// Copyright 2024 GoEdge CDN goedge.cdn@gmail.com. All rights reserved. Official site: https://goedge.cn .

package bfs

import (
	"errors"
	"fmt"
	"io"
	"os"
	"strings"
	"sync"
	"time"
)

const BFileExt = ".b"

type BlockType string

const (
	BlockTypeHeader BlockType = "header"
	BlockTypeBody   BlockType = "body"
)

type BlocksFile struct {
	opt   *BlockFileOptions
	fp    *os.File
	mFile *MetaFile

	isClosed bool

	mu *sync.RWMutex

	writtenBytes int64
	syncAt       time.Time
}

func NewBlocksFileWithRawFile(fp *os.File, options *BlockFileOptions) (*BlocksFile, error) {
	options.EnsureDefaults()

	var bFilename = fp.Name()
	if !strings.HasSuffix(bFilename, BFileExt) {
		return nil, errors.New("filename '" + bFilename + "' must has a '" + BFileExt + "' extension")
	}

	var mu = &sync.RWMutex{}

	var mFilename = strings.TrimSuffix(bFilename, BFileExt) + MFileExt
	mFile, err := NewMetaFile(mFilename, mu)
	if err != nil {
		_ = fp.Close()
		return nil, fmt.Errorf("load '%s' failed: %w", mFilename, err)
	}

	_, err = fp.Seek(0, io.SeekEnd)
	if err != nil {
		_ = fp.Close()
		_ = mFile.Close()
		return nil, err
	}

	return &BlocksFile{
		fp:     fp,
		mFile:  mFile,
		mu:     mu,
		opt:    options,
		syncAt: time.Now(),
	}, nil
}

func NewBlocksFile(filename string, options *BlockFileOptions) (*BlocksFile, error) {
	// TODO 考虑是否使用flock锁定，防止多进程写冲突
	fp, err := os.OpenFile(filename, os.O_CREATE|os.O_WRONLY, 0666)
	if err != nil {
		return nil, fmt.Errorf("open blocks file failed: %w", err)
	}
	return NewBlocksFileWithRawFile(fp, options)
}

func (this *BlocksFile) Filename() string {
	return this.fp.Name()
}

func (this *BlocksFile) Write(hash string, blockType BlockType, b []byte, originOffset int64) (n int, err error) {
	if len(b) == 0 {
		return
	}

	// TODO 实现 originOffset

	this.mu.Lock()
	defer this.mu.Unlock()

	posBefore, err := this.currentPos()
	if err != nil {
		return 0, err
	}

	err = this.checkStatus()
	if err != nil {
		return
	}

	n, err = this.fp.Write(b)

	if err == nil {
		if n > 0 {
			this.writtenBytes += int64(n)
		}

		if blockType == BlockTypeHeader {
			err = this.mFile.WriteHeaderBlockUnsafe(hash, posBefore, posBefore+int64(n))
		} else if blockType == BlockTypeBody {
			err = this.mFile.WriteBodyBlockUnsafe(hash, posBefore, posBefore+int64(n), originOffset, originOffset+int64(n))
		} else {
			err = errors.New("invalid block type '" + string(blockType) + "'")
		}
	}

	return
}

func (this *BlocksFile) OpenFileWriter(fileHash string, bodySize int64, isPartial bool) (writer *FileWriter, err error) {
	err = CheckHashErr(fileHash)
	if err != nil {
		return nil, err
	}

	// TODO 限制对同一个Hash同时只能有一个Writer

	this.mu.Lock()
	defer this.mu.Unlock()

	err = this.checkStatus()
	if err != nil {
		return
	}

	return NewFileWriter(this, fileHash, bodySize, isPartial)
}

func (this *BlocksFile) OpenFileReader(fileHash string, isPartial bool) (*FileReader, error) {
	err := CheckHashErr(fileHash)
	if err != nil {
		return nil, err
	}

	// TODO 需要设置单个BFile文件的maxOpenFiles

	this.mu.RLock()
	err = this.checkStatus()
	this.mu.RUnlock()
	if err != nil {
		return nil, err
	}

	// 是否存在
	header, ok := this.mFile.CloneHeader(fileHash)
	if !ok {
		return nil, os.ErrNotExist
	}

	// TODO 对于partial content，需要传入ranges，用来判断是否有交集

	if header.IsWriting {
		return nil, ErrFileIsWriting
	}

	if !isPartial && !header.IsCompleted {
		return nil, os.ErrNotExist
	}

	fp, err := os.Open(this.fp.Name())
	if err != nil {
		return nil, err
	}
	return NewFileReader(this, fp, header), nil
}

func (this *BlocksFile) RemoveFile(fileHash string) error {
	err := CheckHashErr(fileHash)
	if err != nil {
		return err
	}

	// TODO 需要实现
	return nil
}

func (this *BlocksFile) Sync() error {
	this.mu.Lock()
	defer this.mu.Unlock()

	err := this.checkStatus()
	if err != nil {
		return err
	}

	return this.sync(false)
}

func (this *BlocksFile) ForceSync() error {
	this.mu.Lock()
	defer this.mu.Unlock()

	err := this.checkStatus()
	if err != nil {
		return err
	}

	return this.sync(true)
}

func (this *BlocksFile) SyncAt() time.Time {
	return this.syncAt
}

func (this *BlocksFile) Compact() error {
	// TODO 需要实现
	return nil
}

func (this *BlocksFile) RemoveAll() error {
	this.mu.Lock()
	defer this.mu.Unlock()

	this.isClosed = true

	_ = this.mFile.RemoveAll()
	_ = this.fp.Close()
	return os.Remove(this.fp.Name())
}

func (this *BlocksFile) Close() error {
	this.mu.Lock()
	defer this.mu.Unlock()

	err := this.sync(true)
	if err != nil {
		return err
	}

	this.isClosed = true

	_ = this.mFile.Close()

	return this.fp.Close()
}

func (this *BlocksFile) checkStatus() error {
	if this.isClosed {
		return ErrClosed
	}
	return nil
}

func (this *BlocksFile) currentPos() (int64, error) {
	return this.fp.Seek(0, io.SeekCurrent)
}

func (this *BlocksFile) sync(force bool) error {
	if !force {
		if this.writtenBytes < this.opt.BytesPerSync {
			return nil
		}
	}

	this.writtenBytes = 0

	err := this.fp.Sync()
	if err != nil {
		return err
	}

	this.syncAt = time.Now()

	if force {
		return this.mFile.SyncUnsafe()
	}

	return nil
}