snapshot of https://github.com/go-gitea/gitea.git (main, 2026-09-15; blobs > 131072B omitted)

services/gitdiff/gitdiff_excerpt.go

@@ -0,0 +1,132 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package gitdiff
+
+import (
+	"bytes"
+	"fmt"
+	"html/template"
+	"io"
+
+	"gitea.dev/modules/git"
+	"gitea.dev/modules/setting"
+
+	"github.com/alecthomas/chroma/v2"
+)
+
+type BlobExcerptOptions struct {
+	// More details in DiffLineSectionInfo struct
+	LastLeft      int
+	LastRight     int
+	LeftIndex     int
+	RightIndex    int
+	LeftHunkSize  int
+	RightHunkSize int
+	Direction     string
+	Language      string
+}
+
+func (diffSection *DiffSection) fillExcerptLines(reader io.Reader, leftStart, rightStart, chunkSize int) error {
+	buf := &bytes.Buffer{}
+	scanner := git.NewGitDiffScanner(reader)
+	var diffLines []*DiffLine
+	for rightLineIdx := 1; rightLineIdx < rightStart+chunkSize; rightLineIdx++ {
+		if ok := scanner.Scan(); !ok {
+			break
+		}
+		lineText := scanner.Text()
+		if buf.Len()+len(lineText) < int(setting.UI.MaxDisplayFileSize) {
+			buf.WriteString(lineText)
+			buf.WriteByte('\n')
+		}
+		if rightLineIdx < rightStart {
+			continue
+		}
+		diffLine := &DiffLine{
+			LeftIdx:  leftStart + (rightLineIdx - rightStart),
+			RightIdx: rightLineIdx,
+			Type:     DiffLinePlain,
+			Content:  " " + lineText,
+		}
+		diffLines = append(diffLines, diffLine)
+	}
+	if err := scanner.Err(); err != nil {
+		return fmt.Errorf("fillExcerptLines scan: %w", err)
+	}
+	diffSection.Lines = diffLines
+	// DiffLinePlain always uses right lines
+	diffSection.highlightedRightLines.value = highlightCodeLines(diffSection.FileName, diffSection.language.value, []*DiffSection{diffSection}, false /* right */, buf.Bytes())
+	return nil
+}
+
+func BuildBlobExcerptDiffSection(filePath string, reader io.Reader, opts BlobExcerptOptions) (*DiffSection, error) {
+	lastLeft, lastRight, idxLeft, idxRight := opts.LastLeft, opts.LastRight, opts.LeftIndex, opts.RightIndex
+	leftHunkSize, rightHunkSize, direction := opts.LeftHunkSize, opts.RightHunkSize, opts.Direction
+
+	expandLimit := BlobExcerptChunkSize
+	section := &DiffSection{
+		language:              &diffVarMutable[string]{value: opts.Language},
+		highlightLexer:        &diffVarMutable[chroma.Lexer]{},
+		highlightedLeftLines:  &diffVarMutable[map[int]template.HTML]{},
+		highlightedRightLines: &diffVarMutable[map[int]template.HTML]{},
+		FileName:              filePath,
+	}
+	var err error
+	remainingLines := idxRight - lastRight
+	if direction == "up" && remainingLines > expandLimit {
+		idxLeft -= expandLimit
+		idxRight -= expandLimit
+		leftHunkSize += expandLimit
+		rightHunkSize += expandLimit
+		err = section.fillExcerptLines(reader, idxLeft, idxRight, expandLimit)
+	} else if direction == "down" && remainingLines > expandLimit {
+		err = section.fillExcerptLines(reader, lastLeft+1, lastRight+1, expandLimit)
+		lastLeft += expandLimit
+		lastRight += expandLimit
+	} else /* "single" or [ ("up" or "down") and (remainingLines <= expandLimit) ] */ {
+		if direction == "up" || direction == "single" {
+			// if the direction is "up" or "single":
+			// * top: last=0, idx=11, chunk=11: line 11 is already rendered, line 0 can be considered as a "virtually rendered line"
+			//   * then need to expand line 10 lines (1-10), so "-1".
+			// * middle: last=100, idx=106, chunk=6: line 100 and 106 are both already rendered
+			//   * then need to expand 5 lines (101-105), so "-1".
+			expandLimit = remainingLines - 1
+		} else {
+			// if the direction is "down": either the hidden lines are too many in the middle (otherwise "single"), or are at the bottom
+			// * "last" line is already rendered, so just render the remaining lines from the next line
+			expandLimit = remainingLines
+		}
+		err = section.fillExcerptLines(reader, lastLeft+1, lastRight+1, expandLimit)
+		// now, the hidden lines are fewer than "expand limit", after expand, no hidden lines anymore,
+		// no need to show new "expand buttons" (setting them to 0 will make GetExpandDirection returns "no direction")
+		leftHunkSize, rightHunkSize, idxLeft, idxRight = 0, 0, 0, 0
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	newLineSection := &DiffLine{
+		Type: DiffLineSection,
+		SectionInfo: &DiffLineSectionInfo{
+			language:      &diffVarMutable[string]{value: opts.Language},
+			Path:          filePath,
+			LastLeftIdx:   lastLeft,
+			LastRightIdx:  lastRight,
+			LeftIdx:       idxLeft,
+			RightIdx:      idxRight,
+			LeftHunkSize:  leftHunkSize,
+			RightHunkSize: rightHunkSize,
+		},
+	}
+	if newLineSection.GetExpandDirection() != "" {
+		newLineSection.Content = fmt.Sprintf("@@ -%d,%d +%d,%d @@\n", idxLeft, leftHunkSize, idxRight, rightHunkSize)
+		switch direction {
+		case "up":
+			section.Lines = append([]*DiffLine{newLineSection}, section.Lines...)
+		case "down":
+			section.Lines = append(section.Lines, newLineSection)
+		}
+	}
+	return section, nil
+}