#8 refactored

kfile/file.go

@@ -11,6 +11,12 @@ type BlockId struct {
 }
 
 func NewBlockId(filename string, blknum int) *BlockId {
+	if err := ValidateFilename(filename); err != nil {
+		panic(err)
+	}
+	if err := ValidateBlockNumber(blknum); err != nil {
+		panic(err)
+	}
 	return &BlockId{
 		Filename: filename,
 		Blknum:   blknum,
@@ -50,3 +56,42 @@ func (b *BlockId) HashCode() uint32 {
 
 	return h.Sum32()
 }
+
+func (b *BlockId) Copy() *BlockId {
+	return NewBlockId(b.Filename, b.Blknum)
+}
+
+func (b *BlockId) NextBlock() *BlockId {
+	return NewBlockId(b.Filename, b.Blknum+1)
+}
+
+func (b *BlockId) PrevBlock() *BlockId {
+	if b.Blknum > 0 {
+		return NewBlockId(b.Filename, b.Blknum-1)
+	}
+	return nil
+}
+
+func (b *BlockId) IsFirst() bool {
+	return b.Blknum == 0
+}
+
+func ValidateBlockNumber(blknum int) error {
+	if blknum < 0 {
+		return fmt.Errorf("block number cannot be negative: %d", blknum)
+	}
+	return nil
+}
+
+func ValidateFilename(filename string) error {
+	if filename == "" {
+		return fmt.Errorf("filename cannot be empty")
+	}
+	return nil
+}
+
+func (b *BlockId) IsValid() bool {
+	return b != nil &&
+		b.Filename != "" &&
+		b.Blknum >= 0
+}