Rename Format to Builder.

builder.go

@@ -0,0 +1,92 @@
+package cid
+
+import (
+	mh "github.com/multiformats/go-multihash"
+)
+
+type Builder interface {
+	Sum(data []byte) (*Cid, error)
+	GetCodec() uint64
+	WithCodec(uint64) Builder
+}
+
+type V0Builder struct{}
+
+type V1Builder struct {
+	Codec   uint64
+	HashFun uint64
+	HashLen int // HashLen <= 0 means the default length
+}
+
+func PrefixToBuilder(p Prefix) Builder {
+	if p.Version == 0 {
+		return V0Builder{}
+	}
+	mhLen := p.MhLength
+	if p.MhType == mh.ID {
+		mhLen = 0
+	}
+	if mhLen < 0 {
+		mhLen = 0
+	}
+	return V1Builder{
+		Codec:   p.Codec,
+		HashFun: p.MhType,
+		HashLen: mhLen,
+	}
+}
+
+func (p Prefix) GetCodec() uint64 {
+	return p.Codec
+}
+
+func (p Prefix) WithCodec(c uint64) Builder {
+	if c == p.Codec {
+		return p
+	}
+	p.Codec = c
+	if c != DagProtobuf {
+		p.Version = 1
+	}
+	return p
+}
+
+func (p V0Builder) Sum(data []byte) (*Cid, error) {
+	hash, err := mh.Sum(data, mh.SHA2_256, -1)
+	if err != nil {
+		return nil, err
+	}
+	return NewCidV0(hash), nil
+}
+
+func (p V0Builder) GetCodec() uint64 {
+	return DagProtobuf
+}
+
+func (p V0Builder) WithCodec(c uint64) Builder {
+	if c == DagProtobuf {
+		return p
+	}
+	return V1Builder{Codec: c, HashFun: mh.SHA2_256}
+}
+
+func (p V1Builder) Sum(data []byte) (*Cid, error) {
+	mhLen := p.HashLen
+	if mhLen <= 0 {
+		mhLen = -1
+	}
+	hash, err := mh.Sum(data, p.HashFun, mhLen)
+	if err != nil {
+		return nil, err
+	}
+	return NewCidV1(p.Codec, hash), nil
+}
+
+func (p V1Builder) GetCodec() uint64 {
+	return p.Codec
+}
+
+func (p V1Builder) WithCodec(c uint64) Builder {
+	p.Codec = c
+	return p
+}