/*
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 hilbert implements a Hilbert R-tree based on PALM principles
to improve multithreaded performance.  This package is not quite complete
and some optimization and delete codes remain to be completed.

This serves as a potential replacement for the interval tree and
rangetree.

Benchmarks:
BenchmarkBulkAddPoints-8	     500	   2589270 ns/op
BenchmarkBulkUpdatePoints-8	    2000	   1212641 ns/op
BenchmarkPointInsertion-8	  200000	      9135 ns/op
BenchmarkQueryPoints-8	  	  500000	      3122 ns/op

*/
package hilbert

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

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

type operation int

const (
	get operation = iota
	add
	remove
)

const multiThreadAt = 1000 // number of keys before we multithread lookups

type keyBundle struct {
	key         hilbert
	left, right rtree.Rectangle
}

type tree struct {
	root            *node
	_               [8]uint64
	number          uint64
	_               [8]uint64
	ary, bufferSize uint64
	actions         *queue.RingBuffer
	cache           []interface{}
	_               [8]uint64
	disposed        uint64
	_               [8]uint64
	running         uint64
}

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

			go tree.operationRunner(tree.cache, true)
		}
	} else if action != nil {
		if atomic.CompareAndSwapUint64(&tree.running, 0, 1) {
			switch action.operation() {
			case get:
				ga := action.(*getAction)
				result := tree.search(ga.lookup)
				ga.result = result
				action.complete()
				tree.reset()
			case add, remove:
				if len(action.keys()) > multiThreadAt {
					tree.operationRunner(interfaces{action}, true)
				} else {
					tree.operationRunner(interfaces{action}, false)
				}
			}
		} else {
			tree.actions.Put(action)
			tree.checkAndRun(nil)
		}
	}
}

func (tree *tree) init(bufferSize, ary uint64) {
	tree.bufferSize = bufferSize
	tree.ary = ary
	tree.cache = make([]interface{}, 0, bufferSize)
	tree.root = newNode(true, newKeys(ary), newNodes(ary))
	tree.root.mbr = &rectangle{}
	tree.actions = queue.NewRingBuffer(tree.bufferSize)
}

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

	tree.reset()
}

func (tree *tree) fetchKeys(xns interfaces, inParallel bool) (map[*node][]*keyBundle, map[*node][]*keyBundle, actions) {
	if inParallel {
		tree.fetchKeysInParallel(xns)
	} else {
		tree.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], &keyBundle{key: action.rects()[i].hilbert, left: action.rects()[i].rect})
			}
			toComplete = append(toComplete, action)
		case remove:
			for i, n := range action.nodes() {
				deleteOperations[n] = append(deleteOperations[n], &keyBundle{key: action.rects()[i].hilbert, left: action.rects()[i].rect})
			}
			toComplete = append(toComplete, action)
		case get:
			action.complete()
		}
	}

	return writeOperations, deleteOperations, toComplete
}

func (tree *tree) fetchKeysInSerial(xns interfaces) {
	for _, ifc := range xns {
		action := ifc.(action)
		switch action.operation() {
		case add, remove:
			for i, key := range action.rects() {
				n := getParent(tree.root, key.hilbert, key.rect)
				action.addNode(int64(i), n)
			}
		case get:
			ga := action.(*getAction)
			rects := tree.search(ga.lookup)
			ga.result = rects
		}
	}
}

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

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

func (tree *tree) 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.rects())) { // someone else is updating i
					continue
				} else if j == int64(len(action.rects())) {
					atomic.StoreInt64(&forCache.i, index+1)
					continue
				}

				switch action.operation() {
				case add, remove:
					hb := action.rects()[j]
					n := getParent(tree.root, hb.hilbert, hb.rect)
					action.addNode(j, n)
				case get:
					ga := action.(*getAction)
					result := tree.search(ga.lookup)
					ga.result = result
				}
			}
			wg.Done()
		}()
	}
	wg.Wait()
}

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

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

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

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

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

	for _, kb := range adds {
		old := n.insert(kb)
		if n.isLeaf && old == nil {
			atomic.AddUint64(&tree.number, 1)
		}
	}
}

func (tree *tree) 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(tree.ary),
			nodes: newNodes(tree.ary),
			mbr:   &rectangle{},
		}
	}

	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 {
			tree.root = n
		}

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

		tree.applyNode(n, adds, deletes)

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

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

// Insert will add the provided keys to the tree.
func (tree *tree) Insert(rects ...rtree.Rectangle) {
	ia := newInsertAction(rects)
	tree.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 (tree *tree) Delete(rects ...rtree.Rectangle) {
	ra := newRemoveAction(rects)
	tree.checkAndRun(ra)
	ra.completer.Wait()
}

func (tree *tree) search(r *rectangle) rtree.Rectangles {
	if tree.root == nil {
		return rtree.Rectangles{}
	}

	result := make(rtree.Rectangles, 0, 10)
	whs := tree.root.searchRects(r)
	for len(whs) > 0 {
		wh := whs[0]
		if n, ok := wh.(*node); ok {
			whs = append(whs, n.searchRects(r)...)
		} else {
			result = append(result, wh)
		}
		whs = whs[1:]
	}

	return result
}

// Search will return a list of rectangles that intersect the provided
// rectangle.
func (tree *tree) Search(rect rtree.Rectangle) rtree.Rectangles {
	ga := newGetAction(rect)
	tree.checkAndRun(ga)
	ga.completer.Wait()
	return ga.result
}

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

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

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

// New will construct a new Hilbert R-Tree and return it.
func New(bufferSize, ary uint64) rtree.RTree {
	return newTree(bufferSize, ary)
}