package mergeset

import (
	"fmt"
	"path/filepath"
	"sync"
	"unsafe"

	"github.com/VictoriaMetrics/VictoriaMetrics/lib/blockcache"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/filestream"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fs"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/memory"
)

var idxbCache = blockcache.NewCache(getMaxIndexBlocksCacheSize)
var ibCache = blockcache.NewCache(getMaxInmemoryBlocksCacheSize)

func getMaxIndexBlocksCacheSize() int {
	maxIndexBlockCacheSizeOnce.Do(func() {
		maxIndexBlockCacheSize = memory.Allowed() / 10
	})
	return maxIndexBlockCacheSize
}

var (
	maxIndexBlockCacheSize     int
	maxIndexBlockCacheSizeOnce sync.Once
)

func getMaxInmemoryBlocksCacheSize() int {
	maxInmemoryBlockCacheSizeOnce.Do(func() {
		maxInmemoryBlockCacheSize = memory.Allowed() / 4
	})
	return maxInmemoryBlockCacheSize
}

var (
	maxInmemoryBlockCacheSize     int
	maxInmemoryBlockCacheSizeOnce sync.Once
)

type part struct {
	ph partHeader

	path string

	size uint64

	mrs []metaindexRow

	indexFile fs.MustReadAtCloser
	itemsFile fs.MustReadAtCloser
	lensFile  fs.MustReadAtCloser
}

func openFilePart(path string) (*part, error) {
	path = filepath.Clean(path)

	var ph partHeader
	if err := ph.ParseFromPath(path); err != nil {
		return nil, fmt.Errorf("cannot parse path to part: %w", err)
	}

	metaindexPath := path + "/metaindex.bin"
	metaindexFile, err := filestream.Open(metaindexPath, true)
	if err != nil {
		return nil, fmt.Errorf("cannot open %q: %w", metaindexPath, err)
	}
	metaindexSize := fs.MustFileSize(metaindexPath)

	indexPath := path + "/index.bin"
	indexFile := fs.MustOpenReaderAt(indexPath)
	indexSize := fs.MustFileSize(indexPath)

	itemsPath := path + "/items.bin"
	itemsFile := fs.MustOpenReaderAt(itemsPath)
	itemsSize := fs.MustFileSize(itemsPath)

	lensPath := path + "/lens.bin"
	lensFile := fs.MustOpenReaderAt(lensPath)
	lensSize := fs.MustFileSize(lensPath)

	size := metaindexSize + indexSize + itemsSize + lensSize
	return newPart(&ph, path, size, metaindexFile, indexFile, itemsFile, lensFile)
}

func newPart(ph *partHeader, path string, size uint64, metaindexReader filestream.ReadCloser, indexFile, itemsFile, lensFile fs.MustReadAtCloser) (*part, error) {
	var errors []error
	mrs, err := unmarshalMetaindexRows(nil, metaindexReader)
	if err != nil {
		errors = append(errors, fmt.Errorf("cannot unmarshal metaindexRows: %w", err))
	}
	metaindexReader.MustClose()

	var p part
	p.path = path
	p.size = size
	p.mrs = mrs

	p.indexFile = indexFile
	p.itemsFile = itemsFile
	p.lensFile = lensFile

	p.ph.CopyFrom(ph)
	if len(errors) > 0 {
		// Return only the first error, since it has no sense in returning all errors.
		err := fmt.Errorf("error opening part %s: %w", p.path, errors[0])
		p.MustClose()
		return nil, err
	}
	return &p, nil
}

func (p *part) MustClose() {
	p.indexFile.MustClose()
	p.itemsFile.MustClose()
	p.lensFile.MustClose()

	idxbCache.RemoveBlocksForPart(p)
	ibCache.RemoveBlocksForPart(p)
}

type indexBlock struct {
	bhs []blockHeader
}

func (idxb *indexBlock) SizeBytes() int {
	bhs := idxb.bhs[:cap(idxb.bhs)]
	n := int(unsafe.Sizeof(*idxb))
	for i := range bhs {
		n += bhs[i].SizeBytes()
	}
	return n
}