// Copyright 2018 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

import (
	"context"
	"fmt"

	"github.com/cayleygraph/cayley/graph/refs"
	"github.com/cayleygraph/quad"
)

// A Resolver iterator consists of it's order, an index (where it is in the,
// process of iterating) and a store to resolve values from.
type Resolver struct {
	qs    refs.Namer
	order []quad.Value
}

// NewResolver creates a new Resolver iterator.
func NewResolver(qs refs.Namer, nodes ...quad.Value) *Resolver {
	it := &Resolver{
		qs:    qs,
		order: make([]quad.Value, len(nodes)),
	}
	copy(it.order, nodes)
	return it
}

func (it *Resolver) Iterate() Scanner {
	return newResolverNext(it.qs, it.order)
}

func (it *Resolver) Lookup() Index {
	return newResolverContains(it.qs, it.order)
}

func (it *Resolver) String() string {
	return fmt.Sprintf("Resolver(%v)", it.order)
}

func (it *Resolver) SubIterators() []Shape {
	return nil
}

// Returns a Null iterator if it's empty so that upstream iterators can optimize it
// away, otherwise there is no optimization.
func (it *Resolver) Optimize(ctx context.Context) (Shape, bool) {
	if len(it.order) == 0 {
		return NewNull(), true
	}
	return it, false
}

func (it *Resolver) Stats(ctx context.Context) (Costs, error) {
	return Costs{
		// Next is (presumably) O(1) from store
		NextCost:     1,
		ContainsCost: 1,
		Size: refs.Size{
			Value: int64(len(it.order)),
			Exact: true,
		},
	}, nil
}

// A Resolver iterator consists of it's order, an index (where it is in the,
// process of iterating) and a store to resolve values from.
type resolverNext struct {
	qs     refs.Namer
	order  []quad.Value
	values []refs.Ref
	cached bool
	index  int
	err    error
	result refs.Ref
}

// Creates a new Resolver iterator.
func newResolverNext(qs refs.Namer, nodes []quad.Value) *resolverNext {
	it := &resolverNext{
		qs:    qs,
		order: make([]quad.Value, len(nodes)),
	}
	copy(it.order, nodes)
	return it
}

func (it *resolverNext) Close() error {
	return nil
}

func (it *resolverNext) TagResults(dst map[string]refs.Ref) {}

func (it *resolverNext) String() string {
	return fmt.Sprintf("ResolverNext(%v, %v)", it.order, it.values)
}

// Resolve nodes to values
func (it *resolverNext) resolve(ctx context.Context) error {
	values, err := refs.RefsOf(ctx, it.qs, it.order)
	if err != nil {
		return err
	}
	it.values = make([]refs.Ref, len(it.order))
	for i, value := range values {
		it.values[i] = value
	}
	it.order = nil
	it.cached = true
	return nil
}

// Next advances the iterator.
func (it *resolverNext) Next(ctx context.Context) bool {
	if !it.cached {
		it.err = it.resolve(ctx)
		if it.err != nil {
			return false
		}
	}
	if it.index >= len(it.values) {
		it.result = nil
		return false
	}
	it.result = it.values[it.index]
	it.index++
	return true
}

func (it *resolverNext) Err() error {
	return it.err
}

func (it *resolverNext) Result() refs.Ref {
	return it.result
}

func (it *resolverNext) NextPath(ctx context.Context) bool {
	return false
}

// A Resolver iterator consists of it's order, an index (where it is in the,
// process of iterating) and a store to resolve values from.
type resolverContains struct {
	qs     refs.Namer
	order  []quad.Value
	nodes  map[interface{}]quad.Value
	cached bool
	err    error
	result refs.Ref
}

// Creates a new Resolver iterator.
func newResolverContains(qs refs.Namer, nodes []quad.Value) *resolverContains {
	it := &resolverContains{
		qs:    qs,
		order: make([]quad.Value, len(nodes)),
	}
	copy(it.order, nodes)
	return it
}

func (it *resolverContains) Close() error {
	return nil
}

func (it *resolverContains) TagResults(dst map[string]refs.Ref) {}

func (it *resolverContains) String() string {
	return fmt.Sprintf("ResolverContains(%v, %v)", it.order, it.nodes)
}

// Resolve nodes to values
func (it *resolverContains) resolve(ctx context.Context) error {
	values, err := refs.RefsOf(ctx, it.qs, it.order)
	if err != nil {
		return err
	}
	// Generally there are going to be no/few duplicates given
	// so allocate maps large enough to accommodate all
	it.nodes = make(map[interface{}]quad.Value, len(it.order))
	for index, value := range values {
		node := it.order[index]
		it.nodes[value.Key()] = node
	}
	it.order = nil
	it.cached = true
	return nil
}

// Check if the passed value is equal to one of the order stored in the iterator.
func (it *resolverContains) Contains(ctx context.Context, value refs.Ref) bool {
	if !it.cached {
		it.err = it.resolve(ctx)
		if it.err != nil {
			return false
		}
	}
	_, ok := it.nodes[value.Key()]
	if ok {
		it.result = value
	}
	return ok
}

func (it *resolverContains) Err() error {
	return it.err
}

func (it *resolverContains) Result() refs.Ref {
	return it.result
}

func (it *resolverContains) NextPath(ctx context.Context) bool {
	return false
}