From ab41926fc0a33ea34540df0ec6f2940b4ad8188c Mon Sep 17 00:00:00 2001
From: Boming Zhang <bomingzh@sjtu.edu.cn>
Date: Sun, 30 Mar 2025 00:28:23 -0400
Subject: [PATCH] feat(parser/diff): option to hide common prefix

---
 internal/parser/diff/meta.go   | 17 +++++++++--------
 internal/parser/diff/parser.go | 25 ++++++++++++++++++++++++-
 2 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/internal/parser/diff/meta.go b/internal/parser/diff/meta.go
index 563b564..cd7ea42 100644
--- a/internal/parser/diff/meta.go
+++ b/internal/parser/diff/meta.go
@@ -14,14 +14,15 @@ type Conf struct {
 	ForceQuitOnFailed bool   `default:"false"`
 	Cases             []struct {
 		Outputs []struct {
-			Score           int
-			FileName        string
-			AnswerPath      string
-			CompareSpace    bool
-			AlwaysHide      bool
-			ForceQuitOnDiff bool
-			MaxDiffLength   int `default:"2048"` // just for reference
-			MaxDiffLines    int `default:"50"`   // just for reference
+			Score            int
+			FileName         string
+			AnswerPath       string
+			CompareSpace     bool
+			AlwaysHide       bool
+			ForceQuitOnDiff  bool
+			MaxDiffLength    int `default:"2048"` // just for reference
+			MaxDiffLines     int `default:"50"`   // just for reference
+			HideCommonPrefix bool
 		}
 	}
 }
diff --git a/internal/parser/diff/parser.go b/internal/parser/diff/parser.go
index 1799f22..7cbce0b 100644
--- a/internal/parser/diff/parser.go
+++ b/internal/parser/diff/parser.go
@@ -85,6 +85,23 @@ func (*Diff) Run(results []stage.ExecutorResult, confAny any) (
 						}
 						answerLines := strings.Split(answerStr, "\n")
 						resultLines := strings.Split(resultStr, "\n")
+						commonPreixLineCount := 0
+						if output.HideCommonPrefix {
+							n := 0
+							for ; n < len(answerLines) &&
+								n < len(resultLines) &&
+								stringsEqual(
+									answerLines[n],
+									resultLines[n],
+									output.CompareSpace,
+								); n += 1 {
+							}
+							if n > 0 {
+								answerLines = answerLines[n:]
+								resultLines = resultLines[n:]
+								commonPreixLineCount = n
+							}
+						}
 						if len(answerLines) > output.MaxDiffLines {
 							answerLines = answerLines[:output.MaxDiffLines]
 							truncated = true
@@ -104,12 +121,18 @@ func (*Diff) Run(results []stage.ExecutorResult, confAny any) (
 						if truncated {
 							diffOutput += "\n\n(truncated)"
 						}
+						if commonPreixLineCount > 0 {
+							diffOutput = fmt.Sprintf(
+								"(%d line(s) of common prefix hidden)\n\n",
+								commonPreixLineCount,
+							) + diffOutput
+						}
 						comment += fmt.Sprintf(
 							"```diff\n%s\n```\n",
 							diffOutput,
 						)
 					} else {
-						comment += "(Content hidden.)\n"
+						comment += "(content hidden)\n"
 					}
 				}
 			}