From 70372a4c3834ca252ce46f5ce72b11ba9839a0d5 Mon Sep 17 00:00:00 2001
From: David Florness <david@florness.com>
Date: Sun, 7 Jun 2020 01:15:12 -0600
Subject: [PATCH] Create preferences matrix for ballot from voting UI

---
 main.go   |  4 +--
 merkle.go |  8 +++---
 ui.go     | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++----
 3 files changed, 76 insertions(+), 11 deletions(-)

diff --git a/main.go b/main.go
index 8e1ffc7..079e384 100644
--- a/main.go
+++ b/main.go
@@ -25,7 +25,7 @@ var (
 	logger     = log.Logger("tallyard")
 	protocolID = protocol.ID("/tallyard/0.0.0")
 
-	candidates    []ElectionOption
+	candidates    []Candidate
 	optionsMerkle *merkletree.MerkleTree
 
 	rendezvousNonce Nonce
@@ -155,7 +155,7 @@ func bootstrap() {
 			}
 			str = stripNewline(str)
 			if str != "" {
-				candidates = append(candidates, ElectionOption(str))
+				candidates = append(candidates, Candidate(str))
 				fmt.Println(str)
 			}
 			if err == io.EOF {
diff --git a/merkle.go b/merkle.go
index 8a2f947..b9b8e4f 100644
--- a/merkle.go
+++ b/merkle.go
@@ -11,9 +11,9 @@ import (
 	"github.com/mr-tron/base58/base58"
 )
 
-type ElectionOption string
+type Candidate string
 
-func (eo ElectionOption) CalculateHash() ([]byte, error) {
+func (eo Candidate) CalculateHash() ([]byte, error) {
 	h := sha256.New()
 	if _, err := h.Write([]byte(eo)); err != nil {
 		return nil, err
@@ -21,8 +21,8 @@ func (eo ElectionOption) CalculateHash() ([]byte, error) {
 	return h.Sum(nil), nil
 }
 
-func (eo ElectionOption) Equals(other merkletree.Content) (bool, error) {
-	return eo == other.(ElectionOption), nil
+func (eo Candidate) Equals(other merkletree.Content) (bool, error) {
+	return eo == other.(Candidate), nil
 }
 
 type Nonce string
diff --git a/ui.go b/ui.go
index 38b4233..be62ba6 100644
--- a/ui.go
+++ b/ui.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"sort"
 	"strconv"
 	"strings"
 	"unicode"
@@ -37,7 +38,7 @@ func createElection() {
 			rendezvousNonce = NewNonce()
 			content := []merkletree.Content{rendezvousNonce}
 			for i := 0; i < n-1; i++ {
-				eo := ElectionOption(form.GetFormItem(i).(*tview.InputField).GetText())
+				eo := Candidate(form.GetFormItem(i).(*tview.InputField).GetText())
 				candidates = append(candidates, eo)
 				content = append(content, eo)
 			}
@@ -80,10 +81,12 @@ func joinElection() {
 	}
 }
 
-func vote(candidates []ElectionOption) []int {
-	result := make([]int, len(candidates))
+// displays a voting UI to the user and returns the encoded ballot
+func vote(candidates []Candidate) []byte {
+	ranks := make([]int, len(candidates))
 	app := tview.NewApplication()
 	form := tview.NewForm()
+
 	for _, eo := range candidates {
 		// TODO: support more than 99 candidates
 		form.AddInputField(string(eo), "", 2,
@@ -91,6 +94,7 @@ func vote(candidates []ElectionOption) []int {
 				return len(textToCheck) < 3 && unicode.IsDigit(lastChar)
 			}, nil)
 	}
+
 	form.AddButton("Submit", func() {
 		app.Stop()
 		for i := 0; i < len(candidates); i++ {
@@ -99,11 +103,72 @@ func vote(candidates []ElectionOption) []int {
 			if err != nil {
 				panic(err)
 			}
-			result[i] = rank
+			ranks[i] = rank
 		}
 	})
+
 	if err := app.SetRoot(form, true).EnableMouse(true).Run(); err != nil {
 		panic(err)
 	}
-	return result
+
+	return GetBallotFromRankings(ranks)
+}
+
+func GetBallotFromRankings(ranks []int) []byte {
+	n := len(ranks)
+	candidates := make([]int, n)
+
+	for i := 0; i < n; i++ {
+		candidates[i] = i
+	}
+
+	// sort candidates by ranking
+	cr := CandidateRanking{candidates, ranks}
+	sort.Sort(&cr)
+
+	// TODO: support more than 255 voters (limit from usage of byte)
+	prefMatrix := make([][]byte, n)
+
+	for len(candidates) > 0 {
+		r := ranks[candidates[0]]
+		i := 1
+		for ; i < len(candidates) && ranks[candidates[i]] == r; i++ {}
+		// i is now index of the first candidate with worse (i.e. higher
+		// in value) rank
+		row := make([]byte, n)
+		for j := i; j < len(candidates); j++ {
+			row[candidates[j]] = 1
+		}
+		for j := 0; j < i; j++ {
+			prefMatrix[candidates[j]] = row
+		}
+		candidates = candidates[i:]
+	}
+
+	// convert 2D array into 1D array
+	barray := make([]byte, 0, n*n)
+	for _, row := range prefMatrix {
+		barray = append(barray, row...)
+	}
+
+	return barray
+}
+
+type CandidateRanking struct {
+	candidates []int // becomes list of candidate IDs sorted by rank
+	ranks      []int // maps candidate ID to rank
+}
+
+func (cr *CandidateRanking) Len() int {
+	return len(cr.ranks)
+}
+
+func (cr *CandidateRanking) Less(i, j int) bool {
+	return cr.ranks[cr.candidates[i]] < cr.ranks[cr.candidates[j]]
+}
+
+func (cr *CandidateRanking) Swap(i, j int) {
+	tmp := cr.candidates[i]
+	cr.candidates[i] = cr.candidates[j]
+	cr.candidates[j] = tmp
 }
-- 
2.38.4