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.go

@@ -0,0 +1,248 @@
+// Defines the And iterator, one of the base iterators. And requires no
+// knowledge of the constituent TripleStore; its sole purpose is to act as an
+// intersection operator across the subiterators it is given. If one iterator
+// contains [1,3,5] and another [2,3,4] -- then And is an iterator that
+// 'contains' [3]
+//
+// It accomplishes this in one of two ways. If it is a Next()ed iterator (that
+// is, it is a top level iterator, or on the "Next() path", then it will Next()
+// it's primary iterator (helpfully, and.primary_it) and Check() the resultant
+// value against it's other iterators. If it matches all of them, then it
+// returns that value. Otherwise, it repeats the process.
+//
+// If it's on a Check() path, it merely Check()s every iterator, and returns the
+// logical AND of each result.
+
+package iterator
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/google/cayley/graph"
+)
+
+// The And iterator. Consists of a Base and a number of subiterators, the primary of which will
+// be Next()ed if next is called.
+type And struct {
+	Base
+	internalIterators []graph.Iterator
+	itCount           int
+	primaryIt         graph.Iterator
+	checkList         []graph.Iterator
+}
+
+// Creates a new And iterator.
+func NewAnd() *And {
+	var and And
+	BaseInit(&and.Base)
+	and.internalIterators = make([]graph.Iterator, 0, 20)
+	and.checkList = nil
+	return &and
+}
+
+// Reset all internal iterators
+func (it *And) Reset() {
+	it.primaryIt.Reset()
+	for _, sub := range it.internalIterators {
+		sub.Reset()
+	}
+	it.checkList = nil
+}
+
+func (it *And) Clone() graph.Iterator {
+	and := NewAnd()
+	and.AddSubIterator(it.primaryIt.Clone())
+	and.CopyTagsFrom(it)
+	for _, sub := range it.internalIterators {
+		and.AddSubIterator(sub.Clone())
+	}
+	if it.checkList != nil {
+		and.optimizeCheck()
+	}
+	return and
+}
+
+// Returns a slice of the subiterators, in order (primary iterator first).
+func (it *And) GetSubIterators() []graph.Iterator {
+	iters := make([]graph.Iterator, len(it.internalIterators)+1)
+	iters[0] = it.primaryIt
+	copy(iters[1:], it.internalIterators)
+	return iters
+}
+
+// Overrides Base TagResults, as it needs to add it's own results and
+// recurse down it's subiterators.
+func (it *And) TagResults(out *map[string]graph.TSVal) {
+	it.Base.TagResults(out)
+	if it.primaryIt != nil {
+		it.primaryIt.TagResults(out)
+	}
+	for _, sub := range it.internalIterators {
+		sub.TagResults(out)
+	}
+}
+
+// DEPRECATED Returns the ResultTree for this iterator, recurses to it's subiterators.
+func (it *And) GetResultTree() *graph.ResultTree {
+	tree := graph.NewResultTree(it.LastResult())
+	tree.AddSubtree(it.primaryIt.GetResultTree())
+	for _, sub := range it.internalIterators {
+		tree.AddSubtree(sub.GetResultTree())
+	}
+	return tree
+}
+
+// Prints information about this iterator.
+func (it *And) DebugString(indent int) string {
+	var total string
+	for i, sub := range it.internalIterators {
+		total += strings.Repeat(" ", indent+2)
+		total += fmt.Sprintf("%d:\n%s\n", i, sub.DebugString(indent+4))
+	}
+	var tags string
+	for _, k := range it.Tags() {
+		tags += fmt.Sprintf("%s;", k)
+	}
+	spaces := strings.Repeat(" ", indent+2)
+
+	return fmt.Sprintf("%s(%s %d\n%stags:%s\n%sprimary_it:\n%s\n%sother_its:\n%s)",
+		strings.Repeat(" ", indent),
+		it.Type(),
+		it.GetUid(),
+		spaces,
+		tags,
+		spaces,
+		it.primaryIt.DebugString(indent+4),
+		spaces,
+		total)
+}
+
+// Add a subiterator to this And iterator.
+//
+// The first iterator that is added becomes the primary iterator. This is
+// important. Calling Optimize() is the way to change the order based on
+// subiterator statistics. Without Optimize(), the order added is the order
+// used.
+func (it *And) AddSubIterator(sub graph.Iterator) {
+	if it.itCount > 0 {
+		it.internalIterators = append(it.internalIterators, sub)
+		it.itCount++
+		return
+	}
+	it.primaryIt = sub
+	it.itCount++
+}
+
+// Returns the Next value from the And iterator. Because the And is the
+// intersection of its subiterators, it must choose one subiterator to produce a
+// candidate, and check this value against the subiterators. A productive choice
+// of primary iterator is therefore very important.
+func (it *And) Next() (graph.TSVal, bool) {
+	NextLogIn(it)
+	var curr graph.TSVal
+	var exists bool
+	for {
+		curr, exists = it.primaryIt.Next()
+		if !exists {
+			return NextLogOut(it, nil, false)
+		}
+		if it.checkSubIts(curr) {
+			it.Last = curr
+			return NextLogOut(it, curr, true)
+		}
+	}
+	panic("Somehow broke out of Next() loop in And")
+}
+
+// Checks a value against the non-primary iterators, in order.
+func (it *And) checkSubIts(val graph.TSVal) bool {
+	var subIsGood = true
+	for _, sub := range it.internalIterators {
+		subIsGood = sub.Check(val)
+		if !subIsGood {
+			break
+		}
+	}
+	return subIsGood
+}
+
+func (it *And) checkCheckList(val graph.TSVal) bool {
+	ok := true
+	for _, c := range it.checkList {
+		ok = c.Check(val)
+		if !ok {
+			break
+		}
+	}
+	if ok {
+		it.Last = val
+	}
+	return CheckLogOut(it, val, ok)
+}
+
+// Check a value against the entire iterator, in order.
+func (it *And) Check(val graph.TSVal) bool {
+	CheckLogIn(it, val)
+	if it.checkList != nil {
+		return it.checkCheckList(val)
+	}
+	mainGood := it.primaryIt.Check(val)
+	if !mainGood {
+		return CheckLogOut(it, val, false)
+	}
+	othersGood := it.checkSubIts(val)
+	if !othersGood {
+		return CheckLogOut(it, val, false)
+	}
+	it.Last = val
+	return CheckLogOut(it, val, true)
+}
+
+// Returns the approximate size of the And iterator. Because we're dealing
+// with an intersection, we know that the largest we can be is the size of the
+// smallest iterator. This is the heuristic we shall follow. Better heuristics
+// welcome.
+func (it *And) Size() (int64, bool) {
+	val, b := it.primaryIt.Size()
+	for _, sub := range it.internalIterators {
+		newval, newb := sub.Size()
+		if val > newval {
+			val = newval
+		}
+		b = newb && b
+	}
+	return val, b
+}
+
+// An And has no NextResult of its own -- that is, there are no other values
+// which satisfy our previous result that are not the result itself. Our
+// subiterators might, however, so just pass the call recursively.
+func (it *And) NextResult() bool {
+	if it.primaryIt.NextResult() {
+		return true
+	}
+	for _, sub := range it.internalIterators {
+		if sub.NextResult() {
+			return true
+		}
+	}
+	return false
+}
+
+// Perform and-specific cleanup, of which there currently is none.
+func (it *And) cleanUp() {}
+
+// Close this iterator, and, by extension, close the subiterators.
+// Close should be idempotent, and it follows that if it's subiterators
+// follow this contract, the And follows the contract.
+func (it *And) Close() {
+	it.cleanUp()
+	it.primaryIt.Close()
+	for _, sub := range it.internalIterators {
+		sub.Close()
+	}
+}
+
+// Register this as an "and" iterator.
+func (it *And) Type() string { return "and" }