/*
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you 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 gremlingo

import (
	"reflect"
	"sync"
)

const defaultCapacity = 1000

// ResultSet interface to define the functions of a ResultSet.
type ResultSet interface {
	setAggregateTo(val string)
	GetAggregateTo() string
	IsEmpty() bool
	Close()
	Channel() chan *Result
	addResult(result *Result)
	One() (*Result, bool, error)
	All() ([]*Result, error)
	GetError() error
	setError(error)
}

// channelResultSet Channel based implementation of ResultSet.
type channelResultSet struct {
	channel         chan *Result
	aggregateTo     string
	closed          bool
	err             error
	waitSignal      chan bool
	channelMutex    sync.Mutex
	waitSignalMutex sync.Mutex
}

func (channelResultSet *channelResultSet) sendSignal() {
	// Lock wait
	channelResultSet.waitSignalMutex.Lock()
	defer channelResultSet.waitSignalMutex.Unlock()
	if channelResultSet.waitSignal != nil {
		channelResultSet.waitSignal <- true
		channelResultSet.waitSignal = nil
	}
}

// GetError returns error from the channelResultSet.
func (channelResultSet *channelResultSet) GetError() error {
	return channelResultSet.err
}

func (channelResultSet *channelResultSet) setError(err error) {
	channelResultSet.err = err
}

// IsEmpty returns true when the channelResultSet is empty.
func (channelResultSet *channelResultSet) IsEmpty() bool {
	channelResultSet.channelMutex.Lock()
	// If our channel is empty and we have no data in it, wait for signal that the state has been updated.
	if len(channelResultSet.channel) != 0 {
		// Channel is not empty.
		channelResultSet.channelMutex.Unlock()
		return false
	} else if channelResultSet.closed {
		// Channel is empty and closed.
		channelResultSet.channelMutex.Unlock()
		return true
	} else {
		// Channel is empty and not closed. Need to wait for signal that state has changed, otherwise
		// we do not know if it is empty or not.
		// We need to grab the wait signal mutex before we release the channel mutex.
		channelResultSet.waitSignalMutex.Lock()
		channelResultSet.channelMutex.Unlock()

		// Create a wait signal and unlock the wait signal mutex.
		waitSignal := make(chan bool)
		channelResultSet.waitSignal = waitSignal
		channelResultSet.waitSignalMutex.Unlock()

		// Technically if we assigned channelResultSet.waitSignal then unlocked, it could be set to nil or
		// overwritten to another channel before we check it, so to be safe, create additional variable and
		// check that instead.
		<-waitSignal
		return channelResultSet.IsEmpty()
	}
}

// Close can be used to close the channelResultSet.
func (channelResultSet *channelResultSet) Close() {
	if !channelResultSet.closed {
		channelResultSet.channelMutex.Lock()
		channelResultSet.closed = true
		close(channelResultSet.channel)
		channelResultSet.channelMutex.Unlock()
		channelResultSet.sendSignal()
	}
}

func (channelResultSet *channelResultSet) setAggregateTo(val string) {
	channelResultSet.aggregateTo = val
}

// GetAggregateTo returns aggregateTo for the channelResultSet.
func (channelResultSet *channelResultSet) GetAggregateTo() string {
	return channelResultSet.aggregateTo
}

// Channel returns channel for the channelResultSet.
func (channelResultSet *channelResultSet) Channel() chan *Result {
	return channelResultSet.channel
}

// One returns the next Result from the channelResultSet, blocking until one is available.
// The value of ok is true if the value received was delivered by a successful send operation to the channel,
// or false if it is a zero value generated because the channel is closed and empty.
func (channelResultSet *channelResultSet) One() (*Result, bool, error) {
	if channelResultSet.err != nil {
		return nil, false, channelResultSet.err
	}
	result, ok := <-channelResultSet.channel
	if channelResultSet.err != nil {
		return nil, false, channelResultSet.err
	}
	return result, ok, nil
}

// All returns all remaining results for the channelResultSet (results grabbed through One will not be present).
func (channelResultSet *channelResultSet) All() ([]*Result, error) {
	var results []*Result
	for result := range channelResultSet.channel {
		results = append(results, result)
	}
	return results, channelResultSet.err
}

func (channelResultSet *channelResultSet) addResult(r *Result) {
	channelResultSet.channelMutex.Lock()
	if r.GetType().Kind() == reflect.Array || r.GetType().Kind() == reflect.Slice {
		for _, v := range r.Data.([]interface{}) {
			if reflect.TypeOf(v) == reflect.TypeOf(&Traverser{}) {
				for i := int64(0); i < (v.(*Traverser)).bulk; i++ {
					channelResultSet.channel <- &Result{(v.(*Traverser)).value}
				}
			} else {
				channelResultSet.channel <- &Result{v}
			}
		}
	} else {
		channelResultSet.channel <- &Result{r.Data}
	}
	channelResultSet.channelMutex.Unlock()
	channelResultSet.sendSignal()
}

func newChannelResultSetCapacity(channelSize int) ResultSet {
	return &channelResultSet{make(chan *Result, channelSize), "", false, nil, nil, sync.Mutex{}, sync.Mutex{}}
}

func newChannelResultSet() ResultSet {
	return newChannelResultSetCapacity(defaultCapacity)
}
