codecrafters submit [skip ci]

1 files changed, 49 insertions, 0 deletions

diff --git a/cmd/mybittorrent/meta.go b/cmd/mybittorrent/meta.go
index 34369c4..27bcc12 100644
--- a/cmd/mybittorrent/meta.go
+++ b/cmd/mybittorrent/meta.go
@@ -1,11 +1,15 @@
 package main
 
 import (
+	"bytes"
 	"crypto/sha1"
+	"math"
 
 	bencode "github.com/jackpal/bencode-go"
 )
 
+const BlockSize = 16 * 1024
+
 type Meta struct {
 	Announce string   `bencode:"announce"`
 	Info     FileInfo `bencode:"info"`
@@ -35,3 +39,48 @@ func (m Meta) PieceHashes() []string {
 
 	return hashes
 }
+
+func (m Meta) CheckHash(pieceIndex int, data []byte) bool {
+	sha := sha1.New()
+
+	if _, err := bytes.NewBuffer(data).WriteTo(sha); err != nil {
+		return false
+	}
+
+	return bytes.Equal([]byte(m.Info.Pieces[pieceIndex*20:pieceIndex*20+20]), sha.Sum(nil))
+}
+
+func (m Meta) PieceCount() int {
+	return len(m.Info.Pieces) / 20
+}
+
+func (m Meta) PieceLens() []int {
+	pieceCnt := m.PieceCount()
+	pieces := make([]int, pieceCnt)
+
+	for i := 0; i < pieceCnt; i++ {
+		if i < pieceCnt-1 {
+			pieces[i] = m.Info.PieceLength
+		} else {
+			pieces[i] = m.Info.Length - i*m.Info.PieceLength
+		}
+	}
+
+	return pieces
+}
+
+func (m Meta) BlockLens(pieceIdx int) []uint32 {
+	pieceLen := m.PieceLens()[pieceIdx]
+	blockCnt := int(math.Ceil(float64(pieceLen) / float64(BlockSize)))
+	blocks := make([]uint32, blockCnt)
+
+	for i := 0; i < blockCnt; i++ {
+		if i < blockCnt-1 {
+			blocks[i] = uint32(BlockSize)
+		} else {
+			blocks[i] = uint32(pieceLen - i*BlockSize)
+		}
+	}
+
+	return blocks
+}