package blockstore

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"math"
	"os"
	"strings"
	"sync"
	"time"
)

type FileOptsType struct {
	MaxSize  int64
	Circular bool
	IJson    bool
}

type FileMeta = map[string]any

type FileInfo struct {
	BlockId   string
	Name      string
	Size      int64
	CreatedTs int64
	ModTs     int64
	Opts      FileOptsType
	Meta      FileMeta
}

const UnitsKB = 1024 * 1024
const UnitsMB = 1024 * UnitsKB
const UnitsGB = 1024 * UnitsMB

const MaxBlockSize = int64(128 * UnitsKB)
const DefaultFlushTimeout = 1 * time.Second

type CacheEntry struct {
	Lock       *sync.Mutex
	CacheTs    int64
	Info       *FileInfo
	DataBlocks []*CacheBlock
	Refs       int64
}

func (c *CacheEntry) IncRefs() {
	c.Refs += 1
}

func (c *CacheEntry) DecRefs() {
	c.Refs -= 1
}

type CacheBlock struct {
	data  []byte
	size  int
	dirty bool
}

func MakeCacheEntry(info *FileInfo) *CacheEntry {
	rtn := &CacheEntry{Lock: &sync.Mutex{}, CacheTs: int64(time.Now().UnixMilli()), Info: info, DataBlocks: []*CacheBlock{}, Refs: 0}
	return rtn
}

// add ctx context.Context to all these methods
type BlockStore interface {
	MakeFile(ctx context.Context, blockId string, name string, meta FileMeta, opts FileOptsType) error
	WriteFile(ctx context.Context, blockId string, name string, meta FileMeta, opts FileOptsType, data []byte) (int, error)
	AppendData(ctx context.Context, blockId string, name string, p []byte) (int, error)
	WriteAt(ctx context.Context, blockId string, name string, p []byte, off int64) (int, error)
	ReadAt(ctx context.Context, blockId string, name string, p *[]byte, off int64) (int, error)
	Stat(ctx context.Context, blockId string, name string) (FileInfo, error)
	CollapseIJson(ctx context.Context, blockId string, name string) error
	WriteMeta(ctx context.Context, blockId string, name string, meta FileMeta) error
	DeleteFile(ctx context.Context, blockId string, name string) error
	DeleteBlock(ctx context.Context, blockId string) error
	ListFiles(ctx context.Context, blockId string) []*FileInfo
	FlushCache(ctx context.Context) error
	GetAllBlockIds(ctx context.Context) []string
}

var blockstoreCache map[string]*CacheEntry = make(map[string]*CacheEntry)
var globalLock *sync.Mutex = &sync.Mutex{}
var appendLock *sync.Mutex = &sync.Mutex{}
var flushTimeout = DefaultFlushTimeout
var lastWriteTime time.Time

// for testing
func clearCache() {
	globalLock.Lock()
	defer globalLock.Unlock()
	blockstoreCache = make(map[string]*CacheEntry)
}

func InsertFileIntoDB(ctx context.Context, fileInfo FileInfo) error {
	metaJson, err := json.Marshal(fileInfo.Meta)
	if err != nil {
		return fmt.Errorf("error writing file %s to db: %v", fileInfo.Name, err)
	}
	txErr := WithTx(ctx, func(tx *TxWrap) error {
		query := `INSERT INTO block_file VALUES (?, ?, ?, ?, ?, ?, ?, ?)`
		tx.Exec(query, fileInfo.BlockId, fileInfo.Name, fileInfo.Opts.MaxSize, fileInfo.Opts.Circular, fileInfo.Size, fileInfo.CreatedTs, fileInfo.ModTs, metaJson)
		return nil
	})
	if txErr != nil {
		return fmt.Errorf("error writing file %s to db: %v", fileInfo.Name, txErr)
	}
	return nil
}

func WriteFileToDB(ctx context.Context, fileInfo FileInfo) error {
	metaJson, err := json.Marshal(fileInfo.Meta)
	if err != nil {
		return fmt.Errorf("error writing file %s to db: %v", fileInfo.Name, err)
	}
	txErr := WithTx(ctx, func(tx *TxWrap) error {
		query := `UPDATE block_file SET blockid = ?, name = ?, maxsize = ?, circular = ?, size = ?, createdts = ?, modts = ?, meta = ? where blockid = ? and name = ?`
		tx.Exec(query, fileInfo.BlockId, fileInfo.Name, fileInfo.Opts.MaxSize, fileInfo.Opts.Circular, fileInfo.Size, fileInfo.CreatedTs, fileInfo.ModTs, metaJson, fileInfo.BlockId, fileInfo.Name)
		return nil
	})
	if txErr != nil {
		return fmt.Errorf("error writing file %s to db: %v", fileInfo.Name, txErr)
	}
	return nil

}

func WriteDataBlockToDB(ctx context.Context, blockId string, name string, index int, data []byte) error {
	txErr := WithTx(ctx, func(tx *TxWrap) error {
		query := `REPLACE INTO block_data values (?, ?, ?, ?)`
		tx.Exec(query, blockId, name, index, data)
		return nil
	})
	if txErr != nil {
		return fmt.Errorf("error writing data block to db: %v", txErr)
	}
	return nil
}

func MakeFile(ctx context.Context, blockId string, name string, meta FileMeta, opts FileOptsType) error {
	curTs := time.Now().UnixMilli()
	fileInfo := FileInfo{BlockId: blockId, Name: name, Size: 0, CreatedTs: curTs, ModTs: curTs, Opts: opts, Meta: meta}
	err := InsertFileIntoDB(ctx, fileInfo)
	if err != nil {
		return err
	}
	curCacheEntry := MakeCacheEntry(&fileInfo)
	SetCacheEntry(ctx, GetCacheId(blockId, name), curCacheEntry)
	return nil
}

func WriteToCacheBlockNum(ctx context.Context, blockId string, name string, p []byte, pos int, length int, cacheNum int, pullFromDB bool) (int64, int, error) {
	cacheEntry, err := GetCacheEntryOrPopulate(ctx, blockId, name)
	if err != nil {
		return 0, 0, err
	}
	cacheEntry.IncRefs()
	cacheEntry.Lock.Lock()
	defer cacheEntry.Lock.Unlock()
	block, err := GetCacheBlock(ctx, blockId, name, cacheNum, pullFromDB)
	if err != nil {
		return 0, 0, fmt.Errorf("error getting cache block: %v", err)
	}
	var bytesWritten = 0
	blockLen := len(block.data)
	fileMaxSize := cacheEntry.Info.Opts.MaxSize
	maxWriteSize := fileMaxSize - (int64(cacheNum) * MaxBlockSize)
	numLeftPad := int64(0)
	if pos > blockLen {
		numLeftPad = int64(pos - blockLen)
		leftPadBytes := []byte{}
		for index := 0; index < int(numLeftPad); index++ {
			leftPadBytes = append(leftPadBytes, 0)
		}
		leftPadPos := int64(pos) - numLeftPad
		b, err := WriteToCacheBuf(&block.data, leftPadBytes, int(leftPadPos), int(numLeftPad), maxWriteSize)
		if err != nil {
			return int64(b), b, err
		}
		numLeftPad = int64(b)
		cacheEntry.Info.Size += (int64(cacheNum) * MaxBlockSize)
	}
	b, writeErr := WriteToCacheBuf(&block.data, p, pos, length, maxWriteSize)
	bytesWritten += b
	blockLenDiff := len(block.data) - blockLen
	block.size = len(block.data)
	cacheEntry.Info.Size += int64(blockLenDiff)
	block.dirty = true
	cacheEntry.DecRefs()
	return numLeftPad, bytesWritten, writeErr
}

func ReadFromCacheBlock(ctx context.Context, blockId string, name string, block *CacheBlock, p *[]byte, pos int, length int, destOffset int, maxRead int64) (int, error) {
	defer func() {
		if r := recover(); r != nil {
			log.Printf("recovered from crash %v ", r)
			log.Printf("values: %v %v %v %v %v %v", pos, length, destOffset, maxRead, p, block)
			os.Exit(0)
		}
	}()
	if pos > len(block.data) {
		return 0, fmt.Errorf("reading past end of cache block, should never happen")
	}
	bytesWritten := 0
	index := pos
	for ; index < length+pos; index++ {
		if int64(index) >= maxRead {
			return index - pos, fmt.Errorf(MaxSizeError)
		}
		if index >= len(block.data) {
			return bytesWritten, nil
		}
		destIndex := index - pos + destOffset
		if destIndex >= len(*p) {
			return bytesWritten, nil
		}
		(*p)[destIndex] = block.data[index]
		bytesWritten++
	}
	if int64(index) >= maxRead {
		return bytesWritten, fmt.Errorf(MaxSizeError)
	}
	return bytesWritten, nil
}

const MaxSizeError = "MaxSizeError"

func WriteToCacheBuf(buf *[]byte, p []byte, pos int, length int, maxWrite int64) (int, error) {
	bytesToWrite := length
	if pos > len(*buf) {
		return 0, fmt.Errorf("writing to a position (%v) in the cache that doesn't exist yet, something went wrong", pos)
	}
	if int64(pos+bytesToWrite) > MaxBlockSize {
		return 0, fmt.Errorf("writing more bytes than max block size, not allowed - length of bytes to write: %v, length of cache: %v", bytesToWrite, len(*buf))
	}
	for index := pos; index < bytesToWrite+pos; index++ {
		if index-pos >= len(p) {
			return len(p), nil
		}
		if int64(index) >= maxWrite {
			return index - pos, fmt.Errorf(MaxSizeError)
		}
		curByte := p[index-pos]
		if len(*buf) == index {
			*buf = append(*buf, curByte)
		} else {
			(*buf)[index] = curByte
		}
	}
	return bytesToWrite, nil
}

func GetCacheId(blockId string, name string) string {
	return blockId + "~SEP~" + name
}

func GetValuesFromCacheId(cacheId string) (blockId string, name string) {
	vals := strings.Split(cacheId, "~SEP~")
	if len(vals) == 2 {
		return vals[0], vals[1]
	} else {
		log.Println("Failure in GetValuesFromCacheId, this should never happen")
		return "", ""
	}
}

func GetCacheEntry(ctx context.Context, blockId string, name string) (*CacheEntry, bool) {
	globalLock.Lock()
	defer globalLock.Unlock()
	if curCacheEntry, found := blockstoreCache[GetCacheId(blockId, name)]; found {
		return curCacheEntry, true
	} else {
		return nil, false
	}
}

func GetCacheEntryOrPopulate(ctx context.Context, blockId string, name string) (*CacheEntry, error) {
	if cacheEntry, found := GetCacheEntry(ctx, blockId, name); found {
		return cacheEntry, nil
	} else {
		log.Printf("populating cache entry\n")
		_, err := Stat(ctx, blockId, name)
		if err != nil {
			return nil, err
		}
		if cacheEntry, found := GetCacheEntry(ctx, blockId, name); found {
			return cacheEntry, nil
		} else {
			return nil, fmt.Errorf("error getting cache entry %v %v", blockId, name)
		}
	}

}

func SetCacheEntry(ctx context.Context, cacheId string, cacheEntry *CacheEntry) {
	globalLock.Lock()
	defer globalLock.Unlock()
	if _, found := blockstoreCache[cacheId]; found {
		return
	}
	blockstoreCache[cacheId] = cacheEntry
}

func DeleteCacheEntry(ctx context.Context, blockId string, name string) {
	globalLock.Lock()
	defer globalLock.Unlock()
	delete(blockstoreCache, GetCacheId(blockId, name))
}

func GetCacheBlock(ctx context.Context, blockId string, name string, cacheNum int, pullFromDB bool) (*CacheBlock, error) {
	curCacheEntry, err := GetCacheEntryOrPopulate(ctx, blockId, name)
	if err != nil {
		return nil, err
	}
	if len(curCacheEntry.DataBlocks) < cacheNum+1 {
		for index := len(curCacheEntry.DataBlocks); index < cacheNum+1; index++ {
			curCacheEntry.DataBlocks = append(curCacheEntry.DataBlocks, nil)
		}
	}
	if curCacheEntry.DataBlocks[cacheNum] == nil {
		var curCacheBlock *CacheBlock
		if pullFromDB {
			cacheData, err := GetCacheFromDB(ctx, blockId, name, 0, MaxBlockSize, int64(cacheNum))
			if err != nil {
				return nil, err
			}
			curCacheBlock = &CacheBlock{data: *cacheData, size: len(*cacheData), dirty: false}
			curCacheEntry.DataBlocks[cacheNum] = curCacheBlock
		} else {
			curCacheBlock = &CacheBlock{data: []byte{}, size: 0, dirty: false}
			curCacheEntry.DataBlocks[cacheNum] = curCacheBlock
		}
		return curCacheBlock, nil
	} else {
		return curCacheEntry.DataBlocks[cacheNum], nil
	}
}

func DeepCopyFileInfo(fInfo *FileInfo) *FileInfo {
	fInfoMeta := make(FileMeta)
	for k, v := range fInfo.Meta {
		fInfoMeta[k] = v
	}
	fInfoOpts := fInfo.Opts
	fInfoCopy := &FileInfo{BlockId: fInfo.BlockId, Name: fInfo.Name, Size: fInfo.Size, CreatedTs: fInfo.CreatedTs, ModTs: fInfo.ModTs, Opts: fInfoOpts, Meta: fInfoMeta}
	return fInfoCopy
}

func Stat(ctx context.Context, blockId string, name string) (*FileInfo, error) {
	cacheEntry, found := GetCacheEntry(ctx, blockId, name)
	if found {
		return DeepCopyFileInfo(cacheEntry.Info), nil
	}
	curCacheEntry := MakeCacheEntry(nil)
	curCacheEntry.Lock.Lock()
	defer curCacheEntry.Lock.Unlock()
	fInfo, err := GetFileInfo(ctx, blockId, name)
	if err != nil {
		return nil, err
	}
	curCacheEntry.Info = fInfo
	SetCacheEntry(ctx, GetCacheId(blockId, name), curCacheEntry)
	return DeepCopyFileInfo(fInfo), nil
}

func SetFlushTimeout(newTimeout time.Duration) {
	flushTimeout = newTimeout
}

func GetClockString(t time.Time) string {
	hour, min, sec := t.Clock()
	return fmt.Sprintf("%v:%v:%v", hour, min, sec)
}

func StartFlushTimer(ctx context.Context) {
	curTime := time.Now()
	writeTimePassed := curTime.UnixNano() - lastWriteTime.UnixNano()
	if writeTimePassed >= int64(flushTimeout) {
		lastWriteTime = curTime
		go func() {
			time.Sleep(flushTimeout)
			FlushCache(ctx)
		}()
	}
}

func WriteAt(ctx context.Context, blockId string, name string, p []byte, off int64) (int, error) {
	return WriteAtHelper(ctx, blockId, name, p, off, true)
}

func WriteAtHelper(ctx context.Context, blockId string, name string, p []byte, off int64, flushCache bool) (int, error) {
	bytesToWrite := len(p)
	bytesWritten := 0
	curCacheNum := int(math.Floor(float64(off) / float64(MaxBlockSize)))
	numCaches := int(math.Ceil(float64(bytesToWrite) / float64(MaxBlockSize)))
	cacheOffset := off - (int64(curCacheNum) * MaxBlockSize)
	if (cacheOffset + int64(bytesToWrite)) > MaxBlockSize {
		numCaches += 1
	}
	fInfo, err := Stat(ctx, blockId, name)
	if err != nil {
		return 0, fmt.Errorf("WriteAt err: %v", err)
	}
	if off > fInfo.Opts.MaxSize && fInfo.Opts.Circular {
		numOver := off / fInfo.Opts.MaxSize
		off = off - (numOver * fInfo.Opts.MaxSize)
	}
	for index := curCacheNum; index < curCacheNum+numCaches; index++ {
		cacheOffset := off - (int64(index) * MaxBlockSize)
		bytesToWriteToCurCache := int(math.Min(float64(bytesToWrite), float64(MaxBlockSize-cacheOffset)))
		pullFromDB := true
		if cacheOffset == 0 && int64(bytesToWriteToCurCache) == MaxBlockSize {
			pullFromDB = false
		}
		_, b, err := WriteToCacheBlockNum(ctx, blockId, name, p, int(cacheOffset), bytesToWriteToCurCache, index, pullFromDB)
		bytesWritten += b
		bytesToWrite -= b
		off += int64(b)
		if err != nil {
			if err.Error() == MaxSizeError {
				if fInfo.Opts.Circular {
					p = p[int64(b):]
					b, err := WriteAtHelper(ctx, blockId, name, p, 0, false)
					bytesWritten += b
					if err != nil {
						return bytesWritten, fmt.Errorf("write to cache error: %v", err)
					}
					break
				}
			} else {
				return bytesWritten, fmt.Errorf("write to cache error: %v", err)
			}
		}
		if len(p) == b {
			break
		}
		p = p[int64(b):]
	}
	if flushCache {
		StartFlushTimer(ctx)
	}
	return bytesWritten, nil
}

func GetAllBlockSizes(dataBlocks []*CacheBlock) (int, int) {
	rtn := 0
	numNil := 0
	for idx, block := range dataBlocks {
		if block == nil {
			numNil += 1
			continue
		}
		rtn += block.size
		if block.size != len(block.data) {
			log.Printf("error: block %v has incorrect block size : %v %v", idx, block.size, len(block.data))
		}
	}
	return rtn, numNil
}

func FlushCache(ctx context.Context) error {
	for _, cacheEntry := range blockstoreCache {
		err := WriteFileToDB(ctx, *cacheEntry.Info)
		if err != nil {
			return err
		}
		clearEntry := true
		cacheEntry.Lock.Lock()
		for index, block := range cacheEntry.DataBlocks {
			if block == nil || block.size == 0 {
				continue
			}
			if !block.dirty {
				clearEntry = false
				continue
			}
			err := WriteDataBlockToDB(ctx, cacheEntry.Info.BlockId, cacheEntry.Info.Name, index, block.data)
			if err != nil {
				return err
			}
			cacheEntry.DataBlocks[index] = nil
		}
		cacheEntry.Lock.Unlock()
		if clearEntry && cacheEntry.Refs <= 0 {
			DeleteCacheEntry(ctx, cacheEntry.Info.BlockId, cacheEntry.Info.Name)
		}
	}
	return nil
}

func ReadAt(ctx context.Context, blockId string, name string, p *[]byte, off int64) (int, error) {
	bytesRead := 0
	fInfo, err := Stat(ctx, blockId, name)
	if err != nil {
		return 0, fmt.Errorf("ReadAt err: %v", err)
	}
	if off > fInfo.Opts.MaxSize && fInfo.Opts.Circular {
		numOver := off / fInfo.Opts.MaxSize
		off = off - (numOver * fInfo.Opts.MaxSize)
	}
	if off > fInfo.Size {
		return 0, fmt.Errorf("ReadAt error: tried to read past the end of the file")
	}
	endReadPos := math.Min(float64(int64(len(*p))+off), float64(fInfo.Size))
	bytesToRead := int64(endReadPos) - off
	curCacheNum := int(math.Floor(float64(off) / float64(MaxBlockSize)))
	numCaches := int(math.Ceil(float64(bytesToRead) / float64(MaxBlockSize)))
	cacheOffset := off - (int64(curCacheNum) * MaxBlockSize)
	if (cacheOffset + int64(bytesToRead)) > MaxBlockSize {
		numCaches += 1
	}
	for index := curCacheNum; index < curCacheNum+numCaches; index++ {
		curCacheBlock, err := GetCacheBlock(ctx, blockId, name, index, true)
		if err != nil {
			return bytesRead, fmt.Errorf("error getting cache block: %v", err)
		}
		cacheOffset := off - (int64(index) * MaxBlockSize)
		if cacheOffset < 0 {
			return bytesRead, nil
		}
		bytesToReadFromCurCache := int(math.Min(float64(bytesToRead), float64(MaxBlockSize-cacheOffset)))
		fileMaxSize := fInfo.Opts.MaxSize
		maxReadSize := fileMaxSize - (int64(index) * MaxBlockSize)
		b, err := ReadFromCacheBlock(ctx, blockId, name, curCacheBlock, p, int(cacheOffset), bytesToReadFromCurCache, bytesRead, maxReadSize)
		if b == 0 {
			log.Printf("something wrong %v %v %v %v %v %v %v %v", index, off, cacheOffset, curCacheNum, numCaches, bytesRead, bytesToRead, curCacheBlock)
			cacheEntry, _ := GetCacheEntry(ctx, blockId, name)
			blockSize, numNil := GetAllBlockSizes(cacheEntry.DataBlocks)
			maybeDBSize := int64(numNil) * MaxBlockSize
			maybeFullSize := int64(blockSize) + maybeDBSize
			log.Printf("block actual sizes: %v %v %v %v %v\n", blockSize, numNil, maybeDBSize, maybeFullSize, len(cacheEntry.DataBlocks))
		}
		bytesRead += b
		bytesToRead -= int64(b)
		off += int64(b)

		if err != nil {
			if err.Error() == MaxSizeError {
				if fInfo.Opts.Circular {
					off = 0
					newP := (*p)[b:]
					b, err := ReadAt(ctx, blockId, name, &newP, off)
					bytesRead += b
					if err != nil {
						return bytesRead, err
					}
					break
				}
			} else {
				return bytesRead, fmt.Errorf("read from cache error: %v", err)
			}
		}
	}
	return bytesRead, nil
}

func AppendData(ctx context.Context, blockId string, name string, p []byte) (int, error) {
	appendLock.Lock()
	defer appendLock.Unlock()
	fInfo, err := Stat(ctx, blockId, name)
	if err != nil {
		return 0, fmt.Errorf("append stat error: %v", err)
	}
	return WriteAt(ctx, blockId, name, p, fInfo.Size)
}

func DeleteFile(ctx context.Context, blockId string, name string) error {
	DeleteCacheEntry(ctx, blockId, name)
	err := DeleteFileFromDB(ctx, blockId, name)
	return err
}

func DeleteBlock(ctx context.Context, blockId string) error {
	for cacheId := range blockstoreCache {
		curBlockId, name := GetValuesFromCacheId(cacheId)
		if curBlockId == blockId {
			err := DeleteFile(ctx, blockId, name)
			if err != nil {
				return fmt.Errorf("error deleting %v %v: %v", blockId, name, err)
			}
		}
	}
	err := DeleteBlockFromDB(ctx, blockId)
	return err
}

func WriteFile(ctx context.Context, blockId string, name string, meta FileMeta, opts FileOptsType, data []byte) (int, error) {
	MakeFile(ctx, blockId, name, meta, opts)
	return AppendData(ctx, blockId, name, data)
}

func WriteMeta(ctx context.Context, blockId string, name string, meta FileMeta) error {
	_, err := Stat(ctx, blockId, name)
	// stat so that we can make sure cache entry is popuplated
	if err != nil {
		return err
	}
	cacheEntry, found := GetCacheEntry(ctx, blockId, name)
	if !found {
		return fmt.Errorf("WriteAt error: cache entry not found")
	}
	cacheEntry.Lock.Lock()
	defer cacheEntry.Lock.Unlock()
	cacheEntry.Info.Meta = meta
	return nil
}

func ListFiles(ctx context.Context, blockId string) []*FileInfo {
	fInfoArr, err := GetAllFilesInDBForBlockId(ctx, blockId)
	if err != nil {
		return nil
	}
	return fInfoArr
}

func ListAllFiles(ctx context.Context) []*FileInfo {
	fInfoArr, err := GetAllFilesInDB(ctx)
	if err != nil {
		return nil
	}
	return fInfoArr
}

func GetAllBlockIds(ctx context.Context) []string {
	rtn, err := GetAllBlockIdsInDB(ctx)
	if err != nil {
		return nil
	}
	return rtn
}