cayley/graph/iterator.go

// 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 graph

// Define the general iterator interface.

import (
	"strings"
	"sync"

	"github.com/barakmich/glog"
)

type Tagger struct {
	tags      []string
	fixedTags map[string]Value
}

// Adds a tag to the iterator.
func (t *Tagger) Add(tag string) {
	t.tags = append(t.tags, tag)
}

func (t *Tagger) AddFixed(tag string, value Value) {
	if t.fixedTags == nil {
		t.fixedTags = make(map[string]Value)
	}
	t.fixedTags[tag] = value
}

// Returns the tags. The returned value must not be mutated.
func (t *Tagger) Tags() []string {
	return t.tags
}

// Returns the fixed tags. The returned value must not be mutated.
func (t *Tagger) Fixed() map[string]Value {
	return t.fixedTags
}

func (t *Tagger) CopyFrom(src Iterator) {
	for _, tag := range src.Tagger().Tags() {
		t.Add(tag)
	}

	for k, v := range src.Tagger().Fixed() {
		t.AddFixed(k, v)
	}

}

type Iterator interface {
	Tagger() *Tagger

	// Fills a tag-to-result-value map.
	TagResults(map[string]Value)

	// Returns the current result.
	Result() Value

	// DEPRECATED -- Fills a ResultTree struct with Result().
	ResultTree() *ResultTree

	// These methods are the heart and soul of the iterator, as they constitute
	// the iteration interface.
	//
	// To get the full results of iteration, do the following:
	// while (!Next()):
	//   emit result
	//   while (!NextResult()):
	//       emit result
	//
	// All of them should set iterator.Last to be the last returned value, to
	// make results work.
	//
	// NextResult() advances iterators that may have more than one valid result,
	// from the bottom up.
	NextResult() bool

	// Check(), given a value, returns whether or not that value is within the set
	// held by this iterator.
	Check(Value) bool

	// Start iteration from the beginning
	Reset()

	// Create a new iterator just like this one
	Clone() Iterator

	// These methods relate to choosing the right iterator, or optimizing an
	// iterator tree
	//
	// Stats() returns the relative costs of calling the iteration methods for
	// this iterator, as well as the size. Roughly, it will take NextCost * Size
	// "cost units" to get everything out of the iterator. This is a wibbly-wobbly
	// thing, and not exact, but a useful heuristic.
	Stats() IteratorStats

	// Helpful accessor for the number of things in the iterator. The first return
	// value is the size, and the second return value is whether that number is exact,
	// or a conservative estimate.
	Size() (int64, bool)

	// Returns a string relating to what the function of the iterator is. By
	// knowing the names of the iterators, we can devise optimization strategies.
	Type() Type

	// Optimizes an iterator. Can replace the iterator, or merely move things
	// around internally. if it chooses to replace it with a better iterator,
	// returns (the new iterator, true), if not, it returns (self, false).
	Optimize() (Iterator, bool)

	// Return a slice of the subiterators for this iterator.
	SubIterators() []Iterator

	// Return a string representation of the iterator, indented by the given amount.
	DebugString(int) string

	// Close the iterator and do internal cleanup.
	Close()

	// UID returns the unique identifier of the iterator.
	UID() uint64
}

type Nexter interface {
	// Next() advances the iterator and returns the next valid result. Returns
	// (<value>, true) or (nil, false)
	Next() (Value, bool)

	Iterator
}

// Next is a convenience function that conditionally calls the Next method
// of an Iterator if it is a Nexter. If the Iterator is not a Nexter, Next
// return a nil Value and false.
func Next(it Iterator) (Value, bool) {
	if n, ok := it.(Nexter); ok {
		return n.Next()
	}
	glog.Errorln("Nexting an un-nextable iterator")
	return nil, false
}

// FixedIterator wraps iterators that are modifiable by addition of fixed value sets.
type FixedIterator interface {
	Iterator
	Add(Value)
}

type IteratorStats struct {
	CheckCost int64
	NextCost  int64
	Size      int64
}

// Type enumerates the set of Iterator types.
type Type int

const (
	Invalid Type = iota
	All
	And
	Or
	HasA
	LinksTo
	Comparison
	Null
	Fixed
	Not
	Optional
)

var (
	// We use a sync.Mutex rather than an RWMutex since the client packages keep
	// the Type that was returned, so the only possibility for contention is at
	// initialization.
	lock sync.Mutex
	// These strings must be kept in order consistent with the Type const block above.
	types = []string{
		"invalid",
		"all",
		"and",
		"or",
		"hasa",
		"linksto",
		"comparison",
		"null",
		"fixed",
		"not",
		"optional",
	}
)

// RegisterIterator adds a new iterator type to the set of acceptable types, returning
// the registered Type.
// Calls to Register are idempotent and must be made prior to use of the iterator.
// The conventional approach for use is to include a call to Register in a package
// init() function, saving the Type to a private package var.
func RegisterIterator(name string) Type {
	lock.Lock()
	defer lock.Unlock()
	for i, t := range types {
		if t == name {
			return Type(i)
		}
	}
	types = append(types, name)
	return Type(len(types) - 1)
}

// String returns a string representation of the Type.
func (t Type) String() string {
	if t < 0 || int(t) >= len(types) {
		return "illegal-type"
	}
	return types[t]
}

// Utility logging functions for when an iterator gets called Next upon, or Check upon, as
// well as what they return. Highly useful for tracing the execution path of a query.
func CheckLogIn(it Iterator, val Value) {
	if glog.V(4) {
		glog.V(4).Infof("%s %d CHECK %d", strings.ToUpper(it.Type().String()), it.UID(), val)
	}
}

func CheckLogOut(it Iterator, val Value, good bool) bool {
	if glog.V(4) {
		if good {
			glog.V(4).Infof("%s %d CHECK %d GOOD", strings.ToUpper(it.Type().String()), it.UID(), val)
		} else {
			glog.V(4).Infof("%s %d CHECK %d BAD", strings.ToUpper(it.Type().String()), it.UID(), val)
		}
	}
	return good
}

func NextLogIn(it Iterator) {
	if glog.V(4) {
		glog.V(4).Infof("%s %d NEXT", strings.ToUpper(it.Type().String()), it.UID())
	}
}

func NextLogOut(it Iterator, val Value, ok bool) (Value, bool) {
	if glog.V(4) {
		if ok {
			glog.V(4).Infof("%s %d NEXT IS %d", strings.ToUpper(it.Type().String()), it.UID(), val)
		} else {
			glog.V(4).Infof("%s %d NEXT DONE", strings.ToUpper(it.Type().String()), it.UID())
		}
	}
	return val, ok
}