From 205a82f081c40b0f9a29b01de9926cf28a6a5baf Mon Sep 17 00:00:00 2001
From: Vincent Batts <vbatts@hashbangbash.com>
Date: Tue, 17 Mar 2015 16:45:01 -0400
Subject: [PATCH] .: stub on merkle nodes

---
 node.go      | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 node_test.go | 66 ++++++++++++++++++++++++++++++++++++++++++
 tree.go      |  5 ++++
 3 files changed, 153 insertions(+)
 create mode 100644 node.go
 create mode 100644 node_test.go
 create mode 100644 tree.go

diff --git a/node.go b/node.go
new file mode 100644
index 0000000..943139b
--- /dev/null
+++ b/node.go
@@ -0,0 +1,82 @@
+package merkle
+
+import (
+	"crypto"
+	_ "crypto/sha1"
+	"fmt"
+)
+
+var (
+	DefaultHash = crypto.SHA1
+)
+
+func NewNode() *Node {
+	return &Node{hash: DefaultHash}
+}
+
+// Node is a fundamental part of the tree.
+type Node struct {
+	hash                crypto.Hash
+	checksum            []byte
+	Parent, Left, Right *Node
+}
+
+// If it is a leaf (no children) Node, then the Checksum is of the block of a
+// payload. Otherwise, the Checksum is of it's two children's Checksum.
+func (n Node) Checksum() ([]byte, error) {
+	if n.checksum != nil {
+		return n.checksum, nil
+	}
+	if n.Left != nil && n.Right != nil {
+
+		// we'll ask our children for their sum and wait til they return
+		var (
+			lSumChan = make(chan childSumResponse)
+			rSumChan = make(chan childSumResponse)
+		)
+		go func() {
+			c, err := n.Left.Checksum()
+			lSumChan <- childSumResponse{checksum: c, err: err}
+		}()
+		go func() {
+			c, err := n.Right.Checksum()
+			rSumChan <- childSumResponse{checksum: c, err: err}
+		}()
+
+		h := n.hash.New()
+
+		// First left
+		lSum := <-lSumChan
+		if lSum.err != nil {
+			return nil, lSum.err
+		}
+		if _, err := h.Write(lSum.checksum); err != nil {
+			return nil, err
+		}
+
+		// then right
+		rSum := <-rSumChan
+		if rSum.err != nil {
+			return nil, rSum.err
+		}
+		if _, err := h.Write(rSum.checksum); err != nil {
+			return nil, err
+		}
+
+		return h.Sum(nil), nil
+	}
+	return nil, ErrNoChecksumAvailable{node: &n}
+}
+
+type ErrNoChecksumAvailable struct {
+	node *Node
+}
+
+func (err ErrNoChecksumAvailable) Error() string {
+	return fmt.Sprintf("no block or children available to derive checksum from: %#v", *err.node)
+}
+
+type childSumResponse struct {
+	checksum []byte
+	err      error
+}
diff --git a/node_test.go b/node_test.go
new file mode 100644
index 0000000..6655c22
--- /dev/null
+++ b/node_test.go
@@ -0,0 +1,66 @@
+package merkle
+
+import (
+	"log"
+	"strings"
+	"testing"
+)
+
+var words string = `Who were expelled from the academy for crazy & publishing obscene odes on the windows of the skull`
+
+func TestNodeSums(t *testing.T) {
+	var (
+		nodes []*Node
+		h     = DefaultHash.New()
+	)
+	for _, word := range strings.Split(words, " ") {
+		h.Reset()
+		if _, err := h.Write([]byte(word)); err != nil {
+			t.Errorf("on word %q, encountered %s", word, err)
+		}
+		sum := h.Sum(nil)
+		nodes = append(nodes, &Node{checksum: sum})
+	}
+
+	for {
+		nodes = levelUp(nodes)
+		if len(nodes) == 1 {
+			break
+		}
+	}
+	for i := range nodes {
+		c, err := nodes[i].Checksum()
+		if err != nil {
+			t.Error(err)
+		}
+		t.Logf("checksum %x", c)
+	}
+	if len(nodes) > 0 {
+		t.Errorf("%d nodes; %d characters", len(nodes), len(words))
+	}
+}
+
+func levelUp(nodes []*Node) []*Node {
+	var (
+		newNodes []*Node
+		last     = len(nodes) - 1
+	)
+
+	for i := range nodes {
+		if i%2 == 0 {
+			if i == last {
+				// TODO rebalance the last parent
+				log.Println("WHOOP")
+			}
+			n := NewNode()
+			n.Left = nodes[i]
+			n.Left.Parent = n
+			newNodes = append(newNodes, n)
+		} else {
+			n := newNodes[len(newNodes)-1]
+			n.Right = nodes[i]
+			n.Right.Parent = n
+		}
+	}
+	return newNodes
+}
diff --git a/tree.go b/tree.go
new file mode 100644
index 0000000..e65b2c5
--- /dev/null
+++ b/tree.go
@@ -0,0 +1,5 @@
+package merkle
+
+type Tree struct {
+	Nodes []Node
+}