats()
+	newIt, changed := a.Optimize()
+	if !changed {
+		t.Error("Didn't optimize")
+	}
+	stats2 := newIt.GetStats()
+	if stats2.NextCost > stats1.NextCost {
+		t.Error("And didn't optimize. Next cost old ", stats1.NextCost, "and new ", stats2.NextCost)
+	}
+}