Index handling, hash calculation

core/pack.go

@@ -1,6 +1,11 @@
 package core
 import (
+	"crypto/sha256"
+	"encoding/hex"
+	"io"
 	"io/ioutil"
+	"os"
+	"path/filepath"
 
 	"github.com/BurntSushi/toml"
 )
@@ -16,6 +21,7 @@ type Pack struct {
 	Versions map[string]string         `toml:"versions"`
 	Client   map[string]toml.Primitive `toml:"client"`
 	Server   map[string]toml.Primitive `toml:"server"`
+	flags    Flags
 }
 
 // LoadPack loads the modpack metadata to a Pack struct
@@ -32,6 +38,56 @@ func LoadPack(flags Flags) (Pack, error) {
 	if len(modpack.Index.File) == 0 {
 		modpack.Index.File = "index.toml"
 	}
+	modpack.flags = flags
 	return modpack, nil
 }
 
+// LoadIndex attempts to load the index file of this modpack
+func (pack Pack) LoadIndex() (Index, error) {
+	if filepath.IsAbs(pack.Index.File) {
+		return LoadIndex(pack.Index.File, pack.flags)
+	}
+	return LoadIndex(filepath.Join(filepath.Dir(pack.flags.PackFile), pack.Index.File), pack.flags)
+}
+
+// UpdateIndexHash recalculates the hash of the index file of this modpack
+func (pack *Pack) UpdateIndexHash() error {
+	indexFile := filepath.Join(filepath.Dir(pack.flags.PackFile), pack.Index.File)
+	if filepath.IsAbs(pack.Index.File) {
+		indexFile = pack.Index.File
+	}
+
+	f, err := os.Open(indexFile)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	// Hash usage strategy (may change):
+	// Just use SHA256, overwrite existing hash regardless of what it is
+	// May update later to continue using the same hash that was already being used
+	h := sha256.New()
+	if _, err := io.Copy(h, f); err != nil {
+		return err
+	}
+	hashString := hex.EncodeToString(h.Sum(nil))
+
+	pack.Index.HashFormat = "sha256"
+	pack.Index.Hash = hashString
+	return nil
+}
+
+// Write saves the pack file
+func (pack Pack) Write() error {
+	f, err := os.Create(pack.flags.PackFile)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	enc := toml.NewEncoder(f)
+	// Disable indentation
+	enc.Indent = ""
+	return enc.Encode(pack)
+}
+