package page_writer

import (
	"fmt"
	"github.com/chrislusf/seaweedfs/weed/glog"
	"github.com/chrislusf/seaweedfs/weed/util"
	"github.com/chrislusf/seaweedfs/weed/util/mem"
	"sync"
	"sync/atomic"
	"time"
)

type LogicChunkIndex int

type UploadPipeline struct {
	filepath             util.FullPath
	ChunkSize            int64
	writableChunks       map[LogicChunkIndex]*MemChunk
	writableChunksLock   sync.Mutex
	sealedChunks         map[LogicChunkIndex]*SealedChunk
	sealedChunksLock     sync.Mutex
	uploaders            *util.LimitedConcurrentExecutor
	uploaderCount        int32
	uploaderCountCond    *sync.Cond
	saveToStorageFn      SaveToStorageFunc
	activeReadChunks     map[LogicChunkIndex]int
	activeReadChunksLock sync.Mutex
}

type SealedChunk struct {
	chunk            *MemChunk
	referenceCounter int // track uploading or reading processes
}

func (sc *SealedChunk) FreeReference(messageOnFree string) {
	sc.referenceCounter--
	if sc.referenceCounter == 0 {
		glog.V(4).Infof("Free sealed chunk: %s", messageOnFree)
		mem.Free(sc.chunk.buf)
	}
}

func NewUploadPipeline(filepath util.FullPath, writers *util.LimitedConcurrentExecutor, chunkSize int64, saveToStorageFn SaveToStorageFunc) *UploadPipeline {
	return &UploadPipeline{
		ChunkSize:         chunkSize,
		writableChunks:    make(map[LogicChunkIndex]*MemChunk),
		sealedChunks:      make(map[LogicChunkIndex]*SealedChunk),
		uploaders:         writers,
		uploaderCountCond: sync.NewCond(&sync.Mutex{}),
		saveToStorageFn:   saveToStorageFn,
		filepath:          filepath,
		activeReadChunks:  make(map[LogicChunkIndex]int),
	}
}

func (cw *UploadPipeline) SaveDataAt(p []byte, off int64) (n int) {
	cw.writableChunksLock.Lock()
	defer cw.writableChunksLock.Unlock()

	logicChunkIndex := LogicChunkIndex(off / cw.ChunkSize)
	offsetRemainder := off % cw.ChunkSize

	memChunk, found := cw.writableChunks[logicChunkIndex]
	if !found {
		memChunk = &MemChunk{
			buf:   mem.Allocate(int(cw.ChunkSize)),
			usage: newChunkWrittenIntervalList(),
		}
		cw.writableChunks[logicChunkIndex] = memChunk
	}
	n = copy(memChunk.buf[offsetRemainder:], p)
	memChunk.usage.MarkWritten(offsetRemainder, offsetRemainder+int64(n))
	cw.maybeMoveToSealed(memChunk, logicChunkIndex)

	return
}

func (cw *UploadPipeline) MaybeReadDataAt(p []byte, off int64) (maxStop int64) {
	logicChunkIndex := LogicChunkIndex(off / cw.ChunkSize)

	// read from sealed chunks first
	cw.sealedChunksLock.Lock()
	sealedChunk, found := cw.sealedChunks[logicChunkIndex]
	if found {
		sealedChunk.referenceCounter++
	}
	cw.sealedChunksLock.Unlock()
	if found {
		maxStop = readMemChunk(sealedChunk.chunk, p, off, logicChunkIndex, cw.ChunkSize)
		glog.V(4).Infof("%s read sealed memchunk [%d,%d)", cw.filepath, off, maxStop)
		sealedChunk.FreeReference(fmt.Sprintf("%s finish reading chunk %d", cw.filepath, logicChunkIndex))
	}

	// read from writable chunks last
	cw.writableChunksLock.Lock()
	defer cw.writableChunksLock.Unlock()
	writableChunk, found := cw.writableChunks[logicChunkIndex]
	if !found {
		return
	}
	writableMaxStop := readMemChunk(writableChunk, p, off, logicChunkIndex, cw.ChunkSize)
	glog.V(4).Infof("%s read writable memchunk [%d,%d)", cw.filepath, off, writableMaxStop)
	maxStop = max(maxStop, writableMaxStop)

	return
}

func (cw *UploadPipeline) FlushAll() {
	cw.writableChunksLock.Lock()
	defer cw.writableChunksLock.Unlock()

	for logicChunkIndex, memChunk := range cw.writableChunks {
		cw.moveToSealed(memChunk, logicChunkIndex)
	}

	cw.waitForCurrentWritersToComplete()
}

func (cw *UploadPipeline) LockForRead(startOffset, stopOffset int64) {
	startLogicChunkIndex := LogicChunkIndex(startOffset / cw.ChunkSize)
	stopLogicChunkIndex := LogicChunkIndex(stopOffset / cw.ChunkSize)
	if stopOffset%cw.ChunkSize > 0 {
		stopLogicChunkIndex += 1
	}
	cw.activeReadChunksLock.Lock()
	defer cw.activeReadChunksLock.Unlock()
	for i := startLogicChunkIndex; i < stopLogicChunkIndex; i++ {
		if count, found := cw.activeReadChunks[i]; found {
			cw.activeReadChunks[i] = count + 1
		} else {
			cw.activeReadChunks[i] = 1
		}
	}
}

func (cw *UploadPipeline) UnlockForRead(startOffset, stopOffset int64) {
	startLogicChunkIndex := LogicChunkIndex(startOffset / cw.ChunkSize)
	stopLogicChunkIndex := LogicChunkIndex(stopOffset / cw.ChunkSize)
	if stopOffset%cw.ChunkSize > 0 {
		stopLogicChunkIndex += 1
	}
	cw.activeReadChunksLock.Lock()
	defer cw.activeReadChunksLock.Unlock()
	for i := startLogicChunkIndex; i < stopLogicChunkIndex; i++ {
		if count, found := cw.activeReadChunks[i]; found {
			if count == 1 {
				delete(cw.activeReadChunks, i)
			} else {
				cw.activeReadChunks[i] = count - 1
			}
		}
	}
}

func (cw *UploadPipeline) IsLocked(logicChunkIndex LogicChunkIndex) bool {
	cw.activeReadChunksLock.Lock()
	defer cw.activeReadChunksLock.Unlock()
	if count, found := cw.activeReadChunks[logicChunkIndex]; found {
		return count > 0
	}
	return false
}

func (cw *UploadPipeline) waitForCurrentWritersToComplete() {
	cw.uploaderCountCond.L.Lock()
	t := int32(100)
	for {
		t = atomic.LoadInt32(&cw.uploaderCount)
		if t <= 0 {
			break
		}
		cw.uploaderCountCond.Wait()
	}
	cw.uploaderCountCond.L.Unlock()
}

func (cw *UploadPipeline) maybeMoveToSealed(memChunk *MemChunk, logicChunkIndex LogicChunkIndex) {
	if memChunk.usage.IsComplete(cw.ChunkSize) {
		cw.moveToSealed(memChunk, logicChunkIndex)
	}
}

func (cw *UploadPipeline) moveToSealed(memChunk *MemChunk, logicChunkIndex LogicChunkIndex) {
	atomic.AddInt32(&cw.uploaderCount, 1)
	glog.V(4).Infof("%s uploaderCount %d ++> %d", cw.filepath, cw.uploaderCount-1, cw.uploaderCount)

	cw.sealedChunksLock.Lock()

	if oldMemChunk, found := cw.sealedChunks[logicChunkIndex]; found {
		oldMemChunk.FreeReference(fmt.Sprintf("%s replace chunk %d", cw.filepath, logicChunkIndex))
	}
	sealedChunk := &SealedChunk{
		chunk:            memChunk,
		referenceCounter: 1, // default 1 is for uploading process
	}
	cw.sealedChunks[logicChunkIndex] = sealedChunk
	delete(cw.writableChunks, logicChunkIndex)

	cw.sealedChunksLock.Unlock()

	cw.uploaders.Execute(func() {
		// first add to the file chunks
		cw.saveOneChunk(sealedChunk.chunk, logicChunkIndex)

		// notify waiting process
		atomic.AddInt32(&cw.uploaderCount, -1)
		glog.V(4).Infof("%s uploaderCount %d --> %d", cw.filepath, cw.uploaderCount+1, cw.uploaderCount)
		// Lock and Unlock are not required,
		// but it may signal multiple times during one wakeup,
		// and the waiting goroutine may miss some of them!
		cw.uploaderCountCond.L.Lock()
		cw.uploaderCountCond.Broadcast()
		cw.uploaderCountCond.L.Unlock()

		// wait for readers
		for cw.IsLocked(logicChunkIndex) {
			time.Sleep(59 * time.Millisecond)
		}

		// then remove from sealed chunks
		cw.sealedChunksLock.Lock()
		defer cw.sealedChunksLock.Unlock()
		delete(cw.sealedChunks, logicChunkIndex)
		sealedChunk.FreeReference(fmt.Sprintf("%s finished uploading chunk %d", cw.filepath, logicChunkIndex))

	})
}

func (cw *UploadPipeline) saveOneChunk(memChunk *MemChunk, logicChunkIndex LogicChunkIndex) {
	if cw.saveToStorageFn == nil {
		return
	}
	for t := memChunk.usage.head.next; t != memChunk.usage.tail; t = t.next {
		reader := util.NewBytesReader(memChunk.buf[t.StartOffset:t.stopOffset])
		cw.saveToStorageFn(reader, int64(logicChunkIndex)*cw.ChunkSize+t.StartOffset, t.Size(), func() {
		})
	}
}

func readMemChunk(memChunk *MemChunk, p []byte, off int64, logicChunkIndex LogicChunkIndex, chunkSize int64) (maxStop int64) {
	memChunkBaseOffset := int64(logicChunkIndex) * chunkSize
	for t := memChunk.usage.head.next; t != memChunk.usage.tail; t = t.next {
		logicStart := max(off, int64(logicChunkIndex)*chunkSize+t.StartOffset)
		logicStop := min(off+int64(len(p)), memChunkBaseOffset+t.stopOffset)
		if logicStart < logicStop {
			copy(p[logicStart-off:logicStop-off], memChunk.buf[logicStart-memChunkBaseOffset:logicStop-memChunkBaseOffset])
			maxStop = max(maxStop, logicStop)
		}
	}
	return
}

func (p2 *UploadPipeline) Shutdown() {

}