Render the git graph on the server (#12333)

Rendering the git graph on the server means that we can properly track flows and switch from the Canvas implementation to a SVG implementation.

* This implementation provides a 16 limited color selection
* The uniqued color numbers are also provided
* And there is also a monochrome version
*In addition is a hover highlight that allows users to highlight commits on the same flow.

Closes #12209

Signed-off-by: Andrew Thornton art27@cantab.net
Co-authored-by: silverwind <me@silverwind.io>

4 files changed, 1209 insertions, 89 deletions

diff --git a/modules/gitgraph/graph.go b/modules/gitgraph/graph.go
index 4ba110c706..257e4f3af0 100644
--- a/modules/gitgraph/graph.go
+++ b/modules/gitgraph/graph.go
@@ -16,26 +16,9 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 )
 
-// GraphItem represent one commit, or one relation in timeline
-type GraphItem struct {
-	GraphAcii    string
-	Relation     string
-	Branch       string
-	Rev          string
-	Date         string
-	Author       string
-	AuthorEmail  string
-	ShortRev     string
-	Subject      string
-	OnlyRelation bool
-}
-
-// GraphItems is a list of commits from all branches
-type GraphItems []GraphItem
-
 // GetCommitGraph return a list of commit (GraphItems) from all branches
-func GetCommitGraph(r *git.Repository, page int) (GraphItems, error) {
-	format := "DATA:|%d|%H|%ad|%an|%ae|%h|%s"
+func GetCommitGraph(r *git.Repository, page int, maxAllowedColors int) (*Graph, error) {
+	format := "DATA:%d|%H|%ad|%an|%ae|%h|%s"
 
 	if page == 0 {
 		page = 1
@@ -51,7 +34,8 @@ func GetCommitGraph(r *git.Repository, page int) (GraphItems, error) {
 		"--date=iso",
 		fmt.Sprintf("--pretty=format:%s", format),
 	)
-	commitGraph := make([]GraphItem, 0, 100)
+	graph := NewGraph()
+
 	stderr := new(strings.Builder)
 	stdoutReader, stdoutWriter, err := os.Pipe()
 	if err != nil {
@@ -64,86 +48,56 @@ func GetCommitGraph(r *git.Repository, page int) (GraphItems, error) {
 	if err := graphCmd.RunInDirTimeoutEnvFullPipelineFunc(nil, -1, r.Path, stdoutWriter, stderr, nil, func(ctx context.Context, cancel context.CancelFunc) error {
 		_ = stdoutWriter.Close()
 		defer stdoutReader.Close()
+		parser := &Parser{}
+		parser.firstInUse = -1
+		parser.maxAllowedColors = maxAllowedColors
+		if maxAllowedColors > 0 {
+			parser.availableColors = make([]int, maxAllowedColors)
+			for i := range parser.availableColors {
+				parser.availableColors[i] = i + 1
+			}
+		} else {
+			parser.availableColors = []int{1, 2}
+		}
 		for commitsToSkip > 0 && scanner.Scan() {
 			line := scanner.Bytes()
 			dataIdx := bytes.Index(line, []byte("DATA:"))
+			if dataIdx < 0 {
+				dataIdx = len(line)
+			}
 			starIdx := bytes.IndexByte(line, '*')
 			if starIdx >= 0 && starIdx < dataIdx {
 				commitsToSkip--
 			}
+			parser.ParseGlyphs(line[:dataIdx])
 		}
+
+		row := 0
+
 		// Skip initial non-commit lines
 		for scanner.Scan() {
-			if bytes.IndexByte(scanner.Bytes(), '*') >= 0 {
-				line := scanner.Text()
-				graphItem, err := graphItemFromString(line, r)
-				if err != nil {
+			line := scanner.Bytes()
+			if bytes.IndexByte(line, '*') >= 0 {
+				if err := parser.AddLineToGraph(graph, row, line); err != nil {
 					cancel()
 					return err
 				}
-				commitGraph = append(commitGraph, graphItem)
 				break
 			}
+			parser.ParseGlyphs(line)
 		}
 
 		for scanner.Scan() {
-			line := scanner.Text()
-			graphItem, err := graphItemFromString(line, r)
-			if err != nil {
+			row++
+			line := scanner.Bytes()
+			if err := parser.AddLineToGraph(graph, row, line); err != nil {
 				cancel()
 				return err
 			}
-			commitGraph = append(commitGraph, graphItem)
 		}
 		return scanner.Err()
 	}); err != nil {
-		return commitGraph, err
-	}
-
-	return commitGraph, nil
-}
-
-func graphItemFromString(s string, r *git.Repository) (GraphItem, error) {
-
-	var ascii string
-	var data = "|||||||"
-	lines := strings.SplitN(s, "DATA:", 2)
-
-	switch len(lines) {
-	case 1:
-		ascii = lines[0]
-	case 2:
-		ascii = lines[0]
-		data = lines[1]
-	default:
-		return GraphItem{}, fmt.Errorf("Failed parsing grap line:%s. Expect 1 or two fields", s)
-	}
-
-	rows := strings.SplitN(data, "|", 8)
-	if len(rows) < 8 {
-		return GraphItem{}, fmt.Errorf("Failed parsing grap line:%s - Should containt 8 datafields", s)
-	}
-
-	/* // see format in getCommitGraph()
-	   0	Relation string
-	   1	Branch string
-	   2	Rev string
-	   3	Date string
-	   4	Author string
-	   5	AuthorEmail string
-	   6	ShortRev string
-	   7	Subject string
-	*/
-	gi := GraphItem{ascii,
-		rows[0],
-		rows[1],
-		rows[2],
-		rows[3],
-		rows[4],
-		rows[5],
-		rows[6],
-		rows[7],
-		len(rows[2]) == 0, // no commits referred to, only relation in current line.
+		return graph, err
 	}
-	return gi, nil
+	return graph, nil
 }
diff --git a/modules/gitgraph/graph_models.go b/modules/gitgraph/graph_models.go
new file mode 100644
index 0000000000..ea6ba96084
--- /dev/null
+++ b/modules/gitgraph/graph_models.go
@@ -0,0 +1,186 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package gitgraph
+
+import (
+	"bytes"
+	"fmt"
+)
+
+// NewGraph creates a basic graph
+func NewGraph() *Graph {
+	graph := &Graph{}
+	graph.relationCommit = &Commit{
+		Row:    -1,
+		Column: -1,
+	}
+	graph.Flows = map[int64]*Flow{}
+	return graph
+}
+
+// Graph represents a collection of flows
+type Graph struct {
+	Flows          map[int64]*Flow
+	Commits        []*Commit
+	MinRow         int
+	MinColumn      int
+	MaxRow         int
+	MaxColumn      int
+	relationCommit *Commit
+}
+
+// Width returns the width of the graph
+func (graph *Graph) Width() int {
+	return graph.MaxColumn - graph.MinColumn + 1
+}
+
+// Height returns the height of the graph
+func (graph *Graph) Height() int {
+	return graph.MaxRow - graph.MinRow + 1
+}
+
+// AddGlyph adds glyph to flows
+func (graph *Graph) AddGlyph(row, column int, flowID int64, color int, glyph byte) {
+	flow, ok := graph.Flows[flowID]
+	if !ok {
+		flow = NewFlow(flowID, color, row, column)
+		graph.Flows[flowID] = flow
+	}
+	flow.AddGlyph(row, column, glyph)
+
+	if row < graph.MinRow {
+		graph.MinRow = row
+	}
+	if row > graph.MaxRow {
+		graph.MaxRow = row
+	}
+	if column < graph.MinColumn {
+		graph.MinColumn = column
+	}
+	if column > graph.MaxColumn {
+		graph.MaxColumn = column
+	}
+}
+
+// AddCommit adds a commit at row, column on flowID with the provided data
+func (graph *Graph) AddCommit(row, column int, flowID int64, data []byte) error {
+	commit, err := NewCommit(row, column, data)
+	if err != nil {
+		return err
+	}
+	commit.Flow = flowID
+	graph.Commits = append(graph.Commits, commit)
+
+	graph.Flows[flowID].Commits = append(graph.Flows[flowID].Commits, commit)
+	return nil
+}
+
+// NewFlow creates a new flow
+func NewFlow(flowID int64, color, row, column int) *Flow {
+	return &Flow{
+		ID:          flowID,
+		ColorNumber: color,
+		MinRow:      row,
+		MinColumn:   column,
+		MaxRow:      row,
+		MaxColumn:   column,
+	}
+}
+
+// Flow represents a series of glyphs
+type Flow struct {
+	ID          int64
+	ColorNumber int
+	Glyphs      []Glyph
+	Commits     []*Commit
+	MinRow      int
+	MinColumn   int
+	MaxRow      int
+	MaxColumn   int
+}
+
+// Color16 wraps the color numbers around mod 16
+func (flow *Flow) Color16() int {
+	return flow.ColorNumber % 16
+}
+
+// AddGlyph adds glyph at row and column
+func (flow *Flow) AddGlyph(row, column int, glyph byte) {
+	if row < flow.MinRow {
+		flow.MinRow = row
+	}
+	if row > flow.MaxRow {
+		flow.MaxRow = row
+	}
+	if column < flow.MinColumn {
+		flow.MinColumn = column
+	}
+	if column > flow.MaxColumn {
+		flow.MaxColumn = column
+	}
+
+	flow.Glyphs = append(flow.Glyphs, Glyph{
+		row,
+		column,
+		glyph,
+	})
+}
+
+// Glyph represents a co-ordinate and glyph
+type Glyph struct {
+	Row    int
+	Column int
+	Glyph  byte
+}
+
+// RelationCommit represents an empty relation commit
+var RelationCommit = &Commit{
+	Row: -1,
+}
+
+// NewCommit creates a new commit from a provided line
+func NewCommit(row, column int, line []byte) (*Commit, error) {
+	data := bytes.SplitN(line, []byte("|"), 7)
+	if len(data) < 7 {
+		return nil, fmt.Errorf("malformed data section on line %d with commit: %s", row, string(line))
+	}
+	return &Commit{
+		Row:    row,
+		Column: column,
+		// 0 matches git log --pretty=format:%d => ref names, like the --decorate option of git-log(1)
+		Branch: string(data[0]),
+		// 1 matches git log --pretty=format:%H => commit hash
+		Rev: string(data[1]),
+		// 2 matches git log --pretty=format:%ad => author date (format respects --date= option)
+		Date: string(data[2]),
+		// 3 matches git log --pretty=format:%an => author name
+		Author: string(data[3]),
+		// 4 matches git log --pretty=format:%ae => author email
+		AuthorEmail: string(data[4]),
+		// 5 matches git log --pretty=format:%h => abbreviated commit hash
+		ShortRev: string(data[5]),
+		// 6 matches git log --pretty=format:%s => subject
+		Subject: string(data[6]),
+	}, nil
+}
+
+// Commit represents a commit at co-ordinate X, Y with the data
+type Commit struct {
+	Flow        int64
+	Row         int
+	Column      int
+	Branch      string
+	Rev         string
+	Date        string
+	Author      string
+	AuthorEmail string
+	ShortRev    string
+	Subject     string
+}
+
+// OnlyRelation returns whether this a relation only commit
+func (c *Commit) OnlyRelation() bool {
+	return c.Row == -1
+}
diff --git a/modules/gitgraph/graph_test.go b/modules/gitgraph/graph_test.go
index a2c7f447b6..ca9d653cee 100644
--- a/modules/gitgraph/graph_test.go
+++ b/modules/gitgraph/graph_test.go
@@ -5,7 +5,9 @@
 package gitgraph
 
 import (
+	"bytes"
 	"fmt"
+	"strings"
 	"testing"
 
 	"code.gitea.io/gitea/modules/git"
@@ -14,40 +16,235 @@ import (
 func BenchmarkGetCommitGraph(b *testing.B) {
 
 	currentRepo, err := git.OpenRepository(".")
-	if err != nil {
+	if err != nil || currentRepo == nil {
 		b.Error("Could not open repository")
 	}
 	defer currentRepo.Close()
 
 	for i := 0; i < b.N; i++ {
-		graph, err := GetCommitGraph(currentRepo, 1)
+		graph, err := GetCommitGraph(currentRepo, 1, 0)
 		if err != nil {
 			b.Error("Could get commit graph")
 		}
 
-		if len(graph) < 100 {
+		if len(graph.Commits) < 100 {
 			b.Error("Should get 100 log lines.")
 		}
 	}
 }
 
 func BenchmarkParseCommitString(b *testing.B) {
-	testString := "* DATA:||4e61bacab44e9b4730e44a6615d04098dd3a8eaf|2016-12-20 21:10:41 +0100|Kjell Kvinge|kjell@kvinge.biz|4e61bac|Add route for graph"
+	testString := "* DATA:|4e61bacab44e9b4730e44a6615d04098dd3a8eaf|2016-12-20 21:10:41 +0100|Kjell Kvinge|kjell@kvinge.biz|4e61bac|Add route for graph"
 
+	parser := &Parser{}
+	parser.Reset()
 	for i := 0; i < b.N; i++ {
-		graphItem, err := graphItemFromString(testString, nil)
-		if err != nil {
+		parser.Reset()
+		graph := NewGraph()
+		if err := parser.AddLineToGraph(graph, 0, []byte(testString)); err != nil {
 			b.Error("could not parse teststring")
 		}
-
-		if graphItem.Author != "Kjell Kvinge" {
+		if graph.Flows[1].Commits[0].Author != "Kjell Kvinge" {
 			b.Error("Did not get expected data")
 		}
 	}
 }
 
+func BenchmarkParseGlyphs(b *testing.B) {
+	parser := &Parser{}
+	parser.Reset()
+	tgBytes := []byte(testglyphs)
+	tg := tgBytes
+	idx := bytes.Index(tg, []byte("\n"))
+	for i := 0; i < b.N; i++ {
+		parser.Reset()
+		tg = tgBytes
+		idx = bytes.Index(tg, []byte("\n"))
+		for idx > 0 {
+			parser.ParseGlyphs(tg[:idx])
+			tg = tg[idx+1:]
+			idx = bytes.Index(tg, []byte("\n"))
+		}
+	}
+}
+
+func TestReleaseUnusedColors(t *testing.T) {
+	testcases := []struct {
+		availableColors []int
+		oldColors       []int
+		firstInUse      int // these values have to be either be correct or suggest less is
+		firstAvailable  int // available than possibly is - i.e. you cannot say 10 is available when it
+	}{
+		{
+			availableColors: []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
+			oldColors:       []int{1, 1, 1, 1, 1},
+			firstAvailable:  -1,
+			firstInUse:      1,
+		},
+		{
+			availableColors: []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
+			oldColors:       []int{1, 2, 3, 4},
+			firstAvailable:  6,
+			firstInUse:      0,
+		},
+		{
+			availableColors: []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
+			oldColors:       []int{6, 0, 3, 5, 3, 4, 0, 0},
+			firstAvailable:  6,
+			firstInUse:      0,
+		},
+		{
+			availableColors: []int{1, 2, 3, 4, 5, 6, 7},
+			oldColors:       []int{6, 1, 3, 5, 3, 4, 2, 7},
+			firstAvailable:  -1,
+			firstInUse:      0,
+		},
+		{
+			availableColors: []int{1, 2, 3, 4, 5, 6, 7},
+			oldColors:       []int{6, 0, 3, 5, 3, 4, 2, 7},
+			firstAvailable:  -1,
+			firstInUse:      0,
+		},
+	}
+	for _, testcase := range testcases {
+		parser := &Parser{}
+		parser.Reset()
+		parser.availableColors = append([]int{}, testcase.availableColors...)
+		parser.oldColors = append(parser.oldColors, testcase.oldColors...)
+		parser.firstAvailable = testcase.firstAvailable
+		parser.firstInUse = testcase.firstInUse
+		parser.releaseUnusedColors()
+
+		if parser.firstAvailable == -1 {
+			// All in use
+			for _, color := range parser.availableColors {
+				found := false
+				for _, oldColor := range parser.oldColors {
+					if oldColor == color {
+						found = true
+						break
+					}
+				}
+				if !found {
+					t.Errorf("In testcase:\n%d\t%d\t%d %d =>\n%d\t%d\t%d %d: %d should be available but is not",
+						testcase.availableColors,
+						testcase.oldColors,
+						testcase.firstAvailable,
+						testcase.firstInUse,
+						parser.availableColors,
+						parser.oldColors,
+						parser.firstAvailable,
+						parser.firstInUse,
+						color)
+				}
+			}
+		} else if parser.firstInUse != -1 {
+			// Some in use
+			for i := parser.firstInUse; i != parser.firstAvailable; i = (i + 1) % len(parser.availableColors) {
+				color := parser.availableColors[i]
+				found := false
+				for _, oldColor := range parser.oldColors {
+					if oldColor == color {
+						found = true
+						break
+					}
+				}
+				if !found {
+					t.Errorf("In testcase:\n%d\t%d\t%d %d =>\n%d\t%d\t%d %d: %d should be available but is not",
+						testcase.availableColors,
+						testcase.oldColors,
+						testcase.firstAvailable,
+						testcase.firstInUse,
+						parser.availableColors,
+						parser.oldColors,
+						parser.firstAvailable,
+						parser.firstInUse,
+						color)
+				}
+			}
+			for i := parser.firstAvailable; i != parser.firstInUse; i = (i + 1) % len(parser.availableColors) {
+				color := parser.availableColors[i]
+				found := false
+				for _, oldColor := range parser.oldColors {
+					if oldColor == color {
+						found = true
+						break
+					}
+				}
+				if found {
+					t.Errorf("In testcase:\n%d\t%d\t%d %d =>\n%d\t%d\t%d %d: %d should not be available but is",
+						testcase.availableColors,
+						testcase.oldColors,
+						testcase.firstAvailable,
+						testcase.firstInUse,
+						parser.availableColors,
+						parser.oldColors,
+						parser.firstAvailable,
+						parser.firstInUse,
+						color)
+				}
+			}
+		} else {
+			// None in use
+			for _, color := range parser.oldColors {
+				if color != 0 {
+					t.Errorf("In testcase:\n%d\t%d\t%d %d =>\n%d\t%d\t%d %d: %d should not be available but is",
+						testcase.availableColors,
+						testcase.oldColors,
+						testcase.firstAvailable,
+						testcase.firstInUse,
+						parser.availableColors,
+						parser.oldColors,
+						parser.firstAvailable,
+						parser.firstInUse,
+						color)
+				}
+			}
+		}
+	}
+}
+
+func TestParseGlyphs(t *testing.T) {
+	parser := &Parser{}
+	parser.Reset()
+	tgBytes := []byte(testglyphs)
+	tg := tgBytes
+	idx := bytes.Index(tg, []byte("\n"))
+	row := 0
+	for idx > 0 {
+		parser.ParseGlyphs(tg[:idx])
+		tg = tg[idx+1:]
+		idx = bytes.Index(tg, []byte("\n"))
+		if parser.flows[0] != 1 {
+			t.Errorf("First column flow should be 1 but was %d", parser.flows[0])
+		}
+		colorToFlow := map[int]int64{}
+		flowToColor := map[int64]int{}
+
+		for i, flow := range parser.flows {
+			if flow == 0 {
+				continue
+			}
+			color := parser.colors[i]
+
+			if fColor, in := flowToColor[flow]; in && fColor != color {
+				t.Errorf("Row %d column %d flow %d has color %d but should be %d", row, i, flow, color, fColor)
+			}
+			flowToColor[flow] = color
+			if cFlow, in := colorToFlow[color]; in && cFlow != flow {
+				t.Errorf("Row %d column %d flow %d has color %d but conflicts with flow %d", row, i, flow, color, cFlow)
+			}
+			colorToFlow[color] = flow
+		}
+		row++
+	}
+	if len(parser.availableColors) != 9 {
+		t.Errorf("Expected 9 colors but have %d", len(parser.availableColors))
+	}
+}
+
 func TestCommitStringParsing(t *testing.T) {
-	dataFirstPart := "* DATA:||4e61bacab44e9b4730e44a6615d04098dd3a8eaf|2016-12-20 21:10:41 +0100|Author|user@mail.something|4e61bac|"
+	dataFirstPart := "* DATA:|4e61bacab44e9b4730e44a6615d04098dd3a8eaf|2016-12-20 21:10:41 +0100|Author|user@mail.something|4e61bac|"
 	tests := []struct {
 		shouldPass    bool
 		testName      string
@@ -62,15 +259,460 @@ func TestCommitStringParsing(t *testing.T) {
 
 		t.Run(test.testName, func(t *testing.T) {
 			testString := fmt.Sprintf("%s%s", dataFirstPart, test.commitMessage)
-			graphItem, err := graphItemFromString(testString, nil)
+			idx := strings.Index(testString, "DATA:")
+			commit, err := NewCommit(0, 0, []byte(testString[idx+5:]))
 			if err != nil && test.shouldPass {
 				t.Errorf("Could not parse %s", testString)
 				return
 			}
 
-			if test.commitMessage != graphItem.Subject {
-				t.Errorf("%s does not match %s", test.commitMessage, graphItem.Subject)
+			if test.commitMessage != commit.Subject {
+				t.Errorf("%s does not match %s", test.commitMessage, commit.Subject)
 			}
 		})
 	}
 }
+
+var testglyphs = `* 
+* 
+* 
+* 
+* 
+* 
+* 
+*   
+|\  
+* | 
+* | 
+* | 
+* | 
+* | 
+| * 
+* | 
+| *   
+| |\  
+* | | 
+| | *   
+| | |\  
+* | | \   
+|\ \ \ \  
+| * | | | 
+| |\| | | 
+* | | | | 
+|/ / / /  
+| | | * 
+| * | | 
+| * | | 
+| * | | 
+* | | | 
+* | | | 
+* | | | 
+* | | | 
+* | | |   
+|\ \ \ \  
+| | * | | 
+| | |\| | 
+| | | * | 
+| | | | * 
+* | | | | 
+* | | | | 
+* | | | | 
+* | | | | 
+* | | | |   
+|\ \ \ \ \  
+| * | | | | 
+|/| | | | | 
+| | |/ / /  
+| |/| | |   
+| | | | * 
+| * | | | 
+|/| | | | 
+| * | | | 
+|/| | | | 
+| | |/ /  
+| |/| |   
+| * | | 
+| * | |   
+| |\ \ \  
+| | * | | 
+| |/| | | 
+| | | |/  
+| | |/|   
+| * | | 
+| * | | 
+| * | | 
+| | * |   
+| | |\ \  
+| | | * | 
+| | |/| | 
+| | | * |   
+| | | |\ \  
+| | | | * | 
+| | | |/| | 
+| | * | | | 
+| | * | | |   
+| | |\ \ \ \  
+| | | * | | | 
+| | |/| | | | 
+| | | | | * | 
+| | | | |/ /  
+* | | | / / 
+|/ / / / /  
+* | | | |   
+|\ \ \ \ \  
+| * | | | | 
+|/| | | | | 
+| * | | | | 
+| * | | | |   
+| |\ \ \ \ \  
+| | | * \ \ \   
+| | | |\ \ \ \  
+| | | | * | | | 
+| | | |/| | | | 
+| | | | | |/ /  
+| | | | |/| |   
+* | | | | | | 
+* | | | | | | 
+* | | | | | | 
+| | | | * | | 
+* | | | | | | 
+| | * | | | | 
+| |/| | | | | 
+* | | | | | | 
+| |/ / / / /  
+|/| | | | |   
+| | | | * | 
+| | | |/ /  
+| | |/| |   
+| * | | | 
+| | | | * 
+| | * | |   
+| | |\ \ \  
+| | | * | | 
+| | |/| | | 
+| | | |/ /  
+| | | * | 
+| | * | |   
+| | |\ \ \  
+| | | * | | 
+| | |/| | | 
+| | | |/ /  
+| | | * | 
+* | | | |   
+|\ \ \ \ \  
+| * \ \ \ \   
+| |\ \ \ \ \  
+| | | |/ / /  
+| | |/| | |   
+| | | | * | 
+| | | | * | 
+* | | | | | 
+* | | | | | 
+|/ / / / /  
+| | | * | 
+* | | | | 
+* | | | | 
+* | | | | 
+* | | | |   
+|\ \ \ \ \  
+| * | | | | 
+|/| | | | | 
+| | * | | |   
+| | |\ \ \ \  
+| | | * | | | 
+| | |/| | | | 
+| |/| | |/ /  
+| | | |/| |   
+| | | | | * 
+| |_|_|_|/  
+|/| | | |   
+| | * | | 
+| |/ / /  
+* | | | 
+* | | | 
+| | * | 
+* | | | 
+* | | | 
+| * | | 
+| | * | 
+| * | | 
+* | | |   
+|\ \ \ \  
+| * | | | 
+|/| | | | 
+| |/ / /  
+| * | |   
+| |\ \ \  
+| | * | | 
+| |/| | | 
+| | |/ /  
+| | * |   
+| | |\ \  
+| | | * | 
+| | |/| | 
+* | | | | 
+* | | | |   
+|\ \ \ \ \  
+| * | | | | 
+|/| | | | | 
+| | * | | | 
+| | * | | | 
+| | * | | | 
+| |/ / / /  
+| * | | |   
+| |\ \ \ \  
+| | * | | | 
+| |/| | | | 
+* | | | | | 
+* | | | | | 
+* | | | | | 
+* | | | | | 
+* | | | | | 
+| | | | * | 
+* | | | | |   
+|\ \ \ \ \ \  
+| * | | | | | 
+|/| | | | | | 
+| | | | | * | 
+| | | | |/ /  
+* | | | | |   
+|\ \ \ \ \ \  
+* | | | | | | 
+* | | | | | | 
+| | | | * | | 
+* | | | | | | 
+* | | | | | |   
+|\ \ \ \ \ \ \  
+| | |_|_|/ / /  
+| |/| | | | |   
+| | | | * | | 
+| | | | * | | 
+| | | | * | | 
+| | | | * | | 
+| | | | * | | 
+| | | | * | | 
+| | | |/ / /  
+| | | * | | 
+| | | * | | 
+| | | * | | 
+| | |/| | | 
+| | | * | | 
+| | |/| | | 
+| | | |/ /  
+| | * | | 
+| |/| | | 
+| | | * | 
+| | |/ /  
+| | * | 
+| * | |   
+| |\ \ \  
+| * | | | 
+| | * | | 
+| |/| | | 
+| | |/ /  
+| | * |   
+| | |\ \  
+| | * | | 
+* | | | | 
+|\| | | | 
+| * | | | 
+| * | | | 
+| * | | | 
+| | * | | 
+| * | | | 
+| |\| | | 
+| * | | | 
+| | * | | 
+| | * | | 
+| * | | | 
+| * | | | 
+| * | | | 
+| * | | | 
+| * | | | 
+| * | | | 
+| * | | | 
+| * | | | 
+| | * | | 
+| * | | | 
+| * | | | 
+| * | | | 
+| * | | | 
+| | * | | 
+* | | | | 
+|\| | | | 
+| | * | | 
+| * | | | 
+| |\| | | 
+| | * | | 
+| | * | | 
+| | * | | 
+| | | * | 
+* | | | | 
+|\| | | | 
+| | * | | 
+| | |/ /  
+| * | | 
+| * | | 
+| |\| | 
+* | | | 
+|\| | | 
+| | * | 
+| | * | 
+| | * | 
+| * | | 
+| | * | 
+| * | | 
+| | * | 
+| | * | 
+| | * | 
+| * | | 
+| * | | 
+| * | | 
+| * | | 
+| * | | 
+| * | | 
+| * | | 
+* | | | 
+|\| | | 
+| * | | 
+| |\| | 
+| | * |   
+| | |\ \  
+* | | | | 
+|\| | | | 
+| * | | | 
+| |\| | | 
+| | * | | 
+| | | * | 
+| | |/ /  
+* | | | 
+* | | | 
+|\| | | 
+| * | | 
+| |\| | 
+| | * | 
+| | * | 
+| | * | 
+| | | * 
+* | | | 
+|\| | | 
+| * | | 
+| * | | 
+| | | *   
+| | | |\  
+* | | | | 
+| |_|_|/  
+|/| | |   
+| * | | 
+| |\| | 
+| | * | 
+| | * | 
+| | * | 
+| | * | 
+| | * | 
+| * | | 
+* | | | 
+|\| | | 
+| * | | 
+|/| | | 
+| |/ /  
+| * |   
+| |\ \  
+| * | | 
+| * | | 
+* | | | 
+|\| | | 
+| | * | 
+| * | | 
+| * | | 
+| * | | 
+* | | | 
+|\| | | 
+| * | | 
+| * | | 
+| | * |   
+| | |\ \  
+| | |/ /  
+| |/| |   
+| * | | 
+* | | | 
+|\| | | 
+| * | | 
+* | | | 
+|\| | | 
+| * | |   
+| |\ \ \  
+| * | | | 
+| * | | | 
+| | | * | 
+| * | | | 
+| * | | | 
+| | |/ /  
+| |/| |   
+| | * | 
+* | | | 
+|\| | | 
+| * | | 
+| * | | 
+| * | | 
+| * | | 
+| * | |   
+| |\ \ \  
+* | | | | 
+|\| | | | 
+| * | | | 
+| * | | | 
+* | | | | 
+* | | | | 
+|\| | | | 
+| | | | *   
+| | | | |\  
+| |_|_|_|/  
+|/| | | |   
+| * | | | 
+* | | | | 
+* | | | | 
+|\| | | | 
+| * | | |   
+| |\ \ \ \  
+| | | |/ /  
+| | |/| |   
+| * | | | 
+| * | | | 
+| * | | | 
+| * | | | 
+| | * | | 
+| | | * | 
+| | |/ /  
+| |/| |   
+* | | | 
+|\| | | 
+| * | | 
+| * | | 
+| * | | 
+| * | | 
+| * | | 
+* | | | 
+|\| | | 
+| * | | 
+| * | | 
+* | | | 
+| * | | 
+| * | | 
+| * | | 
+* | | | 
+* | | | 
+* | | | 
+|\| | | 
+| * | | 
+* | | | 
+* | | | 
+* | | | 
+* | | | 
+| | | * 
+* | | | 
+|\| | | 
+| * | | 
+| * | | 
+| * | | 
+`
diff --git a/modules/gitgraph/parser.go b/modules/gitgraph/parser.go
new file mode 100644
index 0000000000..62e0505652
--- /dev/null
+++ b/modules/gitgraph/parser.go
@@ -0,0 +1,338 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package gitgraph
+
+import (
+	"bytes"
+	"fmt"
+)
+
+// Parser represents a git graph parser. It is stateful containing the previous
+// glyphs, detected flows and color assignments.
+type Parser struct {
+	glyphs           []byte
+	oldGlyphs        []byte
+	flows            []int64
+	oldFlows         []int64
+	maxFlow          int64
+	colors           []int
+	oldColors        []int
+	availableColors  []int
+	nextAvailable    int
+	firstInUse       int
+	firstAvailable   int
+	maxAllowedColors int
+}
+
+// Reset resets the internal parser state.
+func (parser *Parser) Reset() {
+	parser.glyphs = parser.glyphs[0:0]
+	parser.oldGlyphs = parser.oldGlyphs[0:0]
+	parser.flows = parser.flows[0:0]
+	parser.oldFlows = parser.oldFlows[0:0]
+	parser.maxFlow = 0
+	parser.colors = parser.colors[0:0]
+	parser.oldColors = parser.oldColors[0:0]
+	parser.availableColors = parser.availableColors[0:0]
+	parser.availableColors = append(parser.availableColors, 1, 2)
+	parser.nextAvailable = 0
+	parser.firstInUse = -1
+	parser.firstAvailable = 0
+	parser.maxAllowedColors = 0
+}
+
+// AddLineToGraph adds the line as a row to the graph
+func (parser *Parser) AddLineToGraph(graph *Graph, row int, line []byte) error {
+	idx := bytes.Index(line, []byte("DATA:"))
+	if idx < 0 {
+		parser.ParseGlyphs(line)
+	} else {
+		parser.ParseGlyphs(line[:idx])
+	}
+
+	var err error
+	commitDone := false
+
+	for column, glyph := range parser.glyphs {
+		if glyph == ' ' {
+			continue
+		}
+
+		flowID := parser.flows[column]
+
+		graph.AddGlyph(row, column, flowID, parser.colors[column], glyph)
+
+		if glyph == '*' {
+			if commitDone {
+				if err != nil {
+					err = fmt.Errorf("double commit on line %d: %s. %w", row, string(line), err)
+				} else {
+					err = fmt.Errorf("double commit on line %d: %s", row, string(line))
+				}
+			}
+			commitDone = true
+			if idx < 0 {
+				if err != nil {
+					err = fmt.Errorf("missing data section on line %d with commit: %s. %w", row, string(line), err)
+				} else {
+					err = fmt.Errorf("missing data section on line %d with commit: %s", row, string(line))
+				}
+				continue
+			}
+			err2 := graph.AddCommit(row, column, flowID, line[idx+5:])
+			if err != nil && err2 != nil {
+				err = fmt.Errorf("%v %w", err2, err)
+				continue
+			} else if err2 != nil {
+				err = err2
+				continue
+			}
+		}
+	}
+	if !commitDone {
+		graph.Commits = append(graph.Commits, RelationCommit)
+	}
+	return err
+}
+
+func (parser *Parser) releaseUnusedColors() {
+	if parser.firstInUse > -1 {
+		// Here we step through the old colors, searching for them in the
+		// "in-use" section of availableColors (that is, the colors between
+		// firstInUse and firstAvailable)
+		// Ensure that the benchmarks are not worsened with proposed changes
+		stepstaken := 0
+		position := parser.firstInUse
+		for _, color := range parser.oldColors {
+			if color == 0 {
+				continue
+			}
+			found := false
+			i := position
+			for j := stepstaken; i != parser.firstAvailable && j < len(parser.availableColors); j++ {
+				colorToCheck := parser.availableColors[i]
+				if colorToCheck == color {
+					found = true
+					break
+				}
+				i = (i + 1) % len(parser.availableColors)
+			}
+			if !found {
+				// Duplicate color
+				continue
+			}
+			// Swap them around
+			parser.availableColors[position], parser.availableColors[i] = parser.availableColors[i], parser.availableColors[position]
+			stepstaken++
+			position = (parser.firstInUse + stepstaken) % len(parser.availableColors)
+			if position == parser.firstAvailable || stepstaken == len(parser.availableColors) {
+				break
+			}
+		}
+		if stepstaken == len(parser.availableColors) {
+			parser.firstAvailable = -1
+		} else {
+			parser.firstAvailable = position
+			if parser.nextAvailable == -1 {
+				parser.nextAvailable = parser.firstAvailable
+			}
+		}
+	}
+}
+
+// ParseGlyphs parses the provided glyphs and sets the internal state
+func (parser *Parser) ParseGlyphs(glyphs []byte) {
+
+	// Clean state for parsing this row
+	parser.glyphs, parser.oldGlyphs = parser.oldGlyphs, parser.glyphs
+	parser.glyphs = parser.glyphs[0:0]
+	parser.flows, parser.oldFlows = parser.oldFlows, parser.flows
+	parser.flows = parser.flows[0:0]
+	parser.colors, parser.oldColors = parser.oldColors, parser.colors
+
+	// Ensure we have enough flows and colors
+	parser.colors = parser.colors[0:0]
+	for range glyphs {
+		parser.flows = append(parser.flows, 0)
+		parser.colors = append(parser.colors, 0)
+	}
+
+	// Copy the provided glyphs in to state.glyphs for safekeeping
+	parser.glyphs = append(parser.glyphs, glyphs...)
+
+	// release unused colors
+	parser.releaseUnusedColors()
+
+	for i := len(glyphs) - 1; i >= 0; i-- {
+		glyph := glyphs[i]
+		switch glyph {
+		case '|':
+			fallthrough
+		case '*':
+			parser.setUpFlow(i)
+		case '/':
+			parser.setOutFlow(i)
+		case '\\':
+			parser.setInFlow(i)
+		case '_':
+			parser.setRightFlow(i)
+		case '.':
+			fallthrough
+		case '-':
+			parser.setLeftFlow(i)
+		case ' ':
+			// no-op
+		default:
+			parser.newFlow(i)
+		}
+	}
+}
+
+func (parser *Parser) takePreviousFlow(i, j int) {
+	if j < len(parser.oldFlows) && parser.oldFlows[j] > 0 {
+		parser.flows[i] = parser.oldFlows[j]
+		parser.oldFlows[j] = 0
+		parser.colors[i] = parser.oldColors[j]
+		parser.oldColors[j] = 0
+	} else {
+		parser.newFlow(i)
+	}
+}
+
+func (parser *Parser) takeCurrentFlow(i, j int) {
+	if j < len(parser.flows) && parser.flows[j] > 0 {
+		parser.flows[i] = parser.flows[j]
+		parser.colors[i] = parser.colors[j]
+	} else {
+		parser.newFlow(i)
+	}
+}
+
+func (parser *Parser) newFlow(i int) {
+	parser.maxFlow++
+	parser.flows[i] = parser.maxFlow
+
+	// Now give this flow a color
+	if parser.nextAvailable == -1 {
+		next := len(parser.availableColors)
+		if parser.maxAllowedColors < 1 || next < parser.maxAllowedColors {
+			parser.nextAvailable = next
+			parser.firstAvailable = next
+			parser.availableColors = append(parser.availableColors, next+1)
+		}
+	}
+	parser.colors[i] = parser.availableColors[parser.nextAvailable]
+	if parser.firstInUse == -1 {
+		parser.firstInUse = parser.nextAvailable
+	}
+	parser.availableColors[parser.firstAvailable], parser.availableColors[parser.nextAvailable] = parser.availableColors[parser.nextAvailable], parser.availableColors[parser.firstAvailable]
+
+	parser.nextAvailable = (parser.nextAvailable + 1) % len(parser.availableColors)
+	parser.firstAvailable = (parser.firstAvailable + 1) % len(parser.availableColors)
+
+	if parser.nextAvailable == parser.firstInUse {
+		parser.nextAvailable = parser.firstAvailable
+	}
+	if parser.nextAvailable == parser.firstInUse {
+		parser.nextAvailable = -1
+		parser.firstAvailable = -1
+	}
+}
+
+// setUpFlow handles '|' or '*'
+func (parser *Parser) setUpFlow(i int) {
+	// In preference order:
+	//
+	// Previous Row: '\? ' ' |' '  /'
+	// Current Row:  ' | ' ' |' ' | '
+	if i > 0 && i-1 < len(parser.oldGlyphs) && parser.oldGlyphs[i-1] == '\\' {
+		parser.takePreviousFlow(i, i-1)
+	} else if i < len(parser.oldGlyphs) && (parser.oldGlyphs[i] == '|' || parser.oldGlyphs[i] == '*') {
+		parser.takePreviousFlow(i, i)
+	} else if i+1 < len(parser.oldGlyphs) && parser.oldGlyphs[i+1] == '/' {
+		parser.takePreviousFlow(i, i+1)
+	} else {
+		parser.newFlow(i)
+	}
+}
+
+// setOutFlow handles '/'
+func (parser *Parser) setOutFlow(i int) {
+	// In preference order:
+	//
+	// Previous Row: ' |/' ' |_' ' |' ' /' ' _' '\'
+	// Current Row:  '/| ' '/| ' '/ ' '/ ' '/ ' '/'
+	if i+2 < len(parser.oldGlyphs) &&
+		(parser.oldGlyphs[i+1] == '|' || parser.oldGlyphs[i+1] == '*') &&
+		(parser.oldGlyphs[i+2] == '/' || parser.oldGlyphs[i+2] == '_') &&
+		i+1 < len(parser.glyphs) &&
+		(parser.glyphs[i+1] == '|' || parser.glyphs[i+1] == '*') {
+		parser.takePreviousFlow(i, i+2)
+	} else if i+1 < len(parser.oldGlyphs) &&
+		(parser.oldGlyphs[i+1] == '|' || parser.oldGlyphs[i+1] == '*' ||
+			parser.oldGlyphs[i+1] == '/' || parser.oldGlyphs[i+1] == '_') {
+		parser.takePreviousFlow(i, i+1)
+		if parser.oldGlyphs[i+1] == '/' {
+			parser.glyphs[i] = '|'
+		}
+	} else if i < len(parser.oldGlyphs) && parser.oldGlyphs[i] == '\\' {
+		parser.takePreviousFlow(i, i)
+	} else {
+		parser.newFlow(i)
+	}
+}
+
+// setInFlow handles '\'
+func (parser *Parser) setInFlow(i int) {
+	// In preference order:
+	//
+	// Previous Row: '| ' '-. ' '| ' '\ ' '/' '---'
+	// Current Row:  '|\' '  \' ' \' ' \' '\' ' \ '
+	if i > 0 && i-1 < len(parser.oldGlyphs) &&
+		(parser.oldGlyphs[i-1] == '|' || parser.oldGlyphs[i-1] == '*') &&
+		(parser.glyphs[i-1] == '|' || parser.glyphs[i-1] == '*') {
+		parser.newFlow(i)
+	} else if i > 0 && i-1 < len(parser.oldGlyphs) &&
+		(parser.oldGlyphs[i-1] == '|' || parser.oldGlyphs[i-1] == '*' ||
+			parser.oldGlyphs[i-1] == '.' || parser.oldGlyphs[i-1] == '\\') {
+		parser.takePreviousFlow(i, i-1)
+		if parser.oldGlyphs[i-1] == '\\' {
+			parser.glyphs[i] = '|'
+		}
+	} else if i < len(parser.oldGlyphs) && parser.oldGlyphs[i] == '/' {
+		parser.takePreviousFlow(i, i)
+	} else {
+		parser.newFlow(i)
+	}
+}
+
+// setRightFlow handles '_'
+func (parser *Parser) setRightFlow(i int) {
+	// In preference order:
+	//
+	// Current Row:  '__' '_/' '_|_' '_|/'
+	if i+1 < len(parser.glyphs) &&
+		(parser.glyphs[i+1] == '_' || parser.glyphs[i+1] == '/') {
+		parser.takeCurrentFlow(i, i+1)
+	} else if i+2 < len(parser.glyphs) &&
+		(parser.glyphs[i+1] == '|' || parser.glyphs[i+1] == '*') &&
+		(parser.glyphs[i+2] == '_' || parser.glyphs[i+2] == '/') {
+		parser.takeCurrentFlow(i, i+2)
+	} else {
+		parser.newFlow(i)
+	}
+}
+
+// setLeftFlow handles '----.'
+func (parser *Parser) setLeftFlow(i int) {
+	if parser.glyphs[i] == '.' {
+		parser.newFlow(i)
+	} else if i+1 < len(parser.glyphs) &&
+		(parser.glyphs[i+1] == '-' || parser.glyphs[i+1] == '.') {
+		parser.takeCurrentFlow(i, i+1)
+	} else {
+		parser.newFlow(i)
+	}
+}