/*
Copyright 2014 Workiva, LLC

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 palm

import (
	"log"
	"runtime"
	"sync"
	"sync/atomic"

	"github.com/Workiva/go-datastructures/common"
	"github.com/Workiva/go-datastructures/queue"
)

type operation int

const (
	get operation = iota
	add
	remove
	apply
)

const multiThreadAt = 400 // number of keys before we multithread lookups

type keyBundle struct {
	key         common.Comparator
	left, right *node
}

func (kb *keyBundle) dispose(ptree *ptree) {
	if ptree.kbRing.Len() == ptree.kbRing.Cap() {
		return
	}
	kb.key, kb.left, kb.right = nil, nil, nil
	ptree.kbRing.Put(kb)
}

type ptree struct {
	root            *node
	_padding0       [8]uint64
	number          uint64
	_padding1       [8]uint64
	ary, bufferSize uint64
	actions         *queue.RingBuffer
	cache           []interface{}
	buffer0         [8]uint64
	disposed        uint64
	buffer1         [8]uint64
	running         uint64
	_padding2       [8]uint64
	kbRing          *queue.RingBuffer
	disposeChannel  chan bool
	mpChannel       chan map[*node][]*keyBundle
}

func (ptree *ptree) checkAndRun(action action) {
	if ptree.actions.Len() > 0 {
		if action != nil {
			ptree.actions.Put(action)
		}
		if atomic.CompareAndSwapUint64(&ptree.running, 0, 1) {
			var a interface{}
			var err error
			for ptree.actions.Len() > 0 {
				a, err = ptree.actions.Get()
				if err != nil {
					return
				}
				ptree.cache = append(ptree.cache, a)
				if uint64(len(ptree.cache)) >= ptree.bufferSize {
					break
				}
			}

			go ptree.operationRunner(ptree.cache, true)
		}
	} else if action != nil {
		if atomic.CompareAndSwapUint64(&ptree.running, 0, 1) {
			switch action.operation() {
			case get:
				ptree.read(action)
				action.complete()
				ptree.reset()
			case add, remove:
				if len(action.keys()) > multiThreadAt {
					ptree.operationRunner(interfaces{action}, true)
				} else {
					ptree.operationRunner(interfaces{action}, false)
				}
			case apply:
				q := action.(*applyAction)
				n := getParent(ptree.root, q.start)
				ptree.apply(n, q)
				q.complete()
				ptree.reset()
			}
		} else {
			ptree.actions.Put(action)
			ptree.checkAndRun(nil)
		}
	}
}

func (ptree *ptree) init(bufferSize, ary uint64) {
	ptree.bufferSize = bufferSize
	ptree.ary = ary
	ptree.cache = make([]interface{}, 0, bufferSize)
	ptree.root = newNode(true, newKeys(ary), newNodes(ary))
	ptree.actions = queue.NewRingBuffer(ptree.bufferSize)
	ptree.kbRing = queue.NewRingBuffer(1024)
	for i := uint64(0); i < ptree.kbRing.Cap(); i++ {
		ptree.kbRing.Put(&keyBundle{})
	}
	ptree.disposeChannel = make(chan bool)
	ptree.mpChannel = make(chan map[*node][]*keyBundle, 1024)
	var wg sync.WaitGroup
	wg.Add(1)
	go ptree.disposer(&wg)
	wg.Wait()
}

func (ptree *ptree) newKeyBundle(key common.Comparator) *keyBundle {
	if ptree.kbRing.Len() == 0 {
		return &keyBundle{key: key}
	}
	ifc, err := ptree.kbRing.Get()
	if err != nil {
		return nil
	}
	kb := ifc.(*keyBundle)
	kb.key = key
	return kb
}

func (ptree *ptree) operationRunner(xns interfaces, threaded bool) {
	writeOperations, deleteOperations, toComplete := ptree.fetchKeys(xns, threaded)
	ptree.recursiveMutate(writeOperations, deleteOperations, false, threaded)
	for _, a := range toComplete {
		a.complete()
	}

	ptree.reset()
}

func (ptree *ptree) read(action action) {
	for i, k := range action.keys() {
		n := getParent(ptree.root, k)
		if n == nil {
			action.keys()[i] = nil
		} else {
			key, _ := n.keys.withPosition(k)
			if key == nil {
				action.keys()[i] = nil
			} else {
				action.keys()[i] = key
			}
		}
	}
}

func (ptree *ptree) fetchKeys(xns interfaces, inParallel bool) (map[*node][]*keyBundle, map[*node][]*keyBundle, actions) {
	if inParallel {
		ptree.fetchKeysInParallel(xns)
	} else {
		ptree.fetchKeysInSerial(xns)
	}

	writeOperations := make(map[*node][]*keyBundle)
	deleteOperations := make(map[*node][]*keyBundle)
	toComplete := make(actions, 0, len(xns)/2)
	for _, ifc := range xns {
		action := ifc.(action)
		switch action.operation() {
		case add:
			for i, n := range action.nodes() {
				writeOperations[n] = append(writeOperations[n], ptree.newKeyBundle(action.keys()[i]))
			}
			toComplete = append(toComplete, action)
		case remove:
			for i, n := range action.nodes() {
				deleteOperations[n] = append(deleteOperations[n], ptree.newKeyBundle(action.keys()[i]))
			}
			toComplete = append(toComplete, action)
		case get, apply:
			action.complete()
		}
	}

	return writeOperations, deleteOperations, toComplete
}

func (ptree *ptree) apply(n *node, aa *applyAction) {
	i := n.search(aa.start)
	if i == n.keys.len() { // nothing to apply against
		return
	}

	var k common.Comparator
	for n != nil {
		for j := i; j < n.keys.len(); j++ {
			k = n.keys.byPosition(j)
			if aa.stop.Compare(k) < 1 || !aa.fn(k) {
				return
			}
		}
		n = n.right
		i = 0
	}
}

func (ptree *ptree) disposer(wg *sync.WaitGroup) {
	wg.Done()

	for {
		select {
		case mp := <-ptree.mpChannel:
			ptree.cleanMap(mp)
		case <-ptree.disposeChannel:
			return
		}
	}
}

func (ptree *ptree) fetchKeysInSerial(xns interfaces) {
	for _, ifc := range xns {
		action := ifc.(action)
		for i, key := range action.keys() {
			n := getParent(ptree.root, key)
			switch action.operation() {
			case add, remove:
				action.addNode(int64(i), n)
			case get:
				if n == nil {
					action.keys()[i] = nil
				} else {
					k, _ := n.keys.withPosition(key)
					if k == nil {
						action.keys()[i] = nil
					} else {
						action.keys()[i] = k
					}
				}
			case apply:
				q := action.(*applyAction)
				ptree.apply(n, q)
			}
		}
	}
}

func (ptree *ptree) reset() {
	for i := range ptree.cache {
		ptree.cache[i] = nil
	}

	ptree.cache = ptree.cache[:0]
	atomic.StoreUint64(&ptree.running, 0)
	ptree.checkAndRun(nil)
}

func (ptree *ptree) fetchKeysInParallel(xns []interface{}) {
	var forCache struct {
		i      int64
		buffer [8]uint64 // different cache lines
		js     []int64
	}

	for j := 0; j < len(xns); j++ {
		forCache.js = append(forCache.js, -1)
	}
	numCPU := runtime.NumCPU()
	if numCPU > 1 {
		numCPU--
	}
	var wg sync.WaitGroup
	wg.Add(numCPU)

	for k := 0; k < numCPU; k++ {
		go func() {
			for {
				index := atomic.LoadInt64(&forCache.i)
				if index >= int64(len(xns)) {
					break
				}
				action := xns[index].(action)

				j := atomic.AddInt64(&forCache.js[index], 1)
				if j > int64(len(action.keys())) { // someone else is updating i
					continue
				} else if j == int64(len(action.keys())) {
					atomic.StoreInt64(&forCache.i, index+1)
					continue
				}

				n := getParent(ptree.root, action.keys()[j])
				switch action.operation() {
				case add, remove:
					action.addNode(j, n)
				case get:
					if n == nil {
						action.keys()[j] = nil
					} else {
						k, _ := n.keys.withPosition(action.keys()[j])
						if k == nil {
							action.keys()[j] = nil
						} else {
							action.keys()[j] = k
						}
					}
				case apply:
					q := action.(*applyAction)
					ptree.apply(n, q)
				}
			}
			wg.Done()
		}()
	}
	wg.Wait()
}

func (ptree *ptree) splitNode(n, parent *node, nodes *[]*node, keys *common.Comparators) {
	if !n.needsSplit(ptree.ary) {
		return
	}

	length := n.keys.len()
	splitAt := ptree.ary - 1

	for i := splitAt; i < length; i += splitAt {
		offset := length - i
		k, left, right := n.split(offset, ptree.ary)
		left.right = right
		*keys = append(*keys, k)
		*nodes = append(*nodes, left, right)
		left.parent = parent
		right.parent = parent
	}
}

func (ptree *ptree) applyNode(n *node, adds, deletes []*keyBundle) {
	for _, kb := range deletes {
		if n.keys.len() == 0 {
			break
		}

		deleted := n.keys.delete(kb.key)
		if deleted != nil {
			atomic.AddUint64(&ptree.number, ^uint64(0))
		}
	}

	for _, kb := range adds {
		if n.keys.len() == 0 {
			oldKey, _ := n.keys.insert(kb.key)
			if n.isLeaf && oldKey == nil {
				atomic.AddUint64(&ptree.number, 1)
			}
			if kb.left != nil {
				n.nodes.push(kb.left)
				n.nodes.push(kb.right)
			}
			continue
		}

		oldKey, index := n.keys.insert(kb.key)
		if n.isLeaf && oldKey == nil {
			atomic.AddUint64(&ptree.number, 1)
		}
		if kb.left != nil {
			n.nodes.replaceAt(index, kb.left)
			n.nodes.insertAt(index+1, kb.right)
		}
	}
}

func (ptree *ptree) cleanMap(op map[*node][]*keyBundle) {
	for _, bundles := range op {
		for _, kb := range bundles {
			kb.dispose(ptree)
		}
	}
}

func (ptree *ptree) recursiveMutate(adds, deletes map[*node][]*keyBundle, setRoot, inParallel bool) {
	if len(adds) == 0 && len(deletes) == 0 {
		return
	}

	if setRoot && len(adds) > 1 {
		panic(`SHOULD ONLY HAVE ONE ROOT`)
	}

	ifs := make(interfaces, 0, len(adds))
	for n := range adds {
		if n.parent == nil {
			setRoot = true
		}
		ifs = append(ifs, n)
	}

	for n := range deletes {
		if n.parent == nil {
			setRoot = true
		}

		if _, ok := adds[n]; !ok {
			ifs = append(ifs, n)
		}
	}

	var dummyRoot *node
	if setRoot {
		dummyRoot = &node{
			keys:  newKeys(ptree.ary),
			nodes: newNodes(ptree.ary),
		}
	}

	var write sync.Mutex
	nextLayerWrite := make(map[*node][]*keyBundle)
	nextLayerDelete := make(map[*node][]*keyBundle)

	var mutate func(interfaces, func(interface{}))
	if inParallel {
		mutate = executeInterfacesInParallel
	} else {
		mutate = executeInterfacesInSerial
	}

	mutate(ifs, func(ifc interface{}) {
		n := ifc.(*node)
		adds := adds[n]
		deletes := deletes[n]

		if len(adds) == 0 && len(deletes) == 0 {
			return
		}

		if setRoot {
			ptree.root = n
		}

		parent := n.parent
		if parent == nil {
			parent = dummyRoot
			setRoot = true
		}

		ptree.applyNode(n, adds, deletes)

		if n.needsSplit(ptree.ary) {
			keys := make(common.Comparators, 0, n.keys.len())
			nodes := make([]*node, 0, n.nodes.len())
			ptree.splitNode(n, parent, &nodes, &keys)
			write.Lock()
			for i, k := range keys {
				kb := ptree.newKeyBundle(k)
				kb.left = nodes[i*2]
				kb.right = nodes[i*2+1]
				nextLayerWrite[parent] = append(nextLayerWrite[parent], kb)
			}
			write.Unlock()
		}
	})

	ptree.mpChannel <- adds
	ptree.mpChannel <- deletes

	ptree.recursiveMutate(nextLayerWrite, nextLayerDelete, setRoot, inParallel)
}

// Insert will add the provided keys to the tree.
func (ptree *ptree) Insert(keys ...common.Comparator) {
	ia := newInsertAction(keys)
	ptree.checkAndRun(ia)
	ia.completer.Wait()
}

// Delete will remove the provided keys from the tree.  If no
// matching key is found, this is a no-op.
func (ptree *ptree) Delete(keys ...common.Comparator) {
	ra := newRemoveAction(keys)
	ptree.checkAndRun(ra)
	ra.completer.Wait()
}

// Get will retrieve a list of keys from the provided keys.
func (ptree *ptree) Get(keys ...common.Comparator) common.Comparators {
	ga := newGetAction(keys)
	ptree.checkAndRun(ga)
	ga.completer.Wait()
	return ga.result
}

// Len returns the number of items in the tree.
func (ptree *ptree) Len() uint64 {
	return atomic.LoadUint64(&ptree.number)
}

// Query will return a list of Comparators that fall within the
// provided start and stop Comparators.  Start is inclusive while
// stop is exclusive, ie [start, stop).
func (ptree *ptree) Query(start, stop common.Comparator) common.Comparators {
	cmps := make(common.Comparators, 0, 32)
	aa := newApplyAction(func(cmp common.Comparator) bool {
		cmps = append(cmps, cmp)
		return true
	}, start, stop)
	ptree.checkAndRun(aa)
	aa.completer.Wait()
	return cmps
}

// Dispose will clean up any resources used by this tree.  This
// must be called to prevent a memory leak.
func (ptree *ptree) Dispose() {
	if atomic.LoadUint64(&ptree.disposed) == 1 {
		return
	}
	ptree.actions.Dispose()
	atomic.StoreUint64(&ptree.disposed, 1)
	close(ptree.disposeChannel)
}

func (ptree *ptree) print(output *log.Logger) {
	println(`PRINTING TREE`)
	if ptree.root == nil {
		return
	}

	ptree.root.print(output)
}

func newTree(bufferSize, ary uint64) *ptree {
	ptree := &ptree{}
	ptree.init(bufferSize, ary)
	return ptree
}

// New will allocate, initialize, and return a new B-Tree based
// on PALM principles.  This type of tree is suited for in-memory
// indices in a multi-threaded environment.
func New(bufferSize, ary uint64) BTree {
	return newTree(bufferSize, ary)
}