wp

storage/pageno_provider.go

@@ -0,0 +1,55 @@
+package storage
+
+import (
+	"errors"
+	"math"
+	"os"
+
+	"gordenko.dev/dima/qb/freelist"
+)
+
+type PageNoProvider struct {
+	freeList   *freelist.FreeList
+	pagesCount uint32
+}
+
+type PageNoProviderOptions struct {
+	FilePath string
+	PageSize int
+	FreeList *freelist.FreeList
+}
+
+func NewPageNoProvider(opt PageNoProviderOptions) (_ *PageNoProvider, err error) {
+	if opt.FreeList == nil {
+		return nil, errors.New("FreeList option is required")
+	}
+	file, err := os.Open(opt.FilePath)
+	if err != nil {
+		return
+	}
+	defer file.Close()
+	info, err := file.Stat()
+	if err != nil {
+		return
+	}
+	pagesCount := info.Size() / int64(opt.PageSize)
+	return &PageNoProvider{
+		freeList:   opt.FreeList,
+		pagesCount: uint32(pagesCount),
+	}, nil
+}
+
+func (s *PageNoProvider) GetPageNumber() (uint32, bool, error) {
+	pageNo, err := s.freeList.GetPageNumber()
+	if err != nil {
+		return 0, false, err
+	}
+	if pageNo > 0 {
+		return pageNo, true, nil
+	}
+	if s.pagesCount < math.MaxUint32 {
+		s.pagesCount++
+		return s.pagesCount, false, nil
+	}
+	return 0, false, errors.New("no space")
+}