Expand/Collapse Files and Blob Excerpt while Reviewing/Comparing code (#8924)

* update #8659 fold/unfold code diffs

* add fold button style

* update #8659 implement expand up/down codes (blob excerpt)

* fix golint errors

* fix expand direction

* remove debug message

* update css style for blob exceprt

* fix typo in comment

* update style sheet with less

* update expect diff (add SectionInfo)

* update #8942 accept suggested change (fix typo)

* close reader and check file type before get tail section

* adjust button position and check file type before insert fold button

* move index js to web_src

* merge index.js with master

* generate index.js

* update js coding style

4 files changed, 118 insertions, 1 deletions

diff --git a/routers/repo/commit.go b/routers/repo/commit.go
index f067729ca9..2a123a2eb9 100644
--- a/routers/repo/commit.go
+++ b/routers/repo/commit.go
@@ -245,6 +245,7 @@ func Diff(ctx *context.Context) {
 	}
 
 	ctx.Data["CommitID"] = commitID
+	ctx.Data["AfterCommitID"] = commitID
 	ctx.Data["Username"] = userName
 	ctx.Data["Reponame"] = repoName
 
diff --git a/routers/repo/compare.go b/routers/repo/compare.go
index e45f046435..203b740082 100644
--- a/routers/repo/compare.go
+++ b/routers/repo/compare.go
@@ -5,21 +5,26 @@
 package repo
 
 import (
+	"bufio"
 	"fmt"
+	"html"
 	"path"
+	"path/filepath"
 	"strings"
 
 	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/highlight"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/services/gitdiff"
 )
 
 const (
-	tplCompare base.TplName = "repo/diff/compare"
+	tplCompare     base.TplName = "repo/diff/compare"
+	tplBlobExcerpt base.TplName = "repo/diff/blob_excerpt"
 )
 
 // setPathsCompareContext sets context data for source and raw paths
@@ -434,3 +439,109 @@ func CompareDiff(ctx *context.Context) {
 
 	ctx.HTML(200, tplCompare)
 }
+
+// ExcerptBlob render blob excerpt contents
+func ExcerptBlob(ctx *context.Context) {
+	commitID := ctx.Params("sha")
+	lastLeft := ctx.QueryInt("last_left")
+	lastRight := ctx.QueryInt("last_right")
+	idxLeft := ctx.QueryInt("left")
+	idxRight := ctx.QueryInt("right")
+	leftHunkSize := ctx.QueryInt("left_hunk_size")
+	rightHunkSize := ctx.QueryInt("right_hunk_size")
+	anchor := ctx.Query("anchor")
+	direction := ctx.Query("direction")
+	filePath := ctx.Query("path")
+	gitRepo := ctx.Repo.GitRepo
+	chunkSize := gitdiff.BlobExceprtChunkSize
+	commit, err := gitRepo.GetCommit(commitID)
+	if err != nil {
+		ctx.Error(500, "GetCommit")
+		return
+	}
+	section := &gitdiff.DiffSection{
+		Name: filePath,
+	}
+	if direction == "up" && (idxLeft-lastLeft) > chunkSize {
+		idxLeft -= chunkSize
+		idxRight -= chunkSize
+		leftHunkSize += chunkSize
+		rightHunkSize += chunkSize
+		section.Lines, err = getExcerptLines(commit, filePath, idxLeft-1, idxRight-1, chunkSize)
+	} else if direction == "down" && (idxLeft-lastLeft) > chunkSize {
+		section.Lines, err = getExcerptLines(commit, filePath, lastLeft, lastRight, chunkSize)
+		lastLeft += chunkSize
+		lastRight += chunkSize
+	} else {
+		section.Lines, err = getExcerptLines(commit, filePath, lastLeft, lastRight, idxRight-lastRight-1)
+		leftHunkSize = 0
+		rightHunkSize = 0
+		idxLeft = lastLeft
+		idxRight = lastRight
+	}
+	if err != nil {
+		ctx.Error(500, "getExcerptLines")
+		return
+	}
+	if idxRight > lastRight {
+		lineText := " "
+		if rightHunkSize > 0 || leftHunkSize > 0 {
+			lineText = fmt.Sprintf("@@ -%d,%d +%d,%d @@\n", idxLeft, leftHunkSize, idxRight, rightHunkSize)
+		}
+		lineText = html.EscapeString(lineText)
+		lineSection := &gitdiff.DiffLine{
+			Type:    gitdiff.DiffLineSection,
+			Content: lineText,
+			SectionInfo: &gitdiff.DiffLineSectionInfo{
+				Path:          filePath,
+				LastLeftIdx:   lastLeft,
+				LastRightIdx:  lastRight,
+				LeftIdx:       idxLeft,
+				RightIdx:      idxRight,
+				LeftHunkSize:  leftHunkSize,
+				RightHunkSize: rightHunkSize,
+			}}
+		if direction == "up" {
+			section.Lines = append([]*gitdiff.DiffLine{lineSection}, section.Lines...)
+		} else if direction == "down" {
+			section.Lines = append(section.Lines, lineSection)
+		}
+	}
+	ctx.Data["section"] = section
+	ctx.Data["fileName"] = filePath
+	ctx.Data["highlightClass"] = highlight.FileNameToHighlightClass(filepath.Base(filePath))
+	ctx.Data["AfterCommitID"] = commitID
+	ctx.Data["Anchor"] = anchor
+	ctx.HTML(200, tplBlobExcerpt)
+}
+
+func getExcerptLines(commit *git.Commit, filePath string, idxLeft int, idxRight int, chunkSize int) ([]*gitdiff.DiffLine, error) {
+	blob, err := commit.Tree.GetBlobByPath(filePath)
+	if err != nil {
+		return nil, err
+	}
+	reader, err := blob.DataAsync()
+	if err != nil {
+		return nil, err
+	}
+	defer reader.Close()
+	scanner := bufio.NewScanner(reader)
+	var diffLines []*gitdiff.DiffLine
+	for line := 0; line < idxRight+chunkSize; line++ {
+		if ok := scanner.Scan(); !ok {
+			break
+		}
+		if line < idxRight {
+			continue
+		}
+		lineText := scanner.Text()
+		diffLine := &gitdiff.DiffLine{
+			LeftIdx:  idxLeft + (line - idxRight) + 1,
+			RightIdx: line + 1,
+			Type:     gitdiff.DiffLinePlain,
+			Content:  " " + lineText,
+		}
+		diffLines = append(diffLines, diffLine)
+	}
+	return diffLines, nil
+}
diff --git a/routers/repo/pull.go b/routers/repo/pull.go
index 67849f33e1..a1a4e5e2bb 100644
--- a/routers/repo/pull.go
+++ b/routers/repo/pull.go
@@ -552,6 +552,7 @@ func ViewPullFiles(ctx *context.Context) {
 		ctx.Data["Username"] = pull.MustHeadUserName()
 		ctx.Data["Reponame"] = pull.HeadRepo.Name
 	}
+	ctx.Data["AfterCommitID"] = endCommitID
 
 	diff, err := gitdiff.GetDiffRangeWithWhitespaceBehavior(diffRepoPath,
 		startCommitID, endCommitID, setting.Git.MaxGitDiffLines,
diff --git a/routers/routes/routes.go b/routers/routes/routes.go
index 13a5bb2708..48bba16bf6 100644
--- a/routers/routes/routes.go
+++ b/routers/routes/routes.go
@@ -864,6 +864,10 @@ func RegisterRoutes(m *macaron.Macaron) {
 			m.Get("", repo.Branches)
 		}, repo.MustBeNotEmpty, context.RepoRef(), reqRepoCodeReader)
 
+		m.Group("/blob_excerpt", func() {
+			m.Get("/:sha", repo.SetEditorconfigIfExists, repo.SetDiffViewStyle, repo.ExcerptBlob)
+		}, repo.MustBeNotEmpty, context.RepoRef(), reqRepoCodeReader)
+
 		m.Group("/pulls/:index", func() {
 			m.Get(".diff", repo.DownloadPullDiff)
 			m.Get(".patch", repo.DownloadPullPatch)